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Standard Group Technology

Title: Welding of High Pressure, Temperature Tube and Pipework

Unique Identifier: 36-504

Alternative Reference Number: N/A

Area of Applicability: Engineering

Documentation Type: Standard

Revision: 1

Total Pages: 40

Next Review Date: November 2014

Disclosure Classification: CONTROLLED DISCLOSURE

Compiled by SCOT Process Authorised by

…………………………………..

………………………………….. …………………………………..

P. Doubell

Chief Engineer Welding IWE

R. Stephen

GM (Master Specialist) SCOT Chairman

T. Mathe

Engineering Power Plant Manager

Date: …………………………… Date: …………………………… Date: ……………………………

Welding of High Pressure, Temperature Tube and Pipework

CONTROLLED DISCLOSURE When downloaded from the EDMS, this document is uncontrolled and the responsibility rests with the user to ensure it is in line

with the authorised version on the system.

Unique Identifier: 36-504 Revision: 1 Page: 2 of 40

CONTENTS

Page

FOREWORD ................................................................................................................................................................ 5

1. SCOPE ..................................................................................................................................................................... 7

2. NORMATIVE REFERENCES .................................................................................................................................. 7

2.1 INTERNATIONAL STANDARDS ...................................................................................................................... 7

2.2 NATIONAL STANDARDS ................................................................................................................................. 8

2.3 ESKOM STANDARDS, SPECIFICATIONS AND PROCERURES ................................................................... 8

3. DEFINITIONS AND ABBREVIATIONS ................................................................................................................... 9

3.1 DEFINITIONS .................................................................................................................................................... 9

3.2 CLASSIFICATION ............................................................................................................................................. 9

3.3 ABBREVIATIONS .............................................................................................................................................. 9

4. REQUIREMENTS ................................................................................................................................................... 10

4.1 GENERAL WELDING REQUIREMENTS ....................................................................................................... 10

4.1.1 Statutory Requirements ........................................................................................................................... 10

4.1.2 Basic Welding Principles ......................................................................................................................... 10

4.1.3 AIA Requirements ................................................................................................................................... 11

4.2 WELDING PROCEDURE QUALIFICATION ................................................................................................... 11

4.2.1 WPQR/PQR for Butt Welds ..................................................................................................................... 11

4.2.2 WPQR/PQR for Weld Repairs ................................................................................................................. 11

4.2.3 WPS ........................................................................................................................................................ 11

4.2.4 Weld Joint Map ........................................................................................................................................ 12

4.2.5 Welding Schedule/Technique Sheet ....................................................................................................... 12

4.2.6 Approval of Weld Documentation ............................................................................................................ 12

4.3 WELDER QUALIFICATIONS .......................................................................................................................... 12

4.3.1 Specifications .......................................................................................................................................... 12

4.3.2 Construction Code ................................................................................................................................... 12

4.3.3 Control of WQR ....................................................................................................................................... 12

4.3.4 Validity of WQR ....................................................................................................................................... 13

4.3.5 Performance Records ............................................................................................................................. 13

4.3.6 Training of Welders ................................................................................................................................. 13

4.4 DESIGN FOR WELDING ................................................................................................................................ 13

4.4.1 Weld Joint Designs .................................................................................................................................. 13

4.4.2 Permanent Attachments .......................................................................................................................... 13

4.4.3 Socket Welds........................................................................................................................................... 14

4.4.4 Acceptable Welding Processes ............................................................................................................... 14

4.4.5 Backing Rings.......................................................................................................................................... 14

4.4.6 Weld Contour........................................................................................................................................... 14

4.4.7 Proximity of Welds ................................................................................................................................... 14

4.4.8 Tack Welds .............................................................................................................................................. 14

4.4.9 Bridge Pieces .......................................................................................................................................... 15

4.4.10 Cold Pull ................................................................................................................................................ 15

4.4.11 Identification of Welds on Pipework ...................................................................................................... 15

4.4.12 Valves and Fittings ................................................................................................................................ 15

4.5 PRESSURE BOUNDARY MATERIALS .......................................................................................................... 15

4.5.1 Tube and Pipe Material ........................................................................................................................... 15

4.5.2 Steel Making Process .............................................................................................................................. 16

4.5.3 Material Test Certification ........................................................................................................................ 16

4.6 WELDING CONSUMABLE REQUIREMENTS ............................................................................................... 16

4.6.1 Specification for Consumables ................................................................................................................ 16

4.6.2 Drying of Consumables ........................................................................................................................... 16

4.6.3 Consumable Integrity .............................................................................................................................. 17





4.6.4 Storing and Issuing Consumables........................................................................................................... 17

4.6.5 Selection of Consumables ....................................................................................................................... 17

4.6.6 Dissimilar Weld Joint Consumables ........................................................................................................ 17

4.6.7 Austenitic Weld Consumables used on Ferritic/Martensitc Base Materials ............................................ 17

4.6.8 Shielding and Backing Gas ..................................................................................................................... 18

4.7 PREPARATION FOR WELDING .................................................................................................................... 18

4.7.1 Supervision of Welding Activities ............................................................................................................ 18

4.7.2 Inspection and Test Plans ....................................................................................................................... 18

4.7.3 Inspection of Weld Preparation ............................................................................................................... 19

4.7.4 Equipment ............................................................................................................................................... 19

4.7.5 Surface Cleanliness ................................................................................................................................ 19

4.7.6 Weld Joint Preparation ............................................................................................................................ 19

4.7.7 Residual Magnetism ................................................................................................................................ 20

4.7.8 Installation of Tack Welds ....................................................................................................................... 20

4.7.9 Temporary Attachments .......................................................................................................................... 20

4.7.10 Root Backing Gas ................................................................................................................................. 20

4.7.11 Chimney Effect ...................................................................................................................................... 21

4.7.12 Scaffolding and Shelter ......................................................................................................................... 21

4.8 PREHEATING ................................................................................................................................................. 21

4.8.1 Heating Methods ..................................................................................................................................... 21

4.8.2 Temperature Recording .......................................................................................................................... 21

4.8.3 Gas Preheating ....................................................................................................................................... 21

4.9 EXECUTION OF WELDS ................................................................................................................................ 22

4.9.1 Weld Progression .................................................................................................................................... 22

4.9.2 Joint Root Welding .................................................................................................................................. 22

4.9.3 Measuring Pre-Heat and Interpass Temperature .................................................................................... 22

4.9.4 Interruption of Welding ............................................................................................................................ 23

4.9.5 Attachment Welds ................................................................................................................................... 23

4.9.6 Interpass Cleanliness .............................................................................................................................. 23

4.10 SNAG WELDS ............................................................................................................................................... 24

4.11 DRESSING OF WELDS ................................................................................................................................ 24

4.11.1 Preparation for Inspection ..................................................................................................................... 24

4.11.2 Dressed Weld Profile Requirements ..................................................................................................... 24

4.11.3 Arc Strikes ............................................................................................................................................. 25

4.12 POST WELD HEAT TREATMENT ................................................................................................................ 26

4.12.1 Base Material PWHT Requirements ..................................................................................................... 26

4.12.2 Cooling Down for Transformation ......................................................................................................... 26

4.12.3 Heating and Cooling Rates ................................................................................................................... 26

4.12.4 Heat treatment Procedure Qualifications .............................................................................................. 26

4.12.5 Minimum Heat Treatment Procedure Requirements ............................................................................ 26

4.12.6 Post Weld Heat Treatment Method ....................................................................................................... 27

4.12.7 Temperature Control ............................................................................................................................. 27

4.12.8 Resistance Heating ............................................................................................................................... 28

4.12.9 Area Subjected to Heat Treatment ........................................................................................................ 28

4.12.10 Temperature Recording ...................................................................................................................... 28

4.12.11 Interruption of Heat Treatment ............................................................................................................ 28

4.13 INSPECTION OF COMPLETED WELDS ..................................................................................................... 28

4.13.1 General NDT Requirements .................................................................................................................. 28

4.13.2 Main Inspection ..................................................................................................................................... 29

4.13.3 Acceptance of Welds ............................................................................................................................. 29

4.14 WELD REPAIRS ........................................................................................................................................... 30

4.14.1 Authority to Repair ................................................................................................................................. 30

4.14.2 Removal of Defects ............................................................................................................................... 30

4.14.3 Weld Repair Procedure ......................................................................................................................... 30

5. RECORDS AND CERTIFICATES .......................................................................................................................... 31

5.1 GENERAL REQUIREMENTS ......................................................................................................................... 31





5.1.1 Retainer Period ....................................................................................................................................... 31

5.2 SPECIFIC DOCUMENTS FOR RECORD KEEPING ..................................................................................... 31

6. ANNEXES .............................................................................................................................................................. 32





FOREWORD

Revision History

This is the first edition.

Date Rev. Remarks

17 January 2012 0.1 P. Doubell

24 April 2012 1 P. Doubell

Authorisation

This document has been seen and accepted by:

Name and Surname Designation

Pius Oba Acting Section Manager: Welding & NDE, Welding Engineer

Sumaya Nassiep Acting Senior Manager: Plant Performance and Optimisation

Barry MacColl Acting General Manager: Research, Testing & Development

Titus Mathe Engineering Power Plant Manager

Dhiraj Bhimma Senior Manager (Production Engineering Integration Coal)

Thava Govender Divisional Executive

A Noah Divisional Executive

B Bulunga Divisional Executive

M Ntsokolo Divisional Executive

Anthony Kuzelj Power Station Manager

Bheki Nxumalo Power Station Manager

Bruce Moyo Power Station Manager

Chris Schutte Senior General Manager

Christo van Niekerk Senior General Manager

Christopher Nani Power Station Manager

Deon Beukes Chief Technologist

Des Sheppard Senior Manager: Projects and Outages

Ertjies Bierman Senior Manager Engineering

Gladman Mkwai Power Station Manager

Hennie van Staden Senior Manager: Projects and Outages

Johan Du Preez Boiler Senior Consultant

Johan Prinsloo Power Station Manager

John Dean Power Station Manager

Julian Fourie Senior Manager Engineering

Julian Nair Power Station Manager

Kiren Maharaj Senior General Manager





Name and Surname Designation

Lebo Serekwa Boiler Senior Consultant

Leon Booyens Senior Consultant Boiler Tube Failure Reduction

Mandla Mtembu Senior Manager Engineering

Marcus Nemadodzi Boiler Senior Consultant

Mark Breetzke Corporate Consultant: Boilers

Marthinus Bezuidenhout Corporate Consultant: Materials

Erick van Zyl Chief Engineer

Morris Maroga Chief Engineer

Piet Veldman Outage Integration Manager: Coal Operating Unit 1

Russel Tarr Senior Consultant: Fleet Technology

Ryno Lacock Power Station Manager

Shamiel Jappie Acting Power Station Manager

Shireen Prince Power Station Manager

Thava Govender Divisional Executive: Generation

Thomas Conradie Power Station Manager

Louise Petrick Senior Advisor Welding

Andrew Downes Senior Consultant

Hennie Coetzer Senior Advisor Projects

Werner Smit Chief Engineer

Michael Mkhize Chief Engineer

Frans Havenga Section Manager Physical Metallurgy

Thobeka Pete Chief Engineer

Leslie Too Senior Advisor

Philip van der Meer Senior Engineer

Martin van Daalen Senior Advisor

Nanda Chabula Senior Technologist

Applicability

This standard is applicable to all Eskom high temperature tube and pipework plant during execution of construction, maintenance and repair welding activities. Any anomalies/disputes that fall outside this standard or that appear to be in conflict with it may be resolved with the proper weld engineering and/or metallurgical inputs. Actions and situations that fail to meet these requirements may be assessed to determine the nature and significance of the shortcomings. Eskom will consider the applicability of proposed remedial actions for application with the necessary concessions.

Development Team

The following people were involved in the development of this document:-

• Philip Doubell





1. SCOPE

This standard details Eskom’s mandatory requirements and provides recommendations for welding heat treatment and quality control, as related to international standards in the welding of high pressure tube and pipework in the design, construction and maintenance of fossil fired power stations as defined in Eskom Standard N.PSZ 45-223 [38].

It replaces the previous document NWS 1303: ‘Specification for welding of high pressure/temperature pipework in fossil fired power stations’.

2. NORMATIVE REFERENCES

The following documents contain provisions that, through reference in the text, constitute requirements of this document. At the time of publication, the editions indicated were valid. These documents are subject to revision and users are responsible to ensure that the most recent editions of the documents listed below are referenced. Parties using this document shall use the most recent editions of the documents listed in this section.

2.1 INTERNATIONAL STANDARDS

[1] BS EN 13480 (2002): Metallic industrial piping Parts 1 to 8

[2] BS 12952 (2001): Water-tube boilers and auxiliary plant – Parts 1 to 17

[3] BS EN 10216 (2002): Seamless steel tubes for pressure purposes – Technical delivery conditions – Parts 1 to 5

[4] PD 5500 (2003): Unfired fusion welded pressure vessels

[5] ASME Boiler and Pressure Vessel Construction Code (2010) (Including Addenda): Section I: Power Boilers; Section II: Material Specifications: Part A – ferrous materials, Part C – Welding rods, electrodes and filler metals; Section VIII: Pressure vessels, Division 1, Division 2 – alternative rules; Section IX: Welding

[6] ASME B 31.1: Power piping

[7] TRD Series: 100; 200; 300

[8] ADM 2000

[9] BS EN 1011 (2009): Welding- Recommendations for welding of metallic materials – Part 1 General guidance for arc welding; Part 2 (2001) Arc welding of ferritic steels; Part 3 (2000) Arc welding of stainless steels

[10] BS EN ISO 15607 (2003): Specification and qualification of welding procedures for metallic materials - General rules

[11] BS EN ISO 15613 (2004): Specification and qualification of welding procedures for metallic materials – Qualification based on pre-production welding test

[12] BS EN ISO 5817 (2003): Welding - Fusion-welded joints in steel, nickel, titanium and their alloys (beam welding excluded) – Quality levels for imperfections

[13] BS EN ISO 17663 (2009): Welding – Quality requirements for heat treatment in connection with welding and allied processes

[14] BS 2633 (1987): Specification for Class I arc welding of ferritic steel pipework for carrying fluids

[15] EN 10204 (2004): Metallic products: Types of inspection documents





[16] EN ISO 13916 (1997): Welding – guidance on the measurement of preheating temperature, interpass temperature and preheat maintenance temperature

[17] ISO/TR 15608 (2005): Welding – Guidelines for a metallic material grouping system

[18] ISO 14731 (2006): Welding co-ordination. Tasks and responsibilities

[19] VGB-R 109 - VGB Directive – Material specification for components under pressure in fossil-fired power plants; Second Edition 2008

[20] V&M Material Data Sheet MDS 439 – High Temperature CrWCoVNb-Steel with 12% Cr for Tubes; Rev. 1; 29.01.2008

[21] AWS A 5.01 (2008) (ISO 14344 : 2002 MOD) : Procurement Guidelines for Consumables – Welding and Allied Processes – Flux and Gas Shielded Electrical Welding Processes

[22] EN ISO 3580 (2010) : Welding Electrodes for Manual Metal Arc Welding of creep resisting Steels - Classification

[23] EN ISO 21952 (2007): Welding consumables – Wire Electrodes, Wires, Rods and deposits for Gas Shielded Arc Welding of Creep Resisting Steel - Classification

[24] EN ISO 14175 (2008): Welding Consumables – Gases and Gas Mixtures for Fusion Welding and Allied Processes

[25] BS EN 17640 (2010): Non-destructive Testing of welds – Ultrasonic testing - Techniques, testing levels and assessment

[26] BS EN ISO 23279 (2010): NDT of Welds – Ultrasonic testing – Characterisation of indications in welds

2.2 NATIONAL STANDARDS

[27] SANS 15614 Specification and qualification of welding procedures for metallic materials - Welding procedure test; Part 1: Arc and gas welding of steels and arc welding of nickel and nickel alloys; Part 7: Overlay welding

[28] SANS 15609-1 Specification and qualification of welding procedures for metallic materials - Welding procedure specification Part 1: Arc welding

[29] SANS 9606-1 Approval testing of welders - Fusion welding Part 1: Steels

[30] SANS ISO 3834 (2005): Quality requirements for Welding Part 1 Guidelines for selection and use; Part 2 Comprehensive quality requirements; Part 3 Standard quality requirements; Part 4 Elementary quality requirements

[31] Pressure Equipment Regulations (2009) (PER)

[32] SANS 347 (2010): Specification for categorization and assessment criteria for all pressure equipment in dangerous service

[33] SANS 17025 (2005): General requirements for the competence of testing and calibration laboratories

2.3 ESKOM STANDARDS, SPECIFICATIONS AND PROCERURES

[34] 36-775 Control of Plant Construction, Repair and Maintenance Welding Activities

[35] 32-632 Requirements for NDT on Eskom plant

[36] 32-631 Eskom approval of personnel performing quality related special processes on Eskom plant





[37] GGS 0462 Quality requirements for engineering and construction works in generation

[38] N.PSZ 45-224 High pressure pipework for fossil fired power stations

[39] 36-505 Personnel and Entities Performing Welding Related Special Processes on Eskom Plant

[40] 36-1255 Material procurement standard

[41] 36-1162 Weld defect classification and reporting procedure

3. DEFINITIONS AND ABBREVIATIONS

3.1 DEFINITIONS

3.1.1 Procedure Qualification Record: A record comprising all relevant data from the welding of a test piece needed for the approval of a welding procedure specification as described in the ASME Boiler and Pressure Vessel Code Section IX [5]. 3.1.2 Welding Procedure Qualification Record: A record comprising all relevant data from the welding of a test piece needed for the approval of a welding procedure specification as described in the welding specification SANS 15614 [22]. 3.1.3 Welding Procedure Specification: A document meeting the requirements of SANS 15609 [28] or ASME Boiler and Pressure Vessel Code Section IX [5] and derived from the WPQR/PQR that sets out in detail the required variables for a specific application to assure repeatability. 3.1.4 Welder Qualification Record: A document meeting the requirements of SANS 9606 [29] or ASME Boiler and Pressure Vessel Code Section IX [5], which presents the results of the approval testing of a welder to perform a fusion welding process. 3.1.5 Eskom Welding Co-ordinator: A Welding Engineer/Technologist appointed in writing for a specific business unit or project to oversee all welding activities within Eskom Holdings SOC Ltd. 3.1.6 High Pressure Equipment: Pressure Equipment with design pressure ≥ 50 kPa which include a steam generator, pressure vessel, pressure accessory and piping.

3.1.7 Eskom Engineer: The Engineer/Technologist responsible for the plant or component. Applicable to the contents and intentions of this standard, his decisions may be based on support and recommendations from the applicable Eskom welding, metallurgy, NDT and structural integrity specialists.

3.2 CLASSIFICATION

Controlled Disclosure: Controlled Disclosure to external parties (either enforced by law, or discretionary).

3.3 ABBREVIATIONS

Abbreviation Description

ADM Arbeitsgemeinschaft Druckbehälter Merkblätter

AIA Approved Inspection Authority

ASME BPVC American Society of Mechanical Engineers Boiler and Pressure Vessel Code





Abbreviation Description

AWS American Welding Society

BS EN British Standard European Norm

ISO International Organization for Standardization

ITP Inspection and test plan

IW International Welder registered with the International Institute of Welding

IWE International Welding Engineer registered with the International Institute of Welding

IWS International Welding Specialist registered with the International Institute of Welding

IWT International Welding Technologist registered with the International Institute of Welding

NDT Non-destructive testing

OD Outside diameter

OHS Act Occupational Health and Safety Act of 1993

PER Pressure Equipment Regulations of 2009

PQR Procedure Qualification Record

PWHT Post weld heat treatment

QCP Quality control plan

TCA Technical capability assessment

TPI Third Party Inspector

TRD Technische Regeln für Dampfkessel

WA Welding administrator / coordinator

WPQR Welding Procedure Qualification Record

WPS Welding Procedure Specification

WQR Welder Qualification Record

4. REQUIREMENTS

4.1 GENERAL WELDING REQUIREMENTS

4.1.1 Statutory Requirements

Welding activities on high pressure tube and pipework as defined in the PER [25] and SANS 347 [26] shall be governed by latest version of the plant design code and applied according to the requirements of the Eskom Welding Standard 36-775 [34] and the Eskom High Pressure Pipework Standard N.PSZ 45-223 [38].

4.1.2 Basic Welding Principles

Basic welding rules pertinent to construction and maintenance work on high temperature tube and pipe components are contained in BS 2633 [14]. This specification details arc welding using manual, semi-automatic or automatic processes; parent metals, welding consumables, preparation for welding, butt joints, branches, attachments, flanges, inspection, acceptance criteria, procedure and welder approval





tests. Furthermore, BS EN 1011 [9] provides general guidance principles on how to achieve and control good quality weldments in ferritic and stainless steels

4.1.3 AIA Requirements

The tasks and responsibilities for the AIA pertinent to the high pressure temperature Eskom plan will apply as required by the PER [31].

4.2 WELDING PROCEDURE QUALIFICATION

4.2.1 WPQR/PQR for Butt Welds

For plant designed to ADM [8], TRD [7], PD5500 [4]; BS EN 13480 [1]; BS 12952 [2]; all WPS’s shall be supported by a valid WPQR conforming to SANS 15614 Part 1 [27] as stipulated in Eskom Welding Standard 36-775 [34] according to the relevant plant design codes, unless written concessions have been approved by Eskom where specific situations arise. For plant designed to ASME B31.1[6] or ASME BPVC Section VIII [5], all WPS’s shall be supported by a valid PQR conforming to ASME BPVC Section IX [5]. Prior to commencement of fabrication, the principal Contractor shall submit all welding procedures and procedure qualifications for approval by the plant responsible Eskom Welding Engineer.

4.2.2 WPQR/PQR for Weld Repairs

Where repairs of defect excavations require weld preparations not representative of butt welds, a procedure shall be qualified to incorporate the geometry of the weld preparations as prescribed in BS EN 15613 [11]. If the repair requires a significant amount of weld build-up, the relevant butt weld procedure qualification shall be supported by the test requirements listed in SANS 15614 Part 7 [27].

4.2.3 WPS

The principal Contractor shall be responsible for generating a relevant welding procedure specification to the requirements of SANS 15609 [28] or ASME BPVC Section IX [5] for each joint configuration, showing drawings and parameter details pertinent to each case of application. No generic WPS’s will be allowed. Welding procedure specifications verified by the AIA may be reviewed by Eskom prior to commencement of fabrication.

The WPS shall specify:

• Applications for which the procedures may be used,

• Type of weld process,

• Consumables (identified with the appropriate National Standards for country of origin),

• Base material specification,

• Dimensional range,

• Specific joint configuration,

• Process parameters,

• Heat treatment and

• Reference to required NDT.





4.2.4 Weld Joint Map

Welding procedures submitted to Eskom shall be accompanied by documentation clearly identifying the specific item and contract number to which they refer and shall be indicated on a weld joint map showing an isometric lay-out of the plant stipulated in the contract.

4.2.5 Welding Schedule/Technique Sheet

If a WPS is not issued to each welder, a welding schedule or technique sheet shall at least be generated for all tube and pipework weld joints. This document shall list:

• Principal welding parameters,

• Reference procedure number,

• Weld consumable specification and batch number,

• Welder stamp number,

• Weld number or group of welds and a reference weld map drawing number locating the welds,

• Type and extent of the minimum required NDT.

4.2.6 Approval of Weld Documentation

Before commencing with the work the principal contractor shall submit to the responsible Eskom Welding Engineer/Technologist for approval, verified copies of weld procedures covering all forms of weld which may be used in the contract, conforming to the requirements listed in the Eskom Standard 36-775 [34]. Verified copies of all WPS’s used during the course of the contract shall be included in the maintenance records.

4.3 WELDER QUALIFICATIONS

4.3.1 Specifications

It is the responsibility of the contractor to ensure that all welders employed on the welding of pressure containing parts and non-pressure containing load bearing attachments, to be suitably qualified to SANS 9606 [29] or ASME BPVC Section IX [5] as required by the Eskom Standard 36-775 [34].

Only welders trained and certified as IW (pipe welder) will be allowed for welding on high pressure and temperature tube and pipework on Eskom Level I plant as required by Eskom Standard 36-505 [39].

4.3.2 Construction Code

Welder’s qualification tests shall be carried out in accordance with the relevant plant’s code of construction. Welders employed in the fabrication of all items covered by this document shall be coded, unless the Contractor can produce valid welder qualification records to the satisfaction of the Eskom Welding Engineer/Technologist.

4.3.3 Control of WQR

The principal Contractor shall have under its control all facilities, labour and materials required for the examination and testing of welders, and their re-testing from time to time during the course of the contract, in accordance with the code of construction. All materials required for qualification of both weld procedures and welders shall be certified to the relevant BS EN 10216 [3] or ASME BPV Section II [5] wrought tube/pipe material specification and supplied by the contractor.





No material assigned to the same group but not intended for use on high temperature and pressure tube and pipework, shall be allowed.

4.3.4 Validity of WQR

Only welders who have passed the qualifying tests in accordance with the relevant plant code of construction shall be employed for welding of HP tube and pipework, pressurized systems and their stressed attachments. Unless it can be proven by the Contractor that the individual welders have been practicing their trade continuously since qualifying, they shall be re-tested to the requirements of the code.

4.3.5 Performance Records

The principal contractor shall keep performance records of each welder operating on high pressure and temperature tube and pipework on Eskom Level I plant, traceable to the national identification number (or passport number) of each individual. This information shall be included in the final contract document package, and as a minimum show the individual’s weld repair and production rates.

4.3.6 Training of Welders

Each welder, irrespective of his recent site experience on tube and pipe plant, shall be tested on a mock-up of the relevant plant configuration before the contract commences. For tube welding contracts in challenging site conditions the welder shall prove his skill in out-of-position manipulations to a similar degree of difficulty expected during the contract. For large-bore pipework, the welders shall demonstrate the skill required to perform out of position welding on site. Special attention shall be placed on the correct techniques for successful application of pipe root welds.

4.4 DESIGN FOR WELDING

4.4.1 Weld Joint Designs

Before fabrication starts, the contractor shall submit to Eskom welding procedures complying with the plant design code, showing the weld joint configuration to be used in the fabrication or for the repair to be performed on the tube or pipework. The proposed configuration shall aim to minimise weld metal volumes through the use of U-preparations instead of V-preparations in order to reduce the levels of weld residual stresses while confirming with the welders identified to execute the weld, that full access will be possible. The weld joint shall also be fully inspectable by conventional volumetric NDT techniques.

4.4.2 Permanent Attachments

Welding of attachments to piping shall not be permitted without Eskom approval on the contract design. The location, geometry and size of all attachments shall be accurately indicated on the contract weld map and flagged for the full NDT requirements as for pressure boundary welds. The welds attaching load-bearing attachments to high temperature pipes shall have full penetration weld joint preparations and be continuously welded for the full length of the weld preparation. All load-bearing attachment welds shall be heat treated according to the design code and material requirements, and flagged for grinding to a smooth finish and to eliminate all undercut or stress concentration notches.





4.4.3 Socket Welds

Socket welds shall not be permitted unless specifically approved by Eskom on case by case basis for systems not subjected to vibration or frequent thermal cycling. Great care shall be exercised in the fit-up for such joints in ensuring that the pipe does not butt up against the inner end of the socket.

4.4.4 Acceptable Welding Processes

One or a combination of the following processes may be used for welding on high pressure and temperature tube and pipework:

• Manual Metal Arc Welding (MMAW) (not to be used for full penetration butt welds where the root back is inaccessible);

• Tungsten Inert Gas Welding (TIG);

• Submerged Arc Welding (SAW).

Other processes shall only be used with prior specific approval by Eskom where applicable, for example the case of attachment of fins to economiser tubes where the resistance welding process is commonly used.

4.4.5 Backing Rings

The use of permanent backing rings shall not be permitted.

4.4.6 Weld Contour

Welding parameters shall be optimally set within the range allowed by the WPS to provide properly contoured weld bead profiles to permit complete fusion at the sides of the weld end preparations and to avoid slag entrapment. Weld reinforcement, penetration and finish shall be applied as required by the applicable code and design requirements while aiming for minimum post weld cleaning and profiling by grinding. Weld dimensions as calculated by the designer shall be closely followed. Over-welding which may be conducive to the creation of unnecessary high weld residual stresses shall be avoided as far as practically possible.

4.4.7 Proximity of Welds

Positioning of the toes of adjacent butt welds, branch welds and attachment welds shall meet the requirement of the design code. If not specified, it shall not be nearer than four times the wall thickness of the pipe concerned while allowing adequate access for the deposition of weld metal and for the application of any post-weld operation such as heat treatment and NDT.

4.4.8 Tack Welds

Shall be designed to the requirements of the construction code. Where the construction code allows for incorporation of tack welds into the joint weld, the tack welds shall be of sufficient size to withstand the thermal stresses associated with the installation of the weld root.

Areas to be tack welded must be preheated evenly to the same temperature (as specified for welding in the WPS) over an area up to minimum 150 mm away. The length of the tack welds shall be a minimum of 25 mm and be cleaned prior to welding the main weld beads. The leg length shall be a maximum of 6mm and the minimum distance between tack welds shall be 200 mm as far as practically possible. All tack welds must be ground smooth prior to completion of the joint fill weld beads.





4.4.9 Bridge Pieces

Bridge pieces for weld joint alignment shall not be welded directly to the outside surface of tubes /pipes. Purpose designed bolted clamps or strong-backs, to which bridge pieces may be welded, shall be used. Where required bridge pieces may be welded to the weld preparation surface in cases where the attachment weld will eventually be incorporated into the completed tube/pipe weld.

4.4.10 Cold Pull

For cases where cold pull is used to reduce reaction forces at terminations and anchors, careful and comprehensive evaluation of system layout, supports and geometry shall be performed by competent piping engineers to determine the correct cold pull required for a rigid closing weld as required by the Eskom pipe Standard N.PSZ 45-223 [38]. Where it is necessary to fit straining gear for a cold pull at a joint, such gear shall remain in position during welding and until all repair work, stress relief and subsequent cooling have been completed.

4.4.11 Identification of Welds on Pipework

All welds on piping of wall thickness 5mm and above, up to the first isolating valve, shall have the weld unique number mark which correlates with the approved contract weld map, stamped by low stress stamping or with a round nosed stamp, within the heat treatment zone of the weld (but not in the heat affected zone). Identification methods of welds on piping of wall thickness less than 5mm shall be subject to approval by Eskom.

4.4.12 Valves and Fittings

All valves, fittings and terminal points equal to or greater than 150 mm nominal bore, shall be fitted with transition pieces so that all site welds where practically possible are between the same materials. The material for the transition pieces and welding qualification shall be provided by the principal Contractor or pipework sub-contractor to the valve supplier for welding to the valve in the works of the valve supplier. Care shall be exercised to install transition pieces of correct length, weld built-up shall not be employed to make up for ill fittings transitions pieces.

The WPS for the weld joint between the valve and the transition piece shall be agreed upon between the main Contractor, the pipework sub-contractor, the valve supplier and Eskom. For valves, fittings and terminal points of less than 150mm nominal bore, the provision of the welding procedure and its qualification, if required, shall be the responsibility of the pipework contractor.

4.5 PRESSURE BOUNDARY MATERIALS

4.5.1 Tube and Pipe Material

New material required for use on high-temperature components shall be ordered to the requirements of the Eskom standard 36-1255 [40] which references EN 10216 [3]; the VGB Document VGB-R 109 [19] or ASME BPV Section II [5], depending on the relevant plant design code. For material VM12-SHC not yet listed in the said specifications, the manufacturer´s material data sheet V&M Material Data Sheet MDS 439 [20] shall be referenced until listed in the current pipe material specification. The table in the Annex B shows various high pressure and temperature ferritic and martensitic steels currently allowed for use on Eskom plant.

Any other material proposed for use which is listed in international standardisation specifications BS EN 10216 [3] or ASME BPV Section II [5] may be considered for use when sufficiently motivated by design





calculations. Newly developed alloys may be considered for application on Eskom plant with sufficient support documentations from the supplier pertaining to mechanical properties, creep life properties and workability data.

Substitution of materials installed on existing plant as selected by the original design with another grade is not allowed unless approved by Eskom. The approval will be based on proper supporting design calculation documents that address mechanical properties, creep properties, weldability issues, workability issues, heat treatment requirement, material weight (effects on hanger and support system).

4.5.2 Steel Making Process

The steel shall be made by electric arc process with vacuum degassing or comparable processes which has to be approved. The steel shall be readily weldable and capable of forming by cold working.

4.5.3 Material Test Certification

All material intended for use on level 1 Eskom plant shall be delivered with BS EN 10204 [15] type 3.2 inspection certification. Since this is a certificate concerning a delivery-related test according to information supplied by the purchaser, it is imperative that the scope of testing should be made clear at the time of ordering or even at the enquiry stage. The costs arising will be charged according to contract expenditure.

4.6 WELDING CONSUMABLE REQUIREMENTS

General guidelines for the handling and storage of weld consumables are contained in the Welding Standard 36-775 [34]. Important points pertinent to consumables for use on high pressure and temperature tube and pipework are emphasised here.

4.6.1 Specification for Consumables

Welding consumables for high pressure and temperature tubes and pipework, in particular those intended for use in the creep range, shall be ordered from manufacturers which have evidence and have demonstrated that the properties of their products are suitable for high temperature use. Consumable approval shall conform to the national standard requirements of the country of origin as a minimum. It is recommended that consumables with approval according to BSEN family of consumable specifications, in particular EN ISO 3580 [22] and EN ISO 21952 [23] be used on Level 1 and 2 Eskom plant. Published creep data shall be made available for scrutiny. The basis for the evaluation of test results is creep to rupture properties of the base metals to be joined.

Consumables marketed by companies opting for certification to AWS A5.X family of specifications will be acceptable if supplied with a test report confirming compliance with the applicable AWS standard or the reference to this AWS standard contained in ASME II, Part C [5]. The test report will correspond to "Schedule F" of AWS A5.01 [21] if no further elements are specified. This test report is comparable with a works certificate "2.2" as regards content. Evidence of creep testing shall be available at the point of ordering.

ANNEX C tables the recommended consumable grades for materials used on Eskom plants.

4.6.2 Drying of Consumables

The supplier’s recommended drying procedures for electrodes shall be strictly adhered to. After baking the electrodes shall be kept in a holding oven at a minimum temperature of 120ºC. Submerged arc flux products shall be stored and dried strictly as per supplier’s recommendations. Baked flux shall be kept





in a dispenser maintained at a minimum temperature of 100ºC. Recycled flux is to be re-baked as recommended by the supplier.

4.6.3 Consumable Integrity

Electrodes showing signs of flaked and cracked flux layers shall not be used. Wires with flaking protective coatings or showing traces of rust, oil and other carboniferous contamination shall not be considered for use. Correct storage of flux cored and metal cored wire products in a sufficiently dry environment are of particular importance due to possible moisture pick-up through non-tight long wire seams.

Weld shielding gas regulators and transmission tubes shall be kept dry and free of any traces of oil and grease on the inside surfaces.

4.6.4 Storing and Issuing Consumables

A comprehensive procedure for identifying, drying, storing and handling of electrodes and filler wires related to the electrode manufacturer’s recommendations shall be implemented by the Contractor. The batch numbers of the specified welding consumables shall be recorded. The quality control system shall cover the issue of the correct rods for the weld to be made, and the return of surplus rods to their correct material group and batch.

Welding consumables shall be stored in a dry storage area with temperature controlled at least 30ºC above atmospheric dew point. For Cr-Mo and Cr-Mo-V base materials, low hydrogen potential welding consumables rated at below 5 gram diffusible hydrogen per 100 ml weld metal shall be used. Only sufficient electrodes for a shift’s work shall be issued to welders from the holding oven and transferred directly to a pre-heated hot box / quiver which shall be kept at a minimum temperature of 100ºC at all times. Electrodes not used during any one shift shall be returned to the consumable storage area and considered for re-baking as per the contractors established marking and maximum allowable re-baking works procedure.

4.6.5 Selection of Consumables

Filler rods shall be selected so that the principal elements in the deposited weld metal, joining base metal to base metal, shall be of the same nominal composition as the base metal. The choice of the weld consumables and the welding technology should therefore be to fulfil the requirements of the parent metal used and must be matched to its behaviour.

For ferritic weld deposits, filler wire for automatic welding processes shall contain the principal alloying elements in the wire, not in the flux.

4.6.6 Dissimilar Weld Joint Consumables

For welds between dissimilar base metals the filler metal selected shall be such as to ensure compatibility with regards to metallurgical integrity and quality of the joint. This selection must be made so that, where possible, the weld metal arising should not be too hard, brittle and susceptible to cracks allowing for dilution with the different materials. Weld metal creep properties which exist in the pure weld metal must be retained after dilution with the different base metals.

4.6.7 Austenitic Weld Consumables used on Ferritic/Martensitic Base Materials

The merits of using austenitic stainless steel or nickel based consumables for joining ferritic or martensitic base materials to like grades shall be thoroughly motivated and not used as a perceived





quick – fix joining technique. Factors that need to be considered and evaluated before installing these types of weld joints are:

• Negative effects of difference in coefficients of thermal expansion on joint integrity, in particular the introduction of localised stresses during thermal transients for heavy wall components

• Difficulty to perform and interpret the results of volumetric NDT such as UT due to changes in microstructures.

• Surface crack detection by MT is very difficult if not impossible and cannot be applied with repeatable results; therefore the only option will be the using of a less sensitive technique such as PT.

• Welding with nickel based consumable requires a welder with specific experience that mastered the techniques to avoid problems such as hot cracking and lack of fusion due to a sluggish weld pool.

• Using nickel-based weld consumables may provide lower weld residual stress, but without PWHT the parent material heat affected zones remain untempered and susceptible to degradation by mechanisms such as hydrogen cracking and stress corrosion cracking.

• In addition to the NDT required in the contract, weld joints welded with austenitic consumables and not subsequently subjected to PWHT on materials that normally required PWHT shall be inspected for micro cracks in the base material by surface replication, as well as having hardness measured on at two positions on the base material HAZ

• These joints shall be rated as temporary and flagged to be replaced at the earliest opportunity, not later than 20 k hours of operation.

Based on these factors, austenitic weld consumables used on ferritic/martensitic base materials should be avoided and only used where the situation warrants it. Prior approval by the Eskom Engineer shall be motivated before using this type of consumables, supported by a solid engineering argument.

4.6.8 Shielding and Backing Gas

All grades of shielding and backing gas shall be supplied with supporting documents for certification to EN ISO 14175 [24].

4.7 PREPARATION FOR WELDING

4.7.1 Supervision of Welding Activities

The principle contractor shall appoint an adequate number of supervisors to control all welding activities at site level during the full life cycle of the contract. They shall have the necessary practical experience with supervising contracts on high pressure and temperature tube and pipework and at least be a certified IWS as required by Eskom Standards 36-775 and 36-505.

4.7.2 Inspection and Test Plans

Inspection and test plans/QCP’s shall be prepared and submitted to Eskom in accordance with GGS0462 [37].





4.7.3 Inspection of Weld Preparation

Tube and pipe weld preparations shall be inspected before application of preheat for cleanliness, fit-up, alignment, geometry and access. Each weld preparation for joints on pipes with outside diameter larger than 150 mm shall be inspected according to the check-list in Annex A (Example for Tutuka Power Station), which shall be completed by the authorised persons and included in the contract work package.

4.7.4 Equipment

The principal Contractor shall provide the necessary calibrated equipment for the preparation, execution and testing of weldments, the pre-heating and post-weld heat treatment of welds, and the thermocouples and recorders required to record the temperatures achieved. Where inverter type welding machines with high frequency arc starting capabilities are used, these will be fitted with the required radio wave interference suppressors. All TIG torches shall be fitted with gas lenses for improved shielding efficiency. Earth cables shall be placed as close as practically possible to the weld joints.

4.7.5 Surface Cleanliness

Any surfaces to be welded shall be clean and free from oil, dirt, scale, oxides and paint; the latter being subject to approval in the case of a welding primer. In case of surface contamination of oil or grease, an approved degreaser shall be applied. Weld spatter releasing agent shall not be applied to any part of the weld preparation.

4.7.6 Weld Joint Preparation

No thermal cut weld preparations shall be allowed on the following materials:

• 14MoV6-3;

• 15NiCuMoNb5-6-4;

• 7CrMoVTiB10-10;

• 7CrWVMoNb9-6;

• X20CrMoV12-1;

• X10CrMoVNb9-1;

• X10CrWMoVNb9-2;

• VM12-SHC.

Where thermal cutting by plasma arc or by the oxy-fuel technique is used on other materials, a formal cutting procedure shall be presented by the contractor specifying the following minimum critical parameters pertaining to the base material:

• Pre-heating rate and maintained temperature,

• Cutting travel speed,

• Process gas type,

• Type of flame: Neutral, oxidising or carburising

• Gas pressure

• Gas supply rate

• In the case of plasma cutting the volts and amperage settings.





The weld end preparations shall be trimmed at least 3 mm by abrasive disk grinding normal to the pipe axis to ensure correct root gaps, to unaffected base metal. Material dedicated grinding consumables shall be used, no indiscriminate mixing between low alloy/carbon steel and stainless steel materials shall be allowed. Care shall be exercised during carbon arc gouging or welding to avoid spatter on stainless steel surfaces. A method used to avoid contamination shall be identified by the contractor. For thermal cutting any steel grade, pre-heating requirements equivalent to those for welding, shall be applicable.

Prepared surfaces shall be inspected by thorough visual examination for flaws, cracks, laminations and other defects. Material that requires pre-heat for welding shall be pre-heated in the same manner for tack welding, thermal cutting or gouging. When pipes or fittings have to be internally machined for internal diameters to match adjoining components this process shall not reduce the thickness at the weld preparation to below the minimum calculated design thickness. When this happen a proposal for remedial action shall be reported to Eskom for approval. Buttering or including the thickness of the weld cap shall not be considered acceptable rectification practice, but may be considered by Eskom with sufficient motivation.

4.7.7 Residual Magnetism

Before any welding commences, the weld joint preparation shall be checked for any magnetism that might have resulted from the initial NDT and weld preparation activities, de-gausing may be required for preventing arc blow to occur during welding.

4.7.8 Installation of Tack Welds

These shall be applied to the requirements of the applicable WPS with respect to allowable weld parameters, preheat and only by qualified welders. Where the construction code allows for incorporation of tack welds into the joint weld, the tack welds shall be of sufficient size to withstand the thermal stresses associated with the installation of the weld root. Visibly cracked tacks shall not be fused into the root weld; these shall be excavated and re-welded.

4.7.9 Temporary Attachments

Where approved, temporary attachments shall be welded to tube and pipe surfaces as per the requirements of the relevant WPS with regard to preheat, weld parameters, welder qualification and PWHT.

4.7.10 Root Backing Gas

The other ends of the martensitic and austenitic stainless steel tube/pipe sections to be joined shall be sealed off to provide an enclosed environment through which the root side of the weld joint can be flooded with the grade of inert gas for shielding the root against high temperature oxidation. For the cases where these sections are excessively long requiring large quantities of gas to excavate the air from the root side of the joint, other more practical solutions may be used. Temporary purge dams constructed from inflatable pipe plugs, rice paper, or spiral wound refractory tape may be considered. These devices must be readily extractable through the root gap just before the last section is welded close. Under these circumstances the purging gas can be administered through a small bore tube directly through the weld preparation root gap or through pipe nozzles or gamma-bosses in close proximity to the weld joint. Before welding commences the efficacy of the root purge shall be checked with an oxygen analyser.





4.7.11 Chimney Effect

For all welds in pipes of internal diameter of 50 mm and greater, the root runs shall be made by the TIG process. Care shall be exercised to ensure that the shielding gas inside the pipe is not swept away by the chimney effect. Any flow of air through the pipeline during welding shall be prevented by blanking the ends of the pipes and plugging all other openings such as gamma-ray bosses and branch connections. The plugs shall be readily removable.

4.7.12 Scaffolding and Shelter

Adequate and safe scaffolding shall be available to provide welders and the best possible environment to execute a successful weld in a safe manner.

Tents or screens shall be erected for full protection of the complete weld area against the elements, notably wind and rain during the full period of preparation, welding and PWHT activities, as well as during cooling down afterwards.

4.8 PREHEATING

4.8.1 Heating Methods

Preheating shall be carried out using induction or resistance heating elements, except for cases where heating by gas is permitted due to practical considerations.

4.8.2 Temperature Recording

Temperatures shall be recorded on calibrated and certificated equipment using at least four thermocouples. Whatever method of preheating is used, care shall be taken when working with thick materials that the temperatures recorded are representative of those existing at the inner surface before tacking or making the root runs.

4.8.3 Gas Preheating

Preheating by gas shall be permitted under the following general conditions only:

• Only propane or butane shall be used. The use of oxy-fuel torches for this purpose is not permitted; only ring burners or torches of the “rosebud” type shall be used. When temperature indicating crayons are used, at least three ranges shall be employed, while heating, to give progressive forewarning as the correct temperature is approached

• For the tacking or welding of individual bosses, nipples or attachments to pipes or headers, if post weld heat treatment is required

• For small bore pipes and tubes of carbon steel and 15Mo3, gas preheating may be used in the works and on site

• For welding of protection shells and sleeves of wall penetrations to tubes

• Regarding large bore piping, headers and shells, gas preheating may be used in the shop only for welds in carbon steels and 15Mo3 , including tacking and local repairs for which post weld heat treatment is not required

• For welding form pieces and stubs to pipes if preheating by resistant heating elements is not feasible. This is to be subject to individual concession applications

• For tacking and for welds on carbon steel and 15Mo3 which are to be completed by SAW





• Gas preheating shall not be used for the welding of the following materials:

o 13CrMo4-4;

o 10CrMo9-10;

o 14MoV6-3

o 15NiCuMoNb5-6-4;

o 7CrMoVTiB10-10;

o 7CrWVMoNb9-6;

o X20CrMoV12-1;

o X10CrMoVNb9-1;

o X10CrWMoVNb9-2 and

o VM12-SHC.

NOTE: Gas preheating may be used on site for the welding of carbon steels and 15Mo3 when the dimensions are 250 mm OD or less and a thickness of 12 mm or less.

4.9 EXECUTION OF WELDS

4.9.1 Weld Progression

Pipes with OD larger than 150 mm shall be welded simultaneously from opposite halves by two welders. The welders shall match each other layer by layer in order to achieve a thermally balanced weld. For pipes with long axis orientated horizontally, the starting positions shall be at the six-o’clock position. For each subsequent layer, the start and stop position for the respective welders shall be shifted by at least 25 mm towards or away from that of the previous layer in order to stagger the starts and stops and not positioning it on the same plane radial to the pipe centre line.

4.9.2 Joint Root Welding

Root runs shall be completed without interruption except for changing of position by the welder or weld consumable changes. Confirmation of full penetration welded from one side only, root inside profile acceptance check shall be performed by an assistant to the welder by observing through the root gap at a position conveniently away from the welder. Before final closure the weld supervisor shall confirm by visual inspection that no gross weld defects deemed outside the acceptance criteria exist on the weld root inside surface. The weld root hot pass shall commence immediately after closure of the root gap. Temporary attachments for weld joint alignment shall be kept in place until at least 20% of the thickness of the final weld has been laid down. If welding is interrupted at this critical stage due to a power failure or other emergency event, the weld shall be cut out and a new weld shall be started.

4.9.3 Measuring Pre-Heat and Interpass Temperature

Each welder shall be issued with at least two temperature indicating crayons, one rated at the minimum preheat temperature as required by the WPS, and the other rated at the maximum interpass temperature value. After completion of each weld layer both temperature values shall be checked to be within the WPS requirements at a position 5 mm away from the weld groove preparation edge. In the event that the crayons indicate temperature excursions, the temperature value shall be confirmed by a calibrated digital contact thermometer and recorded. Non-contact infra-red type thermometers shall only be used for non-procedural comparative temperature measurement, not for checking and confirmation purposes.





4.9.4 Interruption of Welding

The welding cycle shall not be interrupted for an unlimited time unless the weld can be maintained at the pre-heat temperature. In the event of a power failure during welding of the root, where the duration of the failure is such that the weld area cools below the pre-heat temperature, the weld operation shall be halted, the weld removed, the tube/pipe ends ground back to bright metal, NDT inspected and re-prepared before the welding operating shall start again.

In the event of a power failure during any stage of the welding of readily hardenable alloys such as:

• 14MoV6-3


• 7CrMoVTiB10-10;

• 7CrWVMoNb9-6;

• X20CrMoV12-1;

• X10CrMoVNb9-1;

• X10CrWMoVNb9-2;

• VM12-SHC

Where the duration of the failure is such that the weld area cools below the pre-heat temperature, the weld operation shall be halted, the weld removed, the tube/pipe ends ground back to bright metal, NDT inspected and re-prepared before the welding operating shall start again.

If the construction code permit an interruption in welding, the preheat temperature shall be maintained until welding can be re-started.

4.9.5 Attachment Welds

All attachments shall be welded by welders appropriately qualified and according to the relevant WPS. Welding arc parameters shall be set at the lowest practical values within the range stipulated by the WPS in order to minimise the possibility of penetration through the tube/pipe wall. Weld geometries and sizes shall be strictly according to the design requirements. Oversizing or welds more than 10% above the dimensions required by the design shall be cause for rejection. No weld shall be started or terminated at high stress intensity positions such as at the ends of attachments, but positioned at least 15 mm away (keep on welding around the corner).

4.9.6 Interpass Cleanliness

Flux, weld spatter and slag shall be removed from the weld joint preparation with parent material dedicated wire brushes (for example stainless steel tubes and pipes require matching brushes) before starting to deposit successive passes. Superficial pneumatic needle peening shall only be permitted to the extent necessary to clean the welds, or where called for in an approved welding procedure. In cases where a pneumatic peener is used, the air release aperture shall be positioned to the effect that the exhaust air stream is directed completely away from the work surface, so that no cold air to be directed towards the weld. Supply air shall be completely dry and free of contaminants such as lubrication oil therefore confirmation of the functionality of filters and traps shall be included in the QC checklist.

Under no circumstances will the practice of so-called slag ‘burn-out’ of a previous weld-stop after changing to a new covered electrode be allowed, chipping or grinding to remove slag of each weld stop before commencing with the next run start shall be performed.





After completion of each weld layer, the completed weld surface shall be smoothly and evenly ground to bare metal.

4.10 SNAG WELDS

Where applicable, the definition of a snag weld shall be specific to each contract and shall be mutually agreed on between Eskom and the principal Contractor before the contract commences. No effort shall be spared to equip the welding team with the best possible equipment and welding aids in an effort to reduce the incidence of snag welds.

4.11 DRESSING OF WELDS

4.11.1 Preparation for Inspection

All welds in high pressure pipework and components shall be subject to in-service inspection and dressing of welds shall be such as to enable ultrasonic testing to be carried out.

Welds shall be dressed before final PWHT, flush with the adjacent pipe outside diameter level to check for transverse and longitudinal indications in the following materials:

• 14MoV6-3;


• 7CrMoVTiB10-10;

• 7CrWVMoNb9-6;

• X20CrMoV12-1;

• X10CrMoVNb9-1;

• X10CrWMoVNb9-2

• VM12-SHC.

For cases where the weld caps are not required to be dressed flat, weld edges shall be smoothed by grinding to blend the weld cap to the pipe and to eliminate undercut. Welds on form pieces shall be dressed all over by grinding to a smooth contour. When the weld reinforcement is fully dressed, wall thickness checks shall be carried out and recorded. The minimum weld thickness shall not be less than the minimum wall thickness. For grinding after final heat treatment, local overheating due to inefficient techniques shall be avoided at all cost. The correct size grinding wheel shall be used for this purpose. All grinding shall be supervised to reduce heat input.

4.11.2 Dressed Weld Profile Requirements

To permit an Examination Level 2 according to BS EN 17640 [25], all welds in HP pipework with OD of 100 mm or greater shall be ground as follows:





4.11.2.1 In all cases the weld cap and the parent metal shall be blended to eliminate undercut.

4.11.2.2 Welds on pipes for carbon steel and 15Mo3, shall be ground to a partially dressed near-flat surface profile category SP3 according to BS EN 17640 [25].

4.11.2.3 All welds for the following alloys:

• 14MoV6-3;

• 15NiCuMoNb5-6-4.

• 7CrMoVTiB10-10;

• 7CrWVMoNb9-6;

• X20CrMoV12-1;

• X10CrMoVNb9-1;

• X10CrWMoVNb9-2;

• VM12-SHC;

Shall be ground to a fully dressed surface profile category SP4 according to BS EN 17640 [25].

4.11.2.4 Fillet welds as on branch pieces, stubs and nipples of greater than 100 mm shall be ground to a profile category SP7 according to BS EN 17640 [25];

4.11.2.5 Fillet welds of load-bearing attachments shall be ground to a dressed flat surface profile category SP7 according to BS EN 17640 [25];

4.11.2.6 The welds of pipework of less than 100 mm OD shall be ground to remove undercut, and to permit an adequate level of NDT;

4.11.2.7 Each wheel used for grinding alloy welds shall be reserved for grinding one composition only, and shall be so marked. The surface finish on the ground area shall conform to BS EN 17640 [25];

4.11.2.8 Butt welds which have been fully dressed to category SP4 shall be checked for remaining thickness if the area of the weld has been ground below the level of the parent metal either side. Such welds shall be delineated by light centre punch marks at 100 mm spacing round the circumference 25 mm away from the centre of the weld.

4.11.3 Arc Strikes

Arc strikes shall be avoided as far as if possible, but if present, ground to smooth contours and surface crack testing shall be carried out in the areas of the arc strike without causing the remaining wall thickness, after grinding, to be less than the minimum calculated design wall thickness. Gouge marks shall be ground to smooth contours and surface crack testing carried out in the areas of the gouge marks. The need for repair welding after grinding of arc strikes and gouge marks shall be determined by Eskom and shall be subject to approval.





4.12 POST WELD HEAT TREATMENT

Heat treatment procedures shall be based on the basic guidelines provided in the Eskom Welding Standard 36-775 [34] and the specification BS EN ISO 17663 [13].

Pertinent to the heat treatment of high pressure and temperature tubes and pipes, emphasis shall be placed on the following:

4.12.1 Base Material PWHT Requirements

The construction codes provide minimum mandatory requirements for different alloys. Carbon steel and 15Mo3 are exempted from PWHT for wall thicknesses up to 30 mm; however Eskom will reserve the right to require stress relief of thick section ISO15608 Group 1 material [17] components. For ferritic grades from 13CrMo4-4 upwards to higher alloyed grades, PWHT for tempering purposes of the HAZ for all components inside and outside the boiler regardless of wall thickness, shall be required by default.

4.12.2 Cooling Down for Transformation

Weld joints involving ferritic/martensitic grades X20CrMoV12-1; X10CrMoVNb9-1; X10CrWMoVNb9-2 and VM12-SHC shall be cooled down from minimum interpass temperature to between 90 and 100ºC (or specific temperature calculated from accepted empirical formulae) to ensure full martensite transformation before commencing with PWHT.

4.12.3 Heating and Cooling Rates

Guidelines as provided in the applicable construction code, BS EN 1011 [9] and BS2633 [14] shall be followed. For weld joints involving components with more than 100 000 accumulated operating hours constructed from 13CrMo4-4 and all higher alloyed grades, the maximum heating and cooling rates shall be 50°C per hour maximum.

4.12.4 Heat treatment Procedure Qualifications

The procedure of qualifications of weld pre-heat and post-weld heat treatment shall be performed in conjunction with welding procedure qualifications in accordance with the applicable construction code. The contractor shall submit heat treatment procedures, including a dummy chart of time versus temperature showing the heating and cooling gradients, to Eskom for approval before the contract commences.

4.12.5 Minimum Heat Treatment Procedure Requirements

The heat treatment procedure shall include the following parameters:





4.12.5.1 Methods of heat treatment;

4.12.5.2 Furnace atmosphere (where applicable);

4.12.5.3 Heat treatment, time at temperature, heating and cooling rates;

4.12.5.4 Number, location and method of attachment of thermocouples (sketches required);

4.12.5.5 Type of insulation and locations (where applicable);

4.12.5.6 Method of heat input control to obtain uniform heating without creating localised hot spots;

4.12.5.7 Results of welded specimens tested, in accordance with the required codes; after heat treatment;

4.12.5.8 Overlap distance of section of pipe requiring heat treatment, to provide the required temperature gradients;

4.12.5.9 Method and frequency of temperature measuring and recording equipment calibration. Calibration shall be in accordance with SANS 17025 [33].

4.12.6 Post Weld Heat Treatment Method

When required by the code, post weld heat treatment shall be carried out in a closely controlled manner, and electric heating shall be the preferred heating source. Methods for heating given below are in order of preference.

4.12.6.1 Temperature controlled electric oven;

4.12.6.2 Portable muffle furnace;

4.12.6.3 Induction coils;

4.12.6.4 Resistance heating elements;

4.12.6.5 Gas fired top hood furnace: Only propane or butane gas shall be permitted to fuel burners with a diffused neutral flame. The use of acetylene as fuel shall not be permitted.

4.12.7 Temperature Control

4.12.7.1 A record of all post-weld heat treatment, on piping of wall thickness equal to or greater than 12 mm, including that carried out with heating torches, shall be chart recorded. All charts shall be submitted for approval after the final heat treatment operation.

4.12.7.2 Cr-Mo steel pipework of outside diameter less than 188mm and or wall thickness less than 20 mm, may be allowed to cool to room temperature prior to post-weld heat treatment.





4.12.8 Resistance Heating

4.12.8.1 The number and position of thermocouples shall be such as to ensure an accurate recording of all heat treatments and is subject to approval by Eskom.

4.12.8.2 The method of attachment of the thermocouples to the pipework shall be submitted by the Contractor for approval.

4.12.8.3 The thermocouple ferrule at the hot junction shall be of carbon steel in the case of carbon steel and grade 15Mo3 steel. For Cr-Mo-V, Cr-Mo and stainless steels, the ferrule shall be of the same alloy steel as the pipe.

4.12.9 Area Subjected to Heat Treatment

The area to be heated each side of the weld shall be sufficient to ensure that the weld itself, its heat affected zone and the adjacent parent metal all achieve the specified temperature for the required time. A zone covering a minimum distance of 100 mm on each side of the weld joint shall be allowed for this.

4.12.10 Temperature Recording

Post weld heat treatment temperatures and times shall be recorded from at least four thermocouples on a calibrated chart recorder. These records shall be submitted to Eskom for approval, and shall include sufficient information, items and their numbers, material, heat number, etc., to allow full identification of the components being heat treated.

For redundancy purposes, each position to be measured shall have at least two thermocouples attached to the work piece, only one thermocouple is required to be connected to the controlling and monitoring devices at any time.

4.12.11 Interruption of Heat Treatment

In the case of a power failure during the post weld heat treatment, if the actual soaking time is equal to or greater than the minimum required soaking time, the weld shall be insulated and allowed to cool slowly at the required cooling rate. If the cooling rate exceeds the permissible cooling rate, the need for a re-heat treatment shall be investigated. This shall be recorded and reported to Eskom.

If the power failure occurs during the heating cycle, the weld shall be cooled slowly and the complete heat treatment cycle repeated. Only two heat treatment cycles shall be permitted. Eskom shall be consulted if indications are found after the second heat treatment. If repair welding and additional heat treatment is authorised it shall be demonstrated by the Contractor that the base metal physical properties are not lower than the specified minimum.

4.13 INSPECTION OF COMPLETED WELDS

4.13.1 General NDT Requirements

The contractor is responsible for ensuring that NDT contractors and their equipment operators are correctly qualified and on the approval list as required by the Eskom Standards 32-631 [36]. All NDT shall be performed to meet the requirements of Eskom NDT Standard 32-632 [35].





In conformance to the Eskom NDT standard 32-632 [35], the contractor shall supply or contract a company to provide instruments, equipment and materials for carrying out NDT in accordance with the construction code, as and when required by the contract. All the associated measuring and recording equipment must be calibrated by a SANAS approved metrology test laboratory, with traceable document proof, to national calibration standard requirements.

For the material grades 14MoV6-3; P24; X20CrMoV12-1; X10CrMoVNb9-1; X10CrWMoVNb9-2 and VM12-SHC, ffinal inspection of welds shall be delayed and performed at least 48 hours after cooling down from welding and PWHT (where applicable all welds shall be visually inspected after completion).

All weld surfaces shall be free from defects indicative of poor workmanship and shall be cleaned of all foreign material after completion of welding.

4.13.2 Main Inspection

4.13.2.1 Characterisation and Recording of Indications

All recordable indications shall be characterised as indicated in ASME BPVC Section V [5] or BS EN ISO 23279 [26] as required by the plant design code, in conjunction with Eskom procedure 36-1162 [41] for further evaluations.

4.13.2.2 Assessment of Indications

All recordable indications shall be assessed as per ASME BPVC [5] or BS EN ISO 17640 [25] where applicable.

4.13.2.3 Acceptance Criteria

When required or specified, weld examination procedures and acceptance criteria shall be in accordance with the applicable construction codes, ISO 5817 [12], ASME BPV Code Section V [5] and BS 2633 [14] in addition to agreement by Eskom.

4.13.2.4 Inspection Records and Reporting

An inspection record shall be kept in conjunction with the welding schedule which shall be updated as soon as a welding location, as indicated in the welding schedule, is completed. It shall indicate all repairs carried out and non-destructive examination performed on the weld or group of welds. Defect rates shall be as required by Eskom Standard 36-1162 [41].

4.13.3 Acceptance of Welds

Acceptance of any weld shall be according to the requirements agreed in the contract, any case that appear to be non-conforming may be accepted at the discretion of the Eskom Engineer. Such an intervention is typically a calculation for flaw acceptance outside the specified acceptance criteria based on engineering principles.





4.14 WELD REPAIRS

4.14.1 Authority to Repair

Repairs on completed welds shall not be affected without approval of the Eskom Engineer. These repairs shall be made as soon as possible after inspection of a weld.

4.14.2 Removal of Defects

4.14.2.1 Defects shall be completely removed by chipping, gouging, grinding or other approved methods (for the type of material being repaired) to clean metal. The excavated area shall be examined by an accepted method to ensure complete removal of the defect.

4.14.2.2 A pneumatic hammer or chisel shall not be used while further welding is in progress on the pipe length.

4.14.2.3 Portable grinders may be employed on all types of steel. Care shall be taken to avoid overheating and contamination of the pipe material by the grinding wheels.

4.14.2.4 Carbon arc air gouging shall not be permitted on X20CrMoV12-1; X10CrMoVNb9-1; X10CrWMoVNb9-2 and VM12-SHC and 14MoV6-3. On all other materials, an appropriate preheat shall be used if air gouging is carried out.

4.14.2.5 All gouged surfaces of welds, prior to repair, shall have a minimum of 2 mm of metal ground away in order to ensure complete removal of any oxidised material before re-welding commences.

4.14.3 Weld Repair Procedure

4.14.3.1 Weld repairs in areas where defects have been correctly removed, shall be made using the same welding procedure used for the original weld, referenced in a concise job specific repair method statement.

4.14.3.2 The repaired areas shall be re-examined using the same inspection procedures by which the defects were originally detected.

4.14.3.3 Only two repair attempts shall be allowed on any one weld areas. No further attempts shall be carried out with-out approval.

4.14.3.4 The Contractor shall submit, for Eskom’s approval, a plan for corrective action in each instance of rejection of a major component due to faulty/defective welding.

4.14.3.5 For very limited excavations, temper bead repairs without subsequent heat treatment may be considered by Eskom on some grades of tubes/pipes. ANNEX D illustrates the concept of temper bead technique.





5. RECORDS AND CERTIFICATES

5.1 GENERAL REQUIREMENTS

5.1.1 Retainer Period

The Contractor shall retain all relevant signed off inspection and test records in hardcopy and electronic format for a minimum of 12 years after commissioning of the plant or for the time specified in the contract after which time the records shall be offered to Eskom before destruction.

5.2 SPECIFIC DOCUMENTS FOR RECORD KEEPING

• Welder qualifications and procedure qualifications test certificate.

• Charts recording the weld preheating and post-weld stress relieving treatment.

• All radiographs together with the relevant means of identification.

• Weld defect reports.

• Records of location and extent of all weld repairs.

• Full test reports on magnetic particle-, ultrasonic-, liquid-penetrant- or radiographic examination in accordance with the relevant Eskom procedure.

• Full test reports on destructive testing.

• Material test certificates for welding consumables.

• Quality Control Plans (Verified and signed).





6. ANNEXES

A. Large Bore Pipe Weld Preparation Check List (Example for Tutuka Power Station)

B. Table of Eskom Plant Materials

C. Table of Recommended Weld Consumables

D. Temper Bead Technique





ANNEX A - Large Bore Pipe Weld Preparation Check List (Example for Tutuka Power Station)





ANNEX B - Table of Eskom Plant Materials

DIN 17175/17459 BS 3059 / 3602 / 3604 Gr: Also known as BSEN 10216 ASME II Werkstof

St35.8 320; HFS320; HFS360 Carbon steel P235GH A106 Grade A 1.0305 / 1.0345

St45.8 440; HFS430 Carbon steel P265GH A106 Grade B 1.0405 / 1.0425

15Mo3 ~243 ½Mo 16Mo3 A335 Grade P1 1.5415 / 1.5423

15NiCuMoNb5 591 15NiCuMo 15NiCuMoNb5-6-4 1.6368

13CrMo4 4 ~ 620 1Cr-½Mo 13CrMo4-4 A213 / A335 Grades T/P12

1.7335

10CrMo9 10 622 2¼Cr-1Mo 10CrMo9-10 A213 / A335 Grades T/P22

1.7380

14MoV6 3 ~ 660 ½Cr-½Mo-¼V 14MoV6-3 1.7715

X20CrMoV12 1 762 12Cr or X20 X20CrMoV12-1 1.4922

P24 7CrMoVTiB10-10 A405 Grade P24 1.7378

P23 7CrWVMoNb9-6 1.8201

T/P91 X10CrMoVNb9-1 A213 / A335 Grades T/P91

1.4903

P92 X10CrWMoVNb9-2 1.4901

VM12 VM12-SHC

X6CrNi18 11 304S25 304H X6CrNi18-10 A213 Grade TP 304H 1.4948

X10CrNiNb18 9 347S18 347H X6CrNiNb18-10 A213 Grade TP347H 1.4550





ANNEX C - Table of Recommended Weld Consumables

Recommended filler metals for welding of materials operated at high temperature including corresponding product standards

Base Material Recommended filler acc. to standard

MMA electrodes Bare wires/rods

EN ISO 3580 (EN 1599) EN 12070

15NiCuMoNb5-6-4 E 50 4 Mo B 42 E 50 4 1 Mo B 42 H5

W MoSi

7CrMoVTiB10-10 E ZCrMo2VNb B 4 2 H5 W ZCrMo2VNb

7CrWVMoNb9-6 E ZCrWV2 1,5 B 4 2 H5 E ZCrWV2 1,5

X20CrMoV11-1 E CrMoWV12 B 4 2 H5 W CrMoWV12Si

X10CrMoVNb9-1 E CrMo9 B 4 2 H5 W CrMo91

X10CrWMoVNb9-2 E ZCrMoWVNb 9 0,5 2 B 4 2 H5 W ZCrMoWVNb9 0.5 1.5

VM12-SHC E Z CrCoW12 2 2 WCrCoW12 2 2





ANNEX D - Temper Bead Technique

APPLICATION OF TEMPER BEAD WELDS Apply a temper bead to the outer edge of the last stringer weld deposit as indicated in the diagram. The edge of the temper bead must be placed as accurately as possible 3mm away from the edge last weld bead.

3mm +- 0,5mm

Weldmetal Base material

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