about delayed coking unit inspections

Raffineria di Gela SPA

European Delayed Coking European Delayed Coking Operations & Technologies Seminar Operations & Technologies Seminar

30 September 30 September –– 1 October 20041 October 2004

Raffineria di Gela – C.da Piana del Signore, 93012 Gela (CL) - Italy

A cooperation of ENI R&M Raffineria di GELA - ConocoPhillips

ABOUT DELAYED COKING UNIT INSPECTIONS

Carmelo Aiello – ENI R&M - Gela Refinery


Introduction

Delayed Coking Units, in the world, like all refinery units in common have the basic process whereas every unit, essentially, has different features like capacity, performances, metallurgy, operation, etc. that give, for a single unit, different troubles.However, even in the diversity, many problems are common. Inspection methods, corrosion and metallurgic knowledge, with the aid of RBI, NDT, assessment or remaining life, consolidated repair welding methodologies, etc. contribuite to provide reliability of operation and security.

A review of knowledges that can help to manage Delayed Coking Unit inspections are given.


DELAYED COKER PROCESS


Heart of Delayed Coking Unit

Raffineria di Gela SPATypical cycle of delayed coker process


COKE DRUMS

API Survey of Findings 1996 – Final Report Nov.2003

- Design

- Operation

- Shell Deterioration

- Shell Bulging

- Shell Cracking

- Shell Materials

- Skirt Deterioration

- Cladding


DESIGN

1) New drum material selection has been towards increasing Chrome Molyalloy content

2) Do not exists some apparent correlation between drum life and drummaterial

Frequency of Selection for Shell and Cone Base Materials

Shell and Cone Material CS C-½ Mo 1 Cr 1-1/4Cr 2-1/4Cr

Percentage 18,5 31,5 29,6 16,7 3,7


OPERATION

1) Do not exists correlation between drum cracking and fill cycle time 2) Drum operating parameters such as initial quench rate and proofing

quench practice rather than metallurgy appears to have a greater influence on drum cracking

Typical short cycle coking operations


SHELL DETERIORATION

1) First bulge appeared sooner than first through wall cracks2) Many drums had cracks in bulging3) Cracks are circumferential 4) Most cracks and bulges were located in shell courses 3#,4# and 5#

(course 1 # is at the bottom)

SHELL BULGING

The average time until the first observed bulge was 11 years. This coincided with the reported experience of the newer drums.


SHELL CRACKING

Cracking did not only occur at bulges but mostly in non-bulged areas (in the weld of shell)

After crack repairs had been performed, has been reported that cracking, mainly, had re-occurred.


SHELL MATERIALS

Table below gives the average, minimum, and maximum cycles for surveys reporting cracked and noncracked drums.


SKIRT DETERIORATION

1) Skirt cracking is a great problem2) Many cracks propagated into the shell3) Skirts with slots experienced cracking4) Many in-line skirts did not experience cracking5) Many skirts that had flush ground welds were found without

cracking

There are two different primary areas of skirt cracking:1. On either side of the skirt to shell weld, and 2. Associated with slots and keyholes


Various Types of Skirt Cracking


CLADDING & CRACKING

1) Some cracks had occurred in the cladding (30% of survey). 2) No one indicated that corrosion had initiated any cracking but that

pitting and general corrosion had occurred.3) Often is some type of corrosion damage, such as pitting, general

corrosion or other types of corrosion.


OTHER ASSOCIATED PROBLEMS IN COKE DRUMS

- Overhead Piping

- Drill Stem

- Bottom Gasket

- External Attachment or Bracket or Pad


1) Coke formation 2) Foam carry-over3) Pressure drop

OVERHEAD PIPING

1) Failure of drill stem2) MaintenanceDRILL STEM

1) Type bottom gasket2) Associated problemsBOTTOM GASKET

EXTERNAL ATTACHMENT or BRACKET or PAD 1) Welding cracking


OVERHEAD PIPING

Coke formation

The vapor overhead line runs from the top of the coke drum to the fractionator. The temperature in the line is around 450°C . The temperature is decreased by about 30°C by injecting hot heavy cokergas oil into the line as quench oil. This prevents coking in the line. The heavy coker gas oil is a wash oil coating the inside of the pipe. If the liquid layer dries out, coke starts to form and often the line plugs, particularly in the elbow.


Foam carry-over and Pressure drop

Possible foam carry-over in overhead lines is even due at radiation level meter of the coke drum that is not accurate. Also, high pressure drops in overhead lines can cause foaming in the cokedrum during the drum switch. Prevention of coke in the line is importantsince this will increase the pressure in the coke drum thus increasing refluxof gas oil in the drum. Decreasing coke drum pressure increases liquid yield (decreases cokeyield).Leave the insulation off the overhead lines helps drop the temperatureand keep the inside wetted.Vapor line sizes are very large in order to obtain the minimum amount ofpressure drop.


DRILL STEM

Failure of drill stem is largely dependant on the type of coke to cut, particularly if coke is hard.It should have periodic checks. Free fall arrestor aux. cable lubrication, check/replace rotary joint gear box lube oil,greasing of air hoist wire rope & its guide, replace air hoist motor lube oil, lubricating all pulley blocks, inspection of nozzle tips can all be monthly activities. Without periodic checks is possible failure of stem in welding and, particularly, in threaded zone.


BOTTOM GASKET

Type bottom gasket can be a problem.If the gasket is double jacketed, flat metal or other sheet material should only be used once since they rely on being compressed to seal. Ring type gaskets can be reused since they rely on a metal-to-metal contact line that does not degrade significantly after each use, but will eventually need to be changed.


EXTERNAL ATTACHMENT or BRACKET or PAD

Normally, after some year of operation is possible to have cracks in welding of radioactive source pad supports. Any plate of support or attachment to weld in the shell of coke drum must be avoided.

If is not possible all weld attachment (see a nozzle reinforcing pad or support bracket or insulation supports) because the drum is heated and cooled, this will result in a cyclical force applied at the perimeter as unequal expansion rates that can cause cracks to develop in the weld or drum metal even insulated. In this case, every turnaround should be checked regularly for cracking


FURNACE/S

Main factors to consider for a coker furnace are :

• Design

• Coker Tube Furnace

• Heater Tube Decoking

Design

Normally the modern-day furnace has two to four passes per furnace. The tubes are mounted horizontally on the side and held in place with alloy hangers. The furnace tubes are around 100 mm ID with 6 to 12 mm wall thickness and are at least a 9% chrome alloy even if someone uses 5% Cr. Higher alloy tubes are being used with the more rapid steam spalling and steam-air decoking methods. Aluminized tubes have been tried, but offer no advantage.


Coker Tube Furnace

The coker tube furnace is the true heart of the delayed coking process. The heater furnishes all of the heat in the process. The outlet temperature of a coker furnace is typically around 500°C with a pressure of about 4 bars.

Heater Tube Decoking

When coke forms in the heater tubes, it insulates the inside of the tube which results in elevated temperatures on the outside of the tube. Normally, when temperatures approach 677°C (1250°F) on the exterior skin thermocouple, the furnace must be steam spalledand/or steam-air decoked or cooled down and cleaned by hydraulic pigging.


Possible troubleshooting in coker heater are following:

• Heater tube deposits

• Skin temperature

• Flame impingement

• Internal tube corrosion

• Creep


Heater tube deposits

Internal coke formation is part of process. Thickness of coke depends of many factors. Coke deposits have very high content of iron, silica and sodium.Deposits recovered from return bend clean-out plugs are sometimes long cylindrical shapes and in another case looked like a thick scallop shell. These depend of feed, steam, water, etc.etc. Iron sulfide is probably not totally removed in steam-air decoking and deposits are mostly sodium, silica and calcium. Nevertheless, normally, shutdown of furnace depends always from achieving skin temperatures and if heater tubes are not designedadeguately can depend even pump feed high pressure to obtain 4-5 bar in outlet piping.


Skin temperature

Skin temperature is important for decocking and for life of furnace. Relatively to tube materials API RP 530 gives maximum allowable temperatures. Allowable max temperature for 9% Cr is 705°C. Nevertheless, there are furnaces with 9% Cr that operate with skin temperature until 730°C and appropriately designed overcome 100.000 hours.

Flame impingement

Flame impingement is a matter. Needs to check periodically burners efficiency to avoid higher skin temperatures that not are possible to look in control room because can be far of skin thermocouples.


Internal tube corrosion

Internal tube corrosion depend of sulphur contents of feed. 9% Cr or P91 are compatible with rate of corrosion by sulphur. McComonycurves gives indications about corrosion rates by sulphur content.Upgrade materials like 347 or H grade SS can be used with some precautions even if there are experience with 347 SS without precautions (steam or Soda ash) by many years.

Creep

Furnace radiant zone operates in creep range with ferritic or austenitic steels.Creep is a mechanism that above 400°C produces, into a material, a intergranular microvoids until microcracks that decrease mechanical strength of material producing failures. Normally, tubes heater design is 100.000 h. It is possibile to operate until 730°C (End Of Run) with 9% Cr. Considerations about allowable stress, corrosion rate, carburization, etc., must be carefully taken.


FURNACE OUTLET PIPING

The heater outlet temperature in DCU is around 480-490°C. If the coke drum inlet temperature is lower can depend from length of outlettransfer line and for this can be heat loss but not only. Normally, for coke deposits, it is possible that oulet piping plugs in any zone. In this case needs to clean, periodically, oulet piping to avoid increased pressure in furnaces.


GENERAL PIPING & FITTINGS

Special areas of piping engineering associated with delayed coker, in the zone of Coke Drums, are :

1) Piping stress analysis and pipe support engineering consideration of thermal expansioncaused by operating temperature and cyclic operating conditions in piping around coke drums.

2) Special consideration for piping subject to coke deposition and

3) Valving considerations that locate valves close to the drum to wichthey are connected such that they appear to be associated with the drum near which they are located.


The most complex system is the coke drum overhead vapour piping attached to the top of coke drums and are subject to:

1) coke drum thermal growth,

2) coke drum “banana effect” which is drum bending of about 8 to 10” in any horizontal direction and according to operators happens in varying degrees of severity and regularity on some cokers that can occur if uneven drum wall quenching take place due to quench water channelling to one side of the drum.

3) most severe cyclical operation on coke drum inlet and overhead piping such that the piping pairs are subject to the alternative hot, during coking, and cold, during quench-decoking operation of any pair of drums and

4) a different set of operating conditions during startup as coke drums undergo commissioning and decommissioning typically every 24 hours.


Other piping and fittings that need annual check, in this case, for corrosion or to verify if has been mounted a CS material instead that 9% Cr or Alloy Steel generally, is related at feed and outlet piping heater.Often is replaced pipe or fitting in CS where needs alloy steel.In this case corrosion rate is higher with possibility of leakage and/or fire due at high temperatures of stream.


HISTORY GELA REFINERY COKE DRUMS

• Design

• Shell Deterioration

• Skirt Deterioration

• Drill Stem

• Radioactive Level Meter Pad

Supports


COKING 1 UNIT

DESIGN

The 4 old coke drums were in C-Moly (1963) with about 6 mt in diameter with the drilling deck and derrick at the top of the two drum pair.New 4 coke drums from 2001 with same size are in 1- ¼% Cr -½% Mo and until now there is not some evidence


SHELL DETERIORATION

Gela Refinery experiended, with 4 old drums (C-Moly) (1963), the first crack after about 2500 cycles (7 years) (1970) due at improperly water quench.After 15 years (1978) the drilling deck and derrick at the top of the two drum pair have been made independent for cracks in welding support plates. Until 1980 internal inspections were made, filling the drum with water and slowely empting, with rubber dinghy. Were old times because it was impossible to inspect accurately the shell apart security matters.Complete internal inspection, with scaffolding was made in 1983 (20 years – 7000 cycles).Were found, with dye penetrant, cracks in bottom four shell courses, bulging and tilting by measurements.


SKIRT DETERIORATION

In old drums every maintenance turnaround were checked skirt-shell welding, bulging and slots of skirt.Many cracks during the life of these drums were found in welding and in slots and keyholes like figure from API survey

In new coke drums, with new in-line skirt/shell design, until now, there is no evidence. In every maintenance turnaround external welding is checked with magnetic particles and all zone with shear waves UT

Cone

Shell

Skirt

Probe UT


COKING 2 UNIT

DESIGN

Two coke drums from 1989 with 8 mt in diameter are in 1- ¼Cr - ½Mo.


SHELL DETERIORATION

The first evidence of cracks (1997) were in welding of radioactive level meter pad supports. In 2003 other cracks in the same zones with “wrinkle” of 190 mm.With video laser scan circumferential crack in 4# - 5# shell course (1# from bottom) was found. In maintenance turnaround, with scaffolding, the crack was 25 mm deep. Always video laser was found others circumferential cracks only in HAZ of cladding in 3# - 4#, - 2# - 3#, 1# - 2# shell courses.

Bulging was measured in all two drums with some major evidence (see Figure)


32 mm

Crack 25 mm x1500 mm Profile of bulging


SKIRT DETERIORATION

Every maintenance turnaround has been performed magnetic particles in external welding and all zone with shear waves UT without no evidence. Attachment skirt-shell welding has a new design that like will say below give better reliability.


DRILL STEM

In Jan 2003 a failure of drill stem involved a shutdown of unit

Failure in threaded zone


Delayed Coking Unit - Areas of Vulnerability

- CORROSION AND METALLURGICAL ASPECTS

- INSPECTION PRACTICES & NDT TECHNIQUES

- GENERAL INSPECTION CONSIDERATIONS

- COKE DRUMS

- OVERHEAD PIPING

- FURNACE/S

- COLUMNS – VESSELS – HEAT EXCHANGERS

- FURNACE OUTLET PIPING - PIPING & FITTINGS


CORROSION AND METALLURGICAL ASPECTS

The knowledge of metallurgy, damages, welding and NDT techniquesgive an effort to plan an inspection program with costs optimitazionand a best reliability and operation security.

METALLURGY

Normally, in Delayed Coking Units, main materials used, for piping and associated components (pumps, valves, etc), related to corrosion, are CS where temperature is low and 5% or 9% Cr for temperatures exceeding 260°C. For temperature lower of 200°C, vessels, heat echangers, columns are in CS except bottom of column that is AISI 410 SS cladding.Metallurgy of Coke Drums can be from CS to 2 ¼ Cr-Mo, with AISI 405-410 cladding.Tubes of furnace/s, normally, are 9% Cr (P9 or P91), but in some case can be AISI 347 SS or 347H SS or 5% Cr.


CORROSION

Main types of corrosion in delayed coking units are the following:

• Sulfidic Corrosion

• Sulphide Stress Corrosion Cracking

• HIC (Hydrogen Induced Cracking) and SWC (Stepwise Cracking)

• Caustic Embrittlement

• Thermal Fatique

• Creep


Sulfidic Corrosion

•Sulfidic Corrosion is often associated with sulphur in crude oil (as organic sulfides and/or H2S).

•The total sulphur content (in wt. percent) is not a precise indicator of corrosivity of a crude oil

•At temperatures above 260°C, in CS and Alloy Steel, can cause severe pitting and general wastage.

•Corrosion rates can be estimated using the McComony curves.

•in Coking Units, particularly in furnace tubes where temperature of stream is higher of 450°C, and from McComony curves the corrosion rate should be very high, corrosivity, on the contrary, decrease for presence of internal deposits of coke that forms a barrier between the stream and base material.

•If the feed to furnace is hot, can be a high corrosion rate thatshould be monitored in feed piping system.


Sulfidic Corrosion

Items involved

•Bottom piping of Fractionator•Feed preheat exchangers and related piping

•Furnace/s tubes•Furnace/s outlet piping•Overhead Coke Drum piping


Sulphide Stress Corrosion Cracking

•Sulfide Stress Corrosion Cracking is a form of hydrogen stress cracking. It is relatively uncommon in carbon steel.

•To start SSCC needs presence of water and temperature up to about 100°C.

•Sulfide stress corrosion cracking can develop in areas of excessive metal hardness in excess of Rockwell C22.

•Even component of amine units are susceptible at this phenomena and other stress corrosion forms (see API 945), particularly GasAbsorber column and Amine Stripper with other associated items (exchangers, piping, etc.)


Sulphide Stress Corrosion Cracking

Items involved

•Column Process and Ammine Absorber•Reflux Vessel, Gasoil Stripper•Vessels in suction Compressor•Fractionator Condenser•Compressor Cooling Exchanger,etc.


HIC (Hydrogen Induced Cracking) and SWC (Stepwise Cracking)

. •This phenomena occurs at room temperature until at about 120°C with presence of H2S > 50 ppm. Reaction is accelerates by presence of CN-.

•Hydrogen Induced Cracking is due at the formation of nascent hydrogen from reaction between H2S, metal and water

•Hydrogen penetrates in metal and, in presence of internal discontinuities (inclusions, segregations or microstructural vacancies) forms even molecular hydrogen that increase in pressure and it gives blistering or SWC (Step Wise Cracking).

•Whereas blistering is easy to detect (visually or with thickness UT measurements), SWC needs accurate testing (see below in section NDT).


HIC (Hydrogen Induced Cracking) and SWC (Stepwise Cracking)

. Items involved

•Reflux Drum, Gasoil Stripper•Vessels in suction Compressor•Fractionator Condenser•Compressor Cooling Exchanger, etc.


Caustic Embrittlement

•The term caustic embrittlement is a misnomer

•Presence of NaOH in CS should be considered regard % of NaOH, operation temperature.

•The loss of ductility characteristic of caustic embrittlement is due to the reduction in load-carrying capability caused by the formation of a network of cracks

•The cracks are caused by alkaline stress corrosion cracking

•Stress relieved should be considered or choice of other materials regard graph for caustic soda service.


Caustic Embrittlement

Items involved

•All items where is utilized Caustic to low pH (Heat Exchangers, Vessels, etc)


Thermal Fatique

•When a material suffers heating and cooling, after several cycles, particularly in welding (HAZ), starts a crack propagating with a rate related to material toughness and produced stress from cycle.

•This phenomena involves mainly Coke Drums

•Is a matter that is always continuously checked to improve design and materials to minimize it.

•In Coke Drums crack initiation depends by many factors:- Water quench time- Warm up- Design and Material


Thermal Fatique

•Water quench time is many important. Shorter water quench time gives major probabilities to have cracking in short time (alwaysthousand of cycles)

•If during warm up fill the Drum before to achieve an adeguatetemperature to receive the feed, material of shell has a thermal shock

•Material appears not much important, but adeguate design for types of shell plates, attachment, skirt welding, pads, with thicker and C-Mo material are the best choice

Items involved

•Coke Drum and associated components


Creep

•Creep is a mechanism that above 400°C produces, into a material, a intergranular microvoids until microcracks that decrease mechanical strength of material producing failures

•Normally, tubes heater design is 100.000 h as API RP 530

•Furnace radiant zone operates in creep range with ferritic or austenitic steels

•Tubes mainly used are 9% Cr (P9 or P91)

•It is possibile to operate until 730°C (End Of Run) with 9% Cr. Considerations about allowable stress, corrosion rate, carburization, etc., must be carefully taken

Items involved

•Heater coker tubes


GENERAL INSPECTION CONSIDERATIONS

•To prepare an inspection program for a refinery unit, like coking unit, utilizing RBI, FFS, etc. needs experience in metallurgy, corrosion, welding, design, NDT techniques

Some considerations, but not exhaustive, about inspection of items are :

1. Regular thickness inspection procedures for corrosion monitoring

2. Hydrocarbon equipment operations above 205°C should receive more concentrated inspection attention

3. Increase inspection concentration on equipment containing environments having average corrosion rates of 0.5 mm per year or higher.


4. Consider special inspection measures where temperature gradientsand fatigue are likely

5. Be alert for wrong material installations, particularly CS vs Low-alloySteels

6. Watch locations where conditions may result in low-temperaturehydrogen attack (HIC or SWC)

7. Check vent, drain pipes and dead points where concentrate moisturescan lead to heavy corrosion with leakage

8. Check plug and connection pipes of pump casing


Be careful !!! Many accidents, about 95%, occur for leakage or failure of small componentsvent, drain pipes, dpcell pipes, pressure gage pipes, termowells, lubricant oil pipes, plug and connection pipes of pump casing,etc. etc.)


COKE DRUMS INSPECTIONS AND NDT

Possible troubleshooting are following:

• Shell welding cracking and bulging• Bulging• Skirt welding cracking • External attachment or bracket or pad welding

cracking• Cladding cracking• Overhead piping plugging• Bottom Gasket failure• Drill stem failure


Shell welding cracking and bulging

Circunferential crack

Circunferential bulging

Cracking of circumferentialwelding is due at thermalfatique related at variations oftemperature during a cycle.Most severity is during waterquench. Start of crack dependsfrom number and severity ofcycles. Often, before cracks,bulging appeared, but can be,in some case, associated.Normally, interested shellcourses are until 5# or 6#starting from bottom.



Grindingsmooth

Grindingsmooth

Circumferentialwelding

Weldingcrown

To minimize or delay welding cracks is possible.

Elimination of welding internal/external crown with a smooth grinding is, securely, a way to delay crack welding formation because, for thermal stress or thermal fatique, presence of initiated zone like non-linear profile increase stress levels in these zones.



Vertical plates

Another approach to minimize circumferential cracks and bulging is to use vertical plates in Coke Drum. Because thermal fatique involves, principally, until 6# shell course, starting from bottom, it is possible, with an appropriated design, to built or repair old Drums with vertical plates.


Skirt welding cracking

Cone

Shell

Skirt

Even for skirt welding, cracks are due at thermal fatique,particularly with old design likein API survey.New skirt welding design is nowmore reliable and is designedwith referential temperaturemeasurement, low-cyclefatique test, time dependenttemperature distribution, stressanalysis by FEM and fatiquecalculation based on strain/stressdata.

With this design scheme there are lower probabilities to have cracking.


External attachment or bracket or pad welding cracking

Normally, after some year of operation is possible to have cracks in welding of radioactive level meter pad supportsAny plate of support or attachment to weld in the shell of coke drum should be avoided.The only thing that can be do is reduce the size of the attachment such as by changing it to a small threaded rod or make it a forging that is integral to the shell with an extension shaped to whatever size need.

Padsupport

Pad supportwelding

Maincracks

propagatedcrack

Secondarycracks

Cracks in radioactive level meter pad

support welding


Cladding cracking

Clad material (type 405 or 410 or 410S) is a ferritic stainless steel and, at operation temperature, it suffers by embrittlement and in HAZ with any type of welding (Inconel 182 or Austenitic stainless steel), after several cycles, starts the crack.Is rarely to have pitting or corrosion and even it is occurs do not is a big problem.Disbonding can be occur, but often is due to cladding process.

Crack in HAZ of cladding


Bottom Basket failure

Type bottom gasket can be a problem.If the gasket is double jacketed, flat metal or other sheet material should only be used once since they rely on being compressed to seal. Ring type gaskets can be reused since they rely on a metal-to-metal contact line that does not degrade significantly after each use, but will eventually need to be changed.


Drill Stem failure

Failure of drill stem is largely dependant on the type of coke to cut, particularly if coke is hard.It should have periodic checks. Free fall arrestor aux. cable lubrication,check/replace rotary joint gear box lube oil,greasing of air hoist wire rope & its guide, replace air hoist motor lube oil, lubricating all pulley blocks, inspection of nozzle tips can all be monthly activities. Without periodic checks is possible failure of stem in welding and, particularly, in threaded zone.

New

Failure


NON DESTRUCTIVE TESTINGS IN COKE DRUMS

Coke Drums are subjected to thermal fatique that gives bulging and cracks in the shell or in skirt welding or attachment or pads.Every turnaround maintenance (about older than four years) should be checked skirt welding, attachment and pads welding.Frequency of internal inspection should be performed after 10 years maximum and then with an average of 4 years.

NDT techniques used to check the drums are:NDT techniques used to check the drums are:

• Video-laser technique

• Magnetic particle testing

• Acoustic Emission Testing

• Strain Gage and Temperature Measurements


Video-laser technique

This technique combines a laser mapping technique with a visual inspection via video camera to detect defects in coke drum shells.


Magnetic particle testing

Are used to check welding of skirt welding (slots, etc) and any external attachment or bracket or pad. Every turnaround should be performed to find cracks in welding of these components.Be careful if are present old repair made with Inconel 182 electrodes because togheter magnetic particles needs dye penetrant.


Acoustic Emission Testing

Most cracks are in the circunferential welds, and are longitudinal to the weld. Some have shown transverse cracks, and on rare occasions vertical cracks in the vertical seams. It is also common to find cracks in the heads, and in the conical section. Skirt attachment welds are also serious candidates for cracking. AET helps to detect and locate active cracking during operation with a map.

Probe

Cone

Shell

Skirt

Guidewave

Probe


Strain Gage and Temperature Measurements

It is possible to determine the interactions between operational parameters and the strain levels responsible for bulging and cracking.CokerPLUS is a program from ERA Technology that includes:• strain gauge and thermocouple

installation• finite element analysis• probabilistic remaining life assessment• operating cycle review and modification• condition assessment and metallographic

examination• sampling and testing• weld repair procedures.


OVERHEAD PIPING INSPECTIONS AND NDT

Some trouble to consider in overhead piping of coke drum is:

•Coke formation •Corrosion

NDT techniques used to check overhead piping are:

1. Infrared Termography2. Tube Thickness Measurements


Infrared Termography

Infrared CameraTypical lay-out of overhead coke drums line


Tube Thickness Measurements

These measurements can be made with :- UT to check tube and elbows thickness or- Digital Radiography (Digital X ray)

Tube

Probe UT

Typical UT measurements zone


Minimum Thickness of insulated elbow with Digital Xray


NON DESTRUCTIVE TESTINGS IN FURNACE/S

Furnace/s are subjected to several problems as following:

• Heater tube deposits• Skin temperature• Flame impingement • Internal/external tubes corrosion• Creep

NDT techniques used to check the furnace are:

1. Infrared Termography2. Tube Thickness Measurements3. Replicas



This NDT can be used to detect :- External temperatureof heater to verifyrefractory conditionsand for EnergyConservation.

- Skin temperatures- Hot spots in tubes byflame impingement

- Hot spots in tubes forheavy coke deposits intubes

Infrared Camera

Adeguate distance

External temperature of heater to verify refractoryconditions and for EnergyConservation



Infrared Camera

- Skin temperatures- Hot spots in tubes by flame

impingement - Hot spots in tubes for heavy

coke deposits in tubes

To consideremissivity value0.8 - 0.9



These measurements can be made with :- UT Thickness Measurements for Tube and Return Bend - EMAT- UT INTELLIGENT PIG

Tube

Probe UT

Typical tube thicknessmeasurements for tube and return bend


EMAT

This method uses a couplant-free EMAT (electromagnetic-acoustic-transducers) technology to send and detect ultrasonic vibrations through steel piping during a shutdown or maintenance turnaround. Global examinations of tubes for corrosion, erosion, pitting, cracking and other defects can be made automatically


UT INTELLIGENT PIG

A pig with UT probes provides to check weldings and wall thickness changes starting from a flange of convective zone and exiting from last tube of radiant zone.

Capabilities are to measure thickness of tubes, return bend, particularly in convective zone where often is impossible to inspect.Some difficulty and often impossible can be passing header tubes.

Disadvantages are poor indications in return bends and when tubes not are cleaned. Even a small layer of coke gives poor results.

Minimum diameter of tube that can be inspected is 4”


REPLICAS

Heater tubes are designed for 100.000 h at design conditions (pressure and temperature).Should be checked tube deteriorations due to creep for assessment and remaining life, after 100.000 h or before if skin temperatures have reached values above design, particularly for long time.Replicas are “stamps” of external microstructure that are examined with an optical microscopic to verify presence of creep (microvoids, linked microvoids, microcracks).


NON DESTRUCTIVE TESTINGS IN COLUMNS – VESSELS –HEAT EXCHANGERS

These items can be subjected to :

• Sulfidic Corrosion • Sulfidic Stress Corrosion Cracking • HIC (Hydrogen Induced Cracking) and SWC (Stepwise Cracking)

NDT techniques used are:

1. Magnetic particles2. Thickness Measurements3. C-Scan4. TOFD



This method is used to check internal welding for presence of cracks due to SCCC or where is possible for Caustic Embrittlement


Applications of this method has been explained in OVERHEAD PIPING


C-Scan

This a method that uses an UT probe and displays presence of HIC


TOFD (Time Of Fligth Diffration)

Even this technique uses UT probes to verify presence of SWC (Step-Wise Cracking) or cracks in skirt/shell welding and in near all zone.


NON DESTRUCTIVE TESTINGS IN FURNACE OUTLET PIPING - PIPING & FITTINGS

NDT techniques used to check these zones are:

1. Tube Thickness Measurements 2. Infrared Termography3. Magnetic particle testing4. Digital Radiography (Digital X ray) 5. PMI (Positive Material Identification)

Tube Thickness Measurements - Infrared TermographyApplications of these methods have been explained in OVERHEAD PIPING



This method is used to check welding after PWHT of 9% Cr and welding piping of Coke Drum zone to verify probable cracks due at thermal stress.

Digital Xray

Thickness measurements on-line on insulated piping


PMI (Positive Material Identification)

This method utilizing a radioactive source gives elements % of material. It is used only in turnaround maintenance. Is very useful to find CS fitting instead 9% Cr.


END OF PRESENTATION

THANK YOU FOR YOUR ATTENTION


IMPLEMENTATIONS FOR COKE DRUMS SECURITY OPERATIONS

Several companies have performed implementations for security operations in Coking Unit, particularly, in Coke Drums.Are listed follow some companies that have implemented or patented some security systems.


A) COKE DRUM TOP AND BOTTOM UNHEADING SYSTEM PATENTED

FOSTER WHEELER BOTTOM UNHEADING


ZIMMERMANN & JANSEN COKER VALVE TOP AND BOTTOM UNHEADING


DELTA VALVE BOTTOM UNHEADING


B) AUTOMATED COKE DRUM SWITCHING AND SAFETY INTERLOCKS

These companies have developed an Automated Coke Drum Switching and Safety Interlocks.

FLUOR DANIEL

CONOCOPHILLIPS


FLUOR DANIEL

about delayed coking unit inspections

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