gu-486 screening & monitoring bacteria guideline

Screening/Monitoring Bacteria Guideline

11/10/2005 i GU-486

Petroleum Development Oman L.L.C.

Screening & Monitoring Bacteria Guideline

UNRESTRICTED Document Number : GU-486 Filing key : UEC/1

Keywords: This document is the property of Petroleum Development Oman, LLC. Neither the whole nor any part of this document may be disclosed to others or reproduced, stored in a retrieval system, or transmitted in any form by any means (electronic, mechanical, reprographic recording or otherwise) without prior written consent of the owner.


11/10/2005 ii GU-486


11/10/2005 iii GU-486

Authorised For Issue 11/10/2005

Signed : ............................................... Michiel Jansen, UEC/1 UER, Head of materials and corrosion

The following table lists the four most recent revisions to this document. Details of all revisions prior to these are held on file by the issuing department.

Version No.

Date Author Scope / Remarks

1 11/10/2005 Suleiman Al-Maskiry UEC/13N

First issue


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Contents:

1.1 Introduction…………………………………………………………………….….1 1.2 Scope……………………………………………………………………………....1 1.3 Distribution………………………………………………………………………..1 2.0 Background…………………………………………………………………….….1 3.0 Bacterial counting/monitoring tests……………………………………………..…1 4.0 Bacteria screening/controlling methodology………………………………..……..2 5.0 Roles and Responsibilities........................................................................................3 6.0 Review and Improvement…………………………………………………..……...3

Appendix A Glossary of Terms, Definitions & Abbreviations


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1.0 Introduction The purpose of the document is to provide guidance to screen and monitor bacterial activity in PDO liquid lines. The guidance will enable exploring lines suffering from bacterial corrosion attack and assessing the need for biocide treatment. 1.1 Scope It is restricted to pipelines and headers carrying liquid phase fluids. 1.2 Distribution The document will be distributed to PDO Corrosion control engineers, contractor corrosion engineers, pipeline maintenance CSR’s, internal corrosion contract holder and production chemists. 2.0 Background Availability of bacterial monitoring data within asset corrosion monitoring system is very important to be able to set the correct corrosion control strategy. Bacterial corrosion is commonly known as a corrosion type. The most significant risks in lines suffering from bacterial corrosion are fouling resulting in plugging and under deposit corrosion. The sources of bacteria are such as:

• Natural growth inside a line; • RO plants reject water injection in water disposal header; • Shallow water aquifers feeding water injection systems; • Reclaimed fluids injection in oil lines; • Un-cleaned static equipment facilities inside stations upstream of lines.

A number of pipelines in PDO do not have bacterial monitoring program and thus, there is a need to establish such a program to take provisions against bacterial corrosion attack. 3.0 Bacterial counting/monitoring tests Bacteria’s testing involves collection of line fluid or solid samples and then run a dilution in a number of bottles. Most Probable Number (MPN) method should be used in this strategy for the calculation of bacteria counts. The method is a triplicate of normal serial dilution method. 3.1 Planktonic bacteria test A water sample is collected from coupons fitting point or a sampling point. The point should be left running for a few minutes before a sample is taken. Sulphate Reducing Bacteria and General Aerobic Bacteria counts should be measured and they represent the existing counts in line production bulk stream. 3.2 Sessile bacteria test The bacterial population on a system metal surface is more relevant to corrosion than the bacterial population in the system’s fluids. This is because only surface or sessile bacteria cause corrosion. Thus a corrosion control program is ineffective unless it kills those surface bacteria. 3.2.1 Bio-probes Bio-Probes are used to collect samples for bacteria counting. A bio-probe is installed in the flow stream. The bio-films grow on the probe and the (typically 6) removable studs. Sequential removal of one or more studs enables to quantify the bio growth over time and also provide information on the morphology of corrosion attack. 3.2.2 Coupons Corrosion coupons are used to collect samples for bacteria counting. It is necessary to crash the top film layer with clean cotton. Then collect a sample from the coupon surface remaining bio-film by separate cotton and immerse the cotton in sterilised water for dilution and counting measurement.


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3.2.3 Sulphide balance This method is used to determine the sulphide concentration on bio-probes and coupons. In systems where there is no indigenous sulphide present, it can be used to assess the activity of Sulphate Reducing Bacteria and the potential for Microbial Induced Corrosion. It is required to preserve solid products containing sulphide in Alkaline solution to avoid oxidising to air. The method steps should be well followed to get reliable data. 4.0 Bacteria screening/controlling Methodology The number of liquid pipelines/headers in PDO is high and it is not practicable to carry out bacteria testing in each individual line. Therefore, it is essential to carry out the testing on basis of the risk of Microbial Induced Corrosion. Thus, a screening program has been established for non-biocide treated lines, which divides the work in four areas. Screening Sequence

Pipeline Type Selection criteria for testing

Bacteria testing Type

Minimum Testing Frequency

Results

1 MOL’s All lines. No criteria required

Planktonic Yearly Report measurement results into PDO database

2 Inter-station oil lines with high reported bacteria counts in down stream MOL’s

Bacteria counts in the down stream MOL is not less than 103/ml

Planktonic Follow up of first screening sequence results

Report measurement results into PDO database

3 Inter-station oil lines with low reported bacteria counts in down stream MOL but have possibility of SRB activity

At least one bacteria source is existing


4 Water lines All lines. No criteria required


Table 1.0

The procedure starts with measuring the Planktonic bacteria counts of a line in the production bulk using MPN calculation method. If the count is equal or greater than 103/ml or there is a change in H2S level or a reported pitting corrosion in non-oxygenated environment, then a sessile bacteria count should be measured to identify the real SRB counts at pipelines internal surface using the same MPN method. Bio-probe tool is more suitable than coupons. Once the line is identified to have SRB problem, then a corrosion mitigation strategy should be applied, which includes;

1- Biocide chemical injection. A treated line should be included in internal corrosion routinely monitoring program, which consists of Planktonic and Sessile bacteria counts in monthly and yearly basis respectively.

2- Physical elimination of bacteria source.


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5.0 Roles and Responsibilities 5.1 Preparation PDO corrosion control engineer should prepare a list of all liquid lines for bacteria screening measurements. He should report the lines that do not have fluid sampling collection point or installed coupons or bio-probes. The suspected source of bacteria should be identified and stated in the list as the line may have a priority. The engineer should also prioritise the lines according to the stated prioritising scheme. 5.2 Execution The contractor should carry out the bacteria screening measurements by MPN calculation method. He should communicate the measurement results to the PDO corrosion control engineers before moving one phase to the next phase. 5.3 Reporting The contractor should deliver a report consisting of line description, sample collection date, measurement date, type of test, bacteria counts number and recommendations. He should update PDO database system such as PACER with the new data. 5.4 Analysis PDO corrosion engineer should perform the analysis and set the correct remedies. He should be responsible for inclusion of lines that are treated with biocide in internal corrosion contract routine monitoring program. He should report the SRB analysis and remedies in ACR reports.

6.0 Review and Improvement The procedure will be reviewed once every five years.

Planktonic counts (Yearly)

Conditions ‘See attached box’

Yes

No

Sessile counts

Problem

1-SRB Source physical elimination remedy

YesNo

Conditions: Planktonic counts ≥ 103 or Change in H2S level or Reported pitting corrosion in non-oxygenated environment

2-Biocide injection remedy

Routine monitoring

or


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Appendix A Glossary of Terms, Definitions & Abbreviations

Company Petroleum Development Oman LLC. Contractor The person or organisation that supplies the Company with

services. Corporate Functional Discipline Head (CFDH)

The person responsible for a discipline in the Company. The CFDH approves Procedures and Specifications that apply to his discipline

User The person or organisation that reads and uses the information in this Procedure

Shall Tells you that you must obey the instruction Should Tells you what the principal recommends May Tells you a possible procedure

gu-486 screening & monitoring bacteria guideline

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