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Cost effective operation in sour service

Connect, no. 105, March/April 2000, p.1

TWI has recently completed a highly successful US$0.8m programme of work to assess the effect of mildly sour production conditions upon the occurrence of sulphide stress corrosion cracking (SSC) of welded ferritic steels.

A combination of factors can lead to sulphide stress corrosion cracking
A combination of factors can lead to sulphide stress corrosion cracking

Under certain conditions of pH and partial pressure of hydrogen sulphide, it was shown that the acceptable hardness limits could be safely relaxed. A characterisation scheme had to be devised to allow successful interpretation of materials behaviour in order to discriminate clearly between pitting corrosion and cracking. This has provided industry with very valuable data to support continued use of assets that were designed for sweet conditions but which are later exposed to mildly sour environments due to field souring or tie-in of fields containing H 2 S.

Different types of attack in sour service
Different types of attack in sour service
Significant savings have accrued through avoidance of replacing flowlines, pressure vessels and pipelines.

Similarly, these environmental conditions will also influence ancillary equipment specification for valves, pumps and compressors. These items often use higher strength materials which may be more susceptible to SSC and therefore data on plain and welded material is required. Derivation of safe material limits based upon pH and P H 2 S offers potential cost savings for existing assets and also the opportunity for re-use of equipment on alternative developments.

Following a very successful meeting in Houston, TWI has prepared a proposal for a two year Joint Industry Project (GP/MAT/1168) aiming to improve cost effective and safe operation of upstream oil and gas production equipment. A guidance document will be produced to assist industrial application of the data derived in the programme.

For further information, or to discuss your company's requirements for support in assessment of materials in production environments, please contact us.

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