Suitability of stainless steel in offshore applications

[midris]

Hello all,

I work in an operating company in which I came across the below criteria for stainless steel:

Stainless steel may be used in offshore applications up to an operating temperature of 60 degC.

As per my understanding, the above temperature limitation governs in case of sour service and a chloride content of 50ppm as per NACE MR0175/ISO 15156.

Appreciate your opinions on this matter.

 

[EdStainless]

Which stainless steel?

= = = = = = = = = = = = = = = = = = = =
Plymouth Tube

 

[midris]

The grade was not specified. Lets assume the two most common grades in this case, 304 and 316.

Thanks

 

[TVP]

60 C is very high for most stainless steels in an offshore environment in consideration of pitting and crevice corrosion. Here is an excerpt from NORSOK M-001:

The following materials are regarded as immune to corrosion when submerged in seawater at ambient temperature:
• Alloy 625 and other nickel alloys with equal or higher PRE value.
• Titanium alloys
• GRP.
• Other materials, provided adequately documented.
Ambient seawater temperature is related to normal North Sea water temperatures.
Note: Stainless steels Type 6Mo and Type 25Cr duplex are borderline cases and should not be used for creviced connections without
cathodic protection when their material temperature exceeds ambient seawater temperature. Threaded connections are particularly
susceptible to crevice corrosion.

You can obtain more information using the following links:

http://www.standard.no/pagefiles/1176/m-001.pdf

http://www.hse.gov.uk/offshore/ageing/stainless-steels-performance.pdf

http://www.outokumpu.com/SiteCollec...-boundaries-of-stainless-steel-Acom2-2012.pdf

http://stainless-steel-world.net/pdf/ssw_0903_sandvik.pdf

http://www.swcc.gov.sa/files\assets...OF SOME CONVENTIONALAND HIGH ALLOY STAINL.pdf

 

[midris]

TVP, thank you for your input, however, I have not specified that the stainless steel is used for seawater or produced water applications, in which case 60 degC would be too high even for SDSS.

I would like to confirm whether SS used in non corrosive service may be susceptible to atmospheric corrosion in offshore plants for example, since our requirement is a generic one.

 

[sanshu1111]

Midris,
Limit of 60 Deg C is coming from NACE MR 0175/ ISO 15156 requirements and is based on combination of H2S partial pressure and chloride content.

For offshore environment, SS 304/ 316 with a suitable external coating syetm can be used at higher temperature also if not limited by NACE requirements or other process reasons.

 

[SJones]

The 'criteria' that you came across is probably for external SCC, whereas ISO 15156 is dealing with internal H2S related SSC/SCC. The latter will apply both onshore and offshore with no distinction. The UK HSL report linked by TVP shows a number of different temperature limits applied by different operators for external chloride SCC and is a good discussion document.



Steve Jones
Corrosion Management Consultant

http://www.linkedin.com/pub/8/83b/b04

All answers are personal opinions only and are in no way connected with any employer.