steel linepipe in sour gas service

[Nat_Gas]

I could use some help with understanding exactly how I should apply NACE MR0175/ISO 15156-1 and 15156-2 to the operating conditions below for linepipe in natural gas service. I'm preparing Specifications for API5L PSL 2 HFW pipe.

1a: 10,000 ppm H2S, 900 psig, dehydrated
1b: 10,000 ppm H2S, 900 psig, non-dehydrated

2a: 10,000 ppm H2S, 100 psig, dehydrated
2b: 10,000 ppm H2S, 100 psig, non-dehydrated

Thanks in advance.

 

[Nat_Gas]

More specifically, producing pipe with HIC and SSC resistance.

 

[SJones]

The help should come from an appropriately qualified person rather than an internet forum.

Since API Spec 5L, Annex H will be applied, it already incorporates the bulk of the requirements to automatically meet ISO 15156. The issues that you will need to definitively tie down in your specification are those items in Table H.3 of API Spec 5L that are to be "agreed:" line items 4 and 9. Line item 4 is a no-brainer and it cannot be waived if the requirements of ISO 15156-2 are to be fully met. Line item 9 will demand a bit more thought as to whether it need be specified since it will not be a requirement to meet ISO 15156-2 should all other quality control tests meet the API requirements. You should note that this test is of 30 days duration and, dependent upon the size of the order, it could mean that the pipe is being shipped before the test results are available - something to bear in mind when holding technical discussions with the selected pipe manufacturer. Some guidance on the efficacy of demanding SSC testing can be gleaned from the ExxonMobil approach outlined in International Offshore And Polar Engineering Conference, 2012, Paper ISOPE-I-12-655

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.

 

[Nat_Gas]

I agree, you are correct about bringing in a qualified person for writing the specification and I'm doing that. I probably should have asked more in a general sense rather than specific. I've studied Annex H and read through the MR0175 documents. I've also read through alot of your posts and I can tell you are very knowledgeable in this area. In general, I'm wanting to understand when I should apply these Standards and Specs in H2S service.

Should I ALWAYS consider Annex H, whether the gas is wet or dry, as long as H2S partial pressure is above the 0.05 psi per ISO15156-2, Sect 6 & 7?

 

[SJones]

So, essentially, your question is: 'is dehydration alone a sufficient corrosion control measure for sulphide stress cracking and hydrogen induced cracking to warrant neglecting Annex H.'

Again, a couple of answers:

1. How dry is dry?

2. How lucky do you feel?

If you feel that your fluid will be "dry" for the design life of the pipeline, then answer question 2 as 'pretty much' and neglect Annex H as you see fit.

Hint: there are plenty of papers dealing with corrosion in nominally dry gas pipelines

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.

 

[SJones]

In order to keep the concepts separate, please also note that there is no such thing as a "0.05 psia H2S partial pressure threshold" for both cracking mechanisms, but especially HIC.

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.

 

[Nat_Gas]

I like your reply with two answers, funny but wise. No dehydration unit operates properly 100% of the time, therefore I do not feel pretty much lucky. Thanks for the hint as well. I appreciate your feedback.

 

[blacksmith37]

If this will be large pipe ,ie. DSA welded, you will need to consider SSC testing of the weld zone. What will acceptance requirements be . This factor was a last minute consideration for the CATS pipe spec. For that pipe we assumed a little sour and wet.

 

[SJones]

@blacksmith37 - the pipe will be HFW (see originating post) which is probably more important to SSC test than SAWH. The test will be a 4 point bend with the test parameters and acceptance criteria detailed in Table B.1 of ISO 15156-2.

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.

 

[Nat_Gas]

SJones - partial pressure of H2S is discussed in ISO 15156-2. By your comment about the 0.05 psia threshold, are you just clarifying that it only applies to SSC or SCC only?

 

[SJones]

I'm clarifying that there is no minimum partial pressure of H2S below which a material may be deemed immune to both SSC and HIC. SCC of carbon steel is a downstream focused damage mechanism that would come under ISO 17945. The 0.05 psia threshold is a relic from the pre-2003 NACE MR0175 that no longer applies. By your post above:

as long as H2S partial pressure is above the 0.05 psi

it seems that you believe this threshold to still stand.

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.

 

[blacksmith37]

Oversight; I always called it ERW regardless of frequency. The former API ( and ASTM ) specs were sloppy about defining re-crystallization of the weld. I would recommend full crystallization of the weld , and verification.