316SS vs 17-4PH stems in H2S service

[Gorman3]

Hi fellas,

I have customers telling their slab pipeline gate valves must have 17-4PH stems insisting they perform far better than 316 stainless in environments where Hydrogen embrittlement can be an issue. I am not so sure that is the case and not looking to spend the extra money on stock when it's not really necessary. To be honest though I cant sell them on that position because I am not really sure how right or wrong they are.

How big of a difference will it make switching to 174-PH? Is it even advantageous in the first place?

thanks,

-G

 

[SJones]

It is generally accepted by the oil and gas industry that the application of NACE MR0175/ISO 15156 to 17-4PH is not correct and not conservative, e.g. NACE Corrosion 2014, Paper 2014-3816. Since, under the terms of ISO 15156, the end user is responsible for selecting and applying the materials, you could have a case for a "you want it, so be it" attitude if you felt sure that any failure didn't have ramifications for your manufacturing entity. Point them towards that NACE paper and ask them if they are still so steadfastly certain that they want to have 17-4PH. If they are, ask them if they wish to impose any restrictive design conditions over and above ISO 15156 for its application. Thus, you would have discharged your duty of care if they maintain their current stance.

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.

 

[Gorman3]

great info, thanks!

BUT, I need to know if there are advantages with the 316 or with the 17-4. I'm a salesman but want to sell them the best product, not steer them towards what I can unload quickest. Currently we stock the 316 stems after a major end user required it over our previous standard 410 stem. Now they say they think the 17-4 is better. I am not so sure, which is why I'm asking you. If it is truly the better material for H2S, I would consider changing my commodity item to have 17-4 stems. But if I am significantly limited because it doesnt meet NACE, then I have a bigger decision to make as we can't afford to keep both on the floor.

 

[Gorman3]

I found this as well:

http://www.nace.org/cstm/Store/Product.aspx?id=8528b695-9e9c-40b2-88c1-4857cb42643e

Leaning towards the 316 after reading but very much appreciate your answer to above if you could.

 

[SJones]

I can't answer your question because I do not know the specific service conditions for the valve. All I can say is that the only two advantages 17-4PH will generally offer are: higher strength and, possibly, cost. 17-4PH is a more complex alloy and the scope for it "going wrong" for H2S service is much higher - see NACE Corrosion 2003, Paper 03102. One of the end users that I am involved with effectively "bans" the use of 17-4PH in H2S containing service because of poor experience.

If the stem of the valve is not actually exposed to the H2S containing fluid, there is scope to accept the end user's directive.

So, how lucky does your customer feel?

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.