NACE MR0175/ISO 15156 & Ball Valves

[rneill]

The typical trim in small floating ball valves is Austenitic Stainless Steel (304 or 316); this is what is stocked and readily available.

In the good old days, 304 & 316 SS was accepted by NACE MR0175 as suitable for sour service so there was no issue with the standard 304 or 316 trim and these valves were installed everywhere.

With the release of NACE MR0175/ISO 15156, there are now environmental restrictions on the use of 304 & 316 SS and these materials can only be used if the service environment meets one of the following two conditions (referring to technical corrigendum 2 to Part 3):

1. Max. chloride content of 50 mg/l, or
2. Max. temp of 60 C and max. pp H2S of 100 kPa

The majority of upstream production system in Western Canada violate both the 50 mg/l chloride restriction and the 100 kPa pp H2S restriction.

Consequently, I have a couple of questions:

1. How do people comply with NACE/ISO for ball valves - or are they ?
2. Who sells a small floating ball valve that complies with NACE/ISO (e.g., ENC/ENP, Nitronic 50, 625) without this being an exotic special order and outrageously expensive?
3. Has anyone ever experienced cracking in a 316 SS ball installed in sour service ?
4. Since the issue is stress corrosion cracking (stress is necessary) and the stresses in a ball valve ball are extremely low, why on earth has the NACE/ISO committee not provided an exemption on Ball Valve balls ?

The valve manufacturers I deal with insist that their standard valves with 316 trim meet NACE/ISO for sour service. However, for the manufacturer the issue is just one of whether the 316 SS material is in the metallurgical condition required by NACE/ISO - they don't need to deal with the issue of the service environment - that's the end user's responsibility.

I'm probably ranting but I'm getting rather frustrated with this issue. If it wasn't a regulatory requirement to have to comply with the latest NACE/ISO, I'd accept the old requirements and the standard valve would perform just fine.

 

[SJones]

Your limits for 316/316L have been modified by Technical Circular 1 if you wish to catch up. ISO 15156 is up to Technical Circular 2 for completeness.

1.
For existing valves, they can comply under the 'field experience' stipulation in Part 1. New valves is where it gets tricky, particularly if the purchaser requires compliance certification to ISO 15156, since how does the valve supplier confirm the specific environmental limits of the application. End users need to rethink their certification requirements because they are the responsible party for materials selection under ISO 15156. And yes, in certification terms, e.g. EN 10204, they can only certify that the material is in the correct condition, hardness, heat treatment etc.

4.
You could write and ask for an interpretation but I would suspect that the reply will be along the lines of: "please note clause 5 of ISO 15156-3 and the WARNING text above clause 1," A blanket waiver may not be given because some valve designs or operating conditions may actually stress the ball to significant levels.

Is your beef with ISO, the manufacturers, or both?

Steve Jones
Materials & Corrosion Engineer

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

 

[rneill]

I've looked at Technical Circular 1 but it increased chloride limits at the expense of H2S partial pressure; we're usually well over the partial pressure limit so the additional chloride allowable doesn't help.

For Question 1. working with an engineering firm, my problem relates to trying to spec and purchase valves for new facilities (plant and pipeline) on behalf of end users.

My frustration is really with the restrictive requirements of the ISO document as it pertains to ball valve trim. It's frustrating since at the end of the day we usually end up paying more and waiting longer to buy non-stocked (and often non standard) ENP trimed valves to achieve compliance while at the same time decreasing long term reliability; In 20 years I've seen numerous ENP trimed valves pulled from service due to corrosion but never seen a 316 SS trimed valve pulled for cracking. Regarding the manufacturer, I have no problem with limiting the manufacturers responsibility for certification to the material condition only - CSA Z245.15 (for example) makes clear that this is their only responsibility.

That said, I have had one or two situations where I have evaluated the environmental limits and requested quotes for other than 316 SS for the valve trim and had the manufacturers sales rep. advise (both me and the end user) that this was unnecessary since their standard valve fully complied with NACE and/or ISO. I have had some rather protracted discussions where I have tried to explain to both the client and the sales rep. that the manufacturer only certified the material condition and not that it was suitable for the environmental conditions. In one case, the vendor declined to quote alternative materials on the basis that the standard product was certified for sour service and the materials did not need to be changed; I don't think the local sales rep understood the issue.

I understand your comments regarding Clause 1 and 5 of Part 3 but despite that there is a blanket exemption for 316 in Table A.4 - could they not do something similiar for Ball Valve Balls (perhaps via Table A.3 and it's notes)?

Can you advise where I might find information on how to submit an interpretation request to ISO ?

 

[rneill]

I did some digging and found the ISO interpretations and the specific question of solid 316 SS balls was raised in MP INQUIRY #2005-03, where the issue of the low stress was also mentioned.

The Maintenance Panel responded that parts loaded solely in compression were a permitted exclusion to the standard since tensile stress was required for SCC. However, they also indicated that there was no threshold specified for tensile stresses.

So, if a ball valve "ball" saw only compression, it would be exempt from ISO but if it sees any tensile stress at all, it must comply with the environmental restrictions. I don't believe there is any significant tensile stress present but I'm sure that there is a tensile stress somewhere during normal operation (certainly in a floater anyway).

 

[SJones]

Glad to see that the maintenance panel reply was as expected! Now you have hit my beef with ISO 15156: blanket exemptions. How is it OK to restrict a material in one table and give the same material a free run in another?!!

I appreciate your position vis a vis clients; I hit the same thing too. I usually try to tie things down in the materials selection philosophy and let the client, as end user, either align with it or steer it another way. It usually starts off from them as "must strictly comply with ISO 15156". I then say "OK - here is your 825 piping, flanges, valves etc". Client: "nooooo way Jose - we've been using 316 for aeons". So "do you wish me to specify 316 without qualification testing based on your satisfactory experience even though this application might not be exactly the same as you have operated before?" Client: "Yes - do so and don't be silly about laboratory testing or nickel alloys ever, ever again!" Me: "Yes sir, yes sir but I have clearly advised you".

Naturally, the above conversation only occurs in a part of the world where regulatory oversight tends to be somewhat more relaxed than where you are.

Steve Jones
Materials & Corrosion Engineer

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

 

[rneill]

I concur with your approach 100% and this is the way I go with Plant Piping where the local regulations do not mandate strict compliance with ISO. However, local regulations do mandate strict compliance for "pipeline systems". Right now, I have a client who has had a pipeline audited by the Regulatory Authority who is requiring them to have an engineer certify that all materials in their installation comply with the latest NACE MR0175/ISO 15156 document ...

Regarding the blanket exceptions, how on earth is it technically justifiable that 304 & 316 SS is unacceptable in general piping and equipment but there are no limits on it whatsoever when used in Compressors (as another example). Further, according to the Interpretations, the exception relating to compressors extends to any and all associated equipment within the scope of API 618 or 617. This means that any interconnecting piping (including valves) and associated vessels (scrubbers and coolers with associated valving and instrumentation) can be 304 or 316 SS with no mandatory restriction on its use at all.

Consider this situation - final compressor discharge piping and valves from the discharge nozzle to the aftercooler and the aftercooler vessel and associated valves and instrumentation can be 316 SS but then 316 SS is prohibited downstream of the aftercooler. How is that technically justifiable?

I sense a certain amount of politics and lobbying going on within the committee.

 

[SJones]

Not so much lobbying, more acquiescence (capitulation) to the MR0175 old guard where materials got into the standard without an auditable basis.

When dealing with clients who have developed materials selection standards it ceases to be an issue because they have generally stipulated materials application limits based on laboratory testing and they get applied to everything. It's when the client is solely dependent upon 15156 for materials selection that it gets tougher. I usually start with the advice: if you don't see any environmental limits for a material, don't trust it and here are some alternative limits (from literature). It usually works until they end up with an expensive alloy somewhere and then it goes out of the window!

Steve Jones
Materials & Corrosion Engineer

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

 

[SJones]

Just to let you know that ISO 15156:2009 is now out. NACE have just initiated their voting process on it.

Steve Jones
Materials & Corrosion Engineer

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

 

[rneill]

This is no longer a joint publication between NACE and ISO as it is no longer dual titled?

 

[SJones]

JOIN THE BALLOT VOTING LIST FOR THE NACE NATIONAL ADOPTION OF THE 2009 VERSION OF ISO 15156

DEADLINE TO RESPOND: December 2, 2009

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Dear Members:

In 2003, NACE adopted ISO 15156, which was based on NACE Standard MR0175, as an identical national standard, ANSI/NACE MR0175/ISO 15156. Since 2003, the ISO Maintenance Panel administered by NACE, along with NACE Task Group 299, have approved more than 15 ballot items, which have now been approved by the member countries of ISO/TC 67 and incorporated into ISO 15156. STG 32 members and interested parties now are being asked to vote on the NACE national adoption of the 2009 version of ISO 15156. We are contacting you to invite you to join the voting group.



Steve Jones
Materials & Corrosion Engineer

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