valves who meet NACE MR 0175 3

This is something you need to be quite careful with ... Does the client require that the valves meet the old 2002 Edition of NACE MR0175, do they require that you meet the 2003 Edition (with addenda) of NACE MR0175/ISO 15156 or do they require you to meet the 2009 Edition of ISO 15156.

The old NACE MR0175 document was significantly restructured and merged into a combined new document called NACE MR0175/ISO 15156 in 2003. This new document contains requirements that can be vastly different than in the old document. In particular, they introduced many new restrictions and requirements on the use of Corrosion Resistant Alloy materials (including stainless steel).

Under the 2003 document, the task of determining the acceptability of a material was split into two separate functions.

Function 1) The manufacturer of the component must ensure that they meet the metallurgical and manufacturing requirements so that the material is in a condition in which it "MAY" be permissible for use in "SOME" sour service environments.

Function 2) The end user must review the specific service environment (pH, chlorides, temperature, partial pressure H2S, etc.) and determine if the material selected is even permitted to be used in their particular service environment.

If we look at 316 SS, in the 2002 Edition of NACE, provided the material had a hardness less than HRC 22, was annealed, and was free of cold work, it could always be used in sour service. If we look at the 2003 Edition of NACE/ISO, we find that per Function (1), it must still be less than HRC 22, be annealed and free of cold work and if it is in this condition, the manufacturer can certify the material as "Sour" meeting NACE MR0175/ISO 15156. However, per Function (2), the end user may only be able to use this material if their particular service has a chloride concentration less than 50 mg/l or alternatively, if they have a temperature less than 60 C and a partial pressure H2S less than 100 kPa.

There are some other complexities that may come into it but really I'm just trying to show that you can't at all say that stainless steel meets NACE anymore - it depends on whether you are the manufacturer or the end user, and on the service environment.

Recommend you go back to the client and clarify which specific document they require compliance with (2002, 2003, or 2009) and then if 2003 or 2009, you do need to advise them of their responsibility under those documents to ensure that any selected materials are compatible with the service environment.

You may want to consult a materials engineer to help you out with this since you could well have a variety of other materials in the valves, all of which could have different limits of acceptability under NACE/ISO (e..g, 17-4 SS, Duplex SS, Inconel 718, Alloy 20, X-750, etc.).

With regards to the question of the type of valve, none of the NACE documents have any opinion on the type of valve that is acceptable - these documents only address what metallic materials can be used, and what the required metallurgical properties of these metallic materials should be.

When you spec out the valve just include the NACE requirement and most manufacturers have been there and done that as they change with the times. Their material certs will also include a note that they are 'NACE MR 0175'.
Your client probably wouldn't even know the differences highlighted by rneill, and as long as you supply the valve with the NACE badge then your client will probably be quite happy.

most manufacturers have been there and done that

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Unfortunately, judging by the number of questions on here and the NACE forum, most manufacturers have not been there and done that. NACE MR0175 on the inspection documents for a number of alloys won't mean a thing because the service environment will not be defined. It really needs an explicit arrangement between supplier and end user as to what will constitute satisfactory inspection documentation in situations where the end user has not explicitly specified the materials. End users no longer have the easy get out of simply specifying 'NACE' and leaving the valve manufacturers to select materials.

Steve Jones
Materials & Corrosion Engineer

Agree with SJones on this one. Lately about 25% of my time has been reviewing MTRs provided by Manufacturers for proper certification of compliance to NACE MR0175/ISO 15156 on behalf of the end user and I find that a good percentage of MTRs are not properly certified.

A small percentage of the MTRs state specific compliance to NACE MR0175-2002, and then a large number state compliance to NACE MR0175 with no reference to the edition (or to ISO 15156). Only a small percentage of the MTRs I see reference NACE MR0175/ISO 15156 and even fewer of these mention the edition.

Regardless, irrespective of what is certified on the MTR, that only covers the metallurgical properties and condition. The end user absolutely must then ensure that the material is acceptable for his service conditions.

In the past 6 months I have seen three separate sets of valves supplied on three different purchase orders where NACE compliance was requested by the customer, and where NACE compliance was certified by the Manufacturer, but where the valves could not in accordance with regulatory requirements be used because the stainless steel trim was not compatible with the end users service environment as required by NACE/ISO. These situations resulted because the customer simply specified NACE MR0175 without properly addressing the issue of the service environment.

Some valve manufacturers today are extremely wary of this whole issue and the potential liability so deliberately avoid the potential problem by certifying compliance only to the 2002 Edition of NACE MR0175 where service environment was not a consideration.

There is a very large segment of industry ignoring this issue but depending on your application, your regulatory authority, and whether or not your facility gets audited, it can cause a lot of headaches.