NACE and Austenite valve Trim

[bmoorthy]

Table 1 of NACE MR 0175/ISO 15156-3 indicates allowable exceptions for items that are subjected to pressure less than 65 PSI (Absolute Pressure): Flow Lines, Gathering lines, field facilities etc.

Valve Stem and Trim: these are considered non pressure parts as per various definitions of API/ANSI.

1) Does that mean valve trimes are emempt from the requirement, That is, can ,A 479 (With out Sol Anneal)be used?

2) Also some of the tables (Like ATable 28) specifically address valve components for some material, whilst table A 1 (Inidicates exclusions against austenitic). When the Table 1 gives exception based on absolute pressure, why the table A 28 still includes non pressure components, is it not contradictory?

 

[gr2vessels]

bmoorthy,
First is to clarify the definition of pressure containing and pressure retaining component. The valve body is containing the pressure, same as the pipe or the shell of a pressure vessel, but the bolting of the body flanges of a valve are retainig the pressure, same as the gland seals, the gaskets or even the wetted internal valving components.
Secondly, the table 28 in the standard refers to non-pressure containing components, hinting towards pressure retaining components, wetted or dry. The corrosive environment has to be associated with a minimum level of stress, in order to produce the H2S induced cracking. The dry bolting or less stressed wetted components (retainig pressure only) are basically excluded from the concern of the "NACE" and as such are listed on column 2 of table 1 or similarly on table 28. I'm not sure about the A479 without annealing (the clause 4 states "...all austenitic grades of stainless steel shall be furnished in the solution annealed condition, with subsequent light cold drawing and straightening permitted...").
Thirdly, table 1 has two columns, the first one is listing the Flow Lines, Gathering lines, field facilities etc., subject of this standard restrictions and the second one is listing all the permitted exclusions which are less stressed than the pressurised pipelines, field static / pressurised processing equipment (vessels, exchangers, etc..) and the like. Say, the bolted internal separating wall in a filter separator is not subject of NACE restrictions or prescriptions, despite retaining some differential pressure and being perhaps submerged in the wet H2S environment. It's not going to crack due to "NACE" non-conformance.
I agree, it's all a big mess, but if you read it carefuly several times, you'll either give up understanding or you'll believe it all without asking anymore questions. It's just a different bible..
cheers,
gr2vessels

 

[SJones]

1. Only if two conditons are satisfied:

a) the design pressure of the equipment is below 4.48 bar AND
b) the end user has given permission to waive the requirements

2. Please refer to the CAUTION note at the end of clause 1 of ISO 15156-1. Table A.28 is essentially based on the principles of the 'old' MR0175 (and has probably just been copied across), i.e. empirical evidence that material below a certain hardness and/or with a certain heat treatment in a specific application did not suffer cracking. Hence, there are no environmental limits in Table A.28. It just so happens that empirical evidence for valve components was available for specific martensitic precipitation hardened stainless steels and not for austenitic stainless steels.

gr2 - your view of Table 1 and your perceptions about no cracking might be classed as dangerous by some users; beware when expounding on corrosion, particularly sulphide stress cracking.

Steve Jones
Materials & Corrosion Engineer

http://www.pdo.co.om/pdoweb/

 

[bmoorthy]

S.Jones

My understanding was that for Austenitic material, when they are non pressure containing part, then the non pressure containing part (Say Trim material) need not comly with NACE MR 0175/ISO 15156 (Even if the user has made a blanket statement all valves needs to meet NACE requirement) and still not invite non conformance, since trims are not pressured (Hence not stressed hence no Stress attack).

If the above assumption is wrong, where in NACE MR 0175/ISO 15156 does it specify that non pressure components needs to comply with the requirement.

As for me, i agree with gr2vessel, it appears to be a big mess.

If all material coming in contact with the fluid has to meet the requirement then MR 0175/ISO 15156 is supposed to clarify and mention (All pressure containing and all non pressure parts) needs to comply.

As of now There appears to be some selective inclusions for selective grade and again by the selective inclusions in Table 28, one understands other grades (Non pressure part) need not comply.

I intend to take up with NACE for disposition and see whether they reply.

Thanks for the input on this hair splitter.

 

[SJones]

Moorthy - it is down to the end user to determine conformance or non-conformance. If they want a 'NACE valve' that could mean that they want all process wetted parts (definition as per ISO 14313), or pressure containing parts (definition as per ISO 14313) to comply, or not, dependent upon the criticality of the valve. ISO 15156 will not provide this distinction for you when dealing with austenitic stainless steels (it will when dealing with martenisitic precipitation hardening stainless steels as explained in Table A.28); therefore, you must clarify with the end user.

ISO 15156 is not a 'big mess'; like all standards, it has some flaws and ambiguities but, users must realise, that the onus is placed squarely on the end user of the materials and that this approach does not lend itself well to undertaking engineering, procurement, and construction contracts unless there is good dialogue between the contractor and the client.

Steve Jones
Materials & Corrosion Engineer

http://www.pdo.co.om/pdoweb/

 

[strider6]

As a user of the NACE /ISO and for my experience on previous project regarding the valve materials in SS.
You can exclude the parts loaded only on compression
Regarding stems, pins, shaft of valves in austenitic materials you've to look in table A.3 that gave you the acceptable austenitic materials.

regards

S.

http://www.corrosionist.com