Relation between NACE MR0103 & MR0175

When there is Sour Service we opt for NACE.
 
But what standard of NACE is applicable?

For us usually these are the two standards that we instrumentation department widely used in upstream and downstream sector.

1.NACE MR0175 is for Petroleum and natural gas industries — Materials for use in H2S-containing environments in oil and gas Production

In short this standard serves the UPSTREAM Oil and Gas sector

2.NACE MR0103 is for --Materials Resistant to Sulfide Stress Cracking in Corrosive Petroleum Refining Environments ( In short Downstream)
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In short this standard serves the DOWNSTREAM Oil and Gas sector

The Origin :-

Initially the was only NACE MR0175 standard only then gradually there was a need in the market to have a standard that specifically serves the need of downstream sector.

And thus a new standard was born. Named NACE MR0103 to especially serve the needs of the downstream industry.
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Certain new thing like sulphide stress cracking were emphasized that especially trouble the downstream industry 

Now the challenge:-

Vendor Catalogs sometime mention compliance to NACE MR0103 or NACE MR0175 only.

So when to accept what?
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Overall when going through the difference between the 2 standards in Technical paper Number 04649 2004 NACE International, I have inferred the following:-

Case 1:-Requirement is of NACE MR0103 and vendor provides NACE MR0175

It seems that MR0175 has stringent requirements as compared to MR0103, and it is also somewhat apparent that offshore/upstream has harsher conditions.
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So for non-critical factors like Paint system for relief valves if vendor states compliance to NACE MR0175 and we are doing a refinery project, we can accept it even if our requirement is MR0103.

For critical factors like material section it is recommended to discuss with a Corrosion specialist whether it could be accepted depending on your typical project conditions.

Example:-While I was doing a Refinery project for Orifice plate the vendor compiled to NACE MR0175 so after discussing with specialist we inferred that this can be accepted.
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For critical parameters it is advised to accept only after consultation with a specialist.

Case 2:-Requirement is of NACE MR0175 and vendor provides NACE MR0103

This is a risky proposition to accept, since offshore/upstream environment generally has harsher conditions.

Here it advised to stick to our requirement of NACE MR0175 and not accept NACE MR0103.

Thanks for reading.

Hope its been of value to you.
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PS: This is as per best of my current understanding