Hello Euskera!
First off, the welding is to be produced as per D1.1/D1.1M correct? Well then, you need to learn the welding terminology relating to this code...
You wrote; "The Owner´s Representative has said to them that, for welding, they have to respect the Specifications of the Contract and perform the works as per AWS D1.1/D1.1M (elaboration of WPS and perform of PQR, Welder Performance Qualification and Welding Operators Qualification)."
"And, for the material, this Representative said that under any circumstances he will accept any change of the material (he suspects the chinese material has lower qualities, but can not say it openly)."
Well, that's just fine & dandy for some but GMAFB!!! WTF??? "(elaboration of WPS (Welding Procedure Specification)? - If you change the base metal, you then have to write up a new WPS because it's more than likely that you'll also change the filler metal as well so you're basically turning Red delicious apples into Green Crab apples...
"Perform of PQR"? I'm not quite sure what you mean here??? Welder Performance Qualification and Welding Operators Qualification... The second part of that sentence is misleading because, unless you're welding the component with adaptive control, automated, mechanized, or robotic welding equipment then the term "Welding Operator Qualification" is moot in this circumstance... In other words: N/A = Not Applicable...
So, A WPS = Welding Procedure Specification: A document providing the required welding variables for a specific application to assure repeatability by properly trained welders and welding operators... Then there's a PQR which is really this instead: WPQR = Welding Procedure Qualification Record: A record of welding variables used to produce an acceptable test weldment and the results of the test conducted on the weldment to qualify a welding procedure specification... And finally, a Welding Operator: One who operates adaptive control, automatic, mechanized or robotic welding equipment...
So it's important to know what the terminology means when one works to AWS D1.1/D1.1M because terms used with other standards & codes are not always the same in meaning once one is working through AWS D1.1 and people in here can get a better understanding of just what you're asking... What does the contract say?
What does the EOR say about producing a quality product less than the minimum of what the contract's written standard specifies? Let the EOR(Engineer Of Record) and either the owners rep or the owner himself decide which direction to proceed!
The Owner Representative couldn't fight his way out of a paper bag by the way he/she is contradicting the WPS against what the Owner told him and what is specified in the contract... So I would go down or up the chain of command, CYA, by getting all of the necessary changes in writing with the appropriate predisposing & follow on paperwork...
If you're QC/QA guy in charge then just do your job by observing & reporting and while you're at it, review how to fill out NCR's & RFI's and get them done properly, hand them in and see what happens...
Who knows!!! They may just call a "meeting of the minds" with the entire cast of characters involved which is how these things usually get straightened out!
I hope this is, or was helpful.
Respectfully,
Henry