I believe you are able too but if you go to the AWS D1.1 Clause 4 Part A is the general requirements. It states in 4.2.1.1 Qualification Responsibility Each manufacturer or contractor shall conduct the tests required by this code to qualify the WPS.
By 803056 
Date 09-20-2017 16:27
Edited 09-22-2017 16:30
I would have to say it depends on the code and the contract arrangements.
Let's assume it is ASME B31.9 Building Services Piping. It is pretty liberal regarding welder qualification and the qualification of the WPS. It allows the WPS and welders to be qualified by another party.
Other ASME piping codes may allow the use of the "prime contractor's" WPSs provided the prime has the authority to hire, fire, and direct the subcontractor's workers.
There are a lot of variables that must be considered. The first and most important is what code is applicable and the terms of the contract and project specifications.
Al
By Joey 
Date 09-22-2017 03:11
Edited 09-22-2017 03:13
What is actually your client's comments? Can you ask your client if you can engage a sub-contractor without getting approval from them?
Client is normally checking the competency of welding organization to perform welding activities in accordance with codes, standards, and specifications. So qualifying a welder based on the main con's approved WPS is more efficient.
Good control practice is that only the WPS/PQR from main-contractor are recognized in the project. All welders must be qualified in accordance with main-con's WPS and all qualified welders involved in production must have the welder badge issued by the main-con.
