I guess there is not much elevation differance between liquid level in the vessel and the suction of the pumps. First of all they need to provide sufficient differance to obtain the required head not to cause cavitation in the pumps. It is not a good practice to leave the problem solution to stess analysis.

It is always expected that there will be small allowables on the pump nozzles.

It seems to me that the pumps need to be relocated in addition to elevation the vessel or lowering the pump levels to be able to provide less resistance to the suction piping as well as complying with the allowable nozzle load under different operating conditions.

Your client needs to provide you this kind of flexibilities. Otherwise solving the problem in stress analysis may be an endless game. Your client and you need to support each other to provide a proper solution.

Hope you will get this help from your client.

Regards,

Ibrahim Demir