Are you responsible for the design and specification of this system?

This is not the right place to be asking your question. You should be asking the lead or project engineer on the project, as he will be the one held responsible.

Consult sprinkler system consultant/contractor.

Since you are dealing with fuel systems, you either need sprinkler or AFFF foam.

Neither of these systems are required to be welded, according to the various fire codes (all contained in NFPA).

There may be other non fire system related codes that will require you to weld the pipe. For instance, many power plants require welded pipe for all systems. Check the codes associated with your facility. If those codes do not require welding, the choice is yours.

@lyn: No, I want to know for preparation of welder qualification and ITP.

@ronseto: You right, But I prefer ask in a Mechanical Engineering Forum where I can get many good advises from other people.

@pnaban; Joshi and WJMFIRE: thank you very much for your helps