yes bro u r right but i work on these welding thing power plant project of ghazi barotha hydro project and u require radiography or xray test to checking the welding joint when u work on the extreme temperature and pressure as well as only simple water leak test will not give u any reliability abt the leakage of the welding joint but good luck
my advise is u must try to block it from one end and from other end compressed air for 4 to 5 psi and then see the leakage its just a crude process to check the welding joints.....
but if u r satisfy with the work good luck with it