By -
Date 01-20-2003 04:41
I have worked the last ten years on construction of floating offshore platforms (TLPs, semi-subs, FPSOs, etc). These are constructed in accordance with a myriad of codes and US Federal regulations, including various ABS rules which require "tank testing" (looking for leaks at tank boundaries including welds and bolted connections such as manways). The test method you are referring to is commonly called vacuum box, and I have found that all things considered it is the most cost effective way to test welds before assemblies go to paint on their way to being erected and becoming tanks (ballast, void spaces, equipment spaces, fluid storage tanks). For testing of bolted connections at completed tank boundaries, we pressurize the entire tank, as mentioned in the previous posting, to 2-5 psi and then soap the joints. Also very effective.
I disagree with the statement, however, that when pressurizing the entire tank to 2 psi leaks at boundary welds would go undetected. 2 psi in such a large volume is a substantial amount of stored energy. If there is a through wall leak you will find it, provided of course that the surface is properly prepared (i.e. clean and unpainted) and examined with a bubble forming solution. As I inferred above, however, this is not a cost effective way to test boundary welds as the welds must remain unpainted. Normal practice at most large shipyards is to paint assemblies before they are taken to erection, therefore it is most convenient to test welds before paint.
Mankenberg