Posted By Charles Robinson Tech IOSH Not sure what you are looking forthough you may find some information at http://stepchangeinsafet...spx?searchquery=Nitrogen

Posted By Ian Waldram I agree with the previous responses. However typical offshore industry guidance is often more about acceptable leak rates, rather than safety of the testing itself. This type of testing normally follows a conventional hydraulic pressure test, or the equivalent, which is designed to 'prove' the physical strength of all components of the pressure system at a pressure loading above the maxium service level (details of the % overpressure vary, depending on the design code you are using). In contrast, the nitrogen/helium test is to identify very small joint leaks, etc. which are not picked up by the hydraulic test, but which could worsen in service and lead to a significant flammable leak. The mix is mostly nitrogen, and the pressure is normally no more than maximum operating, if that, so the safety controls are basically the same as for pure nitrogen - which will typically be used prior to start-up, to inert the system and prevent flammable mixtures from being formed. If the leak test does identify any failures, then of course there should also be suitable controls to prevent excessive force being applied to any leaking component while it is under pressure. In most cases such leaks are due to mechanical defects on seal faces, and these can't be cured by further tightening. If is EXTREMELY hazardous to carry out a pneumatic test on a large pressure system (due to possible sudden release of the compression energy if a component fails) - which is what you are doing if you omit the first hydraulic test. Authority for such work, and the associated safety controls, typically has to be given by the "chief engineer" of the company, not just the most senior person on site.