How car-ber hydro testing works?

The National Board of Boiler and Pressure Vessel Inspectors interprets and enforces the ANSI / ASME codes within the pressure vessel industry throughout North America. "The National Board" stipulates that all pipe welds must have a pressure leak test applied to each assembly before that particular assembly can be put into service. As per B31.3 of the ASME codes the preferred method of testing the integrity of welds is through application of Hydrostatic pressure. All other NDT testing methods e.g. radiography (X-rays), magnetic particle examination, liquid penetrate examination etc. are considered variances to B31.3. Most vessels, flanges, valves and other various pipe assemblies are tested at the manufacturer's facility; the only portion of an assembly that remains untested is the weld (tie-in point) which connects the various assemblies under field conditions. In other instances a leaking flange may require replacement as part of an on-going maintenance program (between turnarounds) creating the need to isolate and hydro-test the connecting weld. It is to these specific areas of the pipe assembly that CAR-BER has focused attention. Traditionally the method of testing welds which connect assemblies in the field involves filling the entire system with testing medium and pressurizing to a pre-determined value (usually 1 1/2 times the working pressure) and maintaining that specific pressure for a pre-determined time. Such a methodology requires extensive person-hours to blank and purge the entire assembly and requires large amounts of medium to perform the test. The requirement for large amounts of medium means that a significant amount of medium must be lost in order to register a noticeable change in pressure. The minuscule amounts of medium required for the CAR-BER equipment to perform, translates to very precise pressure readings should the slightest volume of medium escape the pressurized vessel during testing procedures