Pressure and leakage testing

Pressure retaining systems and components should be subject to  

To the extent practicable, the pressure retaining components shonld be visually examined while the system is operating under the test pressnre and temperature conditions. The test pressure and temperature should be maintained for a sufficient period before the examination to ensure that all possible leakages can be identified. The accessibility of components to be visually examined should be considered (for example, with regard to the possible need for removal of insulation). Acoustic emission methods may be used as part of such inspections. 

The duration of tests performed at a pressure higher than the system s design pressure should be limited so as to prevent excessive stressing and creep of the components. 

A visual examination should be made to yield information on the general condition of the part, component or surface to be examined, including such conditions as the presence of scratches, wear, cracks, corrosion or erosion on the surface, or evidence of leaking. Optical aids such as television cameras, binoculars and mirrors may be used. Surface rephcation as a method of visual examination may be considered acceptable, provided that the resolution at the surface is at least equivalent to that obtainable by visual observation. Any visual examination that requires a clean surface or decontamination for the proper interpretation of results should be preceded by appropriate cleaning processes. 

A surface examination should be made to confirm the presence of or to dehneate surface or near-surface flaws. It may be conducted by a magnetic particle method, liquid penetrant method, eddy current method or electrical contact method. 

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As a result of KU s know-how in this field, the guaranteed shutdown period for converting a 340 000 metric tonne per year NaOH plant from mercury to membrane technology was as short as 8 weeks. This was made possible by a new conversion concept the individual elements were assembled in an adjoining assembly hall and installed in cell racks of 72 elements each. In this way, more than 2600 elements were assembled and installed in 18 two-rack electrolysers, and pressure and leakage tested. As soon as part of the mercury electrolysis plant was dismantled, the completed electrolysers were placed onto the vacated area and connected to the piping already installed beneath the cell rows (Fig. 16.6). 

Finally the insulation caps or moulded parts for the other components as well as the pipe fixtures can be mounted. However, to enable the respective visual control and repairs, the assembly of the insulation caps should occur only after the pressure and leakage tests. 

The carrying out of pressure and leakage tests also requires suitable preparation. Since the vessels-as long as pressure vessels are concerned-have already been subjected to a pressure test in the manufacturer s works, pressure tests are generally limited to the assembled pipes. In certain cases, however the Technical Regulation on Pressure Vessels requires a pressure test of the apparatus in a built-in state /4.18/. 

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