What are the technical requirements for half-tube processing?
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Recently, our unit has a mixing tank; the container category is Class II, and the material used is S30408. There is a Φ89 S30408 semi-tube coil outside the tank body, with a total length of over 30 meters for these semi-tubes. The medium flowing inside this coil is heat transfer oil. We would like to know: what are the technical requirements for these semi-tubes? Are there any requirements for non-destructive testing? What is the basis for the technical requirements? Should the butt weld between the half-tubes be performed using PT or RT? Is a PT requirement necessary for the fillet weld between the half-pipe and the cylinder? Why? I ask my colleagues for their help.
For ordinary equipment, in theory, pressure welds require non-destructive testing; for butt joints, RT is used, and for fillet welds, surface inspection is applied... In cases where RT is not feasible due to structural reasons, surface inspection can be used instead
If there is an insulation layer, perform a 100% RT test on the joints; grade III compliance is sufficient, while PT testing should be carried out on all fillet welds. The main reason is that it is covered. If there is no insulation layer, 20% RT for the joint is sufficient
For heat transfer oil, just using PT along with hydraulic pressure is completely sufficient
Perform PT on both the butt joints of the half-tubes and their welding joints to the shell.
HG/T20569-2013 Mechanical stirring equipment
As required, the half-pipe is generally located within an insulation shell, with the welds covered; therefore 100% RT inspection should be carried out. The wall thickness is too thin to allow for UT inspection. The fillet welds between the half-pipe and the shell are too long, and their quantity is large as well; these welds are much longer than the butt welds, whose length can be considered negligible. Moreover, the quality of butt welds is better than that of fillet welds between a pipe and a shell. So there’s no point in performing inspections on those long fillet welds – what’s the meaning of carrying out butt weld inspections in such cases? As a result, most manufacturers do not conduct any flaw detection. Some manufacturers, however, carry out 100% PT or MT inspections on the welds in order to prevent cracks from spreading and causing leaks, which could lead to the disposal of the tank. In any case, for the half-pipe hydraulic test, it is required to first construct the inner tube, then weld the jacket, and subsequently conduct a hydraulic test on the jacket; only after passing this test can insulation be applied.
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