Section 2 Manufacture and workmanship of fusion welded pressure vessels

2.1.1 Prior to commencing construction, the design of the vessel is to be approved where required by Vol 2, Pt 8, Ch 1, 1.6 Plans and Vol 2, Pt 8, Ch 2, 1.6 Plans.

2.1.2 Pressure vessels will be accepted only if manufactured by firms that have been assessed and approved in accordance with MQPS 0-4.

2.2.1 Where the construction requires post-weld heat treatment, consideration should be given to certifying the material after subjecting the test pieces to a simulated heat treatment.

2.2.2 Pressure vessels are to be constructed and examined in accordance with the requirements specified in Ch 13 Requirements for Welded Construction of the Rules for Materials, unless more stringent requirements are specified.

2.3.1 Measurements are to be made to the surface of the parent plate and not to a weld, fitting or other raised part.

2.3.2 In assessing the out-of-roundness of pressure vessels, the difference between the maximum and minimum internal diameters measured at one cross-section is not to exceed the amount given in Table 4.2.1 Tolerances for cylindrical shells.

2.3.3 The profile measured on the inside or outside of the shell, by means of a gauge of the designed form of the shell, and having a chord length equal to one-quarter of the internal diameter of the vessel, is not to depart from the designed form by more than the amount given in Table 4.2.1 Tolerances for cylindrical shells. This amount corresponds to x in Figure 4.2.1 Tolerances for cylindrical shells.

2.3.4 Shell sections are to be measured for out-of-roundness, either when laid flat on their sides or when set up on end. When the shell sections are checked while lying on their sides, each measurement for diameter is to be repeated after turning the shell through 90° about its longitudinal axis. The two measurements for each diameter are to be averaged, and the amount of out-of-roundness calculated from the average values so determined.

2.3.5 Where there is any local departure from circularity due to the presence of flats or peaks at welded seams, the departure from designed form shall not exceed that of Table 4.2.1 Tolerances for cylindrical shells.

2.3.6 The external circumference of the completed shell is not to depart from the calculated circumference (based upon nominal inside diameter and the actual plate thickness) by more than the amounts given in Table 4.2.2 Circumferential tolerances.

Figure 4.2.1 Tolerances for cylindrical shells