Section 2 Manufacture and workmanship of fusion welded pressure vessels
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Clasifications Register Rules and Regulations - Rules and Regulations for the Classification of Ships, July 2022 - Part 5 Main and Auxiliary Machinery - Chapter 17 Requirements for Fusion Welding of Pressure Vessels and Piping - Section 2 Manufacture and workmanship of fusion welded pressure vessels

Section 2 Manufacture and workmanship of fusion welded pressure vessels

Parent topic: Chapter 17 Requirements for Fusion Welding of Pressure Vessels and Piping

2.1 General requirements

2.1.1 Prior to commencing construction, the design of the vessel is to be approved where required by Pt 5, Ch 10, 1.6 Plans and Pt 5, Ch 11, 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 Materials of construction

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.

2.3 Tolerances for cylindrical shells

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 17.2.1 Tolerances for cylindrical shells.

Table 17.2.1 Tolerances for cylindrical shells

Nominal internal diameter of vessel in mm Difference between maximum and minimum diameters Maximum departure from designed form
≤ 300   1,2 mm
> 300 ≤ 460   1,6 mm
> 460 ≤ 600   2,4 mm
> 600 ≤ 900 1,0 per cent of internal diameter 3,2 mm
> 900 ≤ 1220   4,0 mm
> 1220 ≤ 1520   4,8 mm
> 1520 ≤ 1900   5,6 mm
> 1900 ≤ 2300   6,4 mm
> 2300 ≤ 2670 19 mm 7,2 mm
> 2670 ≤ 3950   8,0 mm
> 3950 ≤ 4650 19 mm 0,2 per cent of internal diameter
> 4650 0,4 per cent of internal diameter

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 17.2.1 Tolerances for cylindrical shells. This amount corresponds to x in Figure 17.2.1 Tolerances for cylindrical shells.

Figure 17.2.1 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 17.2.1 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 17.2.2 Circumferential tolerances

Table 17.2.2 Circumferential tolerances

Outside diameter (nominal inside diameter plus twice actual plate thickness), in mm Circumferential tolerance
300 to 600 inclusive ±5 mm
Greater than 600 ±0,25 per cent
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