5.6 Socket weld joints
5.6.1 Socket weld joints may be used with carbon steel pipes not exceeding 60,3 mm outside diameter. Socket weld fittings are to be of forged steel and the material is to be compatible with the associated piping. Such joints are not to be used where fatigue, severe erosion or crevice corrosion is expected to occur. See also Ch 4,7.3.9.
5.6.2 The thickness of the socket weld fittings is to meet the requirements of 5.1.3 but is to be not less than 1,25 times the nominal thickness of the pipe or tube. The diametrical clearance between the outside diameter of the pipe and the bore of the fitting is not to exceed 0,8 mm, and a gap of approximately 1,5 mm is to be provided between the end of the pipe and the bottom of the socket.
5.6.3 The leg lengths of the fillet weld connecting the pipe to the socket weld fitting are to be such that the throat dimension of the weld is not less than the nominal thickness of the pipe or tube.
5.7 Welded sleeve joints
5.7.1 Welded sleeve joints may be used in Class III systems only, subject to the restrictions and general dimensional requirements given in 5.6 for socket weld joints.
5.7.2 The pipe ends are to be located in the centre of the sleeve with a 1,5 to 2,0 mm gap.
5.8 Other mechanical couplings
5.8.1 Pipe unions, compression couplings, or slip-on joints, as shown in Fig. 1.5.2, may be used if type approved for the service conditions and the intended application. The type approval is to be based on the results of testing of the actual joints. The acceptable use for each service is indicated in Table 1.5.6 and dependence upon the Class of piping, with limiting pipe dimensions, is indicated in Table 1.5.7.
5.8.2 Where the application of mechanical joints results in a reduction in pipe wall thickness due to the use of bite type rings or other structural elements, this is to be taken into account in determining the minimum wall thickness of the pipe to withstand the design pressure.