FlangesUnless specified otherwise, all flanges shall be manufactured from the same material and grade as adjacent pipes or bends.All flanges shall be in accordance with BS 4505: Section 3.1, PN16 or ASME B16.5 unless stated otherwise. The nominal size of the flange shall be to suit the nominal size of the pipe and the type of assembly. Bolt holes shall be off-centre as shown on the standard drawing and in keeping with good engineering practice.The flange type selected must provide adequate sealing and support under normal operating conditions and, when appropriate, flanges should be of a type which enhances installation and future maintenance. All flanges must be assembled having their faces at 90° to the pipe centre line. Generally flanges shall be BS 4505: 3.1, PN16, code 101 or ASME B16.5 class 150Spinning flanges shall consist of a matching set of a code 102 flange (BS 4505: 3.1 or ASME B16.5 ) and preformed pressed collar to ensure that the assembly thickness is equivalent to that of a code 101 flange.