The most common method of joining PU insulated steel pipe is welding, for which weld treatment and welding procedure are subject to quite strict requirements.
I. Pipe cut quality shall comply with the following:
(1) The cut surface shall be smooth and free of cracks, laminations, burrs, unevenness, necking, slag, oxides, iron chips, etc.;
(2) The inclination deviation of the cut end face shall not exceed 1% of the pipe OD and shall not exceed 3 mm;
(3) Where beveling is required, the bevel form shall follow the welding procedure.
Second, during pipe prefabrication, piping components shall be selected by quantity, specification, and material as specified on the isometric drawing, and marked with the system number and the sequence number of each component according to the prefabrication sequence.
Third, during pipe prefabrication, free segments and closing segments shall be selected reasonably. Closing segments must be fabricated to field-measured dimensions. After prefabrication, internal cleanliness shall be checked, ends capped, and pieces stacked in a reasonable order.
Fourth, the positions of butt welds of PU insulated steel pipe shall comply with the following:
(1) The pipe location shall be not less than the pipe OD, or not less than 100 mm, from the start of the bend;
(2) The distance between two pipe butt welds shall not exceed 5 mm.
(3) Support/hanger pipe attachments shall not coincide with pipe butt welds; the weld shall be not less than 50 mm from the edge of the support/hanger;
(4) Pipe joints shall avoid openings for drains, vents, and instrument connections; the distance from the opening edge shall be not less than 50 mm and not less than the opening diameter.
Fifth, the type, material, fabricated dimensions, and accuracy of pipe supports shall strictly follow the relevant standard drawings. The working face of sliding supports shall be smooth and flexible, without binding.
