Welding of steel gas pipes: preparatory works and mounting.

Edging diagram
(pic. 61.1 – Edging diagram)

Before to mount and weld steel gas pipes it is necessary to realize the following works:

  • to delete all obstructions (water, snow, ice, soil, details, construction waste) from inside surface of the pipes.
  • to verify geometrical dimensions of the edges after the making-up, correction of the buckles (to 3,5% of the outside diameter) on the pipes.
  • to clean the joint edges and adjoining surfaces (≥ 1о mm width) from the oxides, paints and rust.

Misshaped ends of steel pipes where there are deep tears (more than 5 mm), cracks, scratches and chipped edges are found out should be cut. Correction of the edges requires heating-up of the pipes if the air temperature is lower than -5ºС.

The edges are prepared for the making-up by mechanical processing or by gas-cutting with polishing. Chamfering provides tightness and durability of the welded joint because of the volume retraction with V-shaped section.

Mounting of welded steel pipes is realized on layers; to make the connection precise there are used different appliances including centralizers (inside and outside).

Welding gas pipes with spiral or single-ended longitudinal seam the mounting is realized with obligatory condition of joint displacement in contacting area of the pipes. Displacement dimension is indicated in the table:

Heating and drying of pipes edges and adjoining areas is also considered as a preparatory work before welding. Drying is realized by heating (50°С) and recommended in case of humidity presence on welded details and at the air temperature of < +5 °С.

Heating of the edges (minimum: 100°С) before the welding is realized for the pipes with wall thickness of more than 5-10 mm and when the air temperature is -10…-20 °С (depending from the type of steel used for the pipes).
 

Pipe ending for welding

(рис. 61.2 – Pipe ending for welding)

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