Welding Method Of Steel Pipe In Diversion Pipeline Engineering
- May 23, 2018 -

A. The pipeline material of the pipeline project is a spiral welded steel pipe with a wall thickness of 20mm. According to the design documents and the specific conditions at the construction site, manual arc welding and submerged arc welding are used for welding. Under normal circumstances, the steel plate is used for connecting materials and pipes. Seam welding is used for submerged arc welding, manual arc welding, pipe ring joints and stiffening rings and manual arc welding, and the rest using manual arc welding.

B. Bevel processing prefabrication:

(1) When the pipe groove is processed, since the wall thickness is less than 25mm, V-grooves (25°~30°) are adopted.

(2) The pipe groove is processed by oxygen-acetylene semi-automatic knife cutting. The special parts that can not be processed by the semi-automatic knife can be manually cut.

(3) After the groove processing, the oxide scale, slag, and the surface affecting the joint quality of the groove surface must be removed, and the unevenness should be smoothed and polished.

C. Welding process: Welds of engineering pipelines are divided into three categories according to their importance. among them:

One type of weld:

A. All welds in the manifold.

B. Steel pipe wall longitudinal joints.

C. Steel pipe seams.

D. Make up the knot to close the loop seam.

E. Bulkhead and pipe wall connection weld.

If such welds are detected by ultrasonic testing at a rate of 50% and the radiographic inspection rate is 5%, the quality requirement is B1.

Type II welds:

A. Steel pipe wall annular seam;

B. Sealing rings, butt welds of stiffener rings and their combined welds with the pipe wall. If such welds are ultrasonically inspected and the sampling rate is 50%, the quality requirement is B2 qualified.

Three kinds of welds: The stress is very small, and the repairs do not stop the power generation or water supply of the accessory component welds.

(1) Before the weld group, the oil, paint, scale, rust, burr, etc. in the range of not less than 10mm of the groove and its inner surface should be removed, and there must be no defects such as cracks or interlayers.

(2) When the pipe or pipe butt joint group is butt-welded, the inner wall should be flush, and the amount of misalignment of the inner wall should not exceed 10% of the pipe wall thickness, and should not exceed 2mm;

(3) The electrode should be dried according to regulations before use, and should be kept dry during use. Before use, the wire should be cleaned of oil, rust, etc. on its surface. The welding rods, welding wires, and fluxes selected for various types of welds in pipeline welding can be selected according to the following table.

(4) Welding materials shall be baked and stored in accordance with the following requirements: Welding rods and fluxes shall be placed in ventilated, dry and specially designed warehouses with room temperature of not less than 5°C, specially designated for custody, baking and distribution, and shall be promptly measured. Temperature and electrode release records. Baking temperature and time should be strictly in accordance with the manufacturer's instructions. After baking, the electrode should be stored in a constant temperature box of 100-150°C. The coating should be free from peeling and obvious cracks. Welding rods used in the field should be packed into a heat-insulating tube. The time for the electrode to be in the heat-insulating tube should not exceed 4 hours. After it is exceeded, it should be re-baked. The number of repeated baking should not exceed 2 times. The wire should be cleaned of rust and oil before use.

(5) In the case of drafts or winds and winds with a wind speed over 8m/s, snow days, ambient temperature below -5°C, and relative humidity above 90%, the welding department shall have reliable protective measures to ensure that the welding site is The required temperature, welder skills are not affected before welding.

(6) Before the welding, the rust, slag, grease, and water traces in the range of 50-100mm on the groove and on both sides of the groove should be removed.

(7) Welds (including tack welds) should be arced and extinguished at the groove. It is forbidden to start the arc on the parent material. When the arc extinguishes, the arc pits should be filled. The interlaminar joints of multi-layer welding should be staggered. .

(8) Tack welds shall meet the following requirements:

The welding process of the first and second welding seams and the requirements for the welders are the same as those for the main joints (that is, the first and second types of welds, the same below); for the steel plates that require preheating welding, the welding position should be centered on the welding position. At least 150mm should be used for preheating. The preheating temperature should be 20-30°C higher than the preheating temperature of the main seam. The tack welding position should be at least 30mm from the end of the weld. The length should be more than 50mm and the spacing should be 100- 400mm, the thickness should not exceed one-half the height of the official weld, the thickest should not exceed 8mm; welding quality should be checked before welding, if any cracks, pores, slag inclusions and other defects should be removed.

(9) Arc welding and arc extinguishing on base metal are strictly prohibited when components such as work clamps are welded.

(11) For double-sided welding, carbon arc gouging or angle grinders are used after the single side welding to remove the roots on the back side, and the tack weld metal welded on the clear root side is removed. When using carbon arc gouging to remove the roots, the grinding wheel is used to trim the gouge after clearing the roots.

(12) Where the weld joint assembly has a partial clearance of more than 5mm but the length is not greater than 15% of the length of the weld, it is permissible to make surfacing on both sides or side of the groove, but the following provisions shall be complied with:

a, it is forbidden to fill in the gap with metal materials;

b. After the surfacing welding, dressing with a grinding wheel;

c. According to the length of the surfacing and the size of the gap, the weld of the surfacing site should be subject to non-destructive testing as appropriate.

(11) Submerged arc welding of longitudinal joints Arc-arcing plates and arc extinguishing plates are installed at both ends of the weld. The arc-extinguishing plate and the extinguishing arc plate must not be knocked down with a hammer. The oxygen-B flame or carbon arc gouging is used for cutting and grinding is performed with the grinding wheel. Chengyuan groove type.

(12) After welding is completed, the welder should perform self-test. After one or two types of welds have passed the self-test, they should be stamped with a stencil near the weld to make a record.