Straight seam double-sided submerged arc welded steel pipe

Product Introduction

Double-sided submerged arc welded straight seam steel pipe is a new welding method invented in 1940. It is the same as the previous manual welding in that it still uses slag protection, but this slag is not the skin of the welding rod, but the welding flux specially melted.

The flux system consists of a funnel-loaded flux delivered through a pipe to the front face to be welded. The second difference is that welding rods are not used, but welding wires are used, because welding wires can be continuously fed. Welding rod, we have to throw away a welding rod head after burning a welding rod, and the operation has to stop, change the welding rod and weld again. After changing to welding wire, the welding wire is continuously fed with the welding wire feeding device and the welding wire disc. This welding method is to continuously feed the welding wire, ignite the arc under the coverage of meltable granular flux, so that part of the welding wire, base metal and flux melts and evaporates to form a cavity. The arc burns stably in the cavity, so it is called submerged arc automatic welding. The arc is buried in the cavity.

The first advantage of this method is that it is fully automated. The second advantage is that it is welded under submerged arc, so its heat exchange and protection performance are relatively strong, and the quality of welding is relatively high. The third advantage is that because the electric arc in submerged arc automatic welding is buried under the welding flux, it can use high current and the welding efficiency is relatively high. Recently, our country is carrying out the West-East Gas Pipeline Project, the pipeline is a kind of high-strength steel. The pipeline is prefabricated into a section in the factory, and then taken to the construction site for welding in the field. The welding process for the pipeline in the factory is submerged arc welding. Now submerged arc welding has developed into double-wire submerged arc welding and multi-wire submerged arc welding, which further improves the efficiency.

Process flow

a. Plate probe: After the steel plate used to manufacture large-diameter longitudinal submerged arc welding steel pipe enters the production line, the full-plate ultrasonic inspection shall be carried out first;

B. edge milling: double-sided milling of the two edges of the steel plate by edge milling machine to achieve the required plate width, plate edge parallelism and groove shape;

c. Pre-bending edge: use pre-bending machine to pre-bend the plate edge, so that the plate edge has the required curvature;

D. forming: on the JCO forming machine, half of the pre-bent steel plate is pressed into a "J" shape after multiple stepping stamping, and then the other half of the steel plate is also bent into a "C" shape, and finally an open "O" shape is formed.

E. pre-welding: make the formed straight seam welded steel pipe seam and adopt gas shielded welding (MAG) for continuous welding;

f. Internal welding: longitudinal multi-wire submerged arc welding (up to four wires) is used to weld on the inner side of the straight seam steel pipe;

g. External welding: longitudinal multi-wire submerged arc welding is used to weld the outside of the longitudinal submerged arc welding steel pipe;

H. Ultrasonic inspection I: 100% inspection of the inner and outer welds of the straight seam welded steel pipe and the base metal on both sides of the welds;

I. X-ray inspection I: 100% of the internal and external welds are inspected by X-ray industrial television, and the image processing system is used to ensure the sensitivity of flaw detection;

J. diameter expansion: the length of the straight seam submerged arc welding steel pipe to expand the diameter to improve the dimensional accuracy of the steel pipe, and improve the distribution of stress in the steel pipe;

k. Hydrostatic test: the expanded steel pipe is inspected one by one on the hydraulic testing machine to ensure that the steel pipe meets the test pressure required by the standard. The machine has the function of automatic recording and storage;

L. chamfering: the qualified steel pipe shall be processed at the pipe end to reach the required groove size at the pipe end;

M. Ultrasonic inspection II: ultrasonic inspection is carried out one by one again to check the defects that may occur after the diameter of the straight seam welded steel pipe is expanded and the water pressure is applied;

N. X-ray inspection II: X-ray industrial television inspection and pipe end weld film for steel pipes after diameter expansion and hydraulic pressure test;

o. Pipe end magnetic particle inspection: this inspection is performed to find pipe end defects;

p. Anti-corrosion and coating: The qualified steel pipe shall be subjected to anti-corrosion and coating according to the user's requirements.

In addition to the above test items, according to API standards and other relevant standards and the special requirements of some users, it is also necessary to carry out damage inspection and other inspection on steel plates and steel pipes, including random inspection on physical and chemical properties of incoming raw materials and appearance inspection of 100% of steel plates.