What Inspections Must Straight Seam Steel Pipes Undergo Before Leaving The Factory?

From the welding process, the straight seam steel pipe will inevitably have a lot of T-weld, so the probability of welding defects is also increased, and the welding residual stress at the T-weld is large, and the weld metal is often in a three-way stress state, increasing the possibility of cracking.

 

 

From the welding process, the straight seam steel pipe will inevitably have a lot of T-weld, so the probability of welding defects is also increased, and the welding residual stress at the T-weld is large, and the weld metal is often in a three-way stress state, increasing the possibility of cracking. Moreover, according to the process regulations of submerged arc welding, each weld should have an arc starting point and an arc extinguishing point, but each steel pipe can not achieve the condition when welding the ring joint, so there may be more welding defects at the arc extinguishing point. The trend of pipeline development is large caliber. With the increase of the diameter of the steel pipe and the increase of the grade of steel used, the stable expansion trend of ductile fracture tip becomes larger. Although the straight seam steel pipe and the steel pipe are the same level, the straight seam steel pipe has a high impact toughness. Due to the change of the transmission volume of the pipeline, in the actual operation process, the steel pipe is subjected to random alternating load. It is of great significance to know the low cycle fatigue strength of steel pipe for judging the service life of pipeline. According to the measured results, the fatigue strength of the straight seam steel pipe is the same as that of the seamless pipe and resistance welded pipe, and the test data is distributed in the same area with the seamless pipe and resistance pipe, and it is higher than the general straight seam steel pipe.

 

What Tests Should Straight Seam Steel Pipes Go Through Before Leaving The Factory?

 

(1) and coating: qualified steel pipe according to user requirements and coating.

 

(2) Special wave inspection I: Check the internal and external welds of the straight seam welded steel pipe and the base material on both sides of the weld;

 

(3) External welding: The longitudinal multi-wire submerged arc welding is performed on the outside of the straight submerged arc welded steel pipe;

 

(4) X-ray inspection I: X-ray industrial television inspection of internal and external welds, using image processing system to detect the sensitivity of the flaw;

 

(5) X-ray inspection II: X-ray industrial television inspection of the steel pipe after expanding and water pressure test and tube end weld film;

 

(6) Tube end magnetic particle inspection: this inspection is carried out to find defects in the tube end;

 

(7) chamfering: the inspected steel pipe will be processed at the end of the pipe to achieve the required size of the pipe end groove;

 

(8) Acoustic inspection II: Special wave inspection is carried out again one by one to check the defects that may occur after the expansion and water pressure of the straight seam welded steel pipe;

 

(9) Expanding diameter: the full length of the submerged arc welded straight seam steel pipe is expanded to improve the dimensional accuracy of the steel pipe and improve the distribution of the internal stress of the steel pipe;

 

(10) Pre-welding: make the straight seam welded steel pipe after forming and use gas shielded welding (MAG) for continuous welding;

 

(11) Internal welding: The use of longitudinal multi-wire submerged arc welding (more than four wires) on the inside of the straight seam steel pipe welding;

 

(12) Water pressure test: in the water pressure test machine to expand the diameter of the steel pipe after the test pressure to meet the standard requirements, the machine has automatic recording and storage function;

 

The production of straight seam steel pipe is basically a stable continuous process under the same working conditions: the steel pipe production process is segmented, including the whole plate, head, pre-coiling, spot welding, welding, finishing, and multiple process processes. This is an important feature of straight seam steel pipe production that is different from steel pipe production. The weldability of the site is mainly determined by the material of the steel pipe and the size tolerance of the port. Considering the requirements of steel pipe installation and construction, the continuity of steel pipe processing and production and the consistency of shape geometry are particularly important. Stable production conditions are very convenient for welding quality control and geometric size. Due to the regularity of the pipe shape and the uniform distribution of the weld, the straight seam steel pipe has a very good ellipticity and verticality of the pipe mouth compared with the steel pipe, which improves the alignment accuracy of the on-site steel pipe welding group. The pressure drop in the pipeline is directly proportional to the length of the pipe, fluid viscosity coefficient, fluid velocity, fluid resistance coefficient, and inversely proportional to the inside diameter of the pipe. The fluid resistance coefficient is related to the Reynolds number and the roughness of the inner surface of the pipe. It has been determined that the influence of the roughness of the inner surface of the straight steel pipe is ten times greater than the influence of the local uplift area (such as the spiral weld or the longitudinal weld, even including the inner annular weld).