First, what are the basic requirements for the appearance of straight seam steel pipe welds?
Before non-destructive testing of straight seam steel pipes, the weld appearance inspection should meet the requirements. The general weld appearance of the straight seam steel pipe weld and the surface of the welded joint should be well-formed, with the width preferably covering the bevel edge by 2mm on each side. The weld leg height of the fillet weld should meet the design specifications, and the shape should have a smooth transition.
1. Surface of the welded joint of straight seam steel pipe:
1) Cracks, lack of fusion, porosity, slag inclusions, and spatter are not allowed.
2) For steel pipes with a design temperature below -29 degrees Celsius, stainless steel, and alloy steel pipes with a high hardening tendency, the weld surface should not have an undercut. For other materials, the undercut depth of the weld should be greater than 0.5mm, the continuous undercut length should not exceed 100mm, and the total length of the undercut on both sides of the weld should not exceed 10% of the total length of the weld.
3) The weld surface should not be lower than the surface of the steel pipe.
4) Weld reinforcement height should not exceed 3mm (the maximum width of the bevel after welding joint assembly).
5) Misalignment of welded joints should not exceed 10% of the wall thickness and should not exceed 2mm.
2. Non-destructive testing of straight seam steel pipes: The principle for selecting non-destructive testing methods for straight seam steel pipes is as follows: For ferromagnetic steel pipes, magnetic particle testing should be used; for non-ferromagnetic steel pipes, penetrant testing should be used. For welded joints with a tendency for delayed cracking, surface non-destructive testing should be performed after the welding cooling time; for welded joints with a tendency for reheat cracking, surface non-destructive testing should be performed once after welding and once after heat treatment. The application of surface non-destructive testing should be carried out according to standard requirements. The detection objects and application occasions are generally as follows:
1) Inspection of the outer surface of steel pipe materials.
2) Detection of surface defects in important butt welds.
3) Detection of surface defects in important fillet welds.
4) Detection of surface defects in welded joints of important socket welds and bridging tee branch steel pipes.
5) Surface defect inspection after steel pipe bending.
6) Beveling inspection of welded joints with high hardening tendency.
7) Beveling inspection of non-austenitic stainless steel pipes with a design temperature below or equal to -29 degrees Celsius.
8) Inspection of welds after root cleaning for double-sided weldments.
9) Defect inspection of the ground area when using oxy-acetylene torches to cut welding fixtures on alloy steel pipes with hardening tendency.
3. Radiographic Inspection and Testing of Straight Seam Steel Pipes: The main targets of radiographic inspection and testing are butt joints of straight seam steel pipes and butt-welded pipe fittings. The selection of non-destructive testing methods should be based on the design documents. Radiographic inspection should be used for welded joints of titanium, aluminum and aluminum alloys, copper and copper alloys, and nickel and nickel alloys. For welds with a tendency for delayed cracking, radiographic inspection and testing should be performed after the welding cooling time. When the main steel pipe inside a jacketed steel pipe has a circumferential weld, this weld should undergo 100% radiographic inspection. Concealed work can only proceed after the pressure test is passed. Welded joints on the steel pipe covered by reinforcing rings or support plates should also undergo 100% radiographic inspection. Covering can only proceed after the inspection is passed. For welds requiring intermediate inspection, non-destructive testing should be performed after visual inspection is passed, and radiographic and wave detection should be performed after surface non-destructive testing. Welding can only continue after the inspected weld has been evaluated and deemed qualified.
Secondly, the production temperature of straight seam steel pipes is crucial:
Strict temperature control is necessary during the production of straight seam steel pipes to ensure weld reliability. If the temperature is too low, the welding position may not reach the required temperature. With most of the metal structure still solid, it is difficult for the metal at both ends to penetrate and bond together. When the temperature is too high, a lot of metal at the welding point is in a molten state. These parts are very soft and fluid, and may carry molten droplets. When these droplets fall, there isn’t enough metal to penetrate each other. Furthermore, uneven welding can lead to weld voids. Therefore, integrated wastewater treatment equipment manufacturers remind users that strict temperature control is crucial during the production of straight seam welded pipes.
Third, how is the material of straight seam steel pipes determined?
Straight seam steel pipes are among the most widely used steel products currently, with extensive applications in engineering, construction, and equipment manufacturing. With continuous technological advancements, the production process of straight seam welded steel pipes is also constantly evolving. However, the material of straight seam steel pipes has significant limitations in use. Straight seam steel pipes differ from seamless steel pipes in terms of compressive strength and elongation. The most common materials for straight seam steel pipes are Q235B, Q345B, and Q345C.
Fourth, Precautions for Purchasing Straight Seam Steel Pipes:
1. Understanding the Types of Steel Pipes Needed for Purchasing:
1) By Type: Straight seam steel pipes, seamless steel pipes, spiral steel pipes, etc.
2) Classification of Straight Seam Steel Pipes by Cross-Sectional Shape: Square pipes, rectangular pipes, elliptical pipes, flat elliptical pipes, semi-circular pipes, etc.
2. Several Points to Note:
1) Using a gate to make the pipe wall thickness appear thicker by slapping it with a hammer, but this will be revealed by actual measurement.
2) Using straight seam steel pipes to pass as seamless steel pipes. Straight seam steel pipes have fewer welds, only one longitudinal weld. The entire pipe is ground down by machine, a process known as polishing, to make it appear seamless.
3) A more sophisticated method now is to create seamless steel pipes, also known as hot-expanded steel pipes. After expansion, there is lead powder inside, and there are also burn marks on the outside. The weld is also invisible. Many large steel pipes are sold as seamless steel pipes to seek higher profits.
4) Circumferentially welded straight seam steel pipes are polished to be sold as seamless steel pipes.
Post time: Mar-03-2026