First, Basic Requirements for the Appearance of Straight Seam Steel Pipe Welds.
Before non-destructive testing of straight seam steel pipes, the appearance of the welds should meet the requirements. The general weld appearance of the straight seam steel pipe welds 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 fillet welds should meet the design specifications, and the shape should have a smooth transition.
1. Welded Joint Surface:
(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 undercut length on both sides of the weld should not exceed 10% of the total weld length.
(3) The weld surface should not be lower than the surface of the steel pipe. The weld reinforcement should not exceed 3mm (the maximum width of the bevel after the weld joint assembly).
(4) The misalignment of the weld joint should not exceed 10% of the wall thickness and should not exceed 2mm.
2. Surface Non-Destructive Testing: The principle for selecting surface 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 weld joints with a tendency for delayed cracking, surface non-destructive testing should be performed after the welding cooling time; for weld 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 weld joints of important socket welds and bridging tee branches.
(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 welding fixtures on alloy steel pipes with hardening tendency are cut using an oxy-acetylene flame.
3. Radiographic Inspection and Testing: 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 pipe inside the jacketed pipe has a circumferential weld, the weld should undergo 100% radiographic inspection. Concealed work can only proceed after the pressure test is passed. Welded joints on steel pipes 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.

Second, the production temperature of straight seam steel pipes is crucial.
Strict temperature control is essential during the production of straight seam steel pipes to ensure weld strength. If the temperature is too low, the welded area may not reach the required temperature. With most of the metal structure still solid, it is difficult for the metal at both ends to interpenetrate and bond together. Conversely, if the temperature is too high, much of the metal in the welded area is in a molten state. These parts are soft and fluid, and may carry molten droplets. When these droplets fall, there is also insufficient metal for interpenetration. Furthermore, uneven welding can lead to weld voids. Therefore, integrated wastewater treatment equipment manufacturers emphasize the need for strict temperature control during the production of straight seam welded pipes. Reputable manufacturers possess advanced temperature control technology, enabling them to meet temperature requirements and ensure product quality. Therefore, it is essential to purchase straight seam welded pipes from reputable manufacturers.

Third, how is the material of straight seam steel pipes determined?
Straight seam steel pipes are among the most widely used steel products currently, finding extensive applications in engineering, construction, and equipment manufacturing. With continuous technological advancements, the production process of straight seam welded pipes is also constantly evolving. However, the material of straight seam steel pipes has significant limitations in usage. Straight seam steel pipes differ from seamless pipes in terms of compressive strength and elongation. The most common materials for straight seam steel pipes are Q235B, Q345B, and Q345C. We welcome customers to choose and order. Our factory produces and sells straight seam steel pipes with diameters ranging from 57 to 1620 mm and wall thicknesses from 2 to 60 mm, including galvanized straight seam steel pipes, hot-expanded straight seam steel pipes, and large-diameter straight seam steel pipes. Commonly used materials include Q235B, 16Mn, Q345B, L245, L290, and X42~X70. Products are manufactured strictly according to GB/T3091-2001 standards, American standards ASTM-A53 and ASTM A500 standards, British and German standards DIN2440/2444 standards, and European standards EN10255/10240 and EN10219 standards.

Fourth, Points to Note When Purchasing Straight Seam Steel Pipes.
1. Purchasing requires understanding the types of steel pipes:
(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 steel pipes, rectangular steel pipes, elliptical steel pipes, flat elliptical steel pipes, semi-circular steel pipes, etc.
2. Several points to note:
(1) Using a gate to make the steel 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 as seamless pipes. Straight seam steel pipes have fewer welds, only one longitudinal weld. The entire steel pipe is ground down by machine, a process known as polishing, to make it appear seamless.
(3) A more sophisticated method is to create “seamless” steel pipes, also known as hot-expanded steel pipes. After expansion, lead powder is inside, and there are burn marks on the outside, making the weld invisible. Many large pipes are sold as seamless pipes to maximize profits.
(4) Polishing circumferential welded straight seam steel pipes to pass them off as seamless steel pipes.