Basic requirements for the appearance of
straight seam steel pipe welds
Before non-destructive testing of straight seam steel pipes, the appearance inspection of welds should meet the requirements. The appearance of the welds of straight seam steel pipes and the general welding appearance of the surface of welded joints should be formed, and the width should cover the edge of the groove by 2mm on each side. The height of the weld leg of the fillet weld should meet the design requirements, and the shape should be smoothly transitioned.
First, the surface of the welded joint:
1. Cracks, unfused, pores, slag inclusions, and spatter are not allowed.
2. The weld surface of steel pipes with a design temperature below -29 degrees, stainless steel, and alloy steel pipes with a greater tendency to harden shall not have undercutting. The undercut depth of other steel pipe welds should be greater than 0.5mm, the continuous undercut length should not be greater than 100mm, and the total length of the undercut on both sides of the weld should not be greater than 10% of the total length of the weld.
3. The weld surface shall not be lower than the surface of the steel pipe. The weld excess height shall not be greater than 3mm (the maximum width of the rear groove of the welded joint group).
4. The misalignment of the welded joint should not exceed 10% of the wall thickness and not exceed 2mm.
Second, surface non-destructive testing:
The principle of selecting the surface non-destructive testing method for straight seam steel pipes: For ferromagnetic steel pipes, magnetic particle testing should be used; for non-ferromagnetic steel pipes, penetration testing should be used. For welded joints with a tendency to delay cracking, surface non-destructive testing should be carried out after the welding cooling time; for welded joints with a tendency to reheat cracking, surface non-destructive testing should be carried out once after welding and after heat treatment. The application of surface non-destructive testing is carried out in accordance with standard requirements, and its detection objects and application occasions are generally as follows:
1. Inspection of the outer surface of steel pipe materials.
2. Surface defect detection of important butt welds.
3. Surface defect detection of important fillet welds.
4. Surface defect detection of welded joints of important socket welds and cross-joint tee branches.
5. Surface defect detection after steel pipe bending.
6. Groove detection of welded joints with a large tendency to material quenching.
7. Inspection of the groove of non-austenitic stainless steel pipes with a design temperature lower than or equal to minus 29 degrees Celsius.
8. Inspection after root cleaning of welds with double-sided weldments that require root cleaning
9. When using an oxyacetylene flame to cut welding fixtures on alloy steel pipes with a tendency to harden, defect detection of the grinding area.
Third, radiographic inspection and testing:
The main objects of radiographic inspection and testing are the butt joints of straight seam steel pipes and the butt joints of butt-welded pipe fittings. The selection of non-destructive testing methods shall be in accordance with the provisions of the design documents. Radiographic inspection methods shall be used for the inspection of welded joints of titanium, aluminum, and aluminum alloys, copper and copper alloys, and nickel and nickel alloys. For welds with a tendency to delay cracking, their radiographic inspection and testing shall be carried out after the cooling time of welding. When there is a girth weld in the main pipe of the jacketed pipe, the weld shall be 100% radiographically inspected, and concealed operations can only be carried out after passing the pressure test. Welded joints covered by reinforcement rings or support pads on steel pipes shall be 100% radiographically inspected, and can only be covered after passing the test. For welds that are required to undergo intermediate welding inspection, nondestructive testing should be carried out after the appearance inspection is qualified, and radiography and wave testing should be carried out after the surface nondestructive testing. The welds that have been inspected can continue to be welded only after they are evaluated as qualified.
The production temperature of straight seam steel pipes is very important:
In the process of producing straight seam steel pipes, the temperature must be strictly controlled to ensure the reliability of welding. If the temperature is too low, the welding position may not reach the required temperature for welding. When most of the metal structures are still solid, it is difficult for the metals at both ends to penetrate each other and combine together. When the temperature is too high, there are many metals in the molten state at the welding position. The texture of these parts is very soft, and some fluidity may carry molten droplets. When such metal drops, there is also not enough metal to penetrate each other. During welding, there will be some unevenness with the weld to form a molten hole. Therefore, the manufacturer of integrated sewage treatment equipment reminds us that the temperature must be strictly controlled during the production process of straight seam welded pipes. Regular manufacturers have very good control technology, so the temperature control requirements can be achieved during the production process to ensure the product, so we need to buy straight seam welded pipes from regular manufacturers.
How is the material of straight seam steel pipe determined?
For straight seam steel pipe, the material should be one of the most widely used steel products at present, and it has a wide range of applications in engineering construction, equipment production, etc. With the continuous improvement of market technology, the production process of straight seam welded pipes is also constantly improving. However, the material of straight seam steel pipe has a relatively significant use instruction during use. Straight seam steel pipe has a gap with a seamless pipe in terms of compression resistance and extension! The materials of straight seam steel pipe are mostly Q235B, Q345B, Q345C, etc.
Precautions for purchasing straight seam steel pipe:
First, you need to understand the types of steel pipes when purchasing:
1. According to the type: straight seam steel pipe, seamless steel pipe, spiral steel pipe, etc.
2. Classification of cross-sectional shapes of straight seam steel pipes: square pipe, rectangular pipe, elliptical pipe, flat elliptical pipe, semicircular pipe, etc.
Second, a few things to note:
1. If the wall thickness of the steel pipe is not enough, use the gate method. Use a hammer to shield the end of the steel pipe to make it look thicker, but it will be exposed when measured with an instrument.
2. Use straight seams to act as seamless steel pipes. There are relatively few welds in straight seams, only one longitudinal weld. Use a machine to polish the entire steel pipe, commonly known as polishing, so that it looks like there is no gap to act as seamless.
3. Now there is another more sophisticated method, which is seamless steel pipes. Seamless steel pipes are also hot-expanded steel pipes. After expansion, there is a lead powder inside, and there are traces of burning on the outside. The welds cannot be seen. Many larger steel pipes use this kind of steel pipe to act as seamless and sell them to seek large profits.
4. Girth weld straight seam steel pipes use polishing to replace seamless steel pipes and straight seam steel pipes.
