How to Conduct On-Site Distinction? Practical Methods and Tips for LSAW and HSAW Tubes
In pipeline engineering construction, on-site distinction between LSAW (Longitudinal Submerged Arc Welded) and HSAW (Helical Submerged Arc Welded) tubes is a crucial practical task. Accurate distinction directly ensures that the selected pipe type matches the project design requirements, avoiding safety hazards and cost losses caused by mismatched materials. However, due to the similar appearance of the two types of tubes after anti-corrosion treatment, on-site distinction often faces certain challenges. How to quickly and accurately distinguish LSAW and HSAW tubes on the construction site? What practical methods and tips are there? This article will sort out systematic on-site distinction methods from multiple perspectives, providing practical guidance for engineering technicians.
First Look: How to Distinguish Weld Direction with Naked Eye Observation?
The most intuitive and primary method for on-site distinction is to observe the direction of the weld, which is also the core feature that distinguishes LSAW and HSAW tubes. LSAW tubes are named for their longitudinal welds, and the key to observation is to find the straight weld parallel to the tube axis.
When observing LSAW tubes, you can place the tube horizontally and look along the length direction. The weld of LSAW tubes is a single straight line running through the entire length of the tube, parallel to the two ends of the tube. Even if the tube is covered with an anti-corrosion layer, the straight trace of the weld can usually be seen through the anti-corrosion layer, or the trace can be clearly felt by touching with hands. In contrast, the weld of HSAW tubes is helical, presenting a continuous spiral line winding around the tube body. When observing horizontally, the weld will show a regular oblique line or spiral curve, and the angle between the weld and the tube axis is usually 30°-60°. It should be noted that for tubes with thick anti-corrosion layers, local removal of the anti-corrosion layer (at the non-key part) may be required to clearly observe the weld direction.
Second Check: What Process Traces Can Assist in Distinction?
In addition to weld direction, the process traces left during the production of LSAW and HSAW tubes can also be used as auxiliary distinction basis. These traces are closely related to their different forming and welding processes and have strong辨识度.
For LSAW tubes, due to the step-by-step forming process (JCOE or UOE), there will be obvious stamping traces at the two ends of the tube or on the inner wall. Especially for JCOE-formed LSAW tubes, the "J-shaped → C-shaped → O-shaped" forming process will leave regular arc transition traces on the inner wall of the tube. In addition, LSAW tubes usually undergo a whole-tube expansion process, and the inner wall is relatively smooth and uniform in thickness. For HSAW tubes, the continuous spiral forming process will leave uniform spiral roller marks on the outer wall of the tube. At the same time, because HSAW tubes adopt continuous welding, the weld seam is relatively uniform in width, but there will be slight periodic fluctuations along the spiral direction, which is different from the stable width of LSAW tube welds. In addition, the end face of HSAW tubes is often slightly inclined due to the spiral forming, while the end face of LSAW tubes is basically perpendicular to the axis.
Third Measure: How to Use Simple Tools for Parameter Verification?
When naked eye observation and process trace judgment are not sufficient, simple measuring tools can be used for parameter verification to further confirm the tube type. The key measurement indicators include weld length, tube diameter tolerance, and wall thickness uniformity.
For weld length measurement, take a 12-meter-long tube as an example. The weld length of LSAW tubes is basically equal to the tube length (about 12 meters). For HSAW tubes, the weld length can be calculated by the formula: weld length = tube length / cos(helix angle). If the helix angle is 45°, the weld length of a 12-meter HSAW tube is about 16.97 meters, which is significantly longer than that of LSAW tubes. For diameter tolerance measurement, LSAW tubes have higher dimensional accuracy, and the diameter tolerance is usually controlled within ±0.2%, while the diameter tolerance of HSAW tubes is relatively large, about ±1%. A simple tape measure can be used to measure the diameter at multiple positions of the tube. If the diameter variation is small, it is more likely to be an LSAW tube. In terms of wall thickness uniformity, LSAW tubes have better wall thickness uniformity due to the use of thick steel plates and expansion processes, while HSAW tubes may have slight wall thickness differences at the spiral weld due to continuous forming.
Fourth Inquire: What Information Can Be Confirmed Through Documentation and Labels?
On-site distinction can also be assisted by inquiring about relevant documents and checking product labels, which is a more reliable supplementary method. Each batch of qualified LSAW and HSAW tubes will be accompanied by product quality certificates and delivery documents.
By checking the product quality certificate, you can directly find the product type (LSAW or HSAW), production process (such as JCOE, UOE for LSAW), and key parameters (wall thickness, diameter, steel grade, etc.), which can directly confirm the tube type. In addition, the outer wall of the tube will be marked with product information by spraying or stamping, including the tube type abbreviation (LSAW or HSAW), specification model, and production batch. It should be noted that when checking labels and documents, it is necessary to confirm that the information matches the actual tube to avoid confusion caused by wrong labeling. For tubes with unclear labels, you can contact the supplier to verify the production information.
Common Pitfalls: What Should Be Paid Attention to in On-Site Distinction?
There are some common pitfalls in on-site distinction of LSAW and HSAW tubes, and engineering technicians need to pay special attention to avoid misjudgment.
First, avoid misjudgment caused by incomplete anti-corrosion layers. Some HSAW tubes may have local anti-corrosion layer damage, and only a short section of the weld can be seen, which may be mistaken for a longitudinal weld. At this time, it is necessary to check the entire length of the tube to confirm the weld direction. Second, do not rely solely on wall thickness to distinguish. Although LSAW tubes are mostly thick-walled and HSAW tubes are mostly thin-walled, there is an overlap in wall thickness specifications (such as 20-25mm). Therefore, wall thickness can only be used as an auxiliary indicator, not a decisive factor. Third, pay attention to the difference between spiral weld and multiple longitudinal welds. Individual special pipes may have multiple longitudinal welds, but their welds are still straight and parallel to the axis, which is different from the continuous spiral of HSAW tubes.
To sum up, on-site distinction between LSAW and HSAW tubes can be carried out through a combination of "naked eye observation of weld direction, inspection of process traces, parameter measurement with simple tools, and verification of documents and labels". Mastering these practical methods can help engineering technicians quickly and accurately distinguish the two types of tubes on the construction site. In actual operation, it is recommended to use multiple methods for cross-verification to ensure the accuracy of the distinction. Accurate on-site distinction not only ensures the smooth progress of the project but also lays a solid foundation for the long-term safe operation of the pipeline.
