Longitudinally Submerged Arc Welding (LSAW) is a professional expression term for LSAW steel pipe. It uses a single medium and thick plate as the raw material, and the steel plate is pressed (rolled) into a tube blank in a mold or a forming machine. The pipe is produced by submerged arc welding and expanded diameter.
The finished products of LSAW steel pipe have a wide range of specifications, and the weld seam has good toughness, plasticity, uniformity and compactness. It has the advantages of large pipe diameter, pipe wall thickness, high pressure resistance, low temperature resistance and strong corrosion resistance. In the construction of high-strength, high-toughness, high-quality long-distance oil and gas pipelines, most of the steel pipes required are large-diameter thick-walled LSAW pipes. According to API standards, in large-scale oil and gas transportation pipelines, when passing through Class 1 and Class 2 areas such as alpine areas, seabeds, and densely populated cities, LSAW pipes are the only designated applicable pipe type.
According to different molding methods, it can be divided into:
UOE welded pipe: After the single steel plate is pre-bent at the edge, it undergoes U forming, O forming, internal welding, external welding, mechanical cold expansion and other processes;
JCOE welded pipe: Pre-welding, forming, and cold expanding after welding according to "J-C-O-E";
HME welded pipe: It is formed by mandrel rolling method according to "C-C-O", and after welding, it is cold-expanded.
Main features of LSAW steel pipe:
1) The steel pipe has a longitudinal weld, and both the inner and outer welds are welded by submerged arc welding.
2) After the overall mechanical expansion treatment, the internal stress of the steel pipe is small and evenly distributed, which can effectively prevent stress corrosion cracking, has high dimensional accuracy, and is convenient for on-site welding construction.
3) Pre-welding and finishing welding process is adopted, the welding process is stable and the weld quality is high.
4) Welding seam is easy to realize non-destructive flaw detection in the production process and non-destructive flaw detection in the field during use.
5) The range of product specifications is large, which can produce steel pipes with small diameter and large wall thickness as well as large diameter and large wall thickness.
LSAW longitudinal welded pipe inspection:
Although the forming process of LSAW straight seam welded pipe is simple, it also needs to go through many steps to form slowly. After the straight seam welded pipe is produced, it also needs to be tested. The main methods to inspect the quality of longitudinally welded pipes are: magnetic inspection, ultrasonic inspection, penetration inspection and radiographic inspection.
1. Magnetic inspection can only detect defects on the surface or near the surface of longitudinally welded pipes. Only quantitative analysis can be done on defects, and the nature and depth of defects can only be estimated. According to the different methods of measuring magnetic flux leakage, it can be divided into magnetic particle method, magnetic induction method and magnetic recording method, and magnetic particle method is the most commonly used.
2. Ultrasonic inspection method is based on the difference between ultrasonic metal and other homogeneous media.
3. Penetration inspection is the use of physical properties such as the permeability of certain liquids to find and detect defects.
4. Radiographic testing is to use the ray to penetrate the material and the attenuation characteristics in the material to perform detection.
The application of longitudinally welded pipes in steel structures and construction industries can be said to be very promising. Because it is characterized by strong earthquake resistance and pressure resistance, and new environmental protection, many large-space, large-span buildings such as stadiums, subway stations and large-scale Industrial plants are built with it, so the application in the construction industry is very extensive. Although the production process of straight seam welded pipe is simple, efficient, and low in cost, it can only be used in thinner and small-diameter steel pipe materials, and cannot be used in thicker and large-diameter steel pipe materials to produce thicker and large-diameter steel pipe materials. The steel pipe material can only use the spiral welding process.
Tips: In case ASTM A53 Grade B in ERW (electric resistance welded) pipe, the weld seam shall be done the heat treatment with a minimum 1000°F [540°C]. In this way the no untempered martensite remains.
In case ASTM A53 B erw pipe in cold expanded, then expansion should not exceed 1.5% of the required OD.
