How welded steel pipes pretend to be seamless steel pipes and inspection methods

First, the feasible fields for welded steel pipes to replace seamless steel pipes
1. At present, welded pipes can replace seamless steel pipes in more and more fields. First, because the thickness of welded pipes is more uniform, they can play a role in decorative pipes, and can also make up for the defects of large-diameter seamless steel pipes (219*6 and above) that are difficult to make. Secondly, they can replace some structural pipes. In addition, with the development of high-strength welded pipe technology, some high-strength welded pipes can replace high-end seamless steel pipes;
2. There is a big gap between my country's welded pipes and foreign countries in replacing high-end seamless steel pipes. As far as oil well pipes are concerned, my country mainly produced by long-process steel mills, with few specifications. The large quantity is not suitable for oil well supply and marketing, while other high-end pipe varieties (such as boiler pipes, petrochemical pipes, mechanical pipes, etc.) lack relevant core technologies;
3. The development of new energy vehicles and hydrogen energy industries in the future will bring more possibilities for welded pipes to replace seamless steel pipes. The replacement of high-end seamless steel pipes not only requires leading enterprises to study related technologies but may also require policies to play a role in it;

Second, China's welded pipes have a big gap in replacing seamless steel pipes compared with foreign countries. Unlike the situation of foreign welded pipes replacing high-end seamless steel pipes, my country only has high-end welded pipes for petroleum that can replace seamless steel pipes. However, it is worth noting that although the strength can be replaced, the proportion of replacement is not large. The reason for the small replacement ratio is mainly related to the steel production process. Most European and American countries are mainly short-process production. The consumption characteristics of oil well pipes vary with the conditions of oil wells in various regions. They have the characteristics of small batches and multiple varieties. This is very similar to the production method of electric furnace steel. my country's production is mainly long-process, and its advantages are small specifications and large batches, which are not suitable for the supply and marketing model of oil well pipes. The reason why oil-welded steel pipes can be replaced and become the world's advanced level is closely related to the supporting industry-university-research cooperation. my country's petroleum system has its own welded pipe enterprises and has supporting petroleum universities, research institutes, and testing institutes, which is the result of the synergy of various aspects. However, the strength of welded pipes in other fields of my country, such as mechanical pipes, boiler pipes, petrochemical pipes, structural pipes, etc., is far from reaching the level of replacing high-end seamless steel pipes.

Third, do you think it is feasible for welded pipes to replace seamless steel pipes?
Hot-rolled welded pipes have the following advantages over ordinary cold-formed welded pipes:
1. More uniform microstructure;
2. No internal stress, reducing cracking of pipes;
3. Reliable and consistent mechanical properties;
4. Greatly improved structural integrity and ductility;
5. Improved toughness of steel pipes;
6. Higher pressure integrity;
7. Higher safety;
8. No strength loss during additional welding and heating;
9. Better corrosion resistance;
10. Better thread processing, grooving, and bending capabilities, even for small pipes, it is not easy to crack, indent, or flatten;
11. It can replace seamless steel pipes in many applications and is more economical than seamless steel pipes;
12. The thickness and roundness are more uniform and consistent, and can better match the connecting pipe.

Fourth, can straight seam steel pipes be used as seamless steel pipes? How to distinguish?
Nowadays, the competition in various industries is fierce. No matter which industry has competition, the steel pipe industry is no exception. To increase profits, many manufacturers will use straight seam steel pipes as seamless steel pipes. This behavior is completely undesirable. Let us introduce it in detail below.
Straight seam steel pipes are made by submerged arc welding or resistance welding. This kind of steel pipe is connected to the weld. These enterprises use polishing machines to grind and polish the welds. After replacement and polishing, the welds will be worn and the surface will be smooth. The overall view is seamless steel pipes. No insiders can see it. This kind of fraudulent equipment cannot detect whether it is a straight seam steel pipe or a seamless steel pipe. Only experts can see that some projects need to be painted with anti-rust paint on the outside, making it more difficult to distinguish, which makes many buyers very uneasy.
So, how to distinguish between straight seam steel pipes and seamless steel pipes? Seamless steel pipes are made to order directly in steel mills. Straight steel pipe manufacturers cannot produce them at all. Generally speaking, they are all foreign cooperation. When we purchase, we try to let suppliers provide guarantees and certificates for steel pipes. Even if they do a good job, there are traces. Generally, the width of the weld of the straight steel pipe is about 2 cm. When we buy seamless steel pipes, if there are traces of about two centimeters in the entire steel pipe, we can verify whether there is a problem. Whether the seamless steel pipe has a problem with the anti-rust paint, we can use a simple and rough method to verify, that is, the steel pipe is verified during the cutting process. The seamless steel pipe has no butt joint, and the straight seam steel pipe is a steel plate folded in half with a joint.
Due to different production processes, seamless steel pipes and welded pipes are produced. Seamless steel pipes include rare cold extrusions such as hot rolling, cold rolling, and cold drawing. Welded pipes are composed of crimped and welded steel plates. Small ones are usually straight seam welds, while large ones are usually spiral welds. Due to the presence of weld seams in welded pipes, the mechanical properties of welded joints are poor, and the application range is limited, but the price is low. The difference is that welded pipes have welds and seamless steel pipes have no welds. Of course, if the welded pipe is well-treated, laymen will not see the difference.
If the welded pipe is not treated, there will be obvious welds and protrusions, such as traces. The better point is to wipe off the weld, but there is still a big difference to the naked eye. There are also a small number of cold-rolled welded pipes with high surface roughness and high precision, which can be sold as fake seamless steel pipes. A careful observation will reveal that there will be a continuous spiral of metallic luster on the pipe wall, that is, the metallographic structure of the original weld is different from that of other parts. To be honest, it may be a bit difficult for laymen to observe this.

Fifth, seamless steel pipe geometric dimensions and appearance inspection:
① Seamless steel pipe wall thickness inspection: micrometer, ultrasonic thickness gauge, no less than 8 points at both ends, and record.
② Seamless steel pipe outer diameter and ovality inspection: caliper, vernier caliper, ring gauge, measure large and small points.
③ Seamless steel pipe length inspection: steel tape measure, manual, automatic length measurement.
④ Seamless steel pipe curvature inspection: ruler, level ruler (1m), feeler gauge, fine wire to measure curvature per meter and full-length curvature.
⑤ Seamless steel pipe end face groove angle and blunt edge inspection: angle ruler, pallet.