The application of steel pipe

The application of steel pipe

Steel pipe are the most common pipe gas engineering in the application. Its main advantages are: high strength, good toughness, bearing stress is big, good impact resistance and rigor, plasticity is good, easy to welding and heating, with thin wall thickness, saving metal. But its corrosion resistance is bad, need to have proper corrosion protection measures. Steel pipe by high quality low carbon steel commonly used in the fuel gas projects (Q235) or low alloy steel (16 mn).

1.1 steel pipe material selection

The main steel pipe for city gas pipeline are of two kinds of seamless steel pipe and straight seam steel pipe. The strength of the seamless steel pipe is very high, but restricted by production process and cost, are typically small diameter steel pipe under DN200. Welded steel pipe sort is more, according to the welding process can be divided into straight seam welded steel pipe and spiral seam welded steel pipe. Among them, the straight seam welded steel pipe (hereinafter referred to as the straight seam pipe), including straight seam double-sided submerged arc welding steel pipe (LSAW) and high frequency electric resistance welding (ERW) pipe, etc. Spiral seam welded steel pipe (hereinafter referred to as the spiral pipe) is the spiral seam double-sided submerged arc welding (HSAW) steel pipe.

Straight seam pipe and spiral pipe manufacturing technology, the advantages of the former is:

(1) of the spiral pipe manufacturing process to determine the residual stress than straight seam pipe, because the whole hole enlargement technology on straight seam pipe, residual stress is close to zero, and the spiral tube can't do this;

(2) the spiral pipe welding line fault mostly within 1.1 ~ 1.2 mm, standard wrong side amount to less than 10% of wall thickness, for thin wall pipe, the wrong side of it is difficult to meet the standard requirements, and thick wall steel pipe straight seam pipe does not exist the problem;

(3) compared with straight seam pipe, spiral pipe welding line is poorer, the stress concentration phenomenon is serious;

(4) spiral tube heat affected zone is greater than the straight seam pipe, and the heat affected zone is the key to the quality of welded pipe;

(5) spiral pipe geometry precision is poor, to the site construction, such as counterpart, bring some difficulties in welding;

6 the same pipe diameter, the thickness of the spiral welded pipe could reach is far less than straight seam pipe, such as straight seam pipe thickness is usually 6 ~ 25 mm, the thickness can reach 45 mm, and the wall thickness biggest can reach 18 mm screw;

All landowners API than straight seam pipe weld spiral pipe shortened by 60%, probability of weld defects is low;

End up straight seam pipe parent metal for single point rolling steel plate, can be 100% nondestructive flaw detection, and the spiral tube base for hot rolled steel plate, can't do 100% of the nondestructive flaw detection;

Pet-name ruby straight seam pipe molding before welding technique, conditional inspection before welding seam forming, the quality of the weld gap, groove, wrong side processing, can be detected and the spiral tube forming and welding process, finds the wrong side, even in the welding process is hard to stop processing at any time, defects such as slotted visible straight seam pipe welding quality is better than spiral pipe [2].

Therefore, straight seam pipe process quality comprehensive performance to sorrow in spiral tube. Straight seam pipe to the current domestic production situation is: nominal diameter DN400 and the following is a high-frequency resistance welding steel pipe, nominal diameter DN400 above with straight seam double-sided submerged arc welding steel pipe. For straight seam double-sided submerged arc welding steel pipe, according to the different molding process, a total of UOE, JCOE, HME, RBE and PFP five into tube, the two most common before. Because the UOE forming welded steel pipe production line of molding equipment high technical content, high production efficiency, forming process is relatively simple, forming good, after forming welding stress is small; And because adopts hydraulic whole hole enlargement in production, which can effectively eliminate the internal stress of steel tube, improve the strength and size precision of the tube, so the quality is better than that of JCOE forming welded steel pipe.

But, spiral pipe work roll plate, cost than low with steel plate straight seam steel pipe. And formed the weld spiral pipe on the pipe line uniform than straight seam pipe, weld to avoid the principal stress direction. So the spiral pipe in city gas pipeline network is still has a certain application.

More information about carbon steel pipe,pls contact us: hunan great steel pipe co.,ltd