1. Introduction to straight seam steel pipe
Straight seam pipe is a kind of welded steel pipe, refers to the welding seam and longitudinal parallel steel pipe. According to the classification of wall thickness, thin wall straight seam pipe and thick wall straight seam pipe; According to the shape of the classification of circular tube, square tube or special-shaped tube; There are general welding pipe, galvanized welding pipe, oxygen blowing welding pipe, wire bushing, metric welding pipe, roller pipe, deep well pump pipe, automobile pipe, transformer pipe, electric welding thin-wall pipe, electric welding special-shaped pipe and spiral welding pipe.
2. Straight seam steel pipe welding process
Straight seam welded steel pipe is made by rolling strip of certain specifications into circular tube and welding straight seam through high frequency welding unit. The shape of the steel pipe may be round, square or profiled, depending on the sizing rolling after welding.
The production process of high frequency welding of straight seam steel pipe is as follows:
(1) Weld clearance control
The strip is sent to the welding tube unit, and the strip is rolled up gradually to form a circular tube blank with an opening gap after rolling by multiple rolls. The pressure down of the extrusion roll is adjusted to control the weld gap within 1~3mm and make both ends of the welding joint flush.
(2) Welding temperature control
The welding temperature is mainly affected by the high frequency eddy current power, which is proportional to the square of the current excitation frequency. The current excitation frequency is affected by the excitation voltage, current, capacitance and inductance. In addition, the welding temperature can be achieved by adjusting the welding speed.
(3) Control of extrusion pressure
The two edges of the billet are heated to the welding temperature, and the common metal grains are formed under the extrusion of the extrusion roller to permeate and crystallize each other, and finally form a firm weld. If the extrusion pressure is too small, the number of common crystals will be small, the strength of the weld metal will decrease, and cracking will occur after stress; If the extrusion pressure is too large, the molten metal will be squeezed out of the weld, not only reduce the strength of the weld, but also produce a large number of internal and external burrs, and even cause defects such as welding lap joints.
(4) Position control of high-frequency induction coil
The high frequency induction ring should be as close to the extrusion roll as possible. If the induction ring is far from the extrusion roll, the effective heating time is longer, the heat affected zone is wider, and the weld strength decreases; On the contrary, the edge of the weld is not heated enough, and it is badly formed after extrusion.
3. Straight seam steel pipe application
Straight seam steel pipe is mainly used in tap water engineering, petrochemical industry, chemical industry, electric power industry, agricultural irrigation, urban construction.
For liquid transportation: water supply, drainage.
For gas transportation: gas, steam, liquefied petroleum gas.
For structural use: for piling pipes, bridges; pipe for wharf, road, building structure, etc.
4. Processing method of straight seam steel pipe
Forging steel: A pressure process in which the blank is changed to the desired shape and size by the reciprocating force of the hammer or by the pressure of the press.
Extrusion: is the steel metal in the closed extrusion, one end of the pressure, so that the metal from the specified die hole extrusion and get the same shape and size of the finished product processing method, mostly used in the production of non-ferrous metal steel.
Rolling: A pressure processing method in which the steel metal billet is passed through the gap between a pair of rotating rollers (of various shapes) to reduce the cross section and increase the length of the material due to the compression of the rollers.
Drawing steel: is to have rolled metal billet (type, pipe, products, etc.) through the die hole drawing into a section to reduce the length of the processing method is mostly used for cold processing.
5. The difference between straight seam steel pipe and seamless steel pipe
A. Different production techniques
Straight seam pipe is iron plate, after bending, closing, welding and other processes produced, allowing a weld. Seamless pipe is the round steel through the mill through hot rolling, cold rolling or cold drawing, is no weld.
B. Different applications
Seamless pipe and straight seam pipe in the case of the same diameter wall thickness, the pressure and strength of seamless pipe, is far greater than the straight seam pipe. General pressure is relatively high engineering pipe on the choice of seamless pipe, no pressure or low pressure engineering in the case of allowing the choice of low cost straight seam pipe.