1. Comparison of ERW and SAW steel pipes
Because the length of SAW (Spiral Steel Pipe) weld is about 4~5 times of the length of ERW weld, and the inner weld nodules are not removed by technological means, the friction of the inner wall of the pipeline is inevitably increased when the medium is conveyed. However, the length of ERW welding seam is short, and the internal weld nodules can be removed. This is very beneficial to the amount of mixed oil produced by Zang Shao’s product oil transportation and the temperature rise caused by reducing friction.
The residual stress identification results show that the internal stress of the ERW welded pipe in the circumferential forming is small, which is beneficial to the pipe.
The welding seam area of SAW welded pipe is large, and the stress state is more complicated than that of ERW steel pipe, which is related to its forming process. The internal stress of the weld is tensile and compressive. The inner surface is the elastic and tensile stress, the axial stress is +450MPa, and the circumferential stress is +344 MPa. This large-scale tensile stress in the weld and heat affected zone will be The cracking and stress corrosion of inner wall defects have an adverse effect. At the same time, ERW steel pipe has short welds (compared to spiral seam steel pipes), uniform steel pipe wall thickness, stable length, high geometric accuracy, easy corrosion and assembly welding quality guarantee.
2. Comparison between ERW and SML steel pipes
(1) Tube blank quality and geometric dimensions ERW special steel grade has the characteristics of high purity. Through desulfurization, dephosphorization, denitrification, carbon treatment and other methods, the sulfur and phosphorus content can be controlled below 0.005%, the nitrogen content below 0.008%, the morphology of the inclusions is controlled to be spherical, and the number is large For lowering. Because the carbon content is controlled below 0.1%, girth welding has good welding performance. By adding trace alloy elements such as Nb, V, Ti, etc. to prevent the growth of austenite grains, the toughness and strength of the steel are improved. The billet of SML (seamless steel pipe) steel pipe is generally A3, No. 20 steel, 16 Mn and other materials, the purity of the material is poor, and the carbon content is high, generally about 0.2%, which is not conducive to girth welding during construction Butt strength is acceptable, but toughness is poor.
Another big difference between the ERW steel tube billet and the SML steel tube billet is that the former is manufactured by cold rolling of hot-rolled steel strip, while the latter is formed by piercing round steel in a hot-rolled state. Obviously, the SML tube billet formed in the hot-rolled state has a larger gap in grain size and microstructure density than the ERW tube billet, and its performance is also very different.
ERW steel tube has higher geometric accuracy than SML. This is because the seamless tube is formed by continuous piercing of round steel in a hot rolling mill, while ERW steel tube is formed by steel strip under cold rolling. In contrast, ERW is easier to control in terms of dimensions than SML. Because of this, the appearance quality of ERW steel pipes is better than SML
Steel pipes have fewer defects.
In addition, due to the use of computer flying saws, the accuracy of the ERW steel tube’s sizing rate and sizing length is high. ERW steel pipe is made of hot-rolled steel strip with high rolling accuracy, the thickness is easy to control, and the steel pipe with thin wall thickness and high steel grade can be produced according to the design requirements. For example, the pipes used for the West-to-East Gas Pipeline project have been determined to use X70 steel grade, φ1016 mm. The wall thickness is 14.7mm steel pipe. The steel grade increases and the wall thickness decreases, which reduces the project investment.
(2) Comparison of the physical quality of ERW and SML steel pipes. After quality inspection by Xi’an Tube Research Institute and Shanghai Technical Supervision Bureau Ferrous Metal Inspection Station, the B grade φ219×8.18 mm and X52 grade φ323.9×6.4 mm and the collected domestically produced TS/52Kφ219X6 mm ERW tube, domestic 20 steel (equivalent to API B or X42 grade) φ159×6 mm, Mexican ST45 (equivalent to API X52 grade) seamless pipe test data, its chemical composition, tensile properties, pressure Flat performance, impact toughness and appearance quality were classified and compared. The results show that the composition of the five steel pipes all meet the requirements of API 5L (41) and GB8163-87. The composition of ERW is low carbon and high manganese, while SML is high carbon and low manganese. Obviously, the former has better weldability than the latter, which is more beneficial to the welding of girth welds on site, and the steel of ERW has higher purity than SML.