How to purchase straight seam steel pipes
First of all, you need to understand the types of steel pipes
1. Divided by type: straight seam steel pipe, seamless steel pipe, spiral steel pipe, etc. 2. Classification of cross-section shape of straight seam steel pipe: square pipe, rectangular pipe, oval tube, flat oval tube, semicircular tube, etc.
Next need to pay attention
1. The wall thickness of the steel pipe is not enough. Using the gate method, the mouth end of the steel pipe looks thicker with a hammer shield, but the original shape will be revealed by measuring with an instrument.
2. Straight seams are used as seamless steel pipes. The number of straight seam welds is less than one longitudinal weld. The whole steel pipe is polished with a machine, commonly known as polishing, which acts as seamless as if there is no gap.
3. Now there is still a more clever method is a seamless steel pipe, which is also a heat-expanded steel pipe. After the expansion, there is lead powder on the inside, and there are burn marks on the outside. The weld is also invisible. Many relatively large steel pipes are sold seamlessly using this kind of steel pipes to seek large profits.
4. Circumferential welded longitudinal seam steel pipes use polishing to represent seamless steel pipes and longitudinal seam steel pipes.
The last is the appearance inspection of the weld
Welded joint surface
1. No cracks, unfused, pores, slag inclusions, and splashes are allowed.
2. The weld surface of pipelines whose design temperature is lower than -29 degrees, stainless steel and alloy steel pipelines with a greater tendency to harden hardening shall not have undercuts. The undercut depth of the weld of other materials should be greater than 0.5mm, the continuous undercut length should not be greater than 100mm, and the total undercut length on both sides of the weld should not be greater than 10% of the full length of the weld.
3. The surface of the weld shall not be lower than the surface of the pipeline. The remaining height of the weld is not more than 3mm, (it is the large width of the back groove of the welded joint assembly).
4. The staggered side of the welded joint should be no more than 10% of the wall thickness and no more than 2mm.