Welding Quality Control Techniques for Straight Seam Steel Pipes

 　　The quality control of straight seam steel pipes can only be carried out safely in the production operation, and it is also an inevitable factor to ensure the personal safety of the operators. Application areas are mainly in large-span power grid engineering, construction steel structure engineering, electric power and UHV transmission and distribution engineering, mechanical engineering, cross-sea bridges, bridges, (railroad station, airport, stadium steel structure engineering), municipal pipeline network, foundation piling , Water and gas pipelines, road construction and other supporting facilities.

　　1. Check whether the welding wire and flux specifications are correct according to the welding process regulations to prevent improper use of the welding wire and flux, which may cause welding quality accidents.

　　2. Supervise the welding environment. When the welding environment is not good (the temperature is lower than 0℃, the relative humidity is greater than 90%), corresponding measures should be taken before welding.

　　3. Before welding, check the groove dimensions, including gaps, blunt edges, angles, misalignments, etc., whether they meet the process requirements.

　　4. Whether the welding current, welding voltage, welding speed and other process parameters selected for the automatic submerged arc welding process are correct.

　　5. Supervise the welding personnel to make full use of the length of the pilot arc plate at the end of the steel pipe during automatic submerged arc internal and external welding, strengthen the use efficiency of the pilot arc plate during internal and external welding, and help improve the quality of pipe end welding.

　　6. Supervise whether the welding personnel clean up the slag first when repairing welding, whether the joints have been thoroughly treated, and whether there are oil, rust, slag inclusions, water, paint and other dirt at the groove.

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Key points of processing technology for large diameter straight seam steel pipe

    Rebar thread processing

    1. The thread head, tooth shape and pitch of the processed steel thread are consistent with the tooth shape and pitch of the connecting sleeve, and they are qualified by the matching gauge.

    2. When processing steel thread, water-soluble cutting lubricant should be used; when the temperature is lower than 0℃, sodium nitrite should be mixed, and engine oil should not be used as lubricating fluid or threaded without lubricating fluid.

    3. The operator should check the appearance of the steel wire head one by one and make the operator mark.

    4. After the self-inspection of the steel wire head, 10% of each specification should be randomly checked, and no less than 10, if one is not qualified, the batch of processed products should be fully inspected. The unqualified silk heads should be reprocessed and used after passing the inspection again.

    5. The silk heads that have passed the inspection shall be protected, put on protective caps, and be neatly classified according to specifications for use.

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Disadvantages of Hot Rolled 20 # Straight Seam Steel Pipe

    Disadvantages of hot rolled 20 # straight seam steel pipe:

    1. Residual stress caused by uneven cooling. Residual stress is the stress of internal self-phase balance without external force. Hot-rolled steel sections of various cross sections have this type of residual stress. The larger the section size of general steel section, the greater the residual stress. Although the residual stress is self-balanced, it still has a certain influence on the performance of the steel member under the action of external forces. Such as deformation, stability, fatigue resistance, etc. may have adverse effects.

    2. After welding, the non-metallic inclusions in the straight seam steel pipe are pressed into thin slices, and the delamination phenomenon occurs. The delamination greatly deteriorates the performance of the 20 # straight seam steel tube in the thickness direction, and there may be interlayer tearing when the weld shrinks. The local strain induced by shrinkage of the weld often reaches several times the yield point strain, which is much larger than the strain caused by the load.

    Submerged arc welding straight seam steel pipe advantages: it can destroy the casting structure of the steel ingot, refine the grain of the steel, and eliminate the defects of the microstructure, so that the steel structure is compact and the mechanical properties are improved. This improvement is mainly reflected in the rolling direction, so that the 20 # straight seam steel tube is no longer an isotropic body to a certain extent; bubbles, cracks and looseness formed during casting can also be affected by high temperature and pressure Welding.

Method for distinguishing between seamless and straight welded steel tubes

　　Nowadays, all walks of life are really very competitive. No matter what industry has competition, the straight seam steel pipe industry is no exception. Many manufacturers will use straight seam steel pipe as a seamless steel pipe in order to increase profits. It is not advisable, let's take a look at it in detail.

　　Straight seam steel pipes are all submerged arc welding or electric resistance welding. There is only one weld seam in this steel pipe. The bad traders use the polishing machine to polish and weld the weld seam. After repeated grinding and polishing, the weld seam will be worn away. The smooth surface as a whole is a seamless steel pipe. It is not seen by professionals. This kind of falsification, the equipment has no way to detect it. Whether it is straight seam or seamless, only the insider can see it. Some projects need appearance. Brushing a layer of anti-rust paint, which makes it harder to distinguish, which makes many buyers very distressed.

　　So how do you distinguish between straight seam steel pipes and seamless steel pipes? Seamless steel tubes are made directly in steel mills. Straight seam steel pipe manufacturers are not produced at all. When we buy, we will try our best to provide the supplier with the guarantee and certificate of steel pipe, and even if they do it well. There are also traces. Generally, the width of a straight seam steel pipe weld is about two centimeters.

　　After buying a seamless steel pipe, if we see a trace of about two centimeters on the whole of the steel pipe, we can cut it to verify whether there is a problem. The seamless steel pipe is painted with anti-rust paint. We can verify it by simple and rough method. It is to cut the steel pipe directly in the middle part. The seamless steel pipe is not butted, and the straight seam steel pipe is a plate. After the folding, the joint is welded.

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