Quality control method of welded steel pipe

We can classify welded pipes according to their material and properties, which can be generally divided into: wire rod, straight seam electric resistance welded pipe (ERW pipe), large diameter straight seam steel pipe (LSAW pipe), stainless steel pipe and so on. They all have one thing in common, that is, they all belong to the type of steel pipe with welding purposes, and they are all used in the product manufacturing process. However, for the size of the products produced, we usually choose to use different welded steel pipes, because only suitable steel pipes can make the products cost-effective. But how do we ensure their quality when purchasing?

Large-diameter straight seam steel pipe has become the first choice for large-scale oil and gas transmission projects at home and abroad because of its large wall thickness, good material and stable processing technology. In the welded joints of large-diameter straight seam submerged arc welded pipes, the weld seam and the heat-affected zone are prone to various defects, while welding undercuts, pores, slag inclusions, incomplete fusion, incomplete penetration, weld bumps, burn-through, Welding cracks are the main form of welding defects, and are often the origin of quality accidents in LSAW pipes.

The quality control measures are:

1. Quality control before welding

(1) First of all, the quality of raw materials must be checked. Only after passing the inspection can they officially enter the construction site, and resolutely prevent the use of unqualified steel.

(2) Followed by the management of welding materials. Check whether the welding material is a qualified product, whether the storage and baking system is implemented, whether the surface of the distributed welding material is clean and rust-free, whether the coating of the welding rod is intact, and whether there is mildew.

(3) Again, it is the cleaning management of the welding area. Check the cleaning quality of the welding area, and there must be no dirt such as water, oil, rust and oxide film, which plays an important role in preventing the occurrence of external defects in the weld.

(4) To select a suitable welding method, the principle of trial welding first and welding later should be implemented.

2. Quality control in welding

(1) Check whether the specifications of welding wire and flux are correct according to the welding procedure specification, and prevent welding quality accidents caused by wrong use of welding wire and flux.

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

(3) Before pre-welding, check whether the groove size, including gaps, blunt edges, angles and gaps, meet the process requirements.

(4) Whether the welding current, welding voltage, welding speed and other process parameters selected in the submerged arc automatic internal and external welding process are correct.

(5) Supervise the welding personnel to make full use of the length of the arc strike plate at the end of the steel pipe during submerged arc automatic internal and external welding.

(6) Supervise whether the welder cleans up the slag first when repairing welding, whether the joint has been thoroughly treated, and whether there is oil, rust, slag, water, paint and other dirt on the groove.

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