How to control the quality of large-diameter steel pipes?

Large-diameter steel pipes (usually LSAW pipes or SSAW pipes) have large wall thickness, good material, and stable processing technology. In the welded joints of large-diameter steel pipes, the weld seam and the heat-affected zone are the places where various defects are most likely to occur. Welding undercuts, pores, slag inclusions, incomplete fusion, incomplete penetration, welding tumors, burn-through, and welding cracks are the main forms of welding defects, and are often the origin of quality accidents in large-diameter steel pipes.

The quality control measures for large-diameter steel pipes are:

1. Quality control before welding
) 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 put an end to 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) The third 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 process regulations, 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, inspect the groove size, including gaps, blunt edges, angles and gaps, etc., to see if they 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 welding personnel have cleaned up the slag first when repairing welding, whether the joints have been thoroughly treated, and whether there is oil, rust, slag, water, paint and other dirt on the groove.

In the production process of large-diameter steel pipes, since the primary processing is performed in a hot state, the heating operation is a very important process that determines the quality of the product. Heating furnaces are divided into heating furnaces and reheating furnaces according to their effects; the former is used to heat the blank from room temperature to the processing temperature; the latter is used to reheat the blank to the necessary processing during the processing temperature. Improper heating will be the cause of waste products such as cracks, folds, and pain on the inner or outer surface of the tube blank.

At the same time, a reasonable design of the forming process of large-diameter steel pipes should be carried out, which usually adopts a spring-back control design, which can effectively control the spring-back state of the tube blank, thereby ensuring that the spring-back state of the tube blank meets the design requirements. The main factor that affects the elastic recovery state of the tube blank is the yield strength of the material.

For example, when designing the structure of large-diameter steel pipes, we can process them into qualified pipe blanks by using materials under different spring-recovery conditions. In fact, the process design can be expressed by a complete mathematical model, so that each The links are presented more clearly.

There are many types of hot-blast stoves, but the most important one is the ring heating stove. This kind of heating furnace has a ring-shaped furnace bottom, which can be slowly transformed. The billet is loaded from the entrance along the diameter of the furnace bottom, and it can be heated and soaked to a regular temperature as soon as it is used at the exit. A kind of stove. The key to this heating operation is to uniformly heat the billet to a temperature suitable for processing. Since the perforation has a great influence on the quality, that is, the temperature during the bending process is an important condition that affects the quality, so it is generally necessary to control the temperature of the blank during the perforation process.

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