Welding technology- Welding Environment

PART 01 Wind Speed Requirements for the welding Environment

For stick electrode arc welding and self-shielded flux-cored wire arc welding, the maximum wind speed in the welding environment should not exceed 8 m/s. For gas shielded arc welding, it should not exceed 2 m/s. Otherwise, effective measures should be taken to ensure that the welding arc area is not affected. A proper welding environment requires wind control.

Explanation: Tests have shown that for stick electrode arc welding, when the wind speed in the welding environment exceeds 3 m/s; for gas shielded arc welding and gas shielded arc welding with flux-cored wire, when the wind speed in the welding environment exceeds 2 m/s, the protective environment provided by slag or gas for the molten weld metal will be destroyed. The molten high-temperature metal will be oxidized by oxygen in the air, and nitrogen in the air will also dissolve into the molten pool. This results in many dense pores in the weld. So a stable welding environment is needed. During actual construction, welding should be avoided under these wind speed conditions, or wind barriers should be set up to ensure that the maximum wind speed in the welding environment does not exceed the specified limits.

PART 02 Circumstances Where Welding Is Prohibited in the Welding Environment

Welding operations should be strictly prohibited under the following circumstances in the welding environment:

• The relative humidity in the welding environment is greater than 90%.

• The surface of the welded part is damp or exposed to rain, ice, or snow.

• When the welding operation conditions do not meet the requirements stipulated in the "Welding Safety Operation Technical Regulations". A poor welding environment leads to risks.

PART 03 Temperature Requirements for the Welding Environment

The welding environment temperature should not be lower than -10℃. When it is below 0℃, heating or protective measures should be taken to ensure that the base metal temperature within the range of greater than or equal to 2 times the steel plate thickness and not less than 100mm in all directions of the welding joint and welding surface is not lower than 20℃, and it should not be lower than this temperature during the welding process. Controlling the welding environment temperature is essential.

PART 04 Special Requirements for a Low-Temperature Welding Environment

When the welding environment temperature is lower than -10℃, corresponding process qualification tests under that welding environment must be conducted. Only after the qualification can welding be carried out; otherwise, welding is strictly prohibited. A cold welding environment needs special attention.

Explanation: GB50661-7.5.2~7.5.4 states that when the welding environment does not meet the requirements, it will have adverse effects on welding construction. It is advisable to avoid operating on damp workpieces or in rainy or snowy weather for any welding method. This is because moisture is the source of hydrogen, and hydrogen is one of the important factors causing delayed cracks in welding. So a dry welding environment is important.

Because low temperature makes steel brittle and also accelerates the cooling rate in the heat-affected zone of the base metal during welding, it is easy to produce hardened microstructures. This is unfavorable for welding low-alloy high-strength steels with relatively high carbon equivalent, especially for thick plates and joints with high restraint. Even low-carbon steel has the possibility of cold cracking. Therefore, this specification makes specific provisions for welding in a low-temperature welding environment. In summary, the welding environment must be controlled to prevent cold cracking.