What problems should be paid attention to in low temperature welding

Under low temperature, the surface of weldment is easy to frost and slide,which brings difficulties to welding operation. It will accelerate the cooling rate of the weld, reduce the important parameters affecting the secondary cry stallization, and then increase the hardness and harden the structure, so the cold crack sensitivity increases accordingly.

The low temperature cooling rate of weld is fast, which is easy to increase the regional segregation of weld crystallization. Under the action of stress, crystal cracks appear in the weld center

The delay effect of cold crack increases. In the process of weld cooling,the dissolution rate of free hydrogen decreases, the hydrogen escape time becomes shorter and the cooling rate becomes faster. Therefore,the residual hydrogen content in the metal increases and increases the tendency of cold cracks.

The possibility of brittle fracture increases at low temperature.

The preheating effect becomes worse at low temperature, the effect at low temperature is not as good as that at normal temperature, and it is relatively difficult to maintain the weld interlayer temperature.

At low temperature, the construction environment will be more complexand severe, and uncontrollable problems are easy to occur.

Low temperature welding construction measures

Environment

The low temperature welding environment is - 15 ~ 0 ℃, and the welding operation shall be stopped when it is lower than - 15 ℃.

Weldingshall be carried out at normal temperature. When the environment cannot be reached, thermal insulation shed shall be set to ensure that the ambient temperature can meet the welding requirements.

When working in wind and snow, wind and snow proof devices shall be set to protect the welding parts locally.

Streng then environm ental observation. When the weather is bad, stop welding in time to ensure personnel safety.

Try to select the time with the highest temperature in a day for welding to reduce the difficulty of welding.

Welding material management

Before use, check whether the welding wire is intact and take moisture-proof measures.

Strictly control the shielding gas, and the purity of the shielding gas shall not be less than 99.5%. In the low temperature environment, check whether the cylinder mouth is blocked and frozen to ensure the smooth and stable use of protective gas.