钢的氢裂纹缺点,预防与最正确实践

Defects - hydrogen cracks in steels - prevention and best practice

钢的氢裂纹缺点,预防和最正确实践

Defects - hydrogen cracks in steels - prevention and best practice

Preheating of a jacket structure

to

prevent

hydrogen cracking

Techniques and practical guidance on the avoidance of hydrogen cracks are described. Preheating, interpass and post heating to prevent hydrogen cracking

There are three factors which combine to cause cracking in arc welding:

? ?

hydrogen generated by the welding process a hard brittle structure which is susceptible to cracking

tensile stresses acting on the welded joint

?

Cracking generally occurs when the temperature has reached normal ambient. In practice, for a given situation (material composition, material thickness, joint type, electrode composition and heat input), the risk of hydrogen cracking is reduced by heating the joint.

Preheat

Preheat, which slows the cooling rate, allows some hydrogen to diffuse away, and prevents a hard, crack-sensitive structure being formed. The recommended levels of preheat for carbon and carbon manganese steel are detailed in EN 1011-2: 2001 (which incorporates the nomograms from BS 5135). The preheat level may be as high as 200°C for example, when welding thick section steels with a high carbon equivalent (CE) value.

Interpass and post heating

As cracking rarely occurs at temperatures above ambient, maintaining the temperature of the weldment during fabrication is equally important. For susceptible steels, it is usually appropriate to