Faqs

WHAT IS A CRACK? HOW TEMPERATURE AT WHICH THE CRACK OCCURS? HOW SUCH CRACK IS DISCOVERED?
A crack is one of most serious defects of welded connection. It may occur on surface or inside a weld as well as in thermal influence area.

The crack may arise at different temperatures:

Hot crack: arising from crystallization of welded connection when temperature is relatively high (over 1,000oC).
Cold crack: arising after completion of welding process and at below 1,000oC. Cold crack may appear after several hours or days.

Cracks have different sizes, including microcrack or rough crack. Rough cracks destroy structure after working. Microcracks gradually extend to form rough cracks during working of structure.

Cracks can be discovered visually or by a magnifier for rough cracks on surface of welded connection. For microcracks inside welds, they can be discovered only when such testing methods as ultrasound, magnetic test, radiography,…