Welding Consumables with Excellent CTOD properties for Offshore and Bridge

2022-07-18

During maintenance of offshore and bridge, these constructions are lashed by various weather conditions. The brittle fracture is caused easily by complicated structure, higher stress, residual stress, weld defect and the non-uniformity of properties of joint structure. The ricks is getting more with the base metal being thicker. The brittle fracture is easier to be caused, especially in the colder ocean.

For avoiding cracking of joint during maintenance and the equipment running safely and reliably, the enough crack resistance and toughness of joints (including base metal, center of weld bead and fusion) must be confirmed. The adopted and usual test method is CTOD. It has been frequently used in Europe, America and Japan in the projects of offshore and bridge.

1、What is CTOD?

CTOD（Crack Tip Opening Displacement），is performed through placing a specimen into bending and measuring the amount of crack opening.The more value of CTOD is, the better toughness and resistance of cracking. Conversely, less value of CTOD means less toughness. 

2、Meaning of CTOD Test

1、The advantages of CTOD test are filtering the materials by toughness, helpingimproving the weld process and PWHT and a reliable test for judging the safety and reliability of offshore.

2、CTOD is an important reference on evaluating the resistance of brittle fracture of base metal and welded joints which are low alloy steel with middle and high strength in offshore. CTOD test is more accurate than Charpy value test on resistance brittle fracture. 

3、PWHT can release stress in parts and improve the toughness of joints. However, it is difficult and increases the costs when building offshore.

According to the regulations of API, AWS and DNV, PWHT is not necessary if there is an enough CTOD value in joints (including weld bead and HAZ) and the thickness of part is not more than the one in test.For offshore building, it can reduce the costs and earn huge economic benefits.

3、Methods

4、Permitted Value of CTOD

There is noa standard about the evaluation of CTOD around the world. And there is less content about it in Chinese standards. Thus, the permitted values are different in the different countries. 

The permitted value of CTOD is confirmed by the designer or owner of projects. If the value is too small, the safety and reliability cannot be confirmed; if it is too big, it will increase costs and waste of materials. The following information is referred:

5、CTOD Properties of Gintune’s Products

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