To be Cracked on base metal after welded

[thaihieu86]

Can anyone help me about a problem as following:

We are building up vessel OD 3800 and use material Q345B made by china.When we was welded for long seam,the cracks appeared vertical weld seam. We have been proceed test for tensile and yield strength and chemical composition on base metal but the results were accepted. The weld procedure specification (WPS) and consumable to be used correctly. We have also preheat before welding but after RT the cracks appeared for full weld. We are intending replace all new material but cost impact take many.

I hope everybody give me the best solution. Thanks so much

 

[metengr]

First, are these axial indications actual cracks? Have you performed local grinding to remove them or remove a sample for metallurgical analysis? What was the welding process - SAW or other?

 

[weldstan]

Are you stating that cracking was first noticed after radiography confirmed weld soundness? If so, please define the time differential between radiography and weld completion. Have you verified the chemistry of the base material. Also provide info per metengr.

 

[r6155]

T believ the problem is welding procedure, not base plate. You don´t mentioned the PQR.
More information, please: thickness, preheat temp., impact test ??.........

Regards
r6155

 

[chicopee]

What did you test specimen show?
Get a copy of ANSI/AWS B1.11 Guide for the Visual Inspection of Welds by the American Welding Society. This guide has a lot of colored photographs showing cracks and explains the causes.
Your cracks appear to be longitudinal types made with a welding machine and the most likely cause per the guide is high welding speed or sometimes such crack is related to porosity that does not show at the face.

 

[chicopee]

The guide also mentions that rapid cooling rates and high restrains could be cause with small welds between heavy sections which does not seems to be what you have shown us.