SA516Gr.70 plate in service cracks 1

[krishh07]

It was observed in SA516Gr.70(50mm & 70mm)cracks developing during service in bend portion.This component was designed to lift 150T of weight.

The plate from four sides was welded with SMAW and SAW welding with other plates,after welding pwht was carried out.There was no cracks observed in welding.Only plate cracked after 2months in bend portion.

What may be the possible reasons of cracks?and how to prevent it.

mks07

 

[metengr]

This type of question cannot be answered properly unless a proper metallurgical lab analysis is performed along with photographs and service conditions. There are multiple failure mechanism possibilities and with little information to go on, it is speculation. Remove a sample containing cracks and send it to a reputable lab.

 

[weldstan]

Preferably have a metallurgist from the lab select the areas for specimen removal. I've seen far to many failure related specimens removed by the untrained, resulting in ruining any chance for a correct analysis.

 

[krishh07]

Dear metengr,

Please sugest, test to be performed,from sample containing cracks.

mks07

 

[metengr]

mks07;
Have you followed the advice of weldstan above? If you have already removed the sample without involvement of the lab metallurgist, the following minimum steps would be recommended;
1. Macrophotos of the sample showing the orientation and location of the crack(s). Orientation of the sample relative to the pressure vessel is critical and must be identified and marked on the sample at the time of removal. Surface NDE might be required to highlight cracks.
2. Dimensions of the sample and observed crack lengths.
3. Careful extraction of one or more cracks to expose (break open) the fracture surface for examination.
4. SEM of the fracture surfaces - option.
5. Depending on the results of step 4, prepare one or more samples containing a cross section of the fracture surface for metallographic examination. Compare with sample removed and prepared for metallographic examination away from the fracture surface.
6. Complete chemical analysis of the sample material.
7. Perform hardness testing to evaluate hardness through thickness.

The above are recommended with other steps added depending on the results.

 

[krishh07]

Dear Metengr,

Thanks for your advise

mks07