wear plate welded to shell subjected to fatigue analysis

[YuJie_PV]

HI, all,
i in behalf of owner is buying a buffer tank, which is subject to cyclic pressure, totally around 500,000 cycles throughout the lifetime.
and many wear plates are requested to welded to the shell to support ladders & platforms, etc.
i have question related to these welds now: is the welds of wear plate susceptible to fatigue failure so much that we need to avoid the necessity to install platforms? generally is it necessary to evaluate the welds of the wear plates for fatigue?

Thanks in advance.

 

[r6155]

I suggest avoiding wear plates to facilitate in-service inspection.

Regards

 

[TGS4]

As I noted in the other thread: I would strongly encourage you to heed r6155's recommendation to avoid wear plates (repads) for equipment in cyclic service. They are inevitably attached with fillet welds, which have very poor cyclic service behaviour. You will likely initiate a crack at either the toe of the fillet weld, or at the root. And as r6155 shared, the presence of the wear plate will make inspection incredibly difficult.

If it is possible, I would avoid external appurtenances altogether (ladders, platforms, etc.). Build any needed platforms and other access separate from the cyclic-service vessel.

To answer you final question about whether it is necessary to evaluate the welds of wear plates for fatigue - my answer is an absolute yes, it is required. You have welds attaching to the pressure boundary - how could you justify not evaluating them?

 

[YuJie_PV]

Thanks R6155 and TSG4,
thanks for your reply,we've changed to an independent platform.
even we can remove the platform, but there are still lifting lugs, which is quite helpful during installation.
i think the presence of two lugs may not cause too much trouble during the service, what do your think?
thanks in advance.

 

[r6155]

If it is a horizontal PV avoid liting lugs, use slings and spreader bar.

Regards

 

[YuJie_PV]

R6155, unfortunately, it is a vertical vessel supported by skirt.

 

[r6155]

Use the same concept.
Regards

 

[TGS4]

Happy to hear that you were able to remove the ladders and platforms. Good for you!

The lifting lugs will remain problematic. But, I would run an analysis to determine if the truly are a problem. You could always grind them off after lifting…

 

[r6155]

Install trunnion with full penetration weld and no pad.

Regards