Weld repair in a high vibration location - ASME BPVC

[EmWaa]

Hi all,

this question concerns a vessel that is in a high vibration area as it is sat immediately below a francis runner in a power scheme.
The wall thickness of the vessel has been measured and is 2mm below the drawing tolerances so the suggestion has been that it could be built back up using a circumferential weld and then finished to the right dimension. Weld build up is a perfectly good repair for a lot of cases, my question is if this is still a good option in an area that sees a lot of radial deflection, or if the weld would work harden and ultimately start cracking at the seam as it undergoes fatigue differently to the base metal.

I have read about welding on machines that in service and vibrating heavily at the point of welding and choosing a consumable with a lower tensile strength to match the base metal is a good idea so it has similar ductility as it goes through life, which makes sense. Has anyone had experience of weld build up on high vibration area? Trying to understand how other industries get around this issue and what repair schemes survive through life ultimately.
TIA

 

[r6155]

See ASME PCC-2 2022

Regards

 

[Dhurjati Sen]

What is the corrosion rate?
Is the thickness (< 2 mm) since commissioning?
If you can manage with the above, better weld build up during total shutdown / complete turnaround.

 

[r6155]

Please more data: PV vertical or horizontal, general dimensions, material, original thickness, pressure / temperature, wind / seismic, .... etc.. ???
Has the design calculation been checked now?

 

[EmWaa]

Hi all,
thank you for your replies. r6155 to answer your questions its a vertical PV which is part of a hydropower scheme so temperatures are very stable and around 15deg mark on average. the medium is only water, and sometimes small debris, but with it being below the water turbine it can be subjected to oscillating water pressures, the negative ones through low pressure pockets below the runner causing implosion and explosion is the key concern here as to how the two different materials would behave through life.

I was hoping to get some albeit anecdotal feedback as to how other industries that have high vibrational equipment repair their equipment, and if weld build up of thinned wall thickness was seen to be an acceptable way of fixing this issue.

Dhurjati - yes these welds would be carried out robotically in a shutdown for the reasons you state here. Valid points

 

[Dhurjati Sen]

Thanks EmWaa for the follow-up.

 

[r6155]

I insist:
"Please more data: PV vertical or horizontal, general dimensions, material, original thickness, pressure / temperature, wind / seismic, .... etc.. ???
Has the design calculation been checked now?"

 

[EdStainless]

What is the cause for the material loss?
Corrosion? erosion? cavitation?
You may need to consider a different alloy.

 

[EmWaa]

What is the cause for the material loss?
Corrosion? erosion? cavitation?
You may need to consider a different alloy.

Hi Ed,

the material loss that we have is that the part has not been fabricated to drawing - so manufacturing error. the fab shop is looking to try and salvage the part rather than scrapping and so are proposing to build up the lost material with SAW bead. this is an accepted repair for a lot of situations, my concern is that in this case the part is subjected to high vibrational loading in a radial direction so the weld would be in a tension compression cycle, trying to determine the level of risk of the base metal to weld letting go ultimately in-service. The assembly is undergoing HT post fabrication, but the research I have done to try and answer if HT would eliminate the HAZ (and therefore reduce the risk of delamination) is inconclusive.
I would say the consumable would need to be matched as best as possible to the tensile strength of the base steel for matched ductility of the two parts.
Was hoping to find out if wall build up in this way is something other industries with high vibrational service loads use as an accepted repair scheme, or if its no good ultimately down the line.

 

[EmWaa]

I insist:
"Please more data: PV vertical or horizontal, general dimensions, material, original thickness, pressure / temperature, wind / seismic, .... etc.. ???
Has the design calculation been checked now?"

PV vertical, approx 2m dia, A516-70 steel, WT in this area just under 30mm, temp ambient. we are an engineering contractor so don't have the original design calculations which are OEM proprietary, the design calcs for this part in this area would be far too complicated to replicate as we have no hydraulic CFD model for the different scenarios by which to start accurate strength calcs of this part. we have a contract for like-for-like replacement, the question is if the SAW weld repair is an appropriate way of getting to like for like

 

[r6155]

I suggest Acoustic Emission Examination, see ASME V.

Regards.

 

[EmWaa]

I suggest Acoustic Emission Examination, see ASME V.

Regards.

that's a good suggestion, will look into that thank you.