Welded Anchor Rod Corrosion Repair

[Rabbit12]

We are working with a client on replacement of a vertical process vessel. The new vessel was grandfathered onto the existing foundation using IBC chapter 34. There was only a small increase in weight so they will take the old vessel off the foundation and replace with the new vessel. Foundation design was done in the early 1980's.

While preparing for the swap, the fireproofing was removed from the baseplate and they discovered that the baseplate enclosed the anchors preventing inspection prior to taking the existing vessel off the foundation. The client came to us asking if we could design a contingent repair should there be corrosion (length of shutdown needs to be minimal). Specifically they want to grind away any corrosion and replace the material with weld metal and grind smooth.

The anchors are A36 so they should be weldable. My initial concern would be the potential to create a stress concentration that might create a path for fatigue failure.

Anyone done anything similar? Maybe this is a horrible idea too. Looking for any and all opinions.

 

[BridgeSmith]

Are these round anchors with enough solid, exposed length to mechanically splice to? That's my only idea. I think your initial concern about fatigue and fracture is right on. Welding can be done, but the repair would need to be carefully tested, most likely with ultrasonic.

 

[Structural_WIZ]

I've replaced existing equipment, vessels and even buildings in the past and was able to reuse the existing foundations with minimal modifications. However, I've never "won the lottery" and have been able to reuse the existing anchor bolts. Most of the time the new equipment, etc. had different attachment locations and anchor bolt patterns to deal with. To deal with this, we mainly post-installed threaded rod with an appropriate chemical/epoxy adhesive(Hilti, Simpson, etc.). You can also core and grout anchor bolts. I typically go with an epoxy grout if vibration or impact loads are an issue or if it is a critical connection. Welding to corroded steel is "risky" and requires a lot of quality control/oversight and is probably not a good plan for a "shutdown" situation when time is crucial and short cuts are always taken out in the field. Here is a good example of what can go wrong

https://www.osha.gov/doc/engineering/2015_r_01.html

 

[dik]

and while you're at it, can you confirm the material is really A36? and, that something else wasn't used.

Added: Putting a torch to something that 'was supposed to be...' can cause some real heartburn...

Dik

 

[StrP88]

Rabbit12 (Structural)
Do you have a couple of pictures that we can see and better comment on?

 

[Rabbit12]

StrP88,

Not really. I did add a picture for folks that may not know what a pressure vessel baseplate looks like. Right now the vessel is in service and the baseplate prevents us from seeing the anchor rods. The client is asking for a "fix" for possible corrosion so when they pull the old vessel they have a plan in place for any corrosion. They suggested grinding and replacing that ground away material with weld.

Dik, I can't confirm with 100% certainty that the material is A36 without further testing. The existing drawing call out A36. Could be accurate, might not be.

HotRod, splicing could be done depending where the corrosion is. How hard would it be to re-tap an anchor rod in the field?

 

[Structural_WIZ]

Thanks for the picture. I didn't realize you had anchor bolt chairs. I think these are your options:

1) Anchor bolt repair: Use mechanical couplings or weld stud extensions. This would require properly identifying and removing the limits of corrosion/damage and having enough anchor bolt projection left to make one of the aforementioned repairs.

2) Full Depth Anchor Bolt Replacement: Depending on the thickness of the foundation, it is possible to core the existing anchor bolts and remove them completely. Then grout in new anchor bolts.

3) Relocate anchor bolts: Cut existing anchor bolts flush and abandon in place. Relocate and post-install new anchor bolts for the new pressure vessel.

All of these options have pros/cons. Your specific situation may justify one over the other. Let me know if you think of anything else.

 

[bones206]

I think Structural_WIZ covered it, but one other potential option is to leave the corroded anchors in place. That option is probably the best case scenario from the client's perspective, since it minimizes downtime and repair cost. You could clean the anchors up and coat them, or take other actions to mitigate further corrosion, but otherwise leave them as-is. Of course this options depends on the extent and severity of the corrosion, but it's a strategy that you could plan for ahead of time by determining a threshold of acceptable corrosion, absolute min. number of anchors required to resist the load, etc.

 

[StrP88]

Rabbit12 (Structural)
(OP)
Can you ask field people to take couple pictures, maybe one showing the vessel and the base of it and one closeup pic of the base of vessel.

I have done repair of chair anchors so I can direct you better after seeing the actual state of it.