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Up Topic Welding Industry / Inspection & Qualification / Rat holes - To fill or not to fill???
- - By thcqci (***) Date 07-22-2003 13:00
Please provide some opinions and guidance as to filling rat holes in beam and column splices for appearance sake. D1.1 does not appear to address the issue. In your experience, do you usually leave them open or fill them? Exposed steel closed and concealed steel open?

Until recent questions arose, it was our practice to plug rat holes after acceptance of ultrasonic testing of the splice. Two questions arise:

1) If the splice passes UT, does the additional "rat hole plug" need to be ultrasonically tested and pass the same criteria? Difficult to plug discontinuity free.

2) Does depositing additional weld metal compromise the already accepted weld splice? Are the results of the UT of the splice that is already accepted by UT compromised and negated and thus the entire splice is again subject to UT?
Parent - - By pipewelder_1999 (****) Date 07-22-2003 13:22
The weld access holes allow both access to the weld and may reduce residual stresses at the joint.

Mark F Mruczek had sent me some info that can be viewed at

There is also an article at which mentions weld access holes.

You can also take a look at the commentary in D1.1 C5.17.1 . This is in the 98 edition of the D1.1 Code.

In my opinion based only on what I have read, welding up the ratholes would normally do more damage than good. It would be best to consult an engineer to confirm this as I am not fully qualified in this area.

From my experience as an inspector. There is no requirement in D1.1 to weld up the access holes.

Gerald Austin
Parent - - By jwright650 (*****) Date 07-22-2003 13:44
We used to weld them up too, but I was concerned about the weld shrinkage in this area creating more stresses in the joint in large section sizes and I elected to not fill them in except when architecturally exposed. I do think that it should be UT'd again after filling if you choose to do so and it should meet the same criteria as the rest of the joint. I'm of the opinion like Gerald, that it is best to leave them unfilled unless the specs call for it to be filled. It is more work and time is money. You may want to get a few more opinions to make up your own mind, but that is what we chose to do here at our shop.
John Wright
Parent - - By jwright650 (*****) Date 07-22-2003 13:52
I forgot to mention, if you fill em in to MT both sides of the web at the rat hole as well to make sure you didn't miss a crack up close to the top of the surface when you UT. In the "K" area on heavy sections you may find "junk" (for lack of a better word) already in there from the mill when you UT.
John Wright
Parent - - By jwright650 (*****) Date 07-22-2003 15:54
I did find in the Commentary, a statement which reads......"Welded closure of weld access holes is not recommended. When weld access holes shall be closed for cosmetic or corrosion protection reasons, sealing by use of mastic materials is preferable to welding."

It is found in the third paragraph under AWS D1.1:2002 C5.17.1 Weld Access Hole Dimns.
Hope this helps,
John Wright
Parent - - By CHGuilford (****) Date 07-22-2003 16:12
There you go John! that commentary is getting a work out now!

The thinking today is as was stated in the other posts. Filling in the weld access holes with weld is considered to risk more harm than good, as you will see in the various AWS and AISC documents. Some customers might still want them welded in for different reasons but they should be aware of industry specs. One of the best ways to fill a hole is to use an appropriate joint sealing compound. (Usually when a welding inspector hears words like "Bond-O" they shudder, but in this case they should breathe easy).
Chet Guilford
Parent - By thcqci (***) Date 07-22-2003 19:29

Your help is much appreciated. More comments, opinions or guidance is welcome, but I think you have provided the written backup for the answer I was looking for. Thank you.

7:30AM Wednesday
Just as a follow up, I contacted AISC Steel Solutions, referenced this forum and I got this response:


It appears that you received several responses to your questions. Although the subject is not directly addressed in the AISC Specifications, we can give you our recommendations.
It is possible to use filler weld metal to fill-in the weld access hole, have it grinded down and tested using magnetic particles. However, AISC would not recommend such a practice as it is prone to cracking and may weaken the welds due to shrinkage of the large filled area. We would recommend using an epoxy or body solder as a non-structural filler. See 10.4.1 of the Code of Standard Practice.

Sergio Zoruba, Ph.D.

AISC Steel Solutions Center


Based upon all the above input, I am recommending we no longer fill rat holes with weld metal. We should only fill exposed steel with non-structural epoxy or body solder. Once again, thank you gentlemen.
Parent - - By MJBAKER Date 11-11-2003 16:31
I did a research project in college on lowering the fatigue characteristics of weld access holes. You do not want to weld them. You need to make sure all flame cut edges are smooth uniform and in a ark (no sharp edges). Hit them with a pencil grinder and let them go. Welding them offers little structural advantage and as most have noted it does more harm than good.
Parent - By vonash (**) Date 11-23-2003 16:56
The AISC governs this one. Leave the access holes (if acceptable ). Any athstetic work should be non-structural.
Parent - - By whoose Date 09-05-2004 15:06
I would say that it would greatly depend on whether the completed joint is in "compression" or "shear". Consulting with the Engineer prior to them being welded is crucial. I have seen it done both ways, and yes it is difficult to do discontinuity free. I believe that it depends on the size of the member as well and on where the job is. In seismic areas, we do not fill them. You might find info in FEMA 350 & 353 for these areas.
Parent - - By swnorris (****) Date 09-30-2004 20:46
Hi all,

I feel like I'm beating a dead horse here, but what the heck. I've nothing better to do at the moment. Weld access holes should not be filled with weld metal. Doing so could create the very same cracking problems the weld access hole was used to prevent. If the hole is to be filled for appearance reasons in architecturally exposed structural steel (AESS), it is possible to use a body filler such as “Bondo”, as Chet mentioned.
Parent - - By thcqci (***) Date 10-01-2004 13:52
As was stated above, as of last year, we have ceased welding weld access holes. My biggest problem now is only getting good finish in accordance with D1.1 in the hole that remains. Since they had been used to filling them, they did not particularly worry about the finish of the holes (within reasonable limits). Now they are forced to finish them per D1.1. So far, we have not been asked to "bondo" any holes either. Sooner or later that will come though and then I wil have to find someone in our paint department that does auto repairs.
Parent - By jwright650 (*****) Date 10-05-2004 11:34
We use a die grinder with a small rotary carbide bit to smooth out the radius in the rathole. Trick is to cut the hole neatly with the torch before fitting the joint and then the die grinder cleans up the finished product pretty nicely without a whole bunch of work. Advoiding any sharp notches or gouges and rounding them nicely is key to finishing off those ratholes to where they are presentable even in exposed work. Some architects will still ask for the rat hole to be filled, and it's hard to convince them that it is not a good idea.
John Wright
Up Topic Welding Industry / Inspection & Qualification / Rat holes - To fill or not to fill???

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