Water Tank Anchor Straps

By yojimbo (***)

Date 08-01-2011 15:07

Fabricating and installing anchor straps on a 250,000 gallon water tank with a 1/4" shell. Anchor attachment in 12 X 20.1 Channel with a 6 X 1/2" flatbar welded to the face that extends down into new foundation at tank perimeter. The flanges of the channel get welded to the tank shell. The tank shell is not perfectly flat on the bottom row. At the top and bottom 6" [approximately] of the channel is a good 1/4" - 3/8" gap from the tank. No big deal but looking to save as much time on the install as possible and still do the job within acceptable ranges. The channels are 48" so there is a total of 9' of weld holding them to the tank. Inspection is curiously not specified in the project manual so I am assuming a visual or at most a mag particle on anchor attachments. I understand 1/4' and less is not inspected with ultra sound- please correct me if I am wrong. My question: would "slugging" the gapped areas with some 1/4" A36 sq. stock and welding them in show on a mag particle test and how great an effect would slugging have on the overall strength of the anchors? A total slug lenght of maybe 18" out of a total of 108" of 1/4" fillet weld. We are using Lincoln 71M .045 on the anchor welds and expect to have to increase weld size to complete the gaps and make the entire length of weld symetrical and uniform. My biggest concern is compromising anchor strength or getting a busted mag particle result. Bridging a 1/4" or better gap on 1/4" material is tedious to say the least and scribing the channels in to the deformity of the tank wal is not an option. Opinions please.

By dbigkahunna (****)

Date 08-02-2011 01:21

1. Pull the shell against the anchor channel. Use nuts and bull pins
or
2. Have someone on the inside hit the shell with a 4 pounder as you are tacking. That is not much of a gap to deal with. If the 4 pounder will not flush up the shell either get a 8 pounder or swing the 4 pounder harder. Be careful as you are tacking up and welding you do not pull the shell in. I do not mind hammering on the shell for fit up as long as the hit is square with the plate. Slugging is a bozo no no.
After you get it fit flush start on the bottom and weld up 6 inches, skip 6 inches, weld 6 etc until you get to the top. Stagger left and right. When you get to the top go back and do the skips. Brush it and grind the stops and starts then run a nice bead. Depending on the specs you may have to do a two pass if it requires a 3/8 filet. Trying to get it in one pass can throw a lot of heat on the shell and end up with a pull in the shell. Don't think you will bend the channel with quarter inch.

By yojimbo (***)

Date 08-02-2011 15:20

BigKahunna-
I've read a number of your posts and am invariably impressed and on occasion floored by the depth of your experience and knowledge. That's not intended as obseqious kowtowing, just recognition of a superior understanding of both theoretical principles and practical application. That said, I want to condition the original question I asked: This is a hardmoney project, already bid and under production, without foreknowledge of the tank's minor distortion, and absolutely no possibility of an adjustment of price to cover the extra cost of fitting the anchors flush to the tankshell. The fact that there is no adjustment of cost relates to the hardassed attitude of the owners rep for the municipality who will just say it's my problem and I should have known- which I can not argue against effectively- and that their attitude from the beggining has been hostile and adversarial the whole time they are lipservicing me and the GC in charge of the project about how interested they are in being cooperative. Fact is, I don't like or respect these people and have decided my best relationship with them will be to adopt the stance as a contrator to screw them for everything I can and I ain't giving them nothing extra. I don't like to operate like that but my conclusion is they don't deserve any better. So, of course you're right about the Bozo NoNo on the slugging. I knew it but wanted confirmation. There's no one going to go inside the tank to swing a hammer either, the pain and paperwork and extra costs are insurmountable and I don't want to draw the attention of the owners to any problems they can make mountains out of molehills from. Also, the gap at the bottom of the anchor is only the first 6" up from the tank ring and as such I don't think I'd get much give from the shell there. That leaves me the option of dogging the tank shell out which may in the end become neccesary but I want to proceed if possible by just welding up the gap, which when I split the difference, top to bottom of the anchors 48", might be 3/8" 6" at the top and bottom. Your suggestion to skip weld and fill in the spaces with a good final cover fillet is what I had in mind, starting with solid tacks on the anchors, filling in the gaps as flush to the flanges of the channels to minimize the fillet reinforcement, and then putting in a single pass 3/8" fillet final pass. If absolutely neccesary, I might try reducing the gap at the top of the anchors with dogs and wedges or screws but if the gap is manageable with out I'd prefer to just weld it up. Do you think that much weld on the 1/4" tank shell to fill the gaps will result in a bad weld or damage the tank? BTW- the contract drawings specify a 3/16" weld for anchorage attachment which using an .045 dual shield 71M wire was never going to be less thn 1/4" anyway and now with the gap issue is going to be a 3/8" fillet for attachment. Your response would be appreciated.

By dbigkahunna (****)

Date 08-03-2011 00:15

With the tank shell being 1/4 inch I think you can dog it in to close the gap. Take your time and work the dogs and pins on each side to close it up. A little at a time until it either gets close or you blow a dog!.Work it from the bottom up. You can be supprised how much the bottom of a tub can move with 1/4 inch material. It stretches a lot! A little on the left a little on the right. You are just going to have to make some noise. Keep it pined as you weld the skips then drop the dogs when you come back to weld up the skips. Try to keep the welds as small as you can.
If you elect to weld up the gap, remember to keep the heat down. If at all possible make the shell fit as flush as possible. Alternate the skips left/right and get a drink of water between welds. If you can get the gap down to 3/16 or less you should be OK.
A single 3/8 fillet on 1/4 inch plate will throw a lot of heat on the shell. Even with the anchors you could pull in at the top of the anchor.
When you get through, weld and grind flush any tear off areas with a flapper disk. Also while the weld is still hot take the flapper disk and blend the toe of the filet to the shell. Could save you a crack on the toe.

By yojimbo (***)

Date 08-03-2011 04:19

Kahunna-

All good advice, you're right, the 1/4" shell should pull easy enough, the bottom at the ring I have my doubts but will find out. A simple stong collar of 1/2" X 3" dog with wedges or 3/4" screws should do it. Just learned from the GC one of the tanks will be filled with water, one empty. These anchors weigh in at about 130# and are going to be cumbersome to move around. My plan is to tack them good on the center area where the touch shell and work out from the center up and down, tack what I get close and keep moving. Do I need to be concerned about distorting the tank shell when dogging in? It aint much but will it show enough to make an engineer nervous? The things we get ourselves into. What did you mean, "Even with the anchors you could pull in at the top of the anchor"?

By dbigkahunna (****)

Date 08-03-2011 11:10

If you throw too much heat on the shell, it will shrink. The steel is tied down with the anchor and the top of the anchor is where the shrinkage is going to go. Just don't get in a hurry. You will be pulling the shell to the anchor so I do not think you will get shell distortion from the dogs. Especially on the bottom. It is at the top of the anchor I would be concerned about and the distortion would come from the heat rather than the fitting.

By yojimbo (***)

Date 08-10-2011 04:16

BigKahunna-

I sent you a PM regarding these water tanks. If you get a chance tell me what you think of the conditions described.

Thanks,

Yojimbo