Preheating Plate buried in concrete??

Date 10-06-2016 17:33 Edited 10-07-2016 14:54

Okay this one has got me both puzzled and worried. I was asked to okay a weld procedure where they are preheating 1.5" A36 Plate to 225F . The plates are in an prexisting slab and they are adding a new welded structure to the plates that were previously used for bolting down the old structure. By code yes you can get away with 150 preheat if you use low hydrogen controls (they are) but they want the higher preheat to help with distortion.

Now I don't deal with this type of field work often. My gut tells me that some water or moisture will be trapped under the plate and once you get past boiling point you'll get spalling or a steam explosion. At the very least heating a base plate buried up to it's face in cement seems like a bad idea?

Anyone heard of this before? This sounds like bad juju written all over it, but I have no technical or code basis as to why this is not allowable.

By welderbrent (*****)

Date 10-06-2016 18:05

Goodness Joel,

You get some good ones don't you.

So, not sure I can give you a code at the moment that would support or reject such a procedure.

Personal experience, yes, heating on/in concrete is a very hazardous situation depending upon the size of the plate for square surface and how much pre-heat is wanted. Pushing it to 225°F is going to take it to the caution zone but the concrete itself should not get that hot. And if the plate has enough surface area so you don't have to get on it with the rosebud/bertha heater then it should be able to be done.

Wear full face shields and heavy shirts, sleeves, etc to protect whole body if popping does occur.

Again, depending upon some of the particulars, you may have to reheat a couple of times.

He Is In Control, Have a Great Day, Brent

By Joey

Date 10-07-2016 02:59

Brent, welding of embed plates in walls is common. Engineering dept consisting of Civil Engineer, Design Engineer must be consulted even before writing a WPS. Proper communication is very important, the Inspector assigned to the job must have access to the Engineer so that possible construction problems can be brought to their attention before they become inspection problems.

By welderbrent (*****)

Date 10-07-2016 03:49

Joey,

I am aware that it is done and have done it myself. As you say, in any thing of any significance it requires engineering consulting. If working on my own small building I could do damage and not be really concerned. In a public building or at least a building of some size it could be really problematic.

Shawn, just making sure, you do know that working with hot materials on concrete, rocks, other porous materials that can and usually do have a moisture content can have explosive results? Even cutting up on a table but allowing the molten metal to accumulate in a concentrated area can cause an explosion and serious damage to the concrete floor, not to mention possible physical injury to anyone too close. It really gets noticeable when cutting with a track burner on rather heavy plate held up on blocks just a few inches off the floor.

He Is In Control, Have a Great Day, Brent

By Cumminsguy71 (*****)

Date 10-06-2016 22:55

I have nothing of value to offer but maybe they should switch to a different code, may I recommend Farm Code 2015? LOL!

Trapped moisture, steam at 225 degrees, what's the concrete going to do at 225 degrees. Maybe some test runs on something fabricated to experiment with?? Put another plate on top with column, drill and blast existing plate and put in mega concrete anchors? I'm just throwing out off the wall things that are popping into my head.

Will be curious to hear how this one plays out.

By Metarinka (****)

Date 10-07-2016 14:56

I voted for just bolting the new structure down, half the job of being a welding engineer is recommending you don't weld.

By jwright650 (*****)

Date 10-07-2016 15:49

I'm glad that this subject is being discussed. I run across this issue of welding to embeds routinely and wondered about the integrity of the concrete immediately under the plate where it has been exposed to the high heat of preheating. Recently there was an embed in a poured wall that was misplaced by 2 feet and there was a new plate anchored to the wall with several adhesive anchors and then the clip angles of the beam were welded to the plate. Which brings a different question to mind that I will start a new thread about.

By 803056

Date 10-07-2016 13:38 Edited 10-07-2016 13:46

Gee, I am hesitant to offer advice to a Welding Engineer. I think you are on the right track with you cautious approach. There could be moisture trapped under the plate even if this is under cover. If nothing else, the concrete could spallfrom the plate expanding while being heated.

I believe I would stay with the lowest preheat possible, use low hydrogen electrode, and be selective with the specific brand/trade name of the electrode I specify. I would select one with the lowest manganese, highest elongation, an lowest UTS. In short, my WPS would list the manufacturer and their specific E7018 with the desired chemistry. Make sure the surfaces are ground to bright metal to minimize the need for high manganese (strong deoxidizer). Use the lowest preheat possible to minimize expansion and to reduce the possibility of creating a steam pocket under the plate. Steam experiences an increase in volume of the water evaporated by something like 1500 times.

Al

By Cumminsguy71 (*****)

Date 10-14-2016 00:05

I do believe I have done something similar to this as an "employee" many, many years ago. Can't recall the specifics now but for some reason I do recall concrete exploding and hitting me. Wish I could remember what it was, probably some more "Farm Code" stuff.

Al, advise to a Welding Engineer, don't be bashful! I was out on a job a month or so ago and the engineer was at a loss. The boss over the job and the engineer both said, "we were hoping that you might have some ideas on what to do".

Not often you get to straighten your back, inflate your chest and look around for a minute, exhale on your fingernails, polish on your shirt and say, well then, let me think. Then come up with the save all fix for the engineer!!

By Metarinka (****)

Date 11-03-2016 23:53

It's thermal expansion is actually around 1700 and yeah I'm very concerned with steam entrapment/explosions.

Don't hesitate to offer advice to little old me. My career is focused in exotic metals, process control and robotics. I can't claim I know much about welding thick materials or using structural steel codes.