Help with a Toe Crack Diagnosis

By pipewelder_1999 (****)

Date 01-29-2008 23:07 Edited 01-30-2008 02:09

Many Possibilities here. Some thoughts

1) If this is a "repair" on something that was used as a lifting device that developed the need for repair after being in service I would proceed with MUCH caution. Find the engineer or designer.

2) On thick sections a filler metal with higher strength than the base metal increses the possibility of underbead cracking as the result of residual stress.

3) Preheat on a 6" thick section with torches could be hard to maintain.

4) Post weld Heat Treatment could be something to look into. A 6" thick piece of carbon steel would often times be stress relieved after welding.

5) A root opening or crush wires can reduce residual stress.

6) Any repairs should be performed only after making sure the underlying defect is gune. MT/PT or possibly UT could be helpful.

Again, I would consult some higher athorities regarding anything with the word LIFTING in it.

Have a nice day

Gerald Austin
http://weldingdata.com/

By 803056

Date 01-30-2008 01:35

I think you hit the important point, especially the "crush wire".

Best regards - Al

By thirdeye (***)

Date 01-30-2008 00:45

Tom,

Gerald brings up some excellent things to consider....One of the things he mentioned, preheat, is an issue I really watch closely, particularly on lift lugs, and especially ones for heavy service. I have seen many failures like the one you described. What was the heat source? And most importantly, where were the readings recorded? In situations like yours, we generally try for a soaking type of heat over the whole area and take measurements at 3" and 6" from the weld joint.

For years only a toe blend was required, but for the last 10 years or so, these welds have been called out with a smooth ground finish. A longer leg on the plate is also common, to move stresses farther out.

Let us know what you come up with....

~thirdeye~

By tom cooper (**)

Date 01-30-2008 15:32 Edited 01-30-2008 15:47

Well thanks all for the ideas. Had to chase one crack all the way in to the root so I made the decision to remove all lugs from all plates and start over.

Apparently I was wrong by not requiring a root opening - will correct that next time.
Agree with extended soaktime on the preheat - will call for 1 hour soak at 400-450 degrees measured at 3-inches from joint. We used a resistance heat blanket on this before. I avoid propane torch local heat whenever I can, but it may be that the blankets can't provide the soak that I will need.
Agree on post weld heat treat but the previous cracks showed up before we got to that step.

Here now is the kicker which I learned only this morning and think this adds to the problem more than anything else. I called in a local lab to check sulfur content (our in-house portable machine is not capable of detecting sulfur). Guess what we found? The base plate has a S content of .120-.130 and about .073 on phospherous !! The lugs are a lot lower at .028, but still higher than I expected. Based on this I am estimating the material to be an 1100 series, like maybe 1116 or 1130 resulphurized steel.

So now my main problem is to find a rod to weld this with. What will be your best suggestions? By the way, the machinery is a early '60s vintage and of unknown origin.

Please keep in touch because I'm being crucified for these mistakes.
Thankyou.

By motgar

Date 01-30-2008 16:48

Tom,

Remember reading something from Lincoln Electric about weld cracking. Not sure if this will help you but, you may be experiencing segregation induced cracking, a form of centerline cracking. Here is the site where I found it, if you are interested.

http://content.lincolnelectric.com/pdfs/knowledge/articles/content/weldcracking.pdf

By GRoberts (***)

Date 01-30-2008 20:15

I would never weld lifting equipment with 9018-B3. It is a 2 1/4 Cr, 1Mo alloy that is designed for high temperature applications, and needs PWHT in order to be ductile. Otherwise it is brittle, especially in thick section as you picture indicates. If the lug is carbon steel and the other piece is not high strenth, a 70 series low hydrogen process should match the strength. With welding high sulfur mateiral, the most important step is to butter the high sulfur material with a low dilution buildup, then MT/UT to make sure there are not any cracks before welding on any other attachemnts. I would typically think about doing this with something like 1/8" diameter 7018-1 using high overlap with previous passes. However, I would think twice about welding anything with high sulfur that is for lifting. Do you really want that liability?

By CWI555

Date 01-30-2008 21:34

excellent points.

By tom cooper (**)

Date 01-30-2008 21:40

GR-
What do you mean by a "low dilution buildup"? I am guessing you are saying a lower amperage pass at the base metal to minimize penetration?
As for the liability you are worrying about, I don't have a choice in the matter, it is part of our own equipment and we are making repairs to something that already existed.
Thankyou.

By GRoberts (***)

Date 01-31-2008 20:07

I guess you have a point about the liability, just make sure you have good insurance, and don't let anyone stand directly beneat it.

Anyhow, to achieve low dilution, you do want to weld at reasonably low amperage settings, but after you deposit your first bead, you want all subsequent beads to be mostly melting into the previusly deposited weld metal and just barely tying into the base metal. So your arc is mostly penetrating the previous weld and not sucking up a whole bunch of that nasty sulfur.

By 803056

Date 02-01-2008 02:30

The sulfur is on the high end of the spectrum.

Select a filler metal with high manganese content. There should be at least ten times more manganese than there is sulfur.

I like the Lincoln Excalibur E7018-H4 electrode for SMAW. I use it when repairing heavy steel castings that tend to be high in sulfur. You can use electrodes from other manufacturers if you select those with the highest manganese content to counter the sulfur. Sulfur, a low melting point constituent, tends to segregate along the grain boundaries, at the toe and underbead in your case, if there is insufficient manganese.

Best regards - Al

By tom cooper (**)

Date 02-01-2008 12:12 Edited 02-01-2008 12:14

Thanks GR for explaining the low dilution process, we will do this.
Al- Your point about the manganese content is well taken, I consulted with an expert at Lincoln just late Thursday and explained my case. He said the stuff is darn near unweldable, but suggested Excalibur 8018-C3 for the high manganese content and also preferred its high nickel content for improved ductility on this type of Tee joint. He also advised on the low dilution butter layer as GR explained!!! So everything is coming together and making some sense now. He urged that I NOT do any PWHT though, which I am not comfortable with, but in view of the nickel content of the 8018-C3 I think I will follow his suggestion.
My simple "Thankyou" doesn't even begin to express appreciation for the help I get from this group.
Thanks.
V/R.

By tom cooper (**)

Date 02-29-2008 14:51

I thought I would close out the thread with a success story and let the information be available for anyone else that is reserching problems on welding high sulfur steel.
Here is what we did:
Chased cracks into the base plate as deep as 3/16" deep in some places;
dye pen all to prove we were clean;
preheated to 450* F and let it soak for hours;
built up the excavations to the baseline surface and sent to the machine shop for finish grinding;
dye pen again;
preheated to 450* F and let it soak for hours;
layed 1/8 beds of 8018-C3 (low amperage) under the footprint of the fillet welds only but not under the body of the lug;
hot magged the beds;
held a 3/32 root gap and filled in the bevel welds.
hot magged the roots;
filled out the filletwelds;
held preheat temp for 2 hours and slow cooled;
waited 48-hours and wet magged;
dimensional checks on lug;
sold off to QA on 2/21.

The above steps might be viewed as extremely cautious and overkill but IT WORKED and we're done with it.
Thanks for the advice and suggestions offered. I learned LOTS on this.
Thankyou again.