Weld Failure (agricultural)

[bill_gj]

At the risk of getting shot at, here's a question.

Since my own personal and practical experience is, by and large, limited to 3mm angle and car sheet metal, I've never been too concerned about post-treatment of welds as I've not been looking at top structural strength.

But, with something that needs to be structurally super-sound - like the welding on this trailer - doesn't anyone do any post-weld heat treatment, like the books tell you to do to modify the heat-affected zone along the weld?

 

[whycanismellburning]

gotta share this one. This is what happens if you park your dozer in the wrong place. Apparently they were moving the earth mover and they diddnt spot the minni d9 in the way! Enjoy!

 

[Archie]

Perhaps the driver dozed off......

I'll get me coat

 

[storm monkey]

Surprisingly, the D9 above (49 500Kg machine) was not that badly damaged, and was later repaired.

The D bit is for dozer, but on the Cats, the letter afterwards is not really related to much, but the higher the number, the bigger the machine. A D11 is about 113 000Kg (248,600lb) with a 34.5l 8 cyl diesel engine, kicking out 850 hp at 1800 rpm, so quite impressive really. It's all controlled by 2 little joysticks too.

Phil

 

[Luke]

Glad the machine lived on, but how the F did they get it down?

Looks like they couldn't even have whacked the earth mover in reverse and waited to see where the dozer landed...

 

[snowcat]

At the risk of getting shot at, here's a question.

Since my own personal and practical experience is, by and large, limited to 3mm angle and car sheet metal, I've never been too concerned about post-treatment of welds as I've not been looking at top structural strength.

But, with something that needs to be structurally super-sound - like the welding on this trailer - doesn't anyone do any post-weld heat treatment, like the books tell you to do to modify the heat-affected zone along the weld?

Thats a whole, yes pre/ post and interpass are technically rule followers...as is peening, they seem to have become a fast forgotten rule, personally I will always pre heat and attempt to reduce cooling cycles on very structural work, normally on multi pass sections, but in all honesty the old skills and techniques have been lost or skewed certainly, by the ease of welding with wire feaders....

Hmmmmm best get me off this subject....

 

[snowcat]

Surprisingly, the D9 above (49 500Kg machine) was not that badly damaged, and was later repaired.

The D bit is for dozer,
Phil

I read it in a book last night, D is for Diesel...., the earlys were DRs and they were Diesel Rosevelts for no other reason that the lumberjacks who made em supported Rosevelt..

Again I must get a life...

 

[malcolm]

Thats a whole, yes pre/ post and interpass are technically rule followers...as is peening, they seem to have become a fast forgotten rule, personally I will always pre heat and attempt to reduce cooling cycles on very structural work, normally on multi pass sections, but in all honesty the old skills and techniques have been lost or skewed certainly, by the ease of welding with wire feaders....

Hmmmmm best get me off this subject....

That's why the forum is here - to pass on skills and techniques. If you have the time it would be great to have a 'how to' thread for welding very thick metal with things like that in it.

 

[snowcat]

That's why the forum is here - to pass on skills and techniques. If you have the time it would be great to have a 'how to' thread for welding very thick metal with things like that in it.

Id be more than willing too, I could only really do it on straight ARC or TIG and ARC, as i am and never pretend to be the worlds best in MIG, Im sure tho some of the other guys such as Runnach, Matt, Hitch,WP etc could offer there advice on heavy sections with wire feeders....

 

[Drains]

There's a thread on UKW on-going, which asks about "old" issues over lamellar tearing etc. I have a feeling Malcolms farmers trailer may be an example of a similar failure...

 

[snowcat]

I was haveing a read of that, Iv often in the past blamed any weld faliures on old materials, to be a high iron content, High point carbon etc, now im thinking lamination is the likely causes, also flicking through an old AWS book I found some stuff on Segregation, is segregation the same as lamination, sounds simlar cystals excludeing alloying elements?????? anyone know....

 

[bigdavesproule]

possoble cause of breakage was metal wasnt heavy enough for a dozer simple. a machine that size needs a trailor strong enough to carry it.

 

[whycanismellburning]

Does impurities in the steel not play a part as well?

 

[snowcat]

possoble cause of breakage was metal wasnt heavy enough for a dozer simple. a machine that size needs a trailor strong enough to carry it.

not entirely the point I was makeing, yes weight caused the faliure but, the fracture is outside the weld pool and across into the HAZ zone, not a usual destructive brake...

and no welds should not fail, It often a case of faults in fuseing the joint, or ,more likely in this case to be material, a destruction tested faliure does not normally look like that..

 

[TechnicAl]

Obviously the steel has a very lamellar structure. This doesnt mean the defect is lamellar tearing.
Basically what it is, is very coarse grained and directional. In the old days (possibly 60's) steel was often rolled into shape in one direction only thus creating a "grain" similar to wood. As in wood its easier to break along the grain than it is across the grain. It looks to me thats what you can see here. The load has exceeded the strength of the steel in that direction.

Lamellar tearing is caused by high impurities in the steel, particularly Sulphur. These sulphides appear as eye shaped inclusions in the steel. If you weld the surface of the steel across the direction of the inclusion the shrikage stresses can pull them apart. This "micro crack" can then propogate into a larger crack like defect.

 

[snowcat]

So is lamination the same as segregation???

 

[TechnicAl]

I was haveing a read of that, Iv often in the past blamed any weld faliures on old materials, to be a high iron content, High point carbon etc, now im thinking lamination is the likely causes, also flicking through an old AWS book I found some stuff on Segregation, is segregation the same as lamination, sounds simlar cystals excludeing alloying elements?????? anyone know....

To some extent it depends on who you talk to. As you say segregation is "bad mixing" this can lead to laminations. So some people call it one thing and some the other.
Another lamination can be caused by oxides on the surface, these dont fuse with the rest of the plate and you can get a layer forming. Often these are also called cold laps.

I think the most common "segregation" occurs in plate where the centre line is higher carbon than the outside, because of decarburisation caused by heat during rolling.

 

[malcolm]

Thanks for the link Si and explanations. Very interesting to learn about the differences in steel manufacture and composition over the years - explains a lot of discrepancies in reading material. This would certainly have been very old steel found in the farmyard somewhere.

The failure would have been down to excessive load for the design of the structure. Digger would have put a bending load on the weld, concentrating stress on the top edge. Better design would have been to brace the I beam at the bottom massively reducing stresses.

I had a look at the beam that fell off - quite a good test for the welds - the I beam bent and twisted before the welds broke. I suspect the other side went first - possibly that side had been damaged when the dozer was loaded on.

 

[Welderpaul]

Obviously the steel has a very lamellar structure. This doesnt mean the defect is lamellar tearing.
Basically what it is, is very coarse grained and directional. In the old days (possibly 60's) steel was often rolled into shape in one direction only thus creating a "grain" similar to wood. As in wood its easier to break along the grain than it is across the grain. It looks to me thats what you can see here. The load has exceeded the strength of the steel in that direction.

Lamellar tearing is caused by high impurities in the steel, particularly Sulphur. These sulphides appear as eye shaped inclusions in the steel. If you weld the surface of the steel across the direction of the inclusion the shrikage stresses can pull them apart. This "micro crack" can then propogate into a larger crack like defect.

Impressive.

So, why do welds that have been ground flush swell when they are galvanised. Seem to have in my mind because the level of Silica needs to be reduced to stop this happening!?

 

[runnach]

Id be more than willing too, I could only really do it on straight ARC or TIG and ARC, as i am and never pretend to be the worlds best in MIG, Im sure tho some of the other guys such as Runnach, Matt, Hitch,WP etc could offer there advice on heavy sections with wire feeders....

In the past using squirty on heavy section, can't recall ever having to get into post heat treatment. One particular job, heavy box section with pads welded to base was given stress relief treatment overall, not done at place of work, sent to a foundry, stressed relieved as per WPS. Huge area this topic, heating band for pre heats, the same for post heats using band sloping down in temp. Pyro meters used to monitor interpass temps, same to monitor post heat ect, basically though, if getting into the complexities of the above, the welder would be working in accordance to WPS as per Metallurgist/weld engineers specification.

TIG process, very few examples of post heat treatment, but when this was asked for as per WPS, tempil sticks used, company was too tight to invest in pyro meters, actually a real pain in the rear, stopping and starting to check during interpass! Post heat was completed in large ovens with a timer to slope down as per WPS.

Snowie, how do you go about a job when you feel pre/post heat is benificial to the work you are doing? A curious interest on how you go about this!

Regarding the make up of steel, high iron concentrations and stuff. I have a couple of = angle sections sections I asked for one time I was up the Forth Rail Bridge during paint/weld operations, these sections had been removed due to high corrosion levels, when I state "high levels" only at certain areas along a particular section, I put this down to high concentration iron levels within certain areas of the length of angle iron. FRB is now 118 years of age, foundry techniques would be no where as refined to todays scientific techniques, yet there are still problems with modern materials resulting in lamination and other imperfections, very strange indeed, or is cost the major factor for having these inbuilt impurities?