Weave v seperate weld runs

[Welderpaul]

Imagine if you will a large prep between two plates, a single side vee prep, 20mm wide, 2mm root gap, 10mm root face. 'Normal' procedure would be to put a root run in then fill her up with a number of runs until she's full Migged.

We had some rework in from an agricultural supplier (Not our job originally), where a welded joint as above has failed.

The supplier tells me it was welded with a single root run with prep as above, then the remaining gap filled by someone pouring in the wire and doing a massive weave. Obviously the heat has been put in, but is this an acceptable way of welding it up? The finished 'cap' is certainly a huge weave, but i cannot see much else.

 

[snowcat]

Iv seen this allot, and I'm guessing the original work has cracked allowing the centre rather than around the toes?

It seams very common for production made equipment to use just a woven cap over a root, I'm assuming for cost?

 

[Welderpaul]

Its cracked along the centre for two thirds of the run, then the crack crosses to the toe of one side and follows this to the end of the run.

No doubt a huge weave is quicker, but is it acceptable? I guess not?

 

[Windy Miller]

A mate of mine did this years ago on some pipeline or another. Passed inspections ok so he prepped the job, ran the root in with a stick, and got some lad to pour masses of mig over the top on a night shift. He talks about it like he'd had a right result on the job, but always sounded a bit iffy to me. Wonder how long before the pipe started leaking. Hope it wasn't gas!

 

[snowcat]

I think its acceptable but bad practice, It depends on the structural integrity, Lemack were one firm that I did quite a few reworks on there Q hitches were welding the cheeks on in the manner described.

Stringers kept to an appropriate weave will always be stronger, especially if other factors such as pre heat and inter pass temps are taken into account.

Were into production territory here mind, where bottom line figures and perceived working lifespan are the main factors.

 

[Lewis Medlock]

I'm struggling to visualise the type of joint (single bevel butt joint, 10mm thick plate?)

MIG's prone to poor interpass fusion caused by not getting the wire right into the guts of the joint (wrong slope/tilt angles) and poor penetration characteristics compared to other processes which might explain the crack migrating to the toe.
Insufficient reinforcement/deposition/lack of sidewall fusion on the root run will lead to longitudinal cracks- particularly when they then welly a load of metal into a filler run in one pass.

Proper sized multi pass runs are preferable to refine the grain structure of the previous runs (columnar into equiaxed)......

I must admit I prefer stick welding important stuff.

Jim

 

[tomb]

I'm afraid were in the realms of agri machinery here. Gone are the days of manufactures calculating a 20mm plate is over kill and using a 25mm to be belt and braces, machines lasting a lifetime, not good business sense. The bottom line is king!
2.5x electrode thickness? should be the limit of weave. 10mm root face

 

[stew]

sounds a strange prep to me. :S whats the thickness of the plate?

prob all about time as said above, quick and easy option. maybe not enough fusion on the root pass too?

i like what ^^^tomb says: its so true, i see it again and again in my job. nothing is built to last like it used to in agri kit. although the pressure and time scales to use the equipment and the speed of the job to be done with it is ever increasing. im maybe lucky to still be able to use the belt and braces approach, as in my line of work, if i fabricate something, or repair an existing bit of kit, i dont wanna be seeing it again (at least for a very long time!). i was taught by an old timer who used to always say "if it needs half inch plate, use 3/4" plate here, their rough b*****ds!!!". so true!!! lol