FAO: All fabricators + Production welders

[stew]

Quick question(s)...

I have a large item, its a 5m long cylinder frame which rotates, with approx 200mm to 250mm (length) butt welds, fixing a gusset plate (6mm) to a large ring (diameter 3000mm). The gusset plates are to strengthen a RHS cross member to either large end ring. There is nothing wrong with the welds themselves, but i wondered wether it is standard practice to leave a butt weld with a slight crater? It looks like most welds on the rings are done in spray transfer, where im pretty sure the rest of the fabrication is in dip transfer.

I feel that the crater/undercut is causing very slight cracking at a 30 degree angle (or so) to the weld.

I know from my own experience, any undercut of a weld is an area where a crack will propogate, but surely this large frame should be made to a standard that it will not crack up under load? Or is it a case these days where things are no longer made to last as long as they used to?

I am yet to contact the manufacturer, as i dont want to disrespect their workmanship, but i also dont want any issues with the frame. (which are prone to cracking with significant use/abuse!)

HELP!!!!!

Cheers,

stew

P.S Ill try get some pics up tomorrow.

 

[Welderpaul]

Photo would help?...
Ah, you editted while i was posting

 

[Hitch]

A picture is worth a thousand words Stew.....

 

[Engineer1964]

Quick question(s)...

I have a large item, its a 5m long cylinder frame which rotates, with approx 200mm to 250mm (length) butt welds, fixing a gusset plate (6mm) to a large ring (diameter 3000mm). The gusset plates are to strengthen a RHS cross member to either large end ring. There is nothing wrong with the welds themselves, but i wondered wether it is standard practice to leave a butt weld with a slight crater? It looks like most welds on the rings are done in spray transfer, where im pretty sure the rest of the fabrication is in dip transfer.

I feel that the crater/undercut is causing very slight cracking at a 30 degree angle (or so) to the weld.

I know from my own experience, any undercut of a weld is an area where a crack will propogate, but surely this large frame should be made to a standard that it will not crack up under load? Or is it a case these days where things are no longer made to last as long as they used to?

I am yet to contact the manufacturer, as i dont want to disrespect their workmanship, but i also dont want any issues with the frame. (which are prone to cracking with significant use/abuse!)

HELP!!!!!

Cheers,

stew

P.S Ill try get some pics up tomorrow.

Stew,

Undercut occurs whe the welder is set too hot and theres not enough wire speed, Strange as if that is a common issue with the welds you would of thought they would of picked up on it, Just as bad is overlap which is just cold weld laying on top of the metal.

Most structural failures originate from weld joint because it is the source of discontinuity or defects. The most visible weld defect we can easily find in visual inspection is undercut, shown in Figure 1 below. Undercut is usually due to overcurrent in electric arc welding. Overcurrent causes wide melting zone in base metal but not enough weld fusion metal to replace the gap. High lapping speed also leaves the gap poorly filled with weld fusion metal and produces undercut.

Undercutting is the burning away of the base metal at the toe of the weld. Undercutting may be caused by the following conditions:

a. Current adjustment that is too high.

b. Arc gap that is too long.

c. Failure to fill up the crater completely with weld metal.


As for the Crater, These need to be filled if there are no visable cracks as cracks can also happen especially if there is any fatigue with the metal.

Definition: A depression left at the termination of the weld where the weld pool is left unfilled.

Cause: Improper weld termination techniques

Repair: If no cracks exist, simply fill in the crater. Generally welding from beyond the crater back into the crater.

If you have a lot of Undercut and Craters i would reject the welding and either get them to recify it or replace, Might be an idea, especially as movement is common to get the welds tested with a non destructive test like Dye Pen

see here http://en.wikipedia.org/wiki/Dye_penetrant_inspection