Welding Tips and Tricks

Hello guys,

Building a stainless steel grease interceptor, 5000l, dimensions are 4300L x 900W x 1600H. Going to have to be in two halves and have minimal bracing on the inside. Has to be done in two halves, bolted together in a flange kind of setup, then I am lap welding a strap over the middle join to seal on site. Whole thing will be 3mm 304.

Will be running 3 braces 50x50x2 all the way round, one on the bottom, one at about 600, one around 1300

Will also have a cover with bolts every 200mm.

Drawings/specs done by someone else, I am thinking I need to run a beam across the width in the middle to stop the thing from bowing, despite it having a lid. Anyone built something similar and have thoughts/pictures.

Also, for ease of building I am thinking open corner but weld all the outside seams, would like to just fuse them with pretty high amps, but thinking I should jam some filler in there for strength. Have done a few destructive tests in the press and it all seems OK, will to an etch test shortly. Any thoughts on this?

I have good success keeping heat down and keeping things neat using 1.5-2 pps pulse on open corner joins, but a bit reluctant to use one in this situation encase I get a weak point with none or little fusion leading to a leak or crack. Also going to back stitch the seams, any advice on sequence? or just tack every 100mm and back stitch along? or start from the middle and work out?

Overall I think it is over engineered, but would like some thoughts or opinions as I haven't really done anything this big. Its not a life or death item, but obviously want to get it right. Thanks in advance

I think you are going to need three braces across the top and another three about halfway down to stop it bowing


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Won't it be full of water most of the time? And if it's buried in the ground then it's supported on the outside.

Nah mate, it's above ground so has to be free standing, water level is about 1300mm.

Thanks for the feedback Coldman. more or less how I would have designed it.

Any advice on back stitching? Want to avoid warping as much as possible. Start from the centre and back stitch both ways or one end to the other?

Cheers.