testing my welds

[BrokenBiker]

not sure if this is in the right place, so mods feel free to move it

if i wanted to weld up a box out of 2mm mild plate, and fit an air inlet, how much pressure would be accepted as reasonable before the welds fail and it either leaks...or blows completely?

that is if this is a recognised testing method that is. my compressor is capable of 6 bar and the box will be made from 6 200mm x 200mm x 2mm mild steel, welded with flux core, and the inlet will be a standard fitting, wrapped in ptfe and fitted into a drilled tapped hole in the centre of one panel

 

[the snooper]

if you welding is upto scratch it will be ok for air but only you will know if its ok
testing of air receivers is usually hydraulic

 

[mike 109444]

You might find it safer to test with water under pressure which I think you will find is how compressor tanks are tested. I expect someone will be along soon to correct me if I am wrong.

 

[hotrodder]

Air is acceptable for a LOW pressure leak test. Because air/gases are compressible they can store a LOT of energy and can ruin your day if a weld or something lets go. Liquids are incompressible which is why they're used for pressure testing aka hydrostatic testing There's a whole section on weld testing in the welding tutorials... http://www.mig-welding.co.uk/wiki/Weld_Testing

 

[madkayaker]

Tanks are tested with pressurised water as it much much safer if they rupture. What is it your trying to build?

 

[BrokenBiker]

i want to build a gokart, with a 1200cc bandit engine, so i want to get as much practice at doing solid strong welds as i can, and use a testing method that will prove their strength without any doubt

 

[BrokenBiker]

and i suppose i should probably mention the reason i want the pressure test for leaks is so i can fabricate a petrol tank for said kart

 

[wyn]

The threaded fitting might let go first if it's only into 2mm plate.

 

[the snooper]

then you only want 20 or 30 psi max if that

 

[BrokenBiker]

excellent. i shall look into a hydrostatic set up.

cheers for all the help

 

[the snooper]

as its not a pressure vessel you dont want much pressure or you will mis-shape the tank

 

[Welderpaul]

If we are fabricating something that will be pressure tested we test it with one of these
We are not ticketed for the test to stand for anything, or issue certs, but at least we know if won't fail when it is tested by the propper boys

 

[rkde]

Agreed with the above, if I need to test for pressure on any units I use the same but mine came from screwfix.

http://www.screwfix.com/p/rothenberger-rp30-pressure-testing-pump/83797

 

[madkayaker]

If we are fabricating something that will be pressure tested we test it with one of these
We are not ticketed for the test to stand for anything, or issue certs, but at least we know if won't fail when it is tested by the propper boys

That a good idea and if it did fail then the only thing you have lost is all the dust in your workshop!

 

[hotrodder]

as its not a pressure vessel you dont want much pressure or you will mis-shape the tank

^ This. Fuel tanks aren't pressure vessels and if they aren't vented will pull a vacuum and cause fuel starvation. Obviously a kart tank is gonna be much smaller than a typical full size car tank but they can start to change shape (elastically/temporarily) with less than 5psi in them. Leaks can be detected with less than 1 psi either by going over all the joints (welds, threaded fittings and hoses/jubilee clips) with some soapy water. I use a pressure gauge with a resolution of 0.25psi and only bother with the soapy water if i have a leak to track down

 

[BrokenBiker]

If we are fabricating something that will be pressure tested we test it with one of these
We are not ticketed for the test to stand for anything, or issue certs, but at least we know if won't fail when it is tested by the propper boys

ive just been onto cromwell (as they run and operate the maintenance stores in my works) and have bought one to be delivered by 10am wednesday morning

 

[Paul G]

i want to build a gokart, with a 1200cc bandit engine, so i want to get as much practice at doing solid strong welds as i can, and use a testing method that will prove their strength without any doubt

As already said, don't test tanks with high pressure air.
Fill to the brim with water, cap, then add 2psi of air on top if you have no water pump.
Even this little pressure could distort the tank, depending on the shape.
Add the air with a bicycle pump so you don't over do it.

A good method of testing practice welds in sheet is to use the ball indent method.

Drill a large hole (or find something with a hole in it). Metal, hard wood, or even kitchen work top will do.

Clamp the weld over the hole and hold the ball end of a hammer above the weld.
Use a wood or nylon mallet to hit the other hammer and dent the weld into the hole.
DO NOT hit two steel hammers together as they can shatter.

The pic shows this method used on an ally TIG weld that had surface pores in it.

HTH
Paul G

 

[rob1]

hi i welded oil tanks for six years, very borring ,all tested low presure ,you only need a bit of presure and soapy water to test for leeks .
leave gap of the wire when tacking up for penatration.
we left an old tank filling up one day and i think it only got to a couple of bar before it went boom