Welding up an air tank

By Darrell T Date 11-03-2001 21:01

I am making a rear bumper air tank for a 4x4. I have welded the whole thing together but now have 40 -50 pin hole leaks in the tank. I have chased these leaks for 5 hours drilling the pin hole and rewelding to no avail. I am welding 3/16 mild steel with a Miller 130XP (MIG)on a power setting of 4 and wire speeds of 60-70 trying different styles of filling the holes air tight. The wire is ER-70S-6 alloy and a 75/25 gas mix. What am I doing wrong here. It is driving me nuts. Any and all tips/tricks welcome.
Thanks
Darrell Tuxworth

By - Date 11-04-2001 12:30

When you say that the repairs were "to no avail", what do you mean exacly? Do you keep getting leaks at the same places where you are attempting the repair, or are you getting new leaks adjacent to the repaired areas?

What does your completed welds look like. Do they appear neat or is it a bit of a mess?

What voltage are you welding at? I do not know what a 4 setting on your machine means.

Regards
Niekie

By Darrell T Date 11-04-2001 16:11

Niekie
The repairs are leaking around my repair welds. The welds are just the size of a spot weld. A round puddle if you will and leak at the edge of the pool. Since the finished product needs to look like it isn't a weld for asthetic reasons it has to be ground smooth. The finished welds look nice, maybe not proffessional grade but pretty darn close. I do have years of practice and work on making the welds look good as well as have good penetration but I have never tried welding a tank before....at least nothing with 16 feet or more of welds.
As best as I can tell from the owners manual for my welder is that setting 4 is 90 Amps at 18 volts Supposedly good enough for welding 3/16 steel in a single pass with 1/8 or so gap between pieces.
Darrell T

By Darrell T Date 11-04-2001 16:13

Niekie
Found some new info on the welder amp range 30-130 and 28 volts max.
Darrell T

By TimGary (****)

Date 11-04-2001 19:50

The problem with compressed air tanks is that if they are not fabricated and welded correctly, they can be a big safety hazard.
What I mean is from what you're saying the original welds are no good. Trying to repair them may eventually stop the leaks, but the overall weld will not be sound and the darn thing could explode when pressurized, sooner or later.
It sounds like you have a lot of weld joints on this thing, so first I would recommend that you change the design to eliminate as may weld joints as possible, thus reducing the chance for error. For example, I've seen good truck bumper air tanks made from a pieces of 4" pipe with two end caps and a pipe nipple. That gives you only three welds for a total of about 27" of weld. From what you said about weld lengths, it sounds like you have a longitudinal weld or two in there...these are not recommend.
What does your design look like?
If you decide to stay with what you have, I would recommend cutting out the bad welds, prep the weld joints with a bevel to ease full penetration, and be sure to clean the welds thouroughly between passes. Also make sure you have 35-40 cfm of gas pressure at the gun and no wind to blow the gas away.
Just keep in mind that what you're building is a potential bomb that could hurt your or someone else if not done correctly.
Why don't you try to explain your design and how you prepped the weld joints. Then maybe we can help you further.
Be Careful!
Tim