[ardavey]

Hello,
I have a repair job on an irrigation system. Its 2 stainless end caps on 8inch pipe which have been repair many times with arc. It get repeated pin holes and hairline cracking along the weld.These pipes are under large pressure (500kpA) Just wondering if anyone had any tips for me. I was thinking about grinding the old welds back to the original joint and welding with 309 rods with an inside purge, but if other people have some better ideas that would be greatly appreciated.

I have attached a photo

[Otto Nobedder]

That looks like it's seen several reapirs with 308 Stick.

This has likely made layers of slag inclusions, from the look of the welds.

Assuming you're going to TIG it, 309 is a good choice, in my opinion. It will handle inclusions better, and have a bit more ductility than 308. Yes, I'd grind all the old BS out I could, and back-purge it if possible. For pipe that size (and the service it's in), you could back-purge it with nitrogen far cheaper than argon.

If this is an ongoing problem, you may be "money ahead" to cut the whole damn thing off, dress it, and re-weld it the right way.

Something to consider...

Steve S

[Superiorwelding]

If this is an ongoing problem, you may be "money ahead" to cut the whole damn thing off, dress it, and re-weld it the right way.

I second Steve's idea. It might be better to start over. At least by doing this you will know exactly what is there and if it was done right.

[weldin mike 27]

Hey,

If you decide to cut off, maybe look in to a blind end cap that you see on piping systems, to turn the dodgy old fillet weld into a butt weld. Maybe.

Mick

[coldman]

I agree that the welds are awful and need re-doing.
You have serious further problems here. The end cap is not an end cap, it is merely a dished sheet welded on the corner. This weld will be subjected to torsional stress because the dished end will billow out every time it is pressurized. The failure of the weld will continue to occur no matter how good the weld is and also made worst that the stainless steel will work harden as a result of moving in and out all the time. You risk this dish being fired off like a cannon if over pressure occurs.

A true end cap consists of a crown radius to dish it, and a knuckle radius either pressed or rolled to bring the edge back to the pipe for a butt weld which is then subjected to normal hoop stress for which it is designed to withstand.

My advice is to scrap the dish end and replace it with either a pipe end cap or a hot pressed code head as used in pressure vessels. 500kPa is not much pressure really, once replaced with the right cap you will have no further problem.

[ardavey]

Thanks everyone for the advice, its really appriciated. I will pass it to the deciding powers. Certainly starting again it a good thought, with a proper endcap. Any thoughts on getting a straight cut to square up an end cap without too many big gaps when I seat it? Plasma and a line? or some other cool trick I don't know about??

Cheers

[weldin mike 27]

Hey mate,

I just saw your location, where abouts are you?

Im in Bendigo.

Mick

[weldin mike 27]

Hey,

Forgive my forwardness, but are you sure its stainless and not aluminium, It looks very whitish silver to me.

Mick

[ardavey]

Hi Mick,
The job is in Ararat. Not too far from you. It is defiantly stainless. I ran some Tig beads to patch it yesterday, but where one plugged another opened. We'll address the issue when irrigation is not required for the season.
Cheers.

[weldin mike 27]

Cool as,

Thanks for the clarification.

If you need a bit of professional assistance, I have access to a facebook page with bulk skilled tradies that could lend a hand if you need.

Mick.

[noddybrian]

Now that is one big pile of nasty stuff ! - the pressure if I got the conversion to proper PSI does'nt seem very high - I would assume though from what little can be seen in the picture it's a manifold of some sort - maybe close to a pump ? - if so it's likely affected by pulsing / hydrostatic shock load causing the end to flex & fatigue - with all that repair goop & the amount of heat input plus unknown compatability of alloy it wants chopping back & a fresh start - I've had jobs like this & they are a pain ! - if you can get a proper end cap - or have one spun if there's a metal spinner close to you - & I prefer the cap to fit inside the pipe if possible - if not I assume the pipe is some sort of standard where you are - the other way is to buy a reducing bush that will be of known quality & will have a suitable radius on the corners - bring it down to the smallest size available & plug the end with a solid flat disc welded inside the collar of sufficient thickness to resist the pressure - worked for me in the past - may not please everyone - but it's for irrigation - not the space shuttle !

[Bill Beauregard]

Hello,
I have a repair job on an irrigation system. Its 2 stainless end caps on 8inch pipe which have been repair many times with arc. It get repeated pin holes and hairline cracking along the weld.These pipes are under large pressure (500kpA) Just wondering if anyone had any tips for me. I was thinking about grinding the old welds back to the original joint and welding with 309 rods with an inside purge, but if other people have some better ideas that would be greatly appreciated.

I have attached a photo

Do what Otto tells you you rarely get this level of expertise to take advantage of. The alternative is to spend the rest of your life repairing it again and again.

[coldman]

Hi ardavey,
RE: cutting square.
You have not told us the diameter of your pipe. Also I see you have a branch underneath near to the end, what is this distance?

Generally we use a "pipe wrap" available from your local welding supplies store. There is a range of sizes for different pipe diameters, I would use the largest size if you have the space for it (and if it is long enough to get around a couple of times!). If is not long enough you can guillotine some thin 4" wide sheet metal long enough to overlap twice around if you can, this will work well too. Mark the cut with a permanent thin marker and cut with a wafer disc on a 5" or similar angle grinder. Depending on the wall thickness, you may have to prep a vee butt joint.

String will give you a wavy joint, not recommended.

Good luck.

[coldman]

Just another thought.

If you have trouble sourcing an end cap or reducer etc, you can always weld on a flange and bolt on a blanking plate. If its an odd sized pipe, you can even have a flange machined to suit for not too many bucks.

[Superiorwelding]

ardavey,
Which direction did you decide to go?

[ardavey]

Thanks again everyone.

We are in the middle of growing grapes at the moment, so water is going on. I have patched it to hold for now and I will look at it in the end of the season. I think my direction will be marking it round and plasma cutting it off, then getting an end cap or a flanged cap with a blank insert. This design is clearly flawed and the newer versions are with a blank insert on a flanged cap.
This pipe looks like a standard 8 inch pipe, with 4 manifolds attached to it.