Old air receiver interior condition

[Ian Helsby]

I bought an old compressor off the internet in the hopes of cleaning and inspecting the tank. If sound, have it galvanised for longevity. Below are some snaps if the inside of the tank. Ends are 2" BSP.
I wasn't too enamoured with the area around the drain so bought an unpainted air receiver. The fab shop I normally deal with when I need things sending to the galvanisers is adamant the tank shouldn't be dipped as it'll warp and potentially crack the welds.
Is there anyone on here who can offer an opinion?

With thanks,
Ian.

Cross threaded end port cleaned up with thread file. I had trouble sealing this with a new fitting when hydrostatic testing the tank post-clean.

 

[Seadog]

If it has passed a hydraulic test, and that is 50% over working pressure, then go for it.

 

[Turbo]

There's no point in galvanising that until you remove the rust. It would be a good candidate for citric acid derusting.

 

[not done it yet]

If it has passed a hydraulic test, and that is 50% over working pressure, then go for it.

Quite agree, but I somehow doubt it has been tested recently. It’s not difficult to test.

I’m not clear what the OP is doing. He indicates he has another receiver that he is using Instead - or is he really wanting to protect the ‘unpainted‘ one? Cleaning and surface coating would be my choice if going to the trouble, not galvanising.

That particular receiver would be more than adequate, if tested properly. Especially if the compressor pump were only an 8 bar machine….

 

[Seadog]

Quite agree, but I somehow doubt it has been tested recently. It’s not difficult to test.

He said he had tested it, didn't he?

 

[cheb]

What would be wrong with slooshing a good load of paint into it after the derusting, rolling it around a bit and then draining out the remaining paint?

 

[not done it yet]

He said he had tested it, didn't he?

Ahh, yes, hidden between the pics. Missed that. As an aside, the seal should have been a washer, so perhaps he only needed a thicker one?

 

[daleyd]

What would be wrong with slooshing a good load of paint into it after the derusting, rolling it around a bit and then draining out the remaining paint?

I could imagine if the paint started chipping later on it might cause some issues.

 

[Seadog]

What would be wrong with slooshing a good load of paint into it after the derusting, rolling it around a bit and then draining out the remaining paint?

That's my plan with a receiver I'm going to repurpose. It's what Bambi do to all of their receivers.

 

[bricol]

Its already 35 yrs old and doesn't look too bad - how much longer then you do you need it to last?

I would talk direct to the galvanisers rather than a fab shop that uses them - the fab shop will have had issues with welded structures, hollow fabications and even flat plate warping all over the place after galvanising, but a pressure vessel should be pretty resistant to distortion.

Issues will be high silicon steel making it deposit unevenly, the slowness of dipping required causing uneven coating, the potential for bath contamination by not getting rid off all the internal paint, rust etc, their worries about you complaining of uneven finish over the welds, from one end to the other from the slow dipping, the threads being bunged up, - ours are now left un-treated,not even painted on the outside, as the coolant used in the machines we build strips the paint off, but also contains inhibitors so they don't rust much anyway.

 

[Ian Helsby]

Hi.
Both end caps of the old tank were removed by warming up with oxy-acetylene torch and then a 6ft cheater pipe on a 3/4" drive ratchet. One side shown in the photo must have had it ends cap cross threaded, either at the factory or subsequently when an outlet was threaded into it. It's this end that won't kindly take a new end cap. The old end cap that came off had threads in too poor a condition to reuse.

User: ---not done it yet---
Yes, perhaps you are right. I should have tried copper washers for sealing it up prior to hydraulic testing. The new BSPT fitting I bought for the side with the damaged threads didn't seal, even when done up tightly. Now enough time has passed since I first tried to test it. I'd be willing to go with better seals, and perhaps some kind of tape / liquid seal over the fitting for the bad end.

The photos shown in the first post are after 4 hours tumble cleaning with water, detergent, and pea gravel:

I'm not too happy with the heavy pitting near the drain hole, the pits looks to be half as deep as the receiver is thick. I decided to buy a new one but have only just done so in the last couple weeks. I figured the simplest, least effort, and most reliable way to protect it would be to have it galvanised. It should be among the cheapest methods too if sent in with a load of other stuff. The compressor will be stored in unconditioned space out of the rain so humidity will be high.
This article from a manufacturer of tanks is a good read:

Galvanised Pressure Vessels and Air Receivers | Air Receivers

Whilst galvanizing Pressure Vessels offers excellent corrosion protection it doesn’t necessarily make it look nice. Galvanising pressure vessels has a numbe ...

www.air-receivers.co.uk

They aren't against it completely and put forward the argument that other parts of the system fail before the tank does.
As with all things, if you have the money to replace or buy new then save yourself the trouble and do so.

The question of the thread is; has anyone any good reasons not to galvanise a tank?

I may come around to sloshing paint or, more likely, some kind of fuel tank sealing liquid within the new tank, especially along the bottom.

User: --bricol--
Thanks for your message. Yes, considering it sat in a barn for years and had 1/2" saw/brick dust all over the top it's in good nick. The photos prove that the real damage is along the bottom where liquid has been left to sit for years. I'm thinking towards resale value afterwards too. A compressor with a galvanised tank should last indefinately. As for the threads getting bunged up, I've already bought stainless steel fittings and screwed them in with some copper slip to protect the female threads from the zinc.

 

[Alan Reynolds]

Any thoughts on using the stuff they use to seal petrol tanks to seal rusty receivers.

 

[brightspark]

you have pressure tested it just use it as it is. if it did leak through rust it would only pinhole 1st and you would hear it

 

[daleyd]

you have pressure tested it just use it as it is. if it did leak through rust it would only pinhole 1st and you would hear it

Yeah agreed, any coating you put on isn’t going to add any strength so to speak, the best it might do is prevent further rusting but keep it drained regular and it’ll last for years.

 

[bricol]

The photos shown in the first post are after 4 hours tumble cleaning with water, detergent, and pea gravel:

I thought I came up with some lash ups to do stuff, but that is brilliant

 

[grim_d]

Yeah agreed, any coating you put on isn’t going to add any strength so to speak, the best it might do is prevent further rusting but keep it drained regular and it’ll last for years.

That reminds me, I haven't drained mine for a few months, about 36 months.

 

[brightspark]

That reminds me, I haven't drained mine for a few months, about 36 months.

that reminds me haven't done mine for a year. must think on

 

[mtt.tr]

Chap at work recently drained one and got 40litres out of it

 

[brightspark]

Chap at work recently drained one and got 40litres out of it

they had a small compressor at a dentists i was doing a job for it seemed to be running all day . it was red hot and the belt was slipping . had a quick look for them tightened the belt up and drained it got a full bucket of water out of it i asked them how often do you drain it . err drain what the tank . we never have well weekly would help .

 

[Ian Helsby]

I mix up Bilt Hamber Deox powder and fill the tanks or cylinders and this cleans all the rust out.

That Deox powder looks great! Did you do any prep work beforehand or does this stuff blast through the lot?