Compressed air safety

[Steamchick]

I worked on the Dinorwic Power station electric busbars from generator to main transformers in the 1970s. Worked on the dry-air feed system to keep the busbars from any condensation. The compressors had auto water traps with auto- drains fitted, then the air at 6 bar went through driers, before expansion to 4in water gauge. The resulting air was dry to a dew point of -40°C. Then fed into the busbar enclosures. To my (lack of) knowledge, the power station has not blown-up yet with a wet insulator shorting-out a 132 Mw generator. There are many uses for dry air. Including food processing.
But in the garage is usually wet air....
K2

 

[ajoeiam]

Getting back on topic: I still hold the opinion that air compressor tanks made from Stainless are far superior to tanks made from soft steel, and somewhat superior to aluminum tanks. I rank normal soft steel tanks in last place because it's not a question of IF the tank will rust through, it's a matter of when will it rust through, and will the rusted areas lead to a rather nasty bang. I rank aluminum tanks in second place as although they may develop pitting, they're not likely to corrode so badly as to cause the tank walls to become thinner, as happens to soft steel tanks with rust scaling.

Considering normal shop conditions, IMHO, Stainless makes the best tank. As has been pointed out, stainless is susceptible to a short list of environmental conditions (ie Chlorine), but, soft steel will be equally affected,...and how likely is it your shop will see high concentrations of air-borne Chlorine.

If you can smell the ocean - - - you are experiencing high concentrations of air-borne chlorine.

 

[ajoeiam]

Stainless is a very good choice if price not an issue. The water condensed is pure water with little or no ions and is thus highly corrosive. Oxygen enhances that effect. The reason its difficult to sell these stainless tanks in Canada is due to its process regulations which vary from province to province. They may very well agree on the design considerations but they may require different inspection procedures and the paperwork can be obnoxious. Pretty much requires getting a Canadian Engineer involved in processing the paper work. I look at this way. My tank is still working and has been for over 20 years. When it goes probably will just buy another compressor because the mechanical stuff will be worn out too. And when it leaks it going to the scrap yard.

snip

Hmmmmm - - - - it seems that this opinion (dump the compressor because the tank rusted) has been developed specifically for non-commercial grade equipment. Quality air compression equipment can be rebuilt - - - and even without can have an extraordinary lifespan. Initial purchase price is often a reasonable indicator of the quality of the equipment. I.e. - - - if you bought it at a terrific sale at your local hardware store - - - and haven't bothered with any maintenance - - - its likely fit for the scrap yard as a total entity when the tank rusts through. Now if you're buying something that runs in the 20+ cfm range at 125 psi (or more) - - - well - - - you will likely not find it on sale at your local hardware store - - - you may find it at your local industrial tool supplier but even they may need to order it in. Now - - - please - - - rebuilding the air compressor - - - I was referring to the 'head' - - - NOT the tank.

 

[Steamchick]

Yup! "As a lad" I worked on refurbishing (Annual overhaul and spares) some Broom Wade large compressors. 1 inch bore and 24 inch stroke, 6 bar, twin cylinder compressors (Carbon piston rings in 3 parts). 6 of them supplied compressed air to a factory. Not the sort of thing to throw away. 20years old and continued in service till the factory closed a decade later.


K2

 

[Toymaker]

Give it a go and let us know what happens. Maybe it will become the new standard.

At my current age of 73, whether or not I apply a sealant to the tank, seems likely I will fail long before my aluminum tank fails

 

[Mike Ginn]

Ken Great video - long before H&S were involved. The sight of those guys in the foundry pouring metal with no eye protection is really scary!!!!
Mike

 

[Steamchick]

Toymaker, don't believe it. My Mother was told by the heart specialist at 81 that "she would not survive another year unless she had the quadruple heart by-pass". She didn't have the operation, as she reckoned she had had enough life anyway, and recently passed away nearly 102! I'll not ask that specialist for the lottery numbers...
Made me think.... At what age should you stop paying life insurance? Seriously, it's only good value if you die young and profit from it? After a certain age you'll have paid more in than you get...
K2

 

[ajoeiam]

Toymaker, don't believe it. My Mother was told by the heart specialist at 81 that "she would not survive another year unless she had the quadruple heart by-pass". She didn't have the operation, as she reckoned she had had enough life anyway, and recently passed away nearly 102! I'll not ask that specialist for the lottery numbers...
Made me think.... At what age should you stop paying life insurance? Seriously, it's only good value if you die young and profit from it? After a certain age you'll have paid more in than you get...
K2

That will very much depend upon what type of life insurance you have!

 

[davidyat]

I'm so glad that I saw this thread. As I was reading the posts, I said to myself, "Did you ever drain your 6 year old compressor tank"? UUHH, no. So yesterday I decided to check. Opened the drain cock with no pressure in the tank. Some water leaking out. OK, turn on the compressor to get it all out. Some small dripping. When enough pressure came up, it blew out sediment blocking the drain cock and I saw almost 1/2 quart of rusty water blow out. Needless to say, I'm shopping for another compressor. And, yes, I learned a valuable lesson here. Thanks.
Grasshopper

 

[ajoeiam]

I'm so glad that I saw this thread. As I was reading the posts, I said to myself, "Did you ever drain your 6 year old compressor tank"? UUHH, no. So yesterday I decided to check. Opened the drain cock with no pressure in the tank. Some water leaking out. OK, turn on the compressor to get it all out. Some small dripping. When enough pressure came up, it blew out sediment blocking the drain cock and I saw almost 1/2 quart of rusty water blow out. Needless to say, I'm shopping for another compressor. And, yes, I learned a valuable lesson here. Thanks.
Grasshopper

Your report is one reason I wish it were possible to easily gauge the thickness of a tank wall.
Its not so I can understand your caution - - - except I think if it were possible to get unbiased
information re: catastrophic tank failure I'm betting that the number of tanks that display such
are actually quite a small fraction of all the tanks in service.
Just so I'm no accused of not caring - - - I think that there a significant difference if result when
comparing a common 'el-cheapo' compressor that maybe can produce a peak of 90 or 100 psi
(5 or 6 bar) in a tank that is maybe 14" ( 350 mm) in diameter to a tank that is used at 150 or 175
psi (10 to 12 bar) that has as 18" (450 mm) dia. There may be a small difference in material
thickness (I wonder - - - haven't tested so dunno!) but the amount of energy stored is - - - well
- - not insignificant.

I would suggest continuing to runr you present setup while your waiting for a great sale price
on its replacement. (I've found that even industrial sized (smaller end for them) units can have
price point reductions occasionally.)

 

[awake]

[/QUOTE]

Very interesting - - - would you care to comment on the concrete build and prolifically used by the Romans that doesn't corrode even in salt water?

Sorry, I wasn't around when the Romans made concrete. I only repeat what I remember that I was taught. (I.E. a small fraction!).
K2

(Snickering) - - - hadn't thought so.
Ran into an interesting article about how roman concrete was still viable where our contemporary stuff had far less longevity - - - especially in salt water.
Can't remember where I saw the article - - - I might have to dig it up - - - wonder - - - would it be considered too far OT for here?

Joe, can I ask for the reason for the snickering? I am asking honestly; it has really puzzled me.

 

[Steamchick]

Didn't puzzle me. I had intended the remark jokingly, as to be around when the Romans built Hadrian's wall, or the Temple of All Gods (Pantheon) would make me famous for being so old. So, as a joke, it was a compliment to chuckle, or "Snicker". Hope I correctly understood the meaning of "Snickering"?
I have learned that the reason the Dome of the Pantheon is so successful is mostly due to the changing density of the concrete as the dome progresses from the rim. The rim concrete has significantly higher density - I guess from sand filler - compared to the top concrete - due to a high use of pumice that has a low density. But the pumice as a filler also chemically improves the longevity of the concrete. I also heard that in Sellafield in Cumbria, they are mining a subterranean store for radioactive waste materials, and have studied the exact chemical composition of Hadrian's wall mortar and cement, as that is the longest known and proven good concrete to last 2000 years in that climate and region.
Sorry, this is off-thread for compressor stuff..
K2

 

[awake]

Ah, thanks. I guess I was hearing it the wrong way. Too much stress at the moment ... skews my perceptions.

 

[Steamchick]

Probably my twisted brain - needs others to tell me so I know to untwist things. Thanks Andy.
K2

 

[ajoeiam]

Didn't puzzle me. I had intended the remark jokingly, as to be around when the Romans built Hadrian's wall, or the Temple of All Gods (Pantheon) would make me famous for being so old. So, as a joke, it was a compliment to chuckle, or "Snicker". Hope I correctly understood the meaning of "Snickering"?
I have learned that the reason the Dome of the Pantheon is so successful is mostly due to the changing density of the concrete as the dome progresses from the rim. The rim concrete has significantly higher density - I guess from sand filler - compared to the top concrete - due to a high use of pumice that has a low density. But the pumice as a filler also chemically improves the longevity of the concrete. I also heard that in Sellafield in Cumbria, they are mining a subterranean store for radioactive waste materials, and have studied the exact chemical composition of Hadrian's wall mortar and cement, as that is the longest known and proven good concrete to last 2000 years in that climate and region.
Sorry, this is off-thread for compressor stuff..
K2

Ah ja - - - - it would be rather a wonder if you had been there - - - yes - - - 'snickering' being the ongoing action of 'to snicker'.
I hope that was polite - - - I wasn't quite at the 'lol' but thought it was at least somewhat funny - - - yes?

Might be thought of as OT but what do most here put their compressor on - - - a floor of some kind and most likely its made out of concrete.
(In my experience there is a lot more poor quality concrete around than good stuff. I think that far too much concrete is pouring in conditions that severely limit long term sustainability. This wasn't the article I read but here's one: Riddle solved: Why was Roman concrete so durable? . Fascinating idea - - using quick lime without slaking it first and by doing so its got an accelerant and self-healing properties all at once - - - what's not to like???)

 

[DKMC]

Interesting thread. The compressor I built in around 1983 using a new propane cylinder (never any propane in it) failed after 35 years probably due to ignorance of not draining it regular. Small pin holes developed in the bottom side of the tank, progressed till it was no longer usable. Considering all the things wrong with the build (less than proper choice of materials and welding procedures) it had a very useful life with no problems. It sat unusable for a couple years until I built a replacement tank, from another new propane tank. Many improvements were incorporated in the build. Proper 'weld-o-let' fittings and knowledgeable welding techniques were employed in the build. Hydro-testing went well. Valves in the Quincy 210 pump were replaced, broken valve springs were found and replaced as well. An automatic drain valve is installed, with a 1" diameter stainless 'accumulation tube' at the bottom of the tank, so water doesn't sit in the bottom of the tank. For 2 years now, it's been in daily service and operating without problems.

The new setup





The old unit on the left

 

[Steamchick]

I understand you have built it "properly", but in the UK you Cannot use used gas cylinders for compressed air and expect your insurance to cover them - and any damage - if they fail.
We all take some risks in life. But businesses cannot. The Model Engineering club I use has just had to reduce the working pressure of an old compressor, to stay within legislation and Insurance limits. They had to change max pressure with a reduced pressure limit switch and relief valve. It's the total stored air energy as well as pressure that limited the size of system. - versus cost of insurance! An old gas cylinder used as a receiver was scrapped.
Know the risks and decide what you can afford versus what you need.
K2

 

[DKMC]

I understand you have built it "properly", but in the UK you Cannot use used gas cylinders for compressed air and expect your insurance to cover them - and any damage - if they fail.
We all take some risks in life. But businesses cannot. The Model Engineering club I use has just had to reduce the working pressure of an old compressor, to stay within legislation and Insurance limits. They had to change max pressure with a reduced pressure limit switch and relief valve. It's the total stored air energy as well as pressure that limited the size of system. - versus cost of insurance! An old gas cylinder used as a receiver was scrapped.
Know the risks and decide what you can afford versus what you need.
K2

Based on past experience and performance, I'm very content with the project. I also don't recommend anyone do what I have done. I find I expect less and less from my insurance every time the premiums increase and the letter about less coverage
comes in the mail. If most business owners had 'proper' concern for regulations and risks, no one would be or stay in business. As they say....YMMV. I repeat, do not do what I have done, it's dangerous and 'improper'!
Oh, and glad for at least one reason that I'm not in the UK.

 

[mnay]

I am retired now, but have worked in several machine/repair shops in my 50 year career. All of those shops had various sizes of compressors that ran and stayed pressurized to over 100 psi 24 hrs per day 7 days per week. Most had some form of automatic drain valves and they all have pressure safety valves on them. I never saw or heard of a tank failure.

I have a compressor that has had reasonable care in my home shops for about 30 years and it has finally started to leak from some pin holes in the bottom of the tank. The tank is ready for the scrap yard. In my opinion you should exercise reasonable caution but not lose sleep if you have a compressor pressurized in your shop and obviously watch for any leaks or rust spot on the bottom of the tank.

 

[Steamchick]

I do not know compressed air regulations.
But I have an idea, that a "Proper" certified receiver is designed to either have special phosphated and zinc coated interior (or something?), or 3mm corrosion allowance on the steel wall thickness, on top of the thickness required for the shell according to the Regs... Propane cylinders do not have the corrosion protection/allowance.
Air receivers must be designed to have a factor of safety of 6 or 8 on hoop stress (not sure on latest regs). Also if ANY penetrations, like a drain, man-hole, air connection, relief valve connection, etc. - in the side of the shell then the stress calculation must include a stress concentration factor of "whatever"... - something like 2.5 to 3.5 depending on Regs.?
This makes a proprietary air receiver (for industrial use where the Company will comply with Regs.) really thick walled compared to LPG cylinders. (which probably only have a factor of safety of "Not enough" in many cases, after considering the corrosion allowance, for air at 6~8 bar!). How thick is the cylinder wall of a propane cylinder?

Interesting to note that a cylinder perforated after 35 years though. Gives us a real clue as to how long they take to rust to a failure. Maybe based on that we should all replace "home" air compressor receivers after 10~20 years - to stay safe?
K2