Antique air compressor tank - inspect & test or replace?
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  1. #1
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    Default Antique air compressor tank - inspect & test or replace?

    I picked up an old Brunner-Century air compressor a while back. The motor on it dates it somewhere between 1918 and the late 1930's. It's in okay shape mechanically for it's age. My only concern with it is the tank. It's roughly 100 years old. I haven't endoscoped it yet but what I could glimpse with a flashlight looks like surface rust. It's got some standing water in it; probably been in there for most of it's life given there is no drain valve.

    I'm wondering what my best options are for getting this machine back into service. My first thought is to have it professionally inspected: ultrasonic tank thickness measurements and hydrostatic pressure testing. I'm not sure if it's possible to re-seal a tank with surface rust inside of it, but that would be nice if so. The second option is replacement. This is a much bigger deal because this style of tank probably hasn't been manufactured since the days of soda-acid fire extinguishers. It would have to be a custom job which obviously means big money.

    It has cast iron feet and mounting brackets which are strapped in place by threaded rods. The tank has some 12 gauge sheet tacked on for reinforcement beneath the brackets. One end of the tank domes inwards, the other domes out.

    Can anyone offer any other insight for this project? Where I might begin to search for inspection and testing services? Who might be willing to take on a fabrication project like this otherwise? Spitball numbers for a new tank?

    Thanks.

    img_20201118_153311727.jpg
    (Big tank on the left)

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    Get it inspected by a qualified professional or cut it in half and use it for a bbq. New compressor tanks can’t be so expensive you would risk using a relic like that for anything more than a display piece at a museum.

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    Fill it full of water and pressurize it to 1.5 times working pressure and if it holds, then you will be fine. If there really is no drain then you should weld one in. If you can't weld then buy a newer tank, a good used one shouldn't be very much.

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    I used to test tanks for MSHA, Scrap the damm thing, the test would look for any changes on the tank, (welds) hydro to tag specks,( every ASME tank would have the specs and date of mfg) Used fiborscope and look inside for rust pitting, and if I liked everything it would get passed on for a year...cost to owner 300.00 then...It was not worth the liability to me and no profit after I paid for the inc. That was 20 years ago. Your old tank will not have the tag, so its scrap, if you weld a drain its scrap, if it has rust pitting its scrap, with the dished in end without engineering data its scrap, if there is any small or big dents it scrap, if the inspector dont like the paint job its scrap ( he has final say and can scrap it for any reason) and it does not matter pass or fail you pay the fee...Phil

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    Well the whole issue with replacing the tank is that this is an antique. I'd like to preserve the cosmetics of it. Any modern off-the-shelf receiver tank is going to have welded feet. Usually they have welded mounting provisions as well - and if I can find one that doesn't have either, it will still need to have the correct O.D. for the cast iron saddles to sit on. (16.25")

    So verifying the existing tank's integrity is vastly preferable to replacing it - but I am not sure who to look for to perform the necessary testing. It's not like small air tank testing shops are a thing. There are some shops in the area who service tank farms and the like, but those are 10k+ gallon monsters for the petroleum industry. Who should I look for to perform ultrasonic and hydro testing?

    EDIT: Phil posted while I was typing.

    In that case I suppose the best option is to look into having a replacement fabricated or hanging onto the slim chance that I can find a bare receiver tank with the right O.D. Or else just give up and scrap everything except the motor, pump and fittings... which would be a real shame.

    Second EDIT: I might have to eat my words.

    It looks like the Campbell Hausfeld AR8021 has roughly the right dimensions to work as a drop-in replacement. I only wonder if they would be willing to accept a special order for one without the welded feet.

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    The motor and compressor are cool but I can't imagine why you'd want to keep that tank. Nothing aesthetic about it and the safety concerns would drive me batty.

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    Keep the tank... as a dummy. Run the pressure line behind the unit and out to a new(er) ASME-rated tank elsewhere. Best of both worlds. No one need know the difference unless you tell them.
    Agreed that the unit is too cool to simply scrap... but like old copper fire extinguishers, they’re awesome to look at, cool to own, but not something I’m willing to risk life or limb on no matter the circumstances.
    Make it a showpiece.



    Be safe and stay healthy




    Jeremy

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    We've had quite a few threads on this 'Board discussing used/old air tanks. As a mechanical engineer who has spent a portion of his career dealing with pressure vessels including old/historic steam locomotive boilers, my professional opinion is: do NOT take a chance on an antique air receiver. Scrap it. Make a planter or water trough out of it, but do NOT use it as an air receiver.

    In evaluating boilers or large industrial air receiver tanks, the matter is a different story. The boiler or industrial air receiver is large enough to be entered in most cases. Ultrasonic thickness gauging (UT) will tell a part of the story of a tank's condition. UT is applied to finite points on a tank shell. It may miss a localized thinned or pitted area. Similarly, a hydrostatic test may not tell the whole story. Tanks or pressure vessels are normally designed with a factor of safety used in the design calculations. Over the years, this factor of safety (at least in ASME pressure vessel and boiler codes) has climbed upwards. It is by virtue of this factor of safety that a tank with thinned areas in its shell can still hold pressure and pass a hydro test. However, some tanks or boilers have locally thinned areas that are 'right on the ragged edge' of failure. In other words, there is just enough metal remaining to contain the pressure of working pressure or hydro testing. No factor of safety remaining. Should any further loss of material due to corrosion occur, or should a pressure spike occur (such as a safety valve not properly set or not functioning), the result can be a catastrophic rupture of an air tank. There is nothing benign about an air tank. Air, being a compressible gas, will 'unzip' a tank and blast it into shrapnel.

    Each year, when I worked at a hydroelectric powerplant, we'd get a visit from a 'risk assessment' team from the insurance underwriters. This team was made up of mechanical and electrical engineers with a wealth of practical experience. Each year, they'd have some new case history of an air receiver explostion. This was due to corrosion from within combined with a lack of regular internal inspections, lack of UT, and lack of maintenance (such as having drains checked to be sure they were clear of scale and blowing down freely).

    As for welding on a pressure vessel: if it has an ASME code stamp, the short answer is "don't". You invalidate the code stamp and unless you use a boiler shop with an "R" (repair) stamp for "U" (unfired) pressure vessels, should the tank let go, you are liable (if you are still around to answer suits brought against you by anyone injured or property damaged from the failure of the tank).

    If the tank has no ASME code stamp, unless you are prepared to run a set of engineering calculations on the tank, and prepared to design the alteration to the tank to provide a drain connection, DON'T. Assuming you are able to handle the engineering end of it, unless you have a qualified welding procedure and are a welder qualified to that procedure (according to ASME), DON'T get any ideas of welding on the tank. Poking a hole into a tank shell with a drill or hole saw, let alone with a torch or plasma cutter and then welding on the tank using a MIG welder is a recipe for a tank failure.

    I can appreciate your wanting to keep the historic old tank for its appearance, particularly if is a riveted tank. However, practicalities and safety outweigh aesthetics and historic appearance. Member John Ruth put it succinctly on this 'board some years ago: "Boiler codes are written in blood". By extension, any pressure vessel containing a compressible substance has the potential to rupture catastrophically and blast shrapnel with enough force to be lethal.

    By way of example: my buddy has an auto repair garage. The next door neighbor has a house in close proximity to the garage. One day, my buddy hear a hell of a bang from the neighbor's place and ran out to see what happened. The neighbor had bought an el-cheapo air compressor at a yard sale. When he fired it up, there was a small pinhole leak in the air receiver. The compressor could keep up with the leak, so the neighbor started using the compressor with the leak in the air receiver. One fine day, he had the compressor in his yard and was using it. The air receiver let go, and the result was the bang my buddy heard. The air receiver unzipped itself, luckily did not blast any shrapnel, and the blast propelled it upwards. Whatever goes up must come down, and the compressor and what was left of the receiver landed on the roof of the neighbor's house.

    I know common wisdom is to say: "they don't build 'em like the used to". This is true of the compressor, and with proper maintenance or repair, the actual compressor can outlast a few generations of owners. The receiver is another matter. It may well have been designed to a lower factor of safety than what we use in current design practice. It has had an unknown service life, and may well have significant 'wastage' (loss of material) from corrosion. Smaller air receivers were often built with a lap-riveted long seam and end heads brazed in before welded construction took hold. Too many unknowns and the potential for that old air tank to become a bomb to justify using it.

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    My CH 5 HP two stage three phase is being scrapped simply because its past 35 years old and who knows how the ASME code stamp tank is inside

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    Very good information. I like the idea of keeping it as a "dummy" display tank... at least in the short term. This will allow me unlimited time to source a suitable replacement whilst still benefiting from the additional 1/2 horsepower of airflow for media blasting, etc.

    On a side note, seeing the gradual evolution of motor technology through the decades makes me smile... see below for a side by side comparison with a modern 1 horse. I've got other repulsion-start motors in my possession, but this Century takes the cake. It's enormous for it's power rating, makes a beautiful sound and emits a unique smell when starting up - almost like gunsmoke. The bearings in it were built to last - with cutouts for eccentric rings which wick a continuous steam of oil for the journals to float on.

    img_20201108_122755627.jpg

    Touching on the matter of relief valves, is there a proper technique for testing them beyond bringing them up to pressure and seeing if they pop? I believe the one on this unit might be adjustable. It would be pointless to replace the tank without also ensuring the safety valve is correctly set.

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    Quote Originally Posted by Just a Sparky View Post
    Very good information. I like the idea of keeping it as a "dummy" display tank... at least in the short term. This will allow me unlimited time to source a suitable replacement whilst still benefiting from the additional 1/2 horsepower of airflow for media blasting, etc.

    On a side note, seeing the gradual evolution of motor technology through the decades makes me smile... see below for a side by side comparison with a modern 1 horse. I've got other repulsion-start motors in my possession, but this Century takes the cake. It's enormous for it's power rating, makes a beautiful sound and emits a unique smell when starting up - almost like gunsmoke. The bearings in it were built to last - with cutouts for eccentric rings which wick a continuous steam of oil for the journals to float on.

    img_20201108_122755627.jpg

    Touching on the matter of relief valves, is there a proper technique for testing them beyond bringing them up to pressure and seeing if they pop? I believe the one on this unit might be adjustable. It would be pointless to replace the tank without also ensuring the safety valve is correctly set.
    The valve should be replaced. Technically, the safety valves are supposed to be set by the manufacturer, safety wired and sealed. They are not to be field adjusted without proper re-certification.

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    Safety valves are cheap at the price. The usual type of safety valve used on smaller shop air receivers has a brass body, and a pull ring on the projecting stem of the safety valve. There should be an ASME (American Society of Mechanical Engineers) 'cloverleaf' stamp on the valve body with a letter in the middle of the cloverleaf. There will also be a 'set' or 'popping' pressure stamped on the body of the valve. Many of these types of safety valves from reputable manufacturers, built to ASME Code, will- as Ziggy note- have a safety wire and lead seal run through drilled holes in the valve body and base/nozzle. This is in place to show if anyone has tampered with the valve and possibly changed its setting.

    A safety valve for a shop sized air receiver (going up to perhaps 120 gallon capacity, but this is my guess on the matter) will take the form of a simple 'pop' type safety valve with a pull ring on top, and vent ports drilled thru the sides of the body. This type of valve is as simple as it gets. The more complex 'pop' type safety valves actually have two (2) settings; the 'set' pressure at which the valve opens, and a 'blowdown', which is a differential pressure. On larger pressure vessels, the differential or 'blow down' allows the safety valve to stay open for a set differential of pressure, so it closes at some pressure below the set pressure. This allows larger pressure vessels to discharge a sufficient quantity of pressurized air, or other gases so that the safety valve can close and seat. If the safety valve did not have this feature, the valve disc might well be chattering on its seat if the contained pressure were too close to the set point.

    I'd buy a new safety valve based on what is known as 'maximum allowable working pressure' or MAWP for the air receiver. If you are using an ASME code receiver, there will be a data plate on the side of the tank shell with this data. If you are using a non-code receiver, you are on your own to figure what a safe MAWP would be. This is where what I call "running the numbers" on a tank (or boiler) happens. Either way, ASME code receiver or not, if the receiver is a used ASME code tank, or you have a new non-code tank of unknown MAWP, you have to find out what working pressure that tank is good for. An inspection is made and if no physical damage or deformation is noted, then a UT of the tank of boiler is done. The thinnest reading in each part of the tank (such as the 'barrel' and 'end heads') is used in the calculations. Since you will not have mill test reports for the steel used in the tank, you have to assume the steel has a 'lowest average ultimate strength' of 50,000 psi. If you then take a minimum factor of safety = 4, this gives you a maximum allowable tensile stress in the steel of 12,500 psi. Personally, I use an FS =5 when I am running numbers on unknown old pressure vessels. This gives a maximum allowable tensile stress = 10,000 psi. Once you have gotten that far, you take measurements of the tank: diameter of the barrel, radius or curvature of the end heads. You then can use the formulas in the ASME pressure vessel code to calculate what MAWP the tank is good for based on 'as-built' dimensions and 'as-found' minimum thicknesses, and 'lowest average minimum tensile strength' and a FS of not less then 4.

    This will give you a MAWP that the tank can contain. At that point, you can then purchase a safety valve for the tank. On smaller air tanks, it is usually a matter of what size tapping is on the tank for the safety valve, with 1/4" NPT being the most common on smaller size air receivers. The 'Relieving capacity' of the safety valve is not something you get into when purchasing a smaller pop safety valve for a shop air receiver. On larger air receivers, it gets complicated as the 'relieving capacity' of the safety valve has to be calculated, then the valve manufacturer installs an orifice sized to give that flow in the safety valve body.

    Once you have your MAWP and safety valve, it then remains to set the pressure switch to cut the compressor in and out. This is where you leave a bit of a margin between the high/cut-out set point on the pressure switch and MAWP/safety valve setting. If the pressure switch is set too close to the setpoint on the safety valve, any inaccuracy in setting the pressure switch (such as going off the tank pressure gauge vs what the safety valve manufacturer used as a standard) could wind up with the safety valve popping anytime the compressor reached the high pressure setpoint on the pressure switch. Or, if the air within the receiver were at MAWP and became heated, this could take things past the popping point.

    My own recommendation is to buy two (2) safety valves. Put one on the shelf, install the other. Every year or two, change out the safety valve and toss the old one. Or, if you have had the safety valve pop off, it may not always reseat properly. Again, remove it and toss it. Install the one you had on the shelf and order a new one as a spare.

    I've lost count of how many pressure vessels I've 'run the numbers' on based on field inspection, as built measurements, and UT readings. Air receiver tanks are simple in design, so the calculations are not lengthy nor are they complex. Steam locomotive boilers, on the other hand, wind up with 100-120 pages of calculations based on 'as built dimensions', inspection and UT readings. Air receiver tanks built to ASME code may seem expensive when you first see the price on them. However, the fact the receiver was built to a known code and data on its manufacture and working pressure are recorded on the tank, aside from all else, is the equivalent of a life and property insurance policy.

    I've seen some hair-raising things done to pressure vessels by people who put not only themselves but the public at risk. In one instance, a farm stand had a 'cannon' for shooting pumpkins to amuse the public. This cannon proved 'ignorance is bliss' and also confirmed a belief in at least guardian angels, if not a Higher Power taking an active interest in it. The people who built the cannon used lengths of pipe for the barrel, and used two (2) large propane tanks (maybe 500 gallons apiece) mounted on the sides of the breech end of the barrel. They stabbed 6" pipe into the shells of the propane tanks and ringed the stab-ins with MIG welding. No reinforcement or 'compensation' provided for the holes cut in the tank shells (known as the 'barrels', not to be confused with gun or cannon barrels). The two tanks were manifolded with 6" pipe and a butterfly valve was used to discharge the stored compressed air into the cannon barrel, blasting the pumpkins out and across a field. A large portable air compressor (looked to be 600 cfm) was used to charge the two air receivers, so probably 120 psig compressed air was stored in the old propane tanks. No safety valves on the propane tanks, aside from all else.

    I saw this abortion of a pumpkin chucking cannon sitting on its trailer beside the farm stand when they were closed. I took a fast look and came away wondering why or how people could take the kind of chances they did with that pumpkin chucking cannon. If the people who built that cannon wanted to fire it off to chuck pumpkins and got blown to bits when the old propane tanks failed, that is their choice. However, to offer the pumpkin chucking cannon as an attraction to the public is quite another matter. Local authorities such as 'code enforcement' officers deal with buildings and related matters, so a pumpkin chucking cannon and horrific alterations to pressure vessels is way out of their purview. Unless the insurer of that farm stand happened to take a hard look at that pumpkin chucking cannon, it slid into a convenient crack, under the radar. I knew if I stuck my nose into the matter and told the people with that farm stand that they were playing with fire given how they had build that pumpkin cannon, I would get told to mind my own business and likely told: "It's worked fine up until now, and so-and-so who's a great welder built it..." I often wondered if I should not have done my duty as a PE and made them aware of the dangerous nature of their pumpkin cannon and the risk they were exposing the public to.

    As I said, there are guardian angels, a Higher Power, or whatever a person chooses to believe in. Counting on such beliefs to keep us safe with unknown air receivers could be called a 'leap of faith'. An air receiver of known construction and known condition, with a code safety valve of correct setting, operated within its MAWP is peace of mind and some very cheap life insurance.

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    What about cutting one end off and sliding a new smaller tank inside?...Phil

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    Here's the valve itself. It is stamped "American Steam Gauge and V. MFG. Co., Boston, USA. T7 775 150LBs"

    I had a suspicion that it was a steam relief valve just from the size of the exhaust ports on it but reading the name sort of gives it away. The top cap unscrews to reveal what I believe is an adjusting mechanism. The shell has a takedown screw on the side which allows the valve to be disassembled for cleaning. There is a large actuating pin in the middle which compresses a spring as it travels upwards towards the adjustment screw.

    I'll probably end up installing a new relief valve alongside this one since the new ones are so tiny they're easy to conceal. Plan 'A' and plan 'B', if you will.

    img_20201129_175654276.jpgimg_20201129_175432524.jpgimg_20201129_175415734.jpg

    As far as the tank, I'm going to reach out to Campbell Hausfeld some time and see if they'd be willing to special order me an AR8021 receiver tank sans the mounting feet. With any luck that will slide right into place plus or minus a little shimming. Bonus points if I can get it in black... because I've got some ideas on how I want to refinish the motor.

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    Sparky:

    The safety valve you have could have been made up for use with compressed air. That type of safety valve was quite commonly used for compressed air service as well as steam. American Steam Gauge & Valve made a wide range of products, not just limited to steam service. More modern safety valves of that same pattern are still made and used for compressed air service, just not so ornamented.

    My suspicions are that the safety valve you show in your post was way oversized for the air receiver on the Brunner compressor. The adjusting stem and nut looks to be chewed-up from someone putting a pipe wrench or similar on them, maybe to try to close the valve completely if it was not closing and seating properly.

    There are other manufacturers of air receiver tanks, built to ASME code. You may be able to find a receiver tank without the welded-on mounting feet. Applications in industry such as air=circuit breakers in powerplant switchyards, airbrake receivers on locomotives, and starting air receivers for smaller marine diesel engines all come to mind as applications where receivers are often mounted with U straps or similar. Campbell-Hausfeld used to build their compressors here in the USA, but, like so many other firms, has offshored most of their manufacturing to China. They may well be buying their receiver tanks from a tank manufacturer, and ordering them in large lots. I would be surprised if C-H did agree to sell you an air receiver without mounting feet.

    The modern air receiver tanks are built out of fairly thin metal, and assembled using automated welding (solid wire MIG) for the seam welds. The mounting feet are welded to the barrel (or cylindrical shell) of the receiver. The obvious question would be: "why can't I just remove the mounting feet myself ?". The answer is the welding done to tie the mounting feet to the receiver shell penetrated into the shell. The likely method would be to remove the mounting feet by cutting them off and leaving perhaps 1/8" of weld/mounting feet metal remaining. This would then have to be ground down carefully to the original profile of the receiver shell. Unfortunately, this would likely produce a wavy surface at best, and grinder gouges and thinner areas at worst. The engineering terms are 'stress risers' and 'discontinuities'. Think in terms of a soft aluminum beer or soda can. That is what is known as a thin-walled cylindrical shell. It does a fine job of holding internal pressure because it is cylindrical and has no discontinuities. A modern consumer-grade compressed air receiver is also a thin-walled cylindrical shell, with much the same behaviors as a soda can.

    An ASME code receiver will be built a bit heavier, and by code will have a few more threaded bushings welded into it (some being for internal inspection). I'd try hunting up an air receiver built without mounting feet that is of the same (or nearly so) dimensions as the original one. Food for thought: If you do find a receiver that differs slightly in diameter vs the original one, possibly the mounting feet can be modified (dressed to a slightly large radius, or shimmed with a 'wrapper' to make a smaller radius), and the U bolts re-shaped to fit the new receiver. A hammer, a good eye, and either an anvil or a piece of steel channel (used to 'shrink' the radius of the U bolts) can re-shape the U bolts.

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    (my understanding of pumpkin cannons is, the pressure in the receiver has to be pretty low - 20 or 30 psi at most. Otherwise it's a pumpkin puree machine.)

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    There are a LOT of Boiler Safety Valves on Ebay which are mis-represented. Many are air valves.

    A boiler safety valve by code HAS to have

    1. A manual lift lever
    2. Marked "Set Pressure" (frequently abbreviated SP)
    3. Marked "Blow down" (frequently abbreviated BD)
    4. And "Capacity" in lbs/hr. (frequently abbreviated CAP)

    Meanwhile, back at the error prone Ebay seller's ranch to whom ANY relief valve automatically becomes a "Boiler Safety Valve" or "Whistle."

    Air Relief valves usually are marked for...

    1. Set Pressure
    2. BD - but not always.
    3. Capacity marked in SCFM, or FPM.

    Notice the dimension units of this last. Air capacity is measured in units of VOLUME, not units of weight.

    Most safety valves seen out there since about 1910 ARE ASME valves. Some are still around from before.

    I have a 2-1/2 Safety Valve from a boiler as "ephemera" now painted up nicely which is a nice Crosby Steam Gauge production from before 1910. It is marked with "SET 125" - and "Mass Std" on the handle. And that's it. Massachusetts was among the first states to get REALLY SERIOUS about boiler code inspections and law. A valve marked as such in that day was almost universally understood to be a boiler safety valve.

    Massachusetts pre-dated the ASME, who built upon the Massachusetts example when ASME Boiler Codes were upgraded after the boiler explosion in Brockton, MA about 1905. Grover Shoe Factory disaster - Wikipedia



    In many ways, air tanks are MORE dangerous than steam boilers. Insidious, is the best way to describe them.

    A former professional engineer myself I had experience with circa 1941 air receiver tanks at Salem Harbor Station which were of riveted construction. Not to imply that riveted tanks are less safe than welded. Riveted tanks would be originally constructed considering "joint efficiency" - which yields a tank with about 40 percent extra thickness than a welded steel tank with joint efficiencies up to 100 percent, and a corrosion allowance of perhaps 15 percent on thickness. Riveted construction has in today's engineering consideration "excessive" margin for corrosion. It is VERY possible that an older riveted tank is MORE safe than a newer and more "engineered" welded steel tank.

    BUT - unless you determine positively if there is a localized "thin spot" - which on horizontal tanks comes from water in the air and occurs the length of the tank along the lowermost tangent as the tank sits - and in parallel with the tank shell longitudinal joint point of greatest stress - you can't know for sure. A sonic or magnetic thickness meter MIGHT be able to pick up a thin spot.

    It's sounding like this tank is ready for a rest...

    Joe in NH

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    While we are on this subject I would like to ask a question. I noticed that John Oder mentioned he was replacing his 35 year old unit. Is there a general rule of thumb for when a tank should be replaced? I purchased my Sanborn 80 gallon 2-stage unit around 1995. Just wondering at what point would be a good time to start shopping for a replacement. Definitely would prefer to be on the safe side of things.

    Jeff

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    With the cheap prices on fiber scopes nowadays, look inside for rust pits, and hydro, your tank might be just fine...Phil

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    Quote Originally Posted by jeff76 View Post
    While we are on this subject I would like to ask a question. I noticed that John Oder mentioned he was replacing his 35 year old unit. Is there a general rule of thumb for when a tank should be replaced? I purchased my Sanborn 80 gallon 2-stage unit around 1995. Just wondering at what point would be a good time to start shopping for a replacement. Definitely would prefer to be on the safe side of things.

    Jeff
    Generally there is not a "life" established for air tanks (or steam boilers.) In the case of Salem Harbor Station, the first air tank went in in 1941 which would make it 60 years old at the time of my departure from Salem.

    The tank at my first inspection was depressurized, and examined internally by "visual" methods - usually a strong light and peering in through the manway door. One could enter the tank up to one's waist and reach across to the other side (vertical tank) without a confined space entry permit (OSHA Rule) so long as one's feet remained on the grating (local interpretation of "enter.") There would commonly be some small loose flakes of rust in the bottom from who knows where above - but an established tank drain system (with local level gauge) maintained a relatively "water free tank." This was for "plant air" so the air was not "dried" or otherwise treated from Ingersoll Rand reciprocating compressors.

    The last time I did this, the examination (with concurrence of the insurance company) was done without entering the tank but simply using a calibrated magnetic thickness tester on the exterior. Again, as there was no "historic water line" in the tank, the examination was straightforward, general, and not confined to the lower reaches of the tank. Did I mention routine?

    And - that examination and the resultant supporting calculations yield a "snapshot in time" for that tank - and permission to run for another "standard interval" by the insurance company. Generally, if insurance companies will gamble their money against engineer's calculation, you can be sure it is a winning bet for the insurance.

    Engineering is "in your face." If the calculations show it will survive the gaff without question, then it is allowed to stand the gaff. This is what engineering does and why it exists. A lot of responsibility goes with engineering, not the least of which is the bridges don't fall down, the buildings don't collapse, and the boilers and air-tanks don't explode. Its why engineers "get the big bucks."

    Horselaugh.

    Those tanks are gone now, removed no doubt with the re-powering of Salem Harbor Station into "Footprint Power," which is a modern "turn the ignition key combined cycle natural gas fired" entity - driven much as your car is to include periodic ball joints, rotate the tires, and computer diagnosis. Kidding on that last but the principle certain exists.

    And - as stationary tanks of some size with some age go, are probably already at Toyota for reprocess into your next automobile. I expect they were removed in perfectly serviceable condition. They might even have been "recycled" into some industrial facility at the Pacific Rim - although even that is stretching credibility these days. The Pacific Rim is now as modern as we are - if not a bit more so - and probably wouldn't waste time trying to re-hab, re-insure, and re-use a now 80 year old tank.

    To answer your question more directly, I have one of the red "SEARS Craftsman" 5 hp air compressors outside my shop. Horizontal on wheels, it runs with little attention, and infrequent draining (I should do this more) and has been perking along since about 1995 when it came to me USED from a yard sale. It probably was from the mid 1980s.

    From elsewhere this is it...



    The red paint is now peeling from the outside, the compressor has been rebuilt once by me with new Torrington Needle Bearings, and will still pump up to 125psi without fail.

    As a welded tank it probably doesn't have a lot of "corrosion margin" being it is a setup which Sears sold CHEAP and often.

    Not owning a thickness tester, I have never examined it.

    I should probably retire it. I have a brand new "TWO STAGE" Harbor Freight setup sitting right next to it I haven't wired in - Italian Pump, USA ASME tank.

    Maybe today is the last day?

    Joe in NH


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