Small air compressors

[PVI7]

I maintain the pressure vessel inventory and inspection records for the vessels in our division. Recently we had an independent inspector from the state out. He rejected two small commercial air compressor tanks (4 gal and 6 gal) because the safety valve was rated above the working pressure and the vessels did not have a MAWP stamped anywhere on them. When we replaced the valves with ones that were rated at the working pressure they left the compressors unusable because when they cycled to the max pressure, the valves tripped. I called the manufacturer and they would verbally give me a test pressure over the phone but would not put that in writing.
Question 1) Are these commercial compressors without a declared MAWP ok to use with the manufacturer's supplied safety valve? 2)how do I convince our inspector?

Part 2 of this. We since purchased an 'ASME coded' air compressor to replace the other two. It came in with a UM symbol but no NB number. 3) Does it have to have an NB number?
It was manufactured in 2007 and right out of the box is up for its 3 year inspection requirement. 4 What is going on with this?
All these items are coming from China through reputable distributes.

 

[jte]

Question 1) Depends on the rules of the jurisdiction in which the vessels are installed. Sounds as though they are not.

2) You probably don't. The manufacturer won't so much as put the test pressure in writing but you feel perfectly comfortable that people you know will not be hurt or killed by this stuff?

3) It depends on the rules of the jurisdiction in which the vessels are installed.

4) It depends on the rules of the jurisdiction in which the vessels are installed. (sound familiar?) Don't forget - corrosion never sleeps. Just 'cause you were not using the equipment doesn't mean it was stored properly and suffered no corrosion during storage.

The rules of ASME VIII will require pressure relief devices or system design (not available in 2007 except via CC). A non-code vessel is not governed by ASME and thus you are free to do whatever the jurisdiction will allow you. However, as an engineer, you have some moral obligations to keep people safe regardless of what the legal possibilities are. Section VIII does not require NB registration. That is an owner/user and/or jurisdictional issue. Some jurisdictions may treat UM vessels differently in this regard.

All these items are coming from China through reputable distributes.

[ROFL][ROFL][ROFL]



No, wait... I mean... "My condolences and good luck with that!"

jt

 

[PVI7]

Thanks jte, I was afraid of that. Clear as mud!
I'm just trying to get a handle on this issue. Why is it ok for Home Depot, Grainger, McMaster Carr and others to sell these items to the general U.S. public but we can't get them approved by our State inspector? I think I am missing some information or something.

 

[jte]

Keep in mind that the US public is one thing... An employer has an entirely different responsibility to safeguard his employees - in the USA, OSHA and state agencies do what they can in that regard.

As one colleague pointed out to me once, when she does her white laundry, she gets a bottle of bleach and pours some into the washer and starts the run. If she were at work, she'd have to don goggles, perhaps a face shield, perhaps a respirator, chem resistant gloves, and be sure she had a written work proceudure prior to handling this caustic chemical. Same stuff. Different rules. I won't get into the merits of why the differences exist - don't think we'd get anywhere with that!

jt

 

[GenB]

the frst tanks were not ASME stamped and were illegal to use
at ress >15 psig
small tanks stamped UM stamped? Most Jurisdictions will allow them. it does not have to be registered with the NB

 

[PVI7]

Thank you jt and GenB for your support and quick responses. I live the reality of the workplace safety on a daily basis. I need to reach out some times to check if we are on track with the rest of you in the U.S. or not.

 

[unclesyd]

We got caught in a similar situation only it was by our insurance carrier instead of the government. We had 8; 100 gal air compressor storage tanks with integrally mounted compressors all duly stamped with all the required information and certification. Along came John, actual name, and told us we had to uncouple the compressor which
was neatly mounted on the tank with a welded support. We dismounted the compressors and support plates and checked the heads where we ground off the welds. We had checked 7 of the tanks and found no cracking, but, on the last one every weld had a crack mostly shallow but one was through wall and had been leaking, very small, for some time. We replaced this tank.
Even though these tanks all had formal approval from everyone, the insurance carrier had exposure to two fatalities from similar exploding air compressor tanks. The site now has no directly mounted compressors on any tanks. We have never allowed anything storage tanks of less than 30 gallons on site and if the compressor is mounted on the tank it has to go.

I can discuss war stories about using chemicals on site as I was considered the go to person on chemical cleaning and had a lab to check out same. i actually had to fight to use everything, the aforementioned bleach, baking soda used for blasting, any type of detergent and so on. The biggest battle was fought over laboratory reagents that stamped with an arbitrary expiration date like 18 months on NaCl. My argument that this material was already 60 million years old fell on deaf ears.

 

[moltenmetal]

OK, let's try to separate the political issues from the stuff with a real safety impact, if we can.

A vessel whose sole relief valve or rupture disc is set above the vessel's stamped MAWP is not properly protected- it is UNSAFE. Reset the relief valve to the MAWP or below because it's the right thing to do. If it's an air compressor and it keeps cycling and popping the valve, then you ALSO need to re-set the pressure switch which starts and stops the compressor motor. If the lower pressure is outside the switch's range, you need to replace the switch. If the required pressure is too close to the relief setpoint to permit this, buy a unit which will do the higher pressure safely. None of this is political- it's just commonsense.

If a packaged unit has no MAWP stamped on the vessel, but has a pressure switch and relief valve which are factory installed, working and have not been tampered with, you have a device which either was not legal for sale in your jurisdiction OR is so small that, right or wrong, the local authorities don't consider it to be a major hazard. The manufacturer assumes liability for failures arising from bad manufacturing or design, but in this case the liability is probably limited to some importer- the Chinese manufacturer thereof will get off free if and when it blows up. For that sort of device you could arbitrarily change the relief valve and pressure switch setting to a lower value to mitigate the risk, if that didn't render the devices useless.

As to what size you're permitted in each jurisdiction to use a non-code tank, and at what size you must use an ASME UM-stamped tank, that's a matter I'll leave to someone knowledgeable in your jurisdiction.