Compressor safety

[Peter Naulls]

Thank you for the many helpful replies. Of course I should have thought about getting it tested; I'll make enquiries. I have a friend who was a live steam engineer before retirement so he should have a contact or two.

My thinking is that it is quiet enough to stay outside (under cover) without disturbing the neighbours. Incidentally the large compressor I now have at work is supposed to be quiet compared to other makes but it would still be too noisy for a residential area in my opinion, even rubber-mounted and indoors.

[dickie65]

Our company insurance assessor takes the bung out of our portable compressors to check for rust in the receiver when he does the inspections.
Common sense is needed, The set up in your picture looks in reasonable condition.
At lot of modern pushbikes have 60 PSI in the tyres and you are looking at about double that.

We regularly test stuff at silly pressure at work up to 40 BAR !! using water.
Think Hatches and connectors for underwater vehicles.

[Denis Sweeney]

A true story. Just before I started my life long career in the design and construction of pressure vessels the company had a major failure of an ammonia converter on test for a new Ammonia plant for ICI.
The vessel was 66” diameter and 6” thick and was in the process of being hydrostatically pressure tested to a test pressure of 7000 psi. This pressure was never reached as the vessel catastrophically failed at only half the test pressure.
Whilst hydro testing was and still is less of an issue than air testing, a 2 tonne piece of steel flew some 46 meters through a wall and parked itself neatly alongside a mini in the car park.
The company allowed the Welding Institute to carry out extensive testing and so much was learned from this incident.
Miraculously no one injured

[Peter Naulls]

Rather worrying that it was (presumably) a new piece of equipment. A bit of a hitch in the design process for it to fail that early?

[Parazine]

Saw a picture of one on the internet which had split open but my opinion for what it’s worth it’s likely to pin hole with rust first. More chance it would be at the bottom where the water sits when not used.

My old compressor (an Italian SIP, direct drive 3hp) failed this summer in exactly the manner quoted above. I noted water on the garage floor some months before, co-incident with the tank no longer holding pressure. The air leak became worse and eventually the tank went "Phut" one day, as I was starting up. Examination showed that the bottom of the tank was extensively pin holed through and the "Phut" noise was a 1p sized piece of steel, bending out.

No drama, no explosion, no insurance claims, just a new compressor needed.

[Denis Sweeney]

Peter, the failure was due to a number of issues, all associated with the manufacture and testing.
The equipment was pushing the boundaries of known technology of that time, nearly 60 years ago.
The failure initiated in two separate locations at weld defects in the circumferential weld seam between the end closure forging and the shell. Whilst all known NDT was applied, this did not pick up these defects.
The pre heat applied before welding and the local post weld heating was insufficient which allowed the welds to cool too fast causing hydrogen cracking.
It was also found that the thermal sensors in the furnace used to carry out the final post weld heat treatment were inaccurate which lead to the heat treatment being ineffective.
Finally the test was carried out over the Christmas break when the shop would have had very few employees on site, but it was cold and the water temperature for the test would have been just a few degrees above freezing, which would increase the probability of brittle fracture and hence an instant catastrophic fracture.
The report says that the temperature of the test water was around 7 degrees but our engineer whom I worked for was told they broke the ice on the canal to fill the vessel!!
Google John Thompson Converter failure and see the photo.
Fortunately this was the only known failure we ever had, but so much was learned from this and instigated many new practises used in the industry to this day.
The failed sections were cut off and removed and new sections fabricated causing much delay but the vessel finally went into service and survived through to the plant being decommissioned.

[Peter Naulls]

Very interesting Dennis and yes, looking at the photo it is remarkable no-one was hurt. I note the emphasis on how much was learned from the failure - a principle which in many industries is being neglected in favour of "who was to blame", or worse still "who can cover their mistakes the quickest"; particularly prevalent in healthcare unfortunately. Now I'm going right off topic however.

Parazine, that's reassuring. glad to hear yours was such a non-event!

[dickie65]

Hi Dennis.
Our test pots are modular with no welds
The billet lid for the new one weighed 800 KG before machining and drilling for the clamping studs.
The base is similar in size with o ring sealed modular sections above it.
Our tests are carried out under GL inspection then certified.

I can not give details of what we test all I can say is its for underwater use.

If curious look at Msubs.com

[Dave Mann]

Thanks now I Know what happened to John Thompson boilers. We were taken over by NEI (Northern Engineering Industries) and our fabrication shop where we made 35 ton engine crankcases was closed with the work transferred to John Thompson. Unfortunately the two crankcases they made were scrap because of dimensional errors by not allowing for shrinkage during welding.    

[Ivor Hawkins]

One thing I can say about this forum is that it invariably contains interesting reading and this thread is no exception.

My interest was kindled by the fact that A) I have a large old compressor and B) during my working life, I was involved in NDT…what a shame those crankcases were scrap!