Piston compressor in flammable service

[iainuts]

For a reciprocating gas compressor in flammable service, if a compressor manufacturer allowed piston ring blowby (leakage) to escape to atmosphere locally, would you consider this:
1) dumb thing to do
2) negligent
3) criminally negligent

This case is not in courts nor is it likely to be so and nobody was injured nor was there a fire. Basically, when the piston rings leaked, the gas leakage went straight out to atmosphere and into a room where the machine was located. This was a 40 hp, high pressure machine.

 

[zdas04]

4) Normal

David Simpson, PE
MuleShoe Engineering

Law is the common force organized to act as an obstacle of injustice Frédéric Bastiat

 

[Compositepro]

And dealing with the issue is the user's responsibility and not the the manufacturer's.
A similar situation is the vent on pressure regulators for propane or natural gas service.

 

[iainuts]

Thanks for the responces. I'm well aware of the hazards around self venting regulators, but the difference there is that regulators you purchase 'off the shelf' are not offered for a specific service. Those that are have features suitable for the service such as captured vents for flammable service.

I'm finding it hard to believe that this would be normal in some industries. Which ones? And how is the hazard mitigated?

Rings and packings normally leak and when they wear out, they leak much more so. Over the course of their lifetime, they could catastrophically fail (ie: blow out). My experience has been that compressors are designed for flammable service with this in mind. Why wouldn't any manufacturer offering a compressor, knowing it will go into flammable service, provide it with a captured vent for seal leakage?

 

[zdas04]

The lion's share of reciprocating compressors in flammable service (millions of horsepower) is double acting so piston ring leakage just takes the gas into the other cylinder.

On the other hand rod packing leakage goes into a distance piece. There are a few machines that vent the distance piece into the the crank case where engine vacuum sucks them into combustion. This only works with naturally aspirated engines so the majority of natural-gas fired compressors (which tend to be turbo charged on larger hp) and all electric drives don't have this option. Mostly the distance pieces are vented locally.

Your list of possible answers shows an amazing lack of understanding and overwhelming disdain for this field of operations.

David Simpson, PE
MuleShoe Engineering

Law is the common force organized to act as an obstacle of injustice Frédéric Bastiat

 

[rotw]

To the OP :

as far as I understand from Zdas, is it an option for you to put a recovery system for the vented gas ? Just thinking loud...
I was thinking about something like the seal gas recovery systems used for centrifugal compressors to recover primary vent leakages (sometimes due to emission limitations imposed by local regulation ..).

"If you want to acquire a knowledge or skill, read a book and practice the skill".

 

[iainuts]

Hi zdas. your comment, "an amazing lack of understanding and overwhelming disdain for this field of operations." is rude and arrogant. Let's not go there. The OP specifically states where piston ring leakge goes directly to atmosphere locally, but you are mentioning double acting pistons where the ring blowby is captured and not vented to atmosphere. You've misunderstood the OP.

I've designed reciprocating compression equipment for 18 years, including hydrogen machinery. Our equipment and all of our competitors that I'm aware of have a captured distance piece. Those distance pieces are enclosed and the gas vented to a safe location. If you didn't do that, the area would go from Class 1, Div 2 to a Class 1, Div 1 area.

 

[rotw]

"And dealing with the issue is the user's responsibility and not the the manufacturer's"

agree with Compositepro.

"If you want to acquire a knowledge or skill, read a book and practice the skill".

 

[iainuts]

Hi rotw. In fact, when we discovered the mistake, we had the compressor manfucturer provide an enclosed distance piece so we could take the flammable gas to a vent stack. We had other precautions on this system such as a flammable gas monitor in the area to detect that atmosphere which safely shut down the system when the piston ring failure occured. Our customer (an oil major) was livid, to be kind.

I would have thought enclosed distance pieces were standard in the oil and gas industry. Perhaps that's my mistake as I work in the industrial gas industry.

 

[iainuts]

PS: If my list in the OP has offended anyone, please accept my sincere appologies. That wasn't intended. I would have thought venting flammable gas at the distance piece was a cardinal sin, but if that is not the case, please feel free to provide your experience.

 

[moltenmetal]

I'm puzzled by this, and I apologize if I'm missing something which is obvious.

I've seen people try to use compressors intended for use with air or other nonhazardous gases for low-pressure flammable gas services. Doing so in ignorance is dangerous, obviously, and with some machines it is totally unsafe and cannot be made safe- machines which are intended to draw their suction directly from the atmosphere which do not have a properly contained suction as an example. Since there's air in the crank case, as well as potentially hot parts, it's a recipie for a fire. It's possible to make some machines intended primarily for air service, tolerably safe with flammable feeds for some applications, by inerting (sweep purging) and venting the crankcase, since this is where any ring blow-by is going in such machines.

I'm not sure how the machine you're describing, without distance piece, is venting its ring blow-by "locally". Does it not have a rod seal at all? Or a totally open distance piece which cannot be vented to a safe location?

 

[iainuts]

Hi moltenmetal. Perhaps this sounds bizarre to you. It does to me. The manufacturer of this particular compressor did not provide any rod seals or other packings so as to contain the piston ring leakage. In fact, it had an open distance piece so gas could not even get into the crankcase. It was a simple, piston in a cylinder with rings on the piston type compressor (multi-stage) with a distance piece that was open to atmosphere. Flammable gas went directly out the distance piece when the rings leaked. It ran for a few dozen hours before enough gas built up and a flammable gas detector in the room detected it and shut the system down. I don't want to go into how this oversight was missed by the engineering team who purchased and installed the machine, the question regards culpability of the compressor manufacturer.

I personally think this is more than just a stupid thing to do, I'd say it is negligent and potentially criminally negligent. I guess I'm curious to see if there's anyone out here that would agree or are my views too extreme here? I'm sure it won't go to court, but I'd be interested in hearing from engineers who understand the issue and can offer an opinion on the responsibility of the compressor manufacturer.

Note that this machine was built from a standard product line, the manufacturer had full knowledge of the gas being compressed and had even documented this in their owners manual for the machine. The manual has the serial number of this compressor on the front page. Also, discharge pressure on this machine was well in excess of 1000 psi.

 

[dcasto]

Caveat emptor

The owner operator has the responsibility to assure the safety of the equipment.

It's a terrible thing when the buyer is not equipped to understand the consequences of failures. Why did you not explore what happens if the rings failed? That's a standard assumption to explore.

 

[iainuts]

Hi dcasto. I wasn't on the engineering team that purchased this equipment, I was only asked to review the incident and make some recommendations. I won't go into it in much detail.

I agree the owner has responsibility for equipment, but when it comes to something like this, I would say the manufacturer has at least some blame. They should know better.

I also design rotating equipment. Part of that requires that we look at the potential of the rotor failing and parts/shrapnel penetrating the housing which could be fatal to anyone nearby. There's no law and I don't know of any industry standard that covers this, but manufacturers of rotating equipment have to take safety into account even if there isn't a standard which specifies it. There was an incident where exactly this happened. A large chunk of steel penetrated a 3/4" thick steel housing, flew across the factory floor and lodged into a cement wall. No one was injured but the manufacturer of that equipment will be at least partly to blame if anyone had been injured.

Having a single acting, reciprocating compressor in flammable service without any method to safely exhaust piston ring blowby is even worse of a position in my opinion. In this case, you can be very sure that the rings will eventually fail and leak flammable gas into the area around the compressor, making the area a Class 1, Div 1 area.

Saying you are ignorant of a law doesn't mean you are not liable for it. There may not be a law or industry regulation/standard that requires a flammable gas compressor have a means to prevent process gas from leaking to atmosphere but I would similarly suggest that doesn't mean you are not liable for it.

 

[iainuts]

I was just thinking of a few other similar situations. I would think this is similar to what toy manufacturers must have to go through. There have been recalls on toys for example, where some child has been injured or died when an unexpected event occured with the toy. If a toy manufacturer for example, made a toy with buttons or pom-poms on it that were easily pulled off and swallowed by a baby and if that baby then were to choke on it and be injured or die, I believe jurys have often held the toy manufacturer liable. There may not be a law regarding buttons or pom-poms on toys but that won't prevent the toy manufacturer from being sued. Here's an example:

http://articles.baltimoresun.com/1993-06-08/news/1993159040_1_edward-cunningham-toy-maker-alexandra

Do we tell the parents of this child, "caveat emptor"?

Why should manufacturers of industry equipment be allowed to sell whatever they please and force buyers to take responsibility?

 

[Compositepro]

"Why should manufacturers of industry equipment be allowed to sell whatever they please and force buyers to take responsibility?"

Because, the economy of the world would grind to a halt. Lawyers would love for that to be the standard, and they have succeeded it making it so for consumer products. The main reason is because the vast majority of consumers are, in fact, ignorant, and need to be protected like children. Industry is inherently dangerous, and the danger can only be avoided by education and competence of the people involved. By law the competence is required to be on the user side because no manufacturer can protect users completely from their own ignorance. But it is not the case that manufacturers have no responsibility for the equipment they sell. They can be sued for negligence, but the case is much harder to prove than for consumers. Industrial users are required to be competent and cannot rely on equipment manufacturers to protect them from "obvious" dangers, particularly misapplication of equipment which is perfectly suited for other applications.

What do you mean by sharing the blame? So you can feel better? Or pay for the damage? As an engineer, do you really want to work in an environment where you are treated like a child who must be protected from his own ignorance. We have the best system for that now. Its peer review by experienced engineers. The government cannot do it any better.

Your concerns are not completely without merit. But in my opinion, the greatest danger to safety is not taking full responsibility for safety upon yourself.

 

[rotw]

Garbage in, garbage out. That's what you if you don't specify the equipment properly.
0
The first thing I would do (after ensuring the equipment is stopped and that no further harm or potential risk can be caused), is to check on the archive system and have in front of me the contract purchase specification of the equipment.
I will look carefully of what has been included in terms of area classification, specified codes and standards check the drawings which should have been mutually agreed between manufacturer and buyer.

Then I would have better insight of what went wrong if any. I would go further by saying that although you may find some non compliance to the purchase contract where the manufacturer is to blame, it remains -again- at least in the good practice and code of conduct of the buyer - if not his responsibility by law - to review or approve that the purchased equipment are conform to the specification of contract.

Otherwise this is just speculations, in my opinion.

"If you want to acquire a knowledge or skill, read a book and practice the skill".

 

[moltenmetal]

OK, now we're into a good question: when a machine is quoted for a service that it is not suitable for, who is responsible- the person who quoted it, or the one who bought it? That answer for this particular case depends on lots of information we're not party to, like the nature of the quotation and disclosure which occurred during the quote/specification process, what was asked for, what was quoted and whether they differed, how the service was identified etc. There's room for screw-ups on both sides of the buy/sell fence for sure.

It's rare in my experience to be offered something which is utterly unsafe for a particular duty, even when you try. Not impossible by any means, but rare. Manufacturers are usually afraid of liability and pound that fear into their sales staff. Unlike regulation, liability is a feedback process, letting the failures happen and compensating the victims afterward, but it does tend to feed back into the design and the sales offerings eventually. Of course if you don't disclose the application properly you aren't using the vendor's sales staff as a check against bad specification.

I don't have enough experience to know whether an open distance piece unit like that is ever used in outdoor locations for flammable gas compression- I just know that indoors or outdoors, we want a captured vent so we can direct the vented gas somewhere safe. If the gas is also toxic, we want a sweep purge on that distance piece as well, or sometimes two distance pieces with seals between them.