Technical Availability Compressor

[eltjo]

Hi All,

I have a relative small question, but I can't find the answer!

We are going to install a compressor (No vendor selected yet) which will have a various demand and will go off line every night.

In the contract we have is a statement that we must meet a technical availability of 99% for a 5 years average. Since this is for the whole system it seems a bit high to me.

What will be the technical availability for such a compressor?

Regards,

Eltjo de Waard (From Holland)

 

[zdas04]

"Availability" is one of those terms that is often tossed around in compression contracts and its only meaning is contained within the contract. Adding qualifiers like "mechanical" or "technical" only makes it more confusing. If the contract does not explicitly define the term then most likely it will not be an enforceable condition because there is no universal standard for availability.

For example, let's say that one morning the compressor fails to start automatically at 3:00 am, but no one knows it until 7:00 am when workers arrive. You call the service company at 7:15 am and they arrive at 9:30 am and spend 5 minutes diagnosing and fixing the problem and the system is restarted, but takes 3 hours to come fully up to pressure. Was the system "technically unavailable from 3:00 am until 9:35 am? 3:00 am to 12:35 pm? 7:00 am to 9:35 am? 7:15 am to 9:35 am? 7:15 am to 12:35 am? 9:30 am to 9:35 am? I've seen contracts that would have made any one of these possibilities the actual "technically unavailable" time for the calculation purposes. If your contract doesn't define the term, then the compressor supplier will claim that the machine was only unavailable from the time they could be reasonably expected to arrive after a call until the compressor is running (i.e., 9:30 am to 9:35 am) and the 99% availability is pretty easy to achieve--arbitrators or courts of law will often side with them. On the other hand you would contend that it was "system technical availability" and the time was 3:00 am to 12:35 pm and the 99% would be very difficult to achieve.

If this term is important to you then the contract has to be precisely explicit in defining it.

David Simpson, PE
MuleShoe Engineering

http://www.muleshoe-eng.com

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

"Everyone is entitled to their own opinion, but not their own facts" Patrick Moynihan

 

[eltjo]

@zdas04,
I know the term availability in the contract is for the whole system. Therefore I am looking for typical values for the availability for compressors. If a typical value is lower I know I need to do something. (Two compressors for instance, redundancy)

 

[zdas04]

As I tried to say above, that is a matter for contracts to be explicit on. I have seen contracts with 99% availability, but the definition very much favors the compression provider (i.e., unavailability starts after notification and after a "reasonable" travel time and ends when the compressor is at speed).

The ones that are around 90% very much favor the compression user (e.g., unavailability starts when the machine goes down and ends when the system is returned to steady state). All of the contracts that I've seen like this have paid a significant premium for numbers higher than about 90%.

Contractual values between 90% and 99.5% abound in industry and every contract will have a specific number based on negotiation, not physical parameters or industry standards

David

 

[BigInch]

Can't give a typical number on such limited information, because reliability is heavily dependent on the type of compressor, service conditions, level of preventive maintenance program, the driver type and fuel/electrical supply availability and other subsequential information, such as, if a backup generator is available during normal electrical power supply blackouts, etc. Utility electric power reliability runs around 99.5% in most areas, so you'll be less than 99% as soon as you consider the availability of the motor that drives the compressor, never mind the compressor itself.

99% is pretty high and I'd guess that you're probably looking at having about 3 of every major component that can possibly break down, if 100% of some given flowrate is required to be meet during that 99% of the time. For example, if you only have to make 80% of a given flowrate for that 99% of the time, redundancy requirements would be lower.



"If stupidity got us into this mess, then why can't it get us out?" - Will Rogers (1879-1935) ***************

http://virtualpipeline.spaces.live.com/

 

[BillBirch]

Five years sounds very high in the context that such standards as API generally only require bearing lives of only three years based on typical refinery / process plant turnaround cycles. You will not want your 1% margin consumed by scheduled outages.

Eltjo, it sounds like your client is trying to get a free compressor to increase the redundancy that you alluded.

 

[Artisi]

Ask those who wrote the spec to explain - that's if they are able to give you a qualified answer - maybe it was included because it sounds good .

 

[eltjo]

Here a little update:

For what I now know, they made a calculation for the availability.

The background info of the project; the transportation of CO2 to greenhouses. In the night there is no consumption because there is no light and in the winter there is less consumption because the sun strength is less.

But the catch is that in the contract there is no link to that calculation. It only says the technical availability must be 99% for the whole consumption rate.

In other words (that's my opinion, please confirm) the availability for our calculation must include night consumption en full winter consumption even though there will be no consumption.

 

[BigInch]

Must be growing some very very high value plants in those greenhouses. It seems like they would also justify the installation of lights to provide 24/7 and wintertime growth support.

"If stupidity got us into this mess, then why can't it get us out?" - Will Rogers (1879-1935) ***************

http://virtualpipeline.spaces.live.com/

 

[mbt22]

Tomatoes in Norfolk are often grown in a CO2 enriched atmosphere, using the offgas from sugar factories (limestone roasting to calcium oxide and CO2, I believe).

99% does sound rather high for such an application. As everyone says, ask the writer of the spec, quote to it, and add a quote for something more realistic!

 

[Artisi]

Could be growing "happy weed" now that's a high value crop.