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API definition of string test for compressors

API definition of string test for compressors

(OP)
Hello,

I refer to is API617 - definition of "Complete unit test".
Is the term "complete unit" intended to mean that every equipment included in the purchase order shall be part of the complete unit test? In particular for variable speed motor driven compressors is it required to include the Job VSDS system in the test?
I would like to interpret this matter from the view point of API.

Thank you in advance for sharing

RE: API definition of string test for compressors

(OP)
no one to give a hint ?

RE: API definition of string test for compressors

I don't have a copy of 617, but if it's anything like 610, the quote for the unit test is "complete with all auxiliaries that make up the unit" and also "The
complete-unit test shall be performed in place of or in addition to separate tests of individual components specified by the purchaser."

That looks pretty much like the whole system including the job VSDS unit needs to be tested as a single item with all parts brought together in a single place prior to installation.

what is the precise quote in API 617??

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

RE: API definition of string test for compressors

(OP)
Hi LittleInch,

This is what API says in clause 4.3.3.2 of chapter 2:

"Complete Unit Test:
Such components as compressors, gears, drivers, and auxiliaries that make up a complete unit shall be tested together during the mechanical running test. A separate auxiliary test may be performed with the purchaser’s approval. The complete unit test may be performed in place of, or in addition to, separate tests of individual components as specified by the purchaser. When specified, torsional vibration measurements shall be made to verify the vendor’s analysis."

I had same understanding as yours ; the point is that use of job VSDS unit would not be helpful/usefull since this test is a mechanical running test ; the terms "complete unit" become then kind of misleading. What is your opinion?

Thanks

RE: API definition of string test for compressors

RotaryW,
API-617 would suggest that the OEM tests all auxilary equipment during the mechanical test of the compressor. the Fact is that this is rarely done. in the description of the test procedure which has been given to the customer, it is usually described what equipment is and what isn't tested during the compressor test. generally, the oil system is not tested during this test, the seal system often is not tested during the compressor test, many times, the main oil pump is not tested during the compressor test.

those items are tested separately and will contain test procedures for those systems. the customer can object to that and require that the OEM tests some of the auxilary equipment during the compressor test, but since it is not standard, there will be additional charges and delays in schedule to do so. for some equipment, it maybe nearly impossible to test during the compressor test. such as the drive motor. i say nearly, because everything can be done, it is just expensive.

The description of string test is used generally to describe testing the entire compressor package and all of the aux equipment. drivers, pumps, oil systems, seal systems etc are all tested together. this is expensive, time consuming but doable if the customer is willing to pay for it. It is not normal for any OEM to do a string test.

the performance test description is usually provided as part of the compressor quotation. up front, the customer knows what type of test is going to be performed and what auxilaries are going to be tested separately from the compressor test. at the time of negoitating the contract, the customer can ask for more testing and the price and delivery will be changed to reflect this request.

John

RE: API definition of string test for compressors

(OP)
Quote
The description of string test is used generally to describe testing the entire compressor package and all of the aux equipment. drivers, pumps, oil systems, seal systems etc are all tested together. this is expensive, time consuming but doable if the customer is willing to pay for it. It is not normal for any OEM to do a string test.
Unquote

Fist remark on this is : does this mean to include also the converter, transformer for instance when a variable speed drive system is involved ? Assuming the customer is willing to pay for it. The point is that - to my opinion - these particular items do not bring any benefit when the unit is supposed to undergo a mechanical test. API terms "complete unit" is something misleading.

Second remark, there is no common definition with regard to the load. Is a string test meant to be at full load, partial load or no load. At the end I get the impression that the term "string" test means everything and nothing.

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