Page 48 - Improving Machinery Reliability

20 Improving Machinery Reliability

(texr contiititedfroni page 15)

2.12.3 (Addition)

Serial numbers shall also be cast-in or steel-stamped on the casing. The Pur-
chase Order number and yard number shall be included on the equipment name-
plates. Compressor nameplates shall include rated capacity and normal capacity.
Here is another example:

4.3.3 Impeller Overspeed Test
Each impeller shall be subjected to an overspeed test at not less than 115 per-
cent of maximum continuous speed for a minimum duration of 1 minute. Impeller
dimensions identified by the manufacturer as critical (such as bore, eye seal, and
outside diameter) shall be measured before and after each overspeed test. All such
measurements and the test speeds shall be recorded and submitted for the purchas-
er’s review following the test. Any permanent deformation of the bore or other
critical dimension outside drawing tolerances might be cause for rejection.

4.3.3 (Substitution)

New impeller designs (without demonstrated operating experience) shall be
subjected to an over-speed test of at least 120%. . . etc.

After continuing to add to, delete from, or substitute for the various requirements
spelled out in API 617, the specifying engineer must further define such items or
design elements as instrumentation, valves, auxiliary piping, allowable sound inten-
sity, etc. Unless supplementary specifications for these items are entirely relevant to
centrifugal compressors, the specifying engineer should extract only those portions
that actually apply to the compressor manufacturer’s scope of supply. Again: the
specifying engineer should not resort to appending a series of general specifications
from which the compressor manufacturer would have to pick an occasional applica-
ble clause.
Instead of developing the narrative specification document, some users assemble
many general plant standards or plant specifications into a thick folder which then
becomes the procurement specification for a centrifugal compressor. In other words,
a general specification describing winterizing of all machinery, and specifications on
“Flush Oil Injection for Rotating Machinery,” “Auxiliary Piping Fabrication and
Installation,” “Pressure Instruments,” “Grouting,” etc. are all handed to the equip-
ment vendor without first culling the relevant information from the extraneous, or
inapplicable, data. Leaving it to the equipment vendor to find relevant clauses hidden
in many separate documents puts a burden on the vendor’s personnel. Very often,
this approach creates bulky specification packages that cause the vendor to add
charges for potential oversights. In some cases vendors have refused to bid or have
taken blanket exception to the entire specification by stating that their bid covers
“Vendor’s Standard”-no more, no less. Although there may be occasions when