Page 30 - Improving Machinery Reliability

Kequirements Specification 3

tains nine data sheets that are to be filled in by the purchaser-usually a major con-
tracting or design firm acting on the owner’s behalf-to the extent necessary to
define the plant or process requirements. All remaining data must be provided by the
vendor. Five of these data sheets merit closer examination.
Our review of the API centrifugal compressor data sheets will be representative of
the structured approach recommended for all API-based machinery. It will be
restricted to those items having an impact on successful startup, operation, reliabili-
ty, and maintainability of centrifugal compressors.
On page 1 of the data sheets (Figure 1-l), we have drawn attention to the check
point “as built.” (The relevance of “as built” data is further highlighted in Figures 1 -
27 and 1-30.) Dimensional records are so important to turnaround maintenance,
emergency repairs, and general troubleshooting that submission of these data should
be made a contractual condition of sale.
011 the same page, we note the item “antisurge bypass.” We highlight this item
because proper and adequate surge-protection devices must be precisely specified in
a narrative supplement. Although surge control via sophisticated process computers
is possible, investigating commercially available, proven hardware devices is strong-
ly recommended. These devices can do a creditable job as stand-alone devices or as
analog emergency controls in case the digital process computer sampling rate,
response time, or application should prove inadequate. Additional details are given
in Chapter 2, “Applying and Reviewing Machinery Reliability Improvements
Derived from Modern Electronics.”
Data sheet page 2 (Figure 1-2) deals with, among other parameters, “other condi-
tions.” It would be prudent to give thought to a reasonable spectrum of alternative
operating conditions to define the safe operating windows for centrifugal compres-
sors from such points of view as performance curves, surge limits, efficiency, power
demand, polymer fouling, etc. If the vendor is asked to generate all applicable per-
formance predictions before issuance of a purchase order, the user will not suffer any
unexpected setbacks later, Moreover, up-front costs are generally only a fraction of
the cost of later analyses performed after the purchase order has been issued or the
machine has been delivered.
Data sheet page 2 also points to the item “mezzanine.” Mezzanine installations are
largely motivated by the desire to use downward-oriented compressor nozzles only.
This greatly facilitates compressor maintenance, since it permits horizontally split
compressor top casing halves to be lifted without disturbing the piping.
The item “acoustic housing” is of interest for other reasons. Intended primarily for
rotary-screw and high-speed centrifugal compressors, acoustic housings are general-
ly constructed to direct the sound upward. Unfortunately, the reduction in noise pol-
lution is often outweighed by such factors as decreased operator surveillance and
housekeeping problems resulting from a reluctance to get near the “screamer,” let
alone get inside the enclosure. Alternative solutions are often available and should
be explored.