Hydrocarbon Processing - March 2021 - 69

Valves, Pumps and Turbomachinery
D3 is branched from the collector and
is routed to the compressor suction nozzles. In case D1 = D3, the risk of liquid
buildup in each leg should be checked by
a process engineer, and provision for collection of the liquid should be foreseen.
Y configuration. Another type of suction piping design is using a Y configuration (FIG. 3). This configuration can
be fabricated in the field or in a vendor's
shop. It is a type of miter design; however, it must have careful and precise dimensions, fit-up and welding.
This arrangement is most preferred by
engineering companies due to lower installation costs. However, the use of miter is sometimes prohibited in the client
piping material specifications or project
piping branch tables. In addition, this arrangement is applicable for flanges with a
maximum pressure rating of 300. Using a
Y configuration may cause unequal flow
distribution to the compressor inlet. If
one leg of the Y has less flow vs. the other
leg, then this may result in one section of
the compressor running near surge, while
the other section runs and operates near
the overload region.
When using this arrangement, the following is recommended:
* A proper upstream straight run
of pipe of 10D-12D should be
considered between the neck of the
Y connection at the inlet and the
weld point of the upstream elbow.
Otherwise, any disturbance in the
piping upstream of the Y will
cause the flow to shift to one leg
of the Y or the other side.
* Try to fabricate the Y in a
controlled shop with a high-quality
weld and dimensional inspection.
Any discontinuity (e.g., weld
penetration or pipe penetration)
in the internal surface of the Y-
especially at points A and C
(FIG. 3)-may cause flow
separation from the wall
and shift the gas flow toward
the other leg. The use of internal
coating in the suction piping
between the suction KO drum
and compressor is recommended
to be studied and decided.
* Piping legs from the drum/
collector or Y assembly to each
compressor inlet nozzle must
be identical to each other, with

FIG. 1. Double-suction arrangement. Source: Google images.

identical slope, elevation and
length. Each leg should create the
same resistance to the gas flow to
minimize the risk of gas switching
to the low-resistance leg/path.
* For a Y-type splitter assembly, the
large radius at the dividing point/
angle B is preferred. A mitered type
of Y joint with a sharp, pointed
dividing geometry could cause flow
separation and uneven distribution
of gas between the legs.
* Low gas velocity will ensure
equal flow distribution.
* Install the Y assembly close to
the compressor casing and
consider a straight pipe run
downstream of the Y assembly or
collector, based on the compressor
manufacturer's recommendation.
In this case, it is recommended to
ask the compressor manufacturer
to review the inlet piping.
Other considerations. Based on specific compressor requirements, it is recommended to study the following requirements:
* The strainer location close to the
Y splitter assembly or collector may
cause flow separation. A T-type
strainer is recommended here.
It is not recommended to use
a cone-type strainer for suction
sizes above 12 in. to minimize the
cost and risk of leakage from extra
flanges. The strainer should be
properly designed and braced to
minimize the risk of collapse and
to mitigate clogging.
* Check with the vendor to see if the
location of the compressor's surge
control sensors should be on both
legs close to the compressor or
upstream of the Y splitter assembly
or collector. Being upstream of the

D1
D2

FIG. 2. Collector or drum arrangement.

FIG. 3. Y-type splitter arrangement.
Source: Google images.

Y splitter assembly or collector
may cause an error, as there is
the possibility that one leg could
be overloaded, and that the other
leg could have less flow.
* Do not install instruments
(such as temperature gauges
or temperature transmitters)
downstream of the strainer.
This is a design mistake. It puts
the compressor at risk if
a thermowell is broken due to
the high-frequency acoustic
vibration and from carryover
of gas into the compressor.
* Consult with the compressor
manufacturer on the proper
Hydrocarbon Processing | MARCH 2021

Hydrocarbon Processing - March 2021

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