Maintenance Technology April 2017 - 36

FIG. 3: SURGE-VESSEL PRESSURE
AT BOOSTER PUMP

FIG. 4: SURGE-VESSEL PRESSURE
AT HIGH-PRESSURE PUMP

Pressure (psi)

OIL
&
GAS
processing

Time (sec.)

Figure 3 shows the pressure inside of a surge vessel at
the booster pump.
ment are necessary to solve the problem. However, what does the
facility do when the plant is pumping in series?

CASE IN POINT
A large oil-industry customer, involved with a chemical-process
application, was looking for a way to protect their pumping system
infrastructure from damage and repair expenses, along with reducing lost product costs from the breaks.
For their application, a booster pump (which requires a minimum of 100 psi NPSH (net-positive suction head) is located approximately 10,000 ft. from a high-pressure injection pump. When power
is lost at the booster pump's location, with the high-pressure pump
operating, a transient negative-pressure wave is generated.
This wave causes a sudden pressure drop at the booster
pump's discharge side and travels at approximately 4,000 ft./sec.,
making contact with the high-pressure pump. In this situation, it's
important to protect the high-pressure pump from cavitation damage and maintain a minimum 100 psi NPSH on the booster pump.

MONITORING AND PROTECTING
Should the high-pressure pump trip when the booster pump is
running, a high-pressure "up surge" transient pressure wave will be
created at the inlet ﬂange of the high-pressure pump. High pressure
can also bypass teh check valve and cause additional damage.
A properly sized surge vessel, with the sizing calculated
through the use of computer surge-analysis software at the highpressure pump, will accept energy from the pump trip. It will also
be able to accept energy (compress vessel gas volume) on a highpressure pump trip.
On the high-pressure pump trip, the ﬂow will stop, based on the
system demand, and will pump dynamic head. However, there is a
concern of reversal of ﬂow back through the high-pressure pump
from the up-surge transient wave due to check-valve closing time.
A properly sized surge vessel will accept the transient energy,
but check-valve closing time will vary, based on factors such as

36 |

RELIABLE PUMPING SUPPLEMENT

Time (sec.)

Figure 4 shows the pressure inside of a 106-ft3 surge
vessel at a high-pressure pump.
type of valve and pipe size. With the speciﬁc closing time a critical factor to the accuracy of the results from the computer surge
analysis, this must be properly entered into the analysis. The results
of the analysis can be veriﬁed at the time of commissioning using
a report from a transient pressure-monitoring system, with the data
being read and recorded at a minimum of 100 times/sec.
When evaluating how to size a surge vessel to deliver energy,
or to keep the high-pressure pump's NPSH correct in time to
de-energize, further computer surge analysis is needed. In this
example, the graph in Fig. 2 (p. 35) shows the booster pump tripped
(pressure shown in green) while the high-pressure-pump suction
pressure is shown in red. In monitoring the liquid level and pressure
in the high-pressure pump's suction-stabilizer surge vessel, the
high-pressure pump can be successfully de-energized in 15 sec.
The pressure drop to the high-pressure pump's minimum
NPSH will keep the pump protected. Figures 3 and 4 (above)
show the change in pressure inside the surge vessel placed at the
booster pump and at the high-pressure pump.
By making use of computer surge analysis to correctly assess
the conditions with the booster and high-pressure pump conditions, the customer was able to understand how properly sized and
placed surge vessels can assure optimize operational performance
by conﬁrming proof of design with transient monitoring of pressure
and ﬂow.
With the surge vessels properly located, potential damage to
the pumps and piping network from hydraulic shock was eliminated.
As a result, considerable time and equipment cost savings were
realized.RP
Frank Knowles Smith III is executive vice president of the Surge
Control team at Blacoh Fluid Controls Inc., Riverside, CA (blacoh.
com). He has three decades of academic, design, and application
experience. Steve Mungari is the business development manager
at Blacoh. He has more than 20 years of process-control experience in the areas of ﬂuid measurement and control technologies.

APRIL 2017

Table of Contents for the Digital Edition of Maintenance Technology April 2017