Hydrocarbon Processing - October 2021 - 82

Valves, Pumps and Turbomachinery
tion. There is a noticeable temperature difference between the
pump discharge piping and the recycle line piping. In addition,
there is no appreciable temperature differential across the recycle
valve. These conditions are clear indications that this recycle
valve is not passing.
The main advantage of this technique is the minimal investment
cost to perform the surveys and detect passing valve conditions.
The main disadvantage of this technique is that it will only
identify a passing condition but will not provide the severity of
the condition by quantifying the leakage rate.
AE or ultrasound measurements. These technologies have
become more prevalent, and are cost-effective solutions for
valve leak detection. The main advantage of these technologies
is the ability to detect leakage when differential temperature
and other methods are not feasible. The main disadvantages
of these methods are the higher initial costs and that they are
limited to detecting passing conditions without quantifying the
leakage rates. Some technologies claim to provide an estimation
of the leakage rate or, at a minimum, a relative assessment of the
leakage severity for maintenance planning.
Portable ultrasonic flow measurement. A portable ultraFIG.
1. Thermal image indicating tight shutoff.
sonic flow device can be utilized to both identify and quantify
recycle valve passing conditions. The initial survey using other
techniques previously mentioned can be implemented and then
followed up with ultrasonic flow measurements to quantify the
leakage rate. FIG. 2 shows a portable ultrasonic flow cell established
on a pump recycle line to both detect and quantify the
leakage. The main advantages of the portable ultrasonic flow
meter are that the leak can be detected and quantified with one
measurement. The main disadvantages of this method are the
higher initial cost, along with the requirement for training.
Energy savings potential. Regardless of the method used
to detect a recycle valve passing condition, it is always advantageous
to also quantify the leakage rate to:
* Calculate the potential energy savings and payback
analysis for overhauling the passing recycle valve
* Determine the relative severity of the leakage
rate for effective maintenance planning efforts-
bigger leakers get overhauled first.
There have been many documented cases of recycle valve passing
conditions on various high-energy pumps, especially in applications
where there is frequent on/off cycling and where there is
a high percentage of total suspended solids (TSS). FIG. 3 shows a
graphical representation of the energy lost to an open bypass.
Based on the current cost of power and load factor (operating
FIG. 2. Ultrasonic flow cell quantifying leakage rate.
100
120
140
160
180
200
20
40
60
80
50
100
Flow, gpm
FIG. 3. Fluid energy lost to bypass flow.
82 OCTOBER 2021 | HydrocarbonProcessing.com
FIG. 4. P&ID of a seawater shipping pump, showing the recycle line
takeoff downstream of the flow meter.
150
200
250
hr/yr), energy savings are readily calculated. Other benefits and
cost savings could also be realized, considering the maintenance
costs from the erosion of the valve seats due to prolonged high
velocities and the possible cavitation experienced by the valve.
Original system
curve
System curve with
open bypass line
Fluid energy lost to bypass
CASE EXAMPLE OF RECYCLE VALVE
ENERGY SAVINGS
Seawater shipping pumps. This case study involved a total
of 12 seawater shipping pumps that are horizontal, singlestage,
radially split between the bearing design, and rated for
Actual flow
Required flow
Head, ft
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