Flow eHandbook
PREEMPT
FLOW PROBLEMS
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TABLE OF CONTENTS Prevent Suction Piping Problems
4
Follow best practices when designing pump systems Create a Preventive Hose Maintenance Plan
9
Follow these five steps to determine the best replacement timeline Consider Portable Flow Instruments
15
Some circumstances warrant the use of such devices Additional Resources
18
AD INDEX ABB • www.abb.com
14
Krohne, Inc. • us.krohne.com/optimass1400
8
Swagelok • www.swagelok.com
3
Flow eHandbook: Preempt Flow Problems 2
PRESSURE
IS RUNNING YOUR PLANT
SHORT-HANDED.
An upturn in production. Urgent customer demands. Shrinking budgets. Today, you are expected to do more with less. And Swagelok is doing more to assist you. From custom fabrication and assembly, to product selection and vendor managed inventory, Swagelok’s extensive fluid systems expertise can help your plant – and your team – operate more efficiently. It’s just one more way we’re engineered to perform under pressure. Visit swagelok.com/support to download “Go-To Strategies for Maximizing the Efficiency of Your Plant’s Fluid Systems.” © 2018 Swagelok Company
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Prevent Suction Piping Problems Follow best practices when designing pump systems By Amin Almasi
P
iping issues can directly affect a
As a result, cavitation and other suction-re-
pump’s performance and life. Poorly
lated problems such as turbulence and air
designed suction piping can result
entrainment cripple pumping systems in
in pump damage and even failure. Quite
many applications. Root-cause analysis of
bluntly, there’s no excuse for substandard
pump failures often points to long suction
piping design.
piping systems as the culprit. The solution to avoiding future failures usually is rede-
Numerous guidelines and mandates in the
signing the suction piping to be as short,
technical literature, textbooks, manuals, codes,
simple and straight as possible.
specifications, etc., call for short and simple suction piping. Yet, some engineers and
You should consider pump location and
designers still treat such dictates only as pref-
suction piping at the layout stage. It’s
erences. They install pumps far from suction
simply wrong to fix the location of every
sources and design long and complex suction
vessel, drum or tank and leave pump
piping systems. I personally can attest that
locations for later. You also should antic-
many design teams don’t heed the guidelines
ipate the addition of small pumps in due
for suction piping. They offer excuses such as
course; for such cases, provide spare space
there’s no space near the suction vessel (tank
around vessels, tanks or other equipment
or drum) or it’s more convenient to install
to accommodate these pumps right at the
pumps near downstream equipment.
layout stage. In addition, make your best Flow eHandbook: Preempt Flow Problems 4
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efforts to place any pumps close to the suc-
operates, even temporarily, at the far-right
tion source.
side of rated point.
Always explore any possible option to
Cavitation can cause a wide range of dam-
install pumps closer (even if only by 1 m)
aging and disturbing effects such as suction
to the suction source. Pump textbooks and
pressure pulsations, erosion damage,
nearly all pump catalogues and manuals
increased vibration, noise, etc. Check the
clearly note that suction piping should be
margin for the worse possible operating
as short, simple and straight as possible.
cases, for instance, when the suction source
Unfortunately, some design teams opt for
is at its minimum head or liquid level, fric-
the easiest design rather than correct one
tion in suction piping is at its maximum, etc.
(as per guidelines). These guidelines may necessitate an
THE BASICS
increase in the suction piping size. For rela-
For any suction piping longer than a few
tively long and complex suction piping, it’s
meters, ensure that you provide enough
common to see suction piping up to four
net positive suction head (NPSH) margin,
sizes larger than the size of the pump’s suc-
i.e., NPSHA - NPSHR, for all potential oper-
tion nozzle; for instance, a 125-mm pump
ating points on the performance curve of
suction nozzle may require 250-mm suction
the pump from shutoff to near the end of
piping (for a relatively long run). If such a
the curve. An adequate margin particularly
size increase isn’t viable, consider installing
is needed at or near the end of the curve
a drum or small tank near the pump to act
where NPSHR is high and NPSHA is low
as the suction source for it.
(because of high flowrate). Connect the pump nozzle to an appropriDifferent guidelines offer various recom-
ate length of straight pipe, per the pump
mendations for margin, for instance, 1 m, 1.5
manufacturer’s guidelines. As a very rough
m or 2 m, depending on the criticality of the
indication, the minimum length of straight
application, pump details, suction energy,
pipe needed between an elbow (or any
sensitivity of pumps, potential damage due
major fitting) and the pump suction nozzle
to cavitation, etc. A good recommenda-
is 4–12 times the diameter of the suction
tion is a minimum NPSH margin of 2 m for
piping. For some high suction energy
the commonly used operating range (say,
pumps, this straight length should be up to
70–120% of the rated point) and a minimum
15 times the diameter; for commonly used
NPSH margin of 1 m for the end of the curve
small pumps, which usually are low suction
to prevent risk of cavitation when the pump
energy units, this required straight length is Flow eHandbook: Preempt Flow Problems 5
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Minimize the number of elbows in the proposed suction piping; numerous elbows might present swirl, disturbances and other damaging effects to suction flow and, consequently, to the pump.
somewhere between three and six times the diameter of suction piping.
TURBULENCE AND AIR ENTRAPMENT Sizing of suction piping isn’t the only area
The straight-run pipe gives a uniform veloc-
requiring attention. Also, seriously evaluate
ity across the suction pipe diameter at the
route, layout and configuration. Suction
pump inlet. Keeping the suction piping
flow disturbances, such as swirl, sudden
short ensures that pressure drop is as low
variations in velocity or imbalance in the
as possible; this directly affects the NPSH
distribution of velocities and pressures,
margin. These two factors are important for
can harm a pump and its performance
achieving optimal suction and trouble-free
and reliability. For any suction piping a bit
pump operation.
longer than usual or not straight and simple, ensure that adverse effects such as turbu-
For any suction piping not conforming to
lence, disturbances, air entrainment, etc.,
short and simple guidelines, check with the
won’t affect the pump set.
pump manufacturer. It’s common to ask the vendor to review suction piping and make
Minimize the number of elbows in the pro-
comments on the performance, functional-
posed suction piping; numerous elbows
ity, reliability and all guarantees of the pump
might present swirl, disturbances and other
with that suction piping. The bottom line is
damaging effects to suction flow and,
that the pump manufacturer should confirm
consequently, to the pump. Eliminate any
that the pump isn’t affected by that suction
elbow mounted close to the inlet nozzle of
piping. Remember that pump guarantees
pump. Especially avoid two elbows at right
often are limited to two or three years, so
angles because they can produce sustained
correct suction-piping design is a better way
damaging swirls. There have been cases
to ensure proper long-term performance.
where a swirl introduced by two elbows Flow eHandbook: Preempt Flow Problems 6
www.ChemicalProcessing.com
in the suction caused high vibration of the
Velocity in the suction piping should rise
pump and subsequent damage to it.
as the liquid moves to the suction nozzle of the pump; this speed increase usually
Another type of damaging flow pattern
comes from reducers. The suction piping
to a pump results from swirling liquid that
design should provide smooth transi-
has traversed several directions in various
tions when changing pipe sizes. Often,
planes; therefore, avoid complex suction
two or three reducers are used (usually
piping routes with multiple directional
back to back) to decrease a large size of
changes. Usually, the higher the suction
suction piping to the size of the pump’s
energy and specific speed of a pump, in
suction nozzle. Pumps should have an
addition to the lower the NPSH margin,
uninterrupted flow into the suction nozzle.
the more sensitive a pump is to suc-
Generally, install eccentric reducers with
tion conditions.
the flat side on top to avoid the potential of forming an air/gas pocket.
Also, eliminate the potential for air entrapment in the suction piping. One of the
Treat isolation valves, strainers and other
sources of air or gas entrainment is the
devices used on the suction side of a pump
suction tank or vessel. You must main-
with great care. Eliminate them if possible.
tain adequate levels in the suction source
I have seen many unnecessary isolation
(drum, vessel or tank) to keep vortices from
valves or permanent strainers on the
forming and causing air/gas entrapment. In
suction of pumps; these cause more harm
addition, ensure there’s no air/gas pocket.
than good. If you absolutely require a valve,
Particularly avoid high pockets in suction
strainer, etc., size and locate any necessary
piping; these can trap air or gas. Suction
device to minimize disturbances of the
flanges or any connection with potential
suction flow. Install these flow-disturbing
leaks can be a source of air entrainment;
items relatively far from the pump to let the
so, minimize the use of flanged connections
provided straight length of piping smooth
and eschew threaded ones. Check that all
and normalize the liquid’s flow pattern.
piping and fitting connections are tight in suction vacuum conditions to prevent air
AMIN ALMASI is a mechanical consultant based in
from getting into the pump.
Sydney, Australia. Email him at
[email protected].
Flow eHandbook: Preempt Flow Problems 7
°F
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fact
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products
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More facts about the OPTIMASS 1400: www.us.krohne.com/optimass1400
t/h
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Create a Preventive Hose Maintenance Plan Follow these five steps to determine the best replacement timeline By Alice Chin, Swagelok
K
nowing the right time to replace
identifying key replacements to have at
hoses in a chemical processing
your facility. While developing such a plan
plant is a common concern among
may seem onerous, the cost-saving ben-
many plant managers and maintenance
efits can make it well worth the upfront
leaders — and with good reason. Wait-
time investment.
ing too long to replace a hose that needs attention can increase your risk of a failure
Each hose in your facility is different
greatly, possibly leading to a safety issue
according to the application parameters it
and unplanned downtime. Replacing a hose
experiences and therefore needs a unique
too early — while not a safety risk — can be
replacement interval based on its environ-
costly in terms of time and money. A pre-
ment. Take into account everything from
ventive hose maintenance plan is a valuable
pressure and temperature to movement
addition to any plant’s standard operat-
demands and nearby equipment.
ing procedures. Consider a process application that uses A preventive maintenance plan can help
50 identical hoses. Half of these hoses
by providing information on each hose in
are steam cleaned and wear out after one
your plant. This means tracking the life and
year. The other half are not cleaned and
performance of all hoses, inspecting them
likely will last much longer, say, four years
frequently, replacing them proactively and
longer. Placing all the hoses on a five-year Flow eHandbook: Preempt Flow Problems 9
www.ChemicalProcessing.com
maintenance cycle is dangerous and can
In a spreadsheet, log additional details,
shut down processes resulting from unex-
including each hose’s length, size, core
pected hose failure.
material and construction, reinforcement layers, end connections, mounting, cover
However, putting all the hoses on a one-
type, operating conditions, cleaning proce-
year replacement interval would mean
dures and the date the hose was installed
replacing hoses with years of life left in
and scheduled for replacement.
them. How much could the plant save if it increased the replacement interval for the
2. Track the lifecycle of each hose. Follow a
second set of hoses to five years? At a cost
schedule of regular hose inspections, exam-
of approximately $200 per hose, the sav-
ining each hose at an interval recommended
ings would be about $20,000 in product
by your supplier. These inspections are
costs alone, plus the savings from reduced
visual and rarely require system downtime.
maintenance and downtime.
Mainly, you are looking for signs of wear, such as scrapes, cuts, corrosion, kinks and
CREATING A PREVENTIVE HOSE MAINTENANCE PLAN
general deterioration. These signs indicate
While your supplier can provide general
observations in your spreadsheet.
the hose is ready to be replaced. Note all
inspection and replacement guidelines, your actual replacement intervals will vary
If the system is in operation at the time
based on each hose’s operating environ-
of your inspection, you can also look for
ment, materials of construction and other
hoses that rub against equipment, experi-
factors. These replacement intervals cannot
ence pulses, are exposed to external heat
be predicted. They can be determined
sources or are set up in arrangements that
only through observation and care-
may cause undue strain (see Table 1). These
ful recordkeeping.
situations should be corrected.
Here are steps to establish your plan:
When a hose has reached the end of its life, it’s critical to note its service interval. This
1. Identify all hoses. First, perform a full
information provides a known replacement
plant audit that includes identifying and
interval for that hose.
tagging every hose. Be thorough and specific, including noting the hose type, part
If and when a hose fails during operation,
number, process fluid, pressure or tem-
document everything, including the location
perature ratings and vendor name and
of the failure on the hose, the severity of
contact information.
the break and how the hose was mounted. Flow eHandbook: Preempt Flow Problems 10
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UNDUE HOSE STRAIN
Table 1. Eliminate these situations that will put strain on your hoses, shortening their service life or causing failure.
Twisting a hose or bending it on more than one plane
Bending the hose beyond its recommended radius
Bending too close to the hose/fitting connection
Allowing insufficient hose length so the hose is strained during impulses
Failing to use elbows and adapters to relieve hose strain on horizontal end connections
Flow eHandbook: Preempt Flow Problems 11
www.ChemicalProcessing.com
These details will help you troubleshoot the
for certain hose categories, it’s a good prac-
failure with your hose supplier and deter-
tice to keep some spares in inventory at
mine how to prevent a reoccurrence.
your plant: • Hoses for Critical Safety or Process Appli-
3. Follow inspection and replacement proto-
cations: You’ll need a readily available
cols. As you learn the replacement interval
spare to correct rapidly any hose applica-
for each hose, your hose maintenance plan
tions that present critical safety hazards
will take shape. However, even after deter-
or severe downtime potential.
mining the replacement interval, you should
• Hoses That Are Likely to Fail: When a
continue with periodic inspections to ensure
hose’s operating environment presents a
that a change in system parameters does
high likelihood of premature failure, you’ll
not place a strain on a hose.
want extra hoses available to accommodate your frequent replacements. For
4. Analyze your data. Periodically analyze
example, hoses kinking, moving in two
your historical data against your established
planes or experiencing vibration likely will
hose inspection and replacement frequen-
fail sooner than others. A better practice
cies to determine whether any intervals
may be to find a more suitable hose for
should be shortened or lengthened for
the application or adjust the system to
safety or budgetary reasons. Performing
remove the strain on the hose.
a destructive test on a replaced hose can
• Hoses for Special Applications: Keep
show whether the hose was replaced too
spares of any hoses that are difficult to
soon (that is, if it has significant life left, you
source due to special materials, lengths,
can extend its replacement interval) or too
end connections and other variables.
late (that is, if it were nearing failure, you
For example, if you know a special-order
should reduce the replacement interval).
hose has a three-week lead time, you may even want to inventory two spares for
In addition, if a specific hose is replaced fre-
good measure.
quently (for example, weekly or after only one cleaning cycle), consider using an alter-
REALIZE LONGER HOSE LIVES
native design that will offer a longer life. In
Regular inspections and meticulous record-
doing so, verify that the cost-benefit analy-
keeping will require a time investment. A
sis works in your favor.
hose maintenance plan could mean significant cost savings and improve your
5. Be prepared with spares. If you know the
plant’s safety. With a plan in place, you
replacement interval of your hoses, you can
should be able to replace hoses less often,
order replacements in advance. In addition,
replace them only when needed and Flow eHandbook: Preempt Flow Problems 12
www.ChemicalProcessing.com
always have fast access to a replacement
manufacturing process is down. If you keep
when necessary.
track, the numbers will tell the story.
These outcomes mean increased profit-
ALICE CHIN is a field engineer for Swagelok Asia
ability, enhanced safety, fewer delays and
Pacific. For more information visit, www.swagelok.com
readily available replacement hoses while a
Flow eHandbook: Preempt Flow Problems 13
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Consider Portable Flow Instruments Some circumstances warrant the use of such devices By Joe Incontri, KROHNE, Inc.
A
ccurate flow measurement is
Situation 1: Operations have changed from
critical for process control and
original conditions. Sometimes opera-
regulatory compliance. Flowme-
tional changes are made, resulting in flow
ters are essential instruments for water and
rates that no longer match the installed
wastewater facilities, installed at multiple
instrument’s performance envelope. As an
locations throughout entire systems. For
example, a flow recirculation process may be
the most part, these are permanent instal-
added for nutrient removal, or flows may be
lations. However, portable flow instruments
split between multiple tanks. The operational
prove beneficial in certain situations.
change also may be temporary, such as flow diversion to another treatment train while a
THE NEED FOR PORTABLE FLOWMETERS
tank is taken out of service for rehabilitation.
Most flowmeters are fixed in place, con-
Situation 2: Flow rates are expected to
nected to a local control system with output
change, with no changes to installed instru-
to a data logging or supervisory control and
ments. Perhaps a new subdivision or large
data acquisition (SCADA) device. However,
commercial facility is coming online or a
some circumstances warrant the use of por-
new process within an industry is added.
table instruments. Here are a few situations
Maybe a section of the service area is
in which the use of portable flowmeters
being transferred to another utility pro-
(Figure 1) could be valuable.
vider. The increased or decreased flow Flow eHandbook: Preempt Flow Problems 15
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may put the existing flowmeter out of its accepted range. Situation 3: Installed instruments need verified. Most regulatory permits require some type of annual verification of flowmeter performance. Verifying that a flowmeter is performing properly is a good idea, even if not required for compliance.
PORTABLE FLOWMETER
Figure 1. These devices can act as a stopgap during process modifications; verify existing meter, pump and valve performance; and help troubleshoot plant upsets.
Situation 4: Performance of pumps or valves
to gather additional data to verify proper
needs verification. Plant personnel may not
equipment performance.
know the actual flow performance of an existing pump, or the flow through a valve.
For situations 1 and 2, a flow change or a
Knowing the flow conditions may yield
plan to change flows is occurring. In these
valuable insight to optimize those elements
cases, a portable instrument provides a
in a process.
stopgap measure until a permanent solution can be procured. If flow rates are steady,
Situation 5: New instruments are being
data can be entered manually into a moni-
considered, but existing flow rates are
toring or control system.
unknown. Process control at a plant could benefit from an additional point of flow
Otherwise, real flow data can be used to
measurement. Information on existing
procure a new permanent flowmeter that
flow rates is needed to specify the best
matches the actual process requirements.
flow instrument.
Using data from a portable instrument avoids over- or under-sizing instruments
Situation 6: Troubleshooting is needed for
based on faulty process engineering data.
unusual or periodic upsets. Unpredictable problems or upsets at a treatment plant
For situations 3 and 4, in which existing
may be due to irregular flow conditions.
flowmeters need verification, use of a portable instrument avoids the need to take
GET THE MOST OUT OF YOUR PORTABLE DEVICE
an existing flowmeter offline or shut down
Portable flowmeters are valuable for all
a pump or valve, the portable unit can be
of these situations as they can be used as
installed on existing pipe. Portable flow-
temporary fixes for changing conditions or
meters can be accompanied by a factory
a process. And to verify performance of
Flow eHandbook: Preempt Flow Problems 16
www.ChemicalProcessing.com
calibration certificate, which then can be used to produce a traceable verification certificate.
PORTABLE ULTRASONIC FLOWMETER
Figure 2. Portable clamp-on ultrasonic meters measure well-conditioned flow in straight pipe applications.
One caveat exists when using a portable clamp-on ultrasonic meter (Figure
For situation 5, when considering a new
2) to verify an electromagnetic “mag”
location for flowmeter installation, a por-
meter or turbine meter. The technique for
table meter will provide flow data at the
measuring flow ultrasonically requires a
proposed point of measurement. This will
well-conditioned flow. Mag and turbine
provide the information necessary to spec-
meters require less straight pipe than ultra-
ify and purchase a permanent flowmeter to
sonic meters. If insufficient straight pipe is
handle the range and conditions necessary.
available, the ultrasonic meter will be much less accurate.
For situation 6, portable instruments may help identify the cause of unexplained
Another option exists for flowmeter ver-
upsets at a treatment facility. Portable flow-
ification. Portable electronic devices are
meters are equipped with data loggers that
available from meter manufacturers that
can record flow levels over time. Correlating
compare the meter’s electronic parameters
the data with the time of upset may reveal
to factory settings. These devices plug into
pertinent issues.
the electronics and sensor, like devices used for troubleshooting automobile issues.
TIME AND COST SAVINGS By using portable flow instruments, utilities
Verification is based on the instrument’s
can verify performance of an existing meter,
serial number. A file specific to the meter
pump or valve quickly. Portable flowmeters
holds values from time stamp of manufac-
can be used as stopgap measures during
ture with all factory-calibrated parameters.
process modifications. By using portable
In the field, the verification tool compares
meters to determine existing flow charac-
the instrument’s readings to factory values.
teristics, utilities save the cost of purchasing
The result is a printed certificate verifying
a poorly specified permanent meter. Finally,
the unit still functions within the operat-
portable flow instruments and data loggers
ing envelope. This type of verification can
can help to troubleshoot and resolve unex-
be sold as a service, or the device can be
plained plant upsets.
rented or sold. Some theorize this method of verification is more reliable than using a
JOE INCONTRI is director of marketing at KROHNE, Inc.
portable meter.
He can be reached at
[email protected].
Flow eHandbook: Preempt Flow Problems 17
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Flow eHandbook: Preempt Flow Problems 18