PREEMPT FLOW PROBLEMS - Chemical Processing

PREEMPTFLOW PROBLEMS

Flow eHandbook

TABLE OF CONTENTSPrevent 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 INDEXABB • www.abb.com 14

Krohne, Inc. • us.krohne.com/optimass1400 8

Swagelok • www.swagelok.com 3

Flow eHandbook: Preempt Flow Problems 2

www.ChemicalProcessing.com

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http://www.swagelok.com/support

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Piping issues can directly affect a

pump’s performance and life. Poorly

designed suction piping can result

in pump damage and even failure. Quite

bluntly, there’s no excuse for substandard

piping design.

Numerous guidelines and mandates in the

technical literature, textbooks, manuals, codes,

specifications, etc., call for short and simple

suction piping. Yet, some engineers and

designers still treat such dictates only as pref-

erences. They install pumps far from suction

sources and design long and complex suction

piping systems. I personally can attest that

many design teams don’t heed the guidelines

for suction piping. They offer excuses such as

there’s no space near the suction vessel (tank

or drum) or it’s more convenient to install

pumps near downstream equipment.

As a result, cavitation and other suction-re-

lated problems such as turbulence and air

entrainment cripple pumping systems in

many applications. Root-cause analysis of

pump failures often points to long suction

piping systems as the culprit. The solution

to avoiding future failures usually is rede-

signing the suction piping to be as short,

simple and straight as possible.

You should consider pump location and

suction piping at the layout stage. It’s

simply wrong to fix the location of every

vessel, drum or tank and leave pump

locations for later. You also should antic-

ipate the addition of small pumps in due

course; for such cases, provide spare space

around vessels, tanks or other equipment

to accommodate these pumps right at the

layout stage. In addition, make your best

Prevent Suction Piping ProblemsFollow best practices when designing pump systems

By Amin Almasi



efforts to place any pumps close to the suc-

tion source.

Always explore any possible option to

install pumps closer (even if only by 1 m)

to the suction source. Pump textbooks and

nearly all pump catalogues and manuals

clearly note that suction piping should be

as short, simple and straight as possible.

Unfortunately, some design teams opt for

the easiest design rather than correct one

(as per guidelines).

THE BASICSFor any suction piping longer than a few

meters, ensure that you provide enough

net positive suction head (NPSH) margin,

i.e., NPSHA - NPSHR, for all potential oper-

ating points on the performance curve of

the pump from shutoff to near the end of

the curve. An adequate margin particularly

is needed at or near the end of the curve

where NPSHR is high and NPSHA is low

(because of high flowrate).

Different guidelines offer various recom-

mendations for margin, for instance, 1 m, 1.5

m or 2 m, depending on the criticality of the

application, pump details, suction energy,

sensitivity of pumps, potential damage due

to cavitation, etc. A good recommenda-

tion is a minimum NPSH margin of 2 m for

the commonly used operating range (say,

70–120% of the rated point) and a minimum

NPSH margin of 1 m for the end of the curve

to prevent risk of cavitation when the pump

operates, even temporarily, at the far-right

side of rated point.

Cavitation can cause a wide range of dam-

aging and disturbing effects such as suction

pressure pulsations, erosion damage,

increased vibration, noise, etc. Check the

margin for the worse possible operating

cases, for instance, when the suction source

is at its minimum head or liquid level, fric-

tion in suction piping is at its maximum, etc.

These guidelines may necessitate an

increase in the suction piping size. For rela-

tively long and complex suction piping, it’s

common to see suction piping up to four

sizes larger than the size of the pump’s suc-

tion nozzle; for instance, a 125-mm pump

suction nozzle may require 250-mm suction

piping (for a relatively long run). If such a

size increase isn’t viable, consider installing

a drum or small tank near the pump to act

as the suction source for it.

Connect the pump nozzle to an appropri-

ate length of straight pipe, per the pump

manufacturer’s guidelines. As a very rough

indication, the minimum length of straight

pipe needed between an elbow (or any

major fitting) and the pump suction nozzle

is 4–12 times the diameter of the suction

piping. For some high suction energy

pumps, this straight length should be up to

15 times the diameter; for commonly used

small pumps, which usually are low suction

energy units, this required straight length is



somewhere between three and six times the

diameter of suction piping.

The straight-run pipe gives a uniform veloc-

ity across the suction pipe diameter at the

pump inlet. Keeping the suction piping

short ensures that pressure drop is as low

as possible; this directly affects the NPSH

margin. These two factors are important for

achieving optimal suction and trouble-free

pump operation.

For any suction piping not conforming to

short and simple guidelines, check with the

pump manufacturer. It’s common to ask the

vendor to review suction piping and make

comments on the performance, functional-

ity, reliability and all guarantees of the pump

with that suction piping. The bottom line is

that the pump manufacturer should confirm

that the pump isn’t affected by that suction

piping. Remember that pump guarantees

often are limited to two or three years, so

correct suction-piping design is a better way

to ensure proper long-term performance.

TURBULENCE AND AIR ENTRAPMENTSizing of suction piping isn’t the only area

requiring attention. Also, seriously evaluate

route, layout and configuration. Suction

flow disturbances, such as swirl, sudden

variations in velocity or imbalance in the

distribution of velocities and pressures,

can harm a pump and its performance

and reliability. For any suction piping a bit

longer than usual or not straight and simple,

ensure that adverse effects such as turbu-

lence, disturbances, air entrainment, etc.,

won’t affect the pump set.

Minimize the number of elbows in the pro-

posed suction piping; numerous elbows

might present swirl, disturbances and other

damaging effects to suction flow and,

consequently, to the pump. Eliminate any

elbow mounted close to the inlet nozzle of

pump. Especially avoid two elbows at right

angles because they can produce sustained

damaging swirls. There have been cases

where a swirl introduced by two elbows

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.



in the suction caused high vibration of the

pump and subsequent damage to it.

Another type of damaging flow pattern

to a pump results from swirling liquid that

has traversed several directions in various

planes; therefore, avoid complex suction

piping routes with multiple directional

changes. Usually, the higher the suction

energy and specific speed of a pump, in

addition to the lower the NPSH margin,

the more sensitive a pump is to suc-

tion conditions.

Also, eliminate the potential for air entrap-

ment in the suction piping. One of the

sources of air or gas entrainment is the

suction tank or vessel. You must main-

tain adequate levels in the suction source

(drum, vessel or tank) to keep vortices from

forming and causing air/gas entrapment. In

addition, ensure there’s no air/gas pocket.

Particularly avoid high pockets in suction

piping; these can trap air or gas. Suction

flanges or any connection with potential

leaks can be a source of air entrainment;

so, minimize the use of flanged connections

and eschew threaded ones. Check that all

piping and fitting connections are tight in

suction vacuum conditions to prevent air

from getting into the pump.

Velocity in the suction piping should rise

as the liquid moves to the suction nozzle

of the pump; this speed increase usually

comes from reducers. The suction piping

design should provide smooth transi-

tions when changing pipe sizes. Often,

two or three reducers are used (usually

back to back) to decrease a large size of

suction piping to the size of the pump’s

suction nozzle. Pumps should have an

uninterrupted flow into the suction nozzle.

Generally, install eccentric reducers with

the flat side on top to avoid the potential of

forming an air/gas pocket.

Treat isolation valves, strainers and other

devices used on the suction side of a pump

with great care. Eliminate them if possible.

I have seen many unnecessary isolation

valves or permanent strainers on the

suction of pumps; these cause more harm

than good. If you absolutely require a valve,

strainer, etc., size and locate any necessary

device to minimize disturbances of the

suction flow. Install these flow-disturbing

items relatively far from the pump to let the

provided straight length of piping smooth

and normalize the liquid’s flow pattern.

AMIN ALMASI is a mechanical consultant based in

Sydney, Australia. Email him at [email protected].



http://us.krohne.com/optimass1400

Knowing the right time to replace

hoses in a chemical processing

plant is a common concern among

many plant managers and maintenance

leaders — and with good reason. Wait-

ing too long to replace a hose that needs

attention can increase your risk of a failure

greatly, possibly leading to a safety issue

and unplanned downtime. Replacing a hose

too early — while not a safety risk — can be

costly in terms of time and money. A pre-

ventive hose maintenance plan is a valuable

addition to any plant’s standard operat-

ing procedures.

A preventive maintenance plan can help

by providing information on each hose in

your plant. This means tracking the life and

performance of all hoses, inspecting them

frequently, replacing them proactively and

identifying key replacements to have at

your facility. While developing such a plan

may seem onerous, the cost-saving ben-

efits can make it well worth the upfront

time investment.

Each hose in your facility is different

according to the application parameters it

experiences and therefore needs a unique

replacement interval based on its environ-

ment. Take into account everything from

pressure and temperature to movement

demands and nearby equipment.

Consider a process application that uses

50 identical hoses. Half of these hoses

are steam cleaned and wear out after one

year. The other half are not cleaned and

likely will last much longer, say, four years

longer. Placing all the hoses on a five-year

Create a Preventive Hose Maintenance Plan Follow these five steps to determine the best replacement timeline

By Alice Chin, Swagelok



maintenance cycle is dangerous and can

shut down processes resulting from unex-

pected hose failure.

However, putting all the hoses on a one-

year replacement interval would mean

replacing hoses with years of life left in

them. How much could the plant save if it

increased the replacement interval for the

second set of hoses to five years? At a cost

of approximately $200 per hose, the sav-

ings would be about $20,000 in product

costs alone, plus the savings from reduced

maintenance and downtime.

CREATING A PREVENTIVE HOSE MAINTENANCE PLANWhile your supplier can provide general

inspection and replacement guidelines,

your actual replacement intervals will vary

based on each hose’s operating environ-

ment, materials of construction and other

factors. These replacement intervals cannot

be predicted. They can be determined

only through observation and care-

ful recordkeeping.

Here are steps to establish your plan:

1. Identify all hoses. First, perform a full

plant audit that includes identifying and

tagging every hose. Be thorough and spe-

cific, including noting the hose type, part

number, process fluid, pressure or tem-

perature ratings and vendor name and

contact information.

In a spreadsheet, log additional details,

including each hose’s length, size, core

material and construction, reinforcement

layers, end connections, mounting, cover

type, operating conditions, cleaning proce-

dures and the date the hose was installed

and scheduled for replacement.

2. Track the lifecycle of each hose. Follow a

schedule of regular hose inspections, exam-

ining each hose at an interval recommended

by your supplier. These inspections are

visual and rarely require system downtime.

Mainly, you are looking for signs of wear,

such as scrapes, cuts, corrosion, kinks and

general deterioration. These signs indicate

the hose is ready to be replaced. Note all

observations in your spreadsheet.

If the system is in operation at the time

of your inspection, you can also look for

hoses that rub against equipment, experi-

ence pulses, are exposed to external heat

sources or are set up in arrangements that

may cause undue strain (see Table 1). These

situations should be corrected.

When a hose has reached the end of its life,

it’s critical to note its service interval. This

information provides a known replacement

interval for that hose.

If and when a hose fails during operation,

document everything, including the location

of the failure on the hose, the severity of

the break and how the hose was mounted.



Twisting a hose or bending it on

more than one plane

Bending the hose beyond its rec-

ommended radius

Bending too close to the hose/fit-

ting 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

UNDUE HOSE STRAINTable 1. Eliminate these situations that will put strain on your hoses, shortening their service life or causing failure.



These details will help you troubleshoot the

failure with your hose supplier and deter-

mine how to prevent a reoccurrence.

3. Follow inspection and replacement proto-

cols. As you learn the replacement interval

for each hose, your hose maintenance plan

will take shape. However, even after deter-

mining the replacement interval, you should

continue with periodic inspections to ensure

that a change in system parameters does

not place a strain on a hose.

4. Analyze your data. Periodically analyze

your historical data against your established

hose inspection and replacement frequen-

cies to determine whether any intervals

should be shortened or lengthened for

safety or budgetary reasons. Performing

a destructive test on a replaced hose can

show whether the hose was replaced too

soon (that is, if it has significant life left, you

can extend its replacement interval) or too

late (that is, if it were nearing failure, you

should reduce the replacement interval).

In addition, if a specific hose is replaced fre-

quently (for example, weekly or after only

one cleaning cycle), consider using an alter-

native design that will offer a longer life. In

doing so, verify that the cost-benefit analy-

sis works in your favor.

5. Be prepared with spares. If you know the

replacement interval of your hoses, you can

order replacements in advance. In addition,

for certain hose categories, it’s a good prac-

tice to keep some spares in inventory at

your plant:

• Hoses for Critical Safety or Process Appli-

cations: You’ll need a readily available

spare to correct rapidly any hose applica-

tions that present critical safety hazards

or severe downtime potential.

• Hoses That Are Likely to Fail: When a

hose’s operating environment presents a

high likelihood of premature failure, you’ll

want extra hoses available to accommo-

date your frequent replacements. For

example, hoses kinking, moving in two

planes or experiencing vibration likely will

fail sooner than others. A better practice

may be to find a more suitable hose for

the application or adjust the system to

remove the strain on the hose.

• Hoses for Special Applications: Keep

spares of any hoses that are difficult to

source due to special materials, lengths,

end connections and other variables.

For example, if you know a special-order

hose has a three-week lead time, you may

even want to inventory two spares for

good measure.

REALIZE LONGER HOSE LIVESRegular inspections and meticulous record-

keeping will require a time investment. A

hose maintenance plan could mean sig-

nificant cost savings and improve your

plant’s safety. With a plan in place, you

should be able to replace hoses less often,

replace them only when needed and



always have fast access to a replacement

when necessary.

These outcomes mean increased profit-

ability, enhanced safety, fewer delays and

readily available replacement hoses while a

manufacturing process is down. If you keep

track, the numbers will tell the story.

ALICE CHIN is a field engineer for Swagelok Asia

Pacific. For more information visit, www.swagelok.com



http://bit.ly/ABBAquaMaster4

Accurate flow measurement is

critical for process control and

regulatory compliance. Flowme-

ters are essential instruments for water and

wastewater facilities, installed at multiple

locations throughout entire systems. For

the most part, these are permanent instal-

lations. However, portable flow instruments

prove beneficial in certain situations.

THE NEED FOR PORTABLE FLOWMETERSMost flowmeters are fixed in place, con-

nected to a local control system with output

to a data logging or supervisory control and

data acquisition (SCADA) device. However,

some circumstances warrant the use of por-

table instruments. Here are a few situations

in which the use of portable flowmeters

(Figure 1) could be valuable.

Situation 1: Operations have changed from

original conditions. Sometimes opera-

tional changes are made, resulting in flow

rates that no longer match the installed

instrument’s performance envelope. As an

example, a flow recirculation process may be

added for nutrient removal, or flows may be

split between multiple tanks. The operational

change also may be temporary, such as flow

diversion to another treatment train while a

tank is taken out of service for rehabilitation.

Situation 2: Flow rates are expected to

change, with no changes to installed instru-

ments. Perhaps a new subdivision or large

commercial facility is coming online or a

new process within an industry is added.

Maybe a section of the service area is

being transferred to another utility pro-

vider. The increased or decreased flow

Consider Portable Flow Instruments Some circumstances warrant the use of such devices

By Joe Incontri, KROHNE, Inc.



may put the existing flowmeter out of its

accepted range.

Situation 3: Installed instruments need veri-

fied. 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.

Situation 4: Performance of pumps or valves

needs verification. Plant personnel may not

know the actual flow performance of an

existing pump, or the flow through a valve.

Knowing the flow conditions may yield

valuable insight to optimize those elements

in a process.

Situation 5: New instruments are being

considered, but existing flow rates are

unknown. Process control at a plant could

benefit from an additional point of flow

measurement. Information on existing

flow rates is needed to specify the best

flow instrument.

Situation 6: Troubleshooting is needed for

unusual or periodic upsets. Unpredictable

problems or upsets at a treatment plant

may be due to irregular flow conditions.

GET THE MOST OUT OF YOUR PORTABLE DEVICEPortable flowmeters are valuable for all

of these situations as they can be used as

temporary fixes for changing conditions or

to gather additional data to verify proper

equipment performance.

For situations 1 and 2, a flow change or a

plan to change flows is occurring. In these

cases, a portable instrument provides a

stopgap measure until a permanent solution

can be procured. If flow rates are steady,

data can be entered manually into a moni-

toring or control system.

Otherwise, real flow data can be used to

procure a new permanent flowmeter that

matches the actual process requirements.

Using data from a portable instrument

avoids over- or under-sizing instruments

based on faulty process engineering data.

For situations 3 and 4, in which existing

flowmeters need verification, use of a por-

table instrument avoids the need to take

an existing flowmeter offline or shut down

a process. And to verify performance of

a pump or valve, the portable unit can be

installed on existing pipe. Portable flow-

meters can be accompanied by a factory

PORTABLE FLOWMETERFigure 1. These devices can act as a stopgap during process modifications; verify existing meter, pump and valve performance; and help troubleshoot plant upsets.



calibration certificate, which then

can be used to produce a trace-

able verification certificate.

One caveat exists when using a

portable clamp-on ultrasonic meter (Figure

2) to verify an electromagnetic “mag”

meter or turbine meter. The technique for

measuring flow ultrasonically requires a

well-conditioned flow. Mag and turbine

meters require less straight pipe than ultra-

sonic meters. If insufficient straight pipe is

available, the ultrasonic meter will be much

less accurate.

Another option exists for flowmeter ver-

ification. Portable electronic devices are

available from meter manufacturers that

compare the meter’s electronic parameters

to factory settings. These devices plug into

the electronics and sensor, like devices used

for troubleshooting automobile issues.

Verification is based on the instrument’s

serial number. A file specific to the meter

holds values from time stamp of manufac-

ture with all factory-calibrated parameters.

In the field, the verification tool compares

the instrument’s readings to factory values.

The result is a printed certificate verifying

the unit still functions within the operat-

ing envelope. This type of verification can

be sold as a service, or the device can be

rented or sold. Some theorize this method

of verification is more reliable than using a

portable meter.

For situation 5, when considering a new

location for flowmeter installation, a por-

table meter will provide flow data at the

proposed point of measurement. This will

provide the information necessary to spec-

ify and purchase a permanent flowmeter to

handle the range and conditions necessary.

For situation 6, portable instruments may

help identify the cause of unexplained

upsets at a treatment facility. Portable flow-

meters are equipped with data loggers that

can record flow levels over time. Correlating

the data with the time of upset may reveal

pertinent issues.

TIME AND COST SAVINGSBy using portable flow instruments, utilities

can verify performance of an existing meter,

pump or valve quickly. Portable flowmeters

can be used as stopgap measures during

process modifications. By using portable

meters to determine existing flow charac-

teristics, utilities save the cost of purchasing

a poorly specified permanent meter. Finally,

portable flow instruments and data loggers

can help to troubleshoot and resolve unex-

plained plant upsets.

JOE INCONTRI is director of marketing at KROHNE, Inc.

He can be reached at [email protected].

PORTABLE ULTRASONIC FLOWMETERFigure 2. Portable clamp-on ultrasonic meters measure well-conditioned flow in straight pipe applications.



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ADDITIONAL RESOURCESEHANDBOOKSCheck out our vast library of past eHandbooks that offer a

wealth of information on a single topic, aimed at providing

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applications to help make your facilities as efficient, safe,

environmentally friendly and economically competitive

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UPCOMING AND ON DEMAND WEBINARSTap into expert knowledge. Chemical Processing editors

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WHITE PAPERSCheck out our library of white papers covering myriad

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utilities, this white paper library has it all.

MINUTE CLINICChemical Processing’s Minute Clinic podcast series is

designed to tackle one critical issue at a time — giving you

hard-hitting information in just minutes.

ASK THE EXPERTSHave a question on a technical issue that needs to be

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PREEMPT FLOW PROBLEMS - Chemical Processing