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Flow eHandbook

PREEMPT

FLOW PROBLEMS

www.ChemicalProcessing.com

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

www.ChemicalProcessing.com

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

www.ChemicalProcessing.com

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

www.ChemicalProcessing.com

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

lb/cf

fact

°Brix lb/h

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products

solutions

services

More facts about the OPTIMASS 1400: www.us.krohne.com/optimass1400

t/h

www.ChemicalProcessing.com

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

www.ChemicalProcessing.com

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

Flow measurement

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www.ChemicalProcessing.com

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

www.ChemicalProcessing.com

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