ESL-IE-82-04-119-YARWAY

STEAM TRAP APPLICATION

John J. Murphy Yarway Corporation

Houston, Texas

The effective application of steam traps encompasses three primary areas which are the selection and sizing, the installation, and the monitoring of the steam trapping system. Proper application of steam traps will improve production rates, product quality, and reduce energy and maintenance costs.

The steam trap is a "self actuating automatic drain valve" that must perform the following functions:

(A) Remove air and condensate

(B) Respond to load and pressure changes.

(C) Close prior to "seeing" live steam or limit the flow of steam.

For these reasons,application of steam traps deserves the same attention as is given to any other critical control device.

This paper will deal with defining the type of service, outlining system parameters, steam trap sizing, proper installation, and system monitoring techniques.

Since there is no Universal Steam Trap, the initial step is to define the type of service. This is necessary to select the type of steam trap that best matches the needs of the application. The two broad application categories are Production/ or Process and Protection. These can be further subdivided as follows:

1. Production/or Process

(a) Steam heating a liquid,indirectly (b) Steam heating a gas, indirectly (c) Steam heating a solid or slurry,indirect

ly (d) Steam heating a solid, directly

2. Protection

(a) Steam line drip (b) Steam Tracing

Process lines Winterization Instrumentation

The following table summarizes the application characteristics.

GENERAL CLASSIFICATION OF APPLICATIONS

TASK PRODUCTION Typical Names I-Steam heats a liquid indirctly of Equipment (e.g. Shell & Tube, Kettle)

2-Steam heats a gas indirectly (e.g. Air Heater, Dryer~

3-Steam heats a solid or slurry indirectly.

(e.g. Cylinder dryer,Platen) 4-Steam heats a solid directly

(e.g. - Autoclave)

Steam Pres Generally variable or fluctuating sures at trap due to varying product through-put, inlet control valve action, intermittent

or batch processes. Some seasonal changes. Pressures are medium, with h~gh pressure occasionally encoun~ered.

Condensate Generally variable with widel changes Loads due to nature of process (st1rt-up)

batch, intermittent) changes in through-put. Loads are medium to high, with very high loads occasionally encountered and can arrive in slugs.

Discharge at Generally require condensate! to or below be discharged at small amount of saturation subcooling (at trap inlet) t9 temperature minimize threats to equipment and

maximize heat transfer for production.

Discharge of Important due to generally l~rge air and non volumes, drainage and process condensible variations. Separate vent n~eded Igases. occasionally. Condensate Usually by gravity - sometimes arrives at syphon or lift. ['rap Ambient tem Frequently indoors and high amperature con bients can be encountered. For ditions outdoor installations concern is

for freezing.

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Proceedings from the Fourth Industrial Energy Technology Conference, Houston, TX, April 4-7, 1982

;,

TASK PROTECTION

Typical Names l-3team line drip, turbine of Equipment drain, control valves.

2-Steam tracing a-Process lines b-Winterization c-Instrumentation

Steam pres- Generally constant with slight sures at variation due to seasonal trap inlet changes.

Steam Line Drip - Low to high pressure common. Very high pressure occasionally encountered. Some Superheat encountered. Steam Tracing - Medium pressures with high pressure encountered occasionally. Superheat is rare.

Condensate Generally constant with sea-Loads sonal changes and occasional

start-up an exception. Steam Line Drip, low load, most common. Medium loads encountered at start-up or with carry-over. Superheat - essentially no load. Steam Tracing - Low load most conunon. 20 lb/hr (10 Kg/hr) typical.

Discharge at Steam line drip - require dis-or below charge at small amount of sub-saturation cooling to prevent damage to temperature pipe line, turbine or control

valve. Drip leg a major variable. Steam Tracing - Process lines generally require small sub-cooling. Winterization and instrumentation lines can occasionally tolerate more subcooling.

Discharge of Seldom an issue due to some-air and non what continuous operation and condensible infrequent start-ups. gases

Condensate Usually by gravity. arrives at trap

Ambient tem- Steam line drip - outdoorperature freezing. conditions Steam tracing - usually out

door freezing.

The users steam and condensate system characteristics and other requirements can affect steam trap function and selection. Of particular importance are seven key variables.

1. System Pressure and Temperature Conditions

Maximum system pressure and temperature may be experienced only occasionally; however, these must be defined to assure that the trap "pressure rating" and materials of construction are suitable for the application. The operational pressure (inlet and/or differential) determine the trap flow rate as well as function. From a functional aspect, operating pressure may prevent the trap from opening or closing. Therefore, the design, normal, maximum and minimum pressure must be defined. If the pressure is constantly fluctuating, its effects on trap reliability require consideration.

Operating temperatures are those the trap experiences when the equipment involved is in its normal running mode, and will not exceed the saturation temperature when the trap is operating properly.

2. System Condensate Requirements

Condensate loads can be constant, variable, fluctuating, arrive in slugs, and change due to ambient conditions. The extreme condition is the start-up load which is generally a large value when compared to the running and minimum loads. Many times the start-up load is over estimated and then a safety factor applied. This results in an oversized steam trap for the running load and unsatisfactory trap performance. In applications where the condensate load fluctuates the steam trap characteristic which is defined as "response" becomes an important factor in trap selection.

3. Condensate Drainage

"Drainage" type is determined by the piping configuration between the steam user and trap inlet. Most applications are of the gravity drainage type. To facilitate proper trap operation and system protection, certain guidelines should be followed.

Some equipment designs require syphon and/or lift drainage. Special piping techniques are required and steam trap selection becomes more critical.

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....n-------::t -------.

Process Equipment Collecting leg, same size as equipment connection but not less than

Install a Yarway Process Trap below be drained. Install a

Provide vacuum strainer with a blow down valve. Use and Yarway Aldrain valves full ported stop valves, (gate or ball). Slopeas needed for freeze pro

breaker

~ f

Vacuum Breaker

1" NPT.

equipment to

than trap pipe size.

-------.

To Return tection. ~ T j::::::!] [l:=::::::t ~

Piping to and from trap not less

GRAVITY TYPE DRAINAGE

Trap Station

TL Lift Fitting

On jacketed or rotating equipment, On lift or syphon drainage. locate pro On submerged heating surfaces with consider a separate air vent. cess trap at lowest possible point. lift to the trap, slope the coil and use

a lift fitting.

,L1FT/ SYPHON TYPE

4. Ambient Conditions

Outdoor equipment in cold climates constitute a freezing hazard. The steam supply, the steam using equipment, steam trap station components and condensate return system should be designed with this in mind. Indoor applications where excessive heat is encountered. (e.g. - dry cans, dry kilns, inside dryer/ heater rooms, etc.) may alter the response and operation of some steam trap types.

DRAINAGE

5. Air and Other Non-Condensibles Venting! Requirements

The venting of air and other non-condensibles for both start-up and running conditions should be investigated. Batch processes or other applications requiring steam only intermittently are subject to becoming air bound. This condition increases start-up time because heat t~ansfer is drastically reduced and accelerates ~orrosion. Steam traps selected for this type of service must have "good" air handling characteristics (trap in fully open position when col air - non condensibles are present) and/or auxiliary air vents installed.

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STEAM TRAP COMPARISON CHART

6. System SHOCK, Vibration and Water Hammer Considerations

The source is normally cold water remaining in the system and coming in contact with live steam. Sudden changes in velocity can also be a factor, and the situation is most damaging when large volumes of water exist. These disturbances can occur in steam and/or condensate return piping. Although generally of short duration,the forces developed can be very damaging to steam trap internals. Parts such as bellows, ball floats, etc. are particularly susceptible to failure from this phenomenon. Any steam-condensate system can experience these conditions; however, storage tank heating systems with the coils installed in a horizontal position on the tank bottom are prime candidates for water hammer problems.

7. Dirt and Corrosion Problems

Like any critical control device the steam trap should be protected from dirt and scale if optimum operation and adequate service life are to be attained. Strainers should be equipped with blowdown valves to provide an effective and efficient method of periodically cleaning the strainer screen. No steam trap is immune to dirt.

Corrosion of heat exchange surfaces (fouling) eventually produces significant changes in the steam pressure at the trap inlet.

The Trap Selection Scoresheet that follows can be used to establish the key trap selection criteria in a logical manner.

Trap Selection Criteria

Steam Line Drip

Steam Tracing Process Lines Type of Steam Tracing Winterization LinesApplication

Steam Tracing Instrument Lines

IOther Light Loads Operating Pressure. Inlet. Mln.lMax. psig

Operating Pressure. Outlet. Mln.lMax. psig

Discharge 10 Sewer or Vented Receiver General Discharge to Pressurized ReturnConditions

End Connection. Size. In. (See Note 1) End Connection. Type, Thread (See Note 1) End Connection. Type. Socket Welding (See Note 1) Design PressurelTemperature. Rating. ANSI Class

Operating Temperature F Design Operating Back Pressure Ratio. 0/0. Min IMax.CondItions

Operating Differential Pressure. psi, Min./Max -

Condensate Load, Ib/hr (Withoul Safety Factor) Rain

Ambient FreezingConditions Ambient above 90F (32 2C) Trap Station Piping-HonzontalInstallation

ReqUIrements Trap Station Plping-Verlical

Discharges Near Steam Temperature

Discharges Slightly Subcool, 1O-40F (6-22C) Below Saturation Discharges More Than 40F (22C) Below Saturation Discharges Intermiltenl (Off-On) Discharges Continuous. Modulating

Integral Strainer Trap

Discharge Integral Blow-Off Valve Characteristics

Renewable In Line Required

and

Features Resists Shock. Vibration, Water Hammer

Vents Air and Non-Condensibtes

Can Drain PiPing If Pressure Is Turned Off

Insulation ReqUired for Trap Freeze Protection

Trap Normalfy Falls Open

Trap Normally Fails Closed

NOTES: 1. Piping Recommendations A-Steam Line Drip

To 300 psi, ~" or 3/4" NPT 300-600 psi, 3/4" NPT Over 600 psi, 1" socket welding

B-Steam Tracing Process Lines - ~" or 3/4" NPT Winterization Lines, ~" NPT Instrumentation Lines, 1/4" or

3/8" NPT

,', j.

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I

Steam trap sizing requires calculating or estimating condensate loads. The common error of sizing a trap based on pipe size must be avoided. Sizing ,by pipe size only,frequently results in an oversized steam trap with undesirable performance. Since the "size" of a steam trap is its ability to discharge condensate at or near steam temperature, multiplying the calculated condensate load by the appropriate Safety Load Factor (SLF) yields the required steam trap flow rate.

In determining condensate loads,consideration must be given to start-up loads, heat-up rate, air handling, ranges in pressure and variations in condensate loads. It is not always possible to calculate these conditions. Therefore, a Safety Load Factor (SLF) is used. The SLF is rarely needed for steam tracing. For steam line drip service, an SLF is used for start up conditions.

The SLF is based on experience and design of steam using equipment. Pressure variations at the trap inlet and outlet, condensate collecting leg design, environment, condensate load variations, and air handling capacity require the consideration of an appropriate SLF.

The protection application (steam line drip and steam tracing) are normally light condensate load applications, and a trap with 300 lbslhr capacity at 100 psi will be sufficient. Steam line drip condensate loads can be estimated by using the following formulas:

(A) Warming Load

C = (L) (W) (Cp )(T2 - Tl) hfg

(B) Time for Warm-up

t = (Temp. Rise) F/hr

(C) Condensate Rate CR = C

t

(D) Running Load

CL - (U)(L)(A) (T - T ) F p a hfg

NOTE: Legend of sYmbols is provided at the end of this paper.

For warming loads a Safety Load Factor (SLF) of 1.5 is adequate. For running loads most steam traps have ample flow rates to accommodate the condensate load produced. The exception would be drip traps at the end of a steam line.

Steam tracer condensate loads generally range from 5 lbs/hr to 50 lbs/hr. If heat transfer cements are used, the manufacturer's heat transfer data should be consulted before sizing trap~. Recommended tracer lengths vary from 25 feet to 400 feet based on the condensate load and steam pressure involved. Lengths of tracer$ should be limited to minimize pressure drop~ maintain uniform temperatures, and assure dtainage. The table below can serve as a designl guideline:

Maximum Tracer Lengths Feet

Steam LoadO.D. of Steam Pressure psiTracer Tub- lb/hr/lOO Ft

ing - in. 150-200of Tubing 30-5015-30

120 200 40010

2601/2 20 13085

80 16040 55

50050010 300

1

500300 320203/4

120 200 42040

10 500 500 500

1-1/8 20 500 500 500

40 500 500 500

Use of 1/4 in. and 3/8 in. O.D.tubingis usually restricted to very short lengths, or for protection of instruments.

Process trap sizing is critical to sadisfactory performance and service life. Three ~teps must be taken to insure proper sizing.

(1) Categorize the type of equipment. (2) Calculate or estimate condensate !load (3) Apply the proper Safety Load Factor

(SLF)

The following tables may be used as guides to develop the sizing criteria noted above.

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EQUIPMENT CATEGORIES Type of Typical Examples

Heating Equip- of Equipment Being ment Heated

Category 1: Submerged surfaces e.g., batch Steam Heats a still, evaporator,fuel heater, Liquid,Indirectly shell & tube heater, tank coil,

vat water heater.

Jacketed vessel, e.g., pan, kettle concentrator Lift or syphon drainage, e.g. , tilting kettle, sulfur pit, submerged pip'e or embossed coil, shipboard tank

Category 2: Natural Circulation, e.g. , Dry Steam Heats Air air - convector, pipe coil Indirectly radiator. Moist Air - blanket

dryer, dry kiln, drying room.

Forced circulation, e.g., air blast heating coil, dry kiln, air dryer, pipe coil, process air heater, unit heater

Category 3: Gravity draine~, e.g. , chest-Steam Heats a type ironer, belt press, Solid or Slurry chamber dryer, hot plate,platen Indirectly

Syphon drained, e.g. , cylinder ironer, cylinder dryer, drum drver dry can naoer machine

Category 4: Gravity drained, e.g. , auto-Steam Heats a clave, reaction chamber retort, Solid Directly sterilizer

Equipment Category

1

Condensate Load Estimating Table Estimate of Condensate Load

CL, lb/hr CL = (Water gpm) X(Temperature

---2-- Rise, F) (Petroleum gpm)X(T t rCL= 4 empera u e

, Rise F)

2 CL = (Air cfm)

900 X (Temperature

Rise F)

3

4

CL = (5) (Surface Area ft 2) Surface Area = Total External

Area of Equipment, Top, Bottom, Sides, Upper & Lower Halves

CL = Estimate based on Steam Pipe Size'& Pressure

CL = Estimate based on Steam Pipe Size & Pressure

Approximate Steam Flows, lb/hr

Typical Steam Flow Rates for Variou!Steam Pressure in Pipe Pipe Sizes (in.) + (psi) 3/4" 1" 2"

70 l~"

100 260 42010 140 200 520 840

90 140 340 600 20 l8p 280 680 1200

165 240 600 100050 330 480 1200 2000

285 420 1050 1800100 570 840 2100 3600

410 600 1550 2600 820

150 1200 3100 5200

520 800 2000 3400200 1040 1600 4000 6800

750 1200 3000 5000300 1500 2400 6000 10000

Approximate Steam Flows, lb/hr

~team Pres- Typical Steam Flow Rates for Various !sure in Pipe Pipe Sizes (in) + I(osi) 6"3" 4" 8"

900 1500 3500 620010 1800 3000 7000 12400

1200 2200 4800 850020 2400 4400 96000 17000

2200 3800 8500 1550050 4400 7600 17000 31000

4000 7000 15000 27000100 8000 14000 30000 54000

5500 220009500 38000150 1900011000 44000 76000

7600 12000 28000 50000200 15200 24000 56000 100000

11000 18500 42000 82000300 22000 37700 84000 164000

+Approximate steam flows, lbs/hr. The smaller values are for velocities of 5000 fpm usually found indoors or heating systems. The larger values are for velocities of 10,000 fpm usually found outdoors and on larger equipment.

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SAFETY LOAD FACTOR SELECTION TABLE

Equipment Safety Load Factor (SLF)Category

Drainage Steam Pressure(psi) Constant Variable

1 Gravity 2 3 Syphon or

Lift 3 4

Ambient Air Constant Variable 2 33F & Higher 2 3

Below 33F 3 4

Equipment Drainage SLF Platen Gravity 3

3 Rotating Syphon 5 Dryer

4 Warm Up Normal Fast

SLF ---3-'-'

5

Steam trap installation is basically just an extension of good piping practices; however, the following items must be taken into consideration if the steam trapping system is to perform effectively.

(1) Piping Practices

The steam using equipment is designed for "dry" steam; therefore the supply piping should be taken from the top of the distribution header. If the supply line has low points, stop valves,control valves, etc. that could collect pockets of condensate, drip traps should be installed.

The steam using equipment manufacturer has installed a discharge connection of the appropriate size. This connection is frequently the same size as the steam supply connection or one pipe size smaller. The size is selected to allow the condensate and entrapped vapor bubbles to drain from the equipment by gravity. For some types of equipment the outlet connection size should be maintained downward for 3 feet or more to provide adequate storage volume. This volume is needed for those applications where pressures can drop suddenly and the environment is freezing. The volume of the collecting leg should be equal to the condensed volume of the steam in the using equipment. The equipment should be installed so that the condensate can flow to the hot well, or collecting leg. Providing "good" drainage reduces the rate of corrosion and eliminates water hammer damage on start-up. If freeze-up occurs, the steam coils or tubes are less likely to be damaged.

At the end of the collecting leg, piping should be the same pipe size (or larger than) the steam trap connection. The piping must be sloped to the trap. This is to ensure that condensate reaches the trap. This assists the trap in responding to the presence of condensate. In addition, it helps maintain a water (liquid) seal to minimize

the risks of steam blowing through the trap. If subcooled traps are used, it prevents stea~ temperature condensate from entering the trap ,and producing undesirable response.

If the equipment requires lift or syption drainage, the condensate must be forced up~ard before reaching the trap. The upward motiqn causes the pressure on the hot condensate Go decrease and this can promote the formatio~ of "flash" or steam bubbles in the condensate.1 The situation is worsened with syphon drainage Ibecause the condensate moves through a steam space and is re-heated. Whenever lift or syphon idrainage exists, the condensate reaches a high point and the trap should be installed as far below ~his point as possible, preferably below the po~nt where the lifting or syphoning starts. This all~ws the vapor bubbles to condense and helps as~ure that only condensate reaches the trap. I

Condensate drainage from the trap is ~qually important, and allowance must be made to a~sure the discharge piping does not freeze. If ~he trap discharges into piping, the piping must be adequate to handle the trap's maximum disc~arge rate including an allowance for flash vapo~ (two phase flow). It is important to consider ~hat the trap discharge rate is usually much greater than the actual condensate load. I

(2) Selection of Piping Components I Pressure drops in piping components a~fect

steam and condensate flow. Since condensa~e can exist at steam temperature (saturation)1 even minimal pressure drops can initiate flashi~g and result in two-phase flow. To minimize !this occurrence, stop valves should be of the g~te or ball type and of a size equal to the pipe. ! Check valves installed downstream of the trap to prevent backflow into the using equipment must, be line size and of a low pressure drop design. Check valve service downstream of a steam trap can be severe; so the check valve manufactu~er should be consulted for recommendations.

The use of air vents and/or vacuum brelakers should be considered on an application by a~plication basis. Key factors to be reviewed i~clude equipment operation (continuous or intermitltent), equipment steam space volume (air and otherl non-condensible venting needs), start-up ti~e reequirements, ambient conditions, type of st~am trap selected (free draining, etc.) and condensate return piping configuration.

Dirt and sediment are normal products pf steam and condensate systems. Since the tr~p is generally installed at the system piping low point, strainers in steam lines remote from the trap do not provide the required protection. Install a strainer at the trap inlet to ins~re proper operation and long service life. '

On the closed return condensate system~, test tees should be installed downstream of the ~rap. This will reduce the time required for trap checking and improve accuracy. The test tee and related stop valve should be equal to the steam trap pipe size where practical.

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Steam trap checking requires a thorough understanding of checking methods, operational characteristics of all ~ypes of steam traps including their normal discharge characteristics and failure mode, and system parameters (pressuretemperature). The three charts that follow are designed to provide insight into steam trap checking and trouble shooting.

Chart 1 - Focuses on trouble shooting the "trapping system". While indications of trap "failure" or "malfunction" are identified, trouble shooting the system for "trapping" problems is often more important. Don't reinstall the problem.

Chart 2 - Focuses on the steam trap itself and identifies the most common sources of problems within the steam trap. Some external or system problems are identified with the hope that further checking will be performed. Corrective action is also shown.

Chart 3 - Focuses on the checking methods and their advantages and limitations. The customer should select more than one method and decide which methods are the most applicable to that particular plant.

Note the emphasis on the following:

1. Understand normal trap characteristics. 2. Understand advantages and limitations of

various checking methods. 3. Use more than one checking method. 4. Understand flash condensate. 5. Condensate makes more noise than steam. 6. Trouble shoot the system. 7. Review trap selection, sizing and install

ation.

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CHART I

INDICATIONS OF TRAP FAILUREINDICATIONS OF ACCEPTABLE CLOSED,OR BACKING CONDENSATEOPENOPERATION

SIGHT-Flash Condensate -Intermittent Discharge Most thermodynamic, inverted bucket & properly sized bellows thermostatic -Continuous Discharge F & T, some thermostatic on light load. Some thermodynamic

en U types with control flow H

-Some traps produce noE-t en H flashp:::

~ ~SOUND-Intermittent or contin

~ uous sound-as above ~ with sight U -Condensate has rough p..~ or gravel sound. E-t -Condensate sound level ~ greater than steam E-t -Can feel vibration U

~ ~ [EMPERATURE

~ -Surface pyrometer may indicate fluctuation due to expected intermittent discharge.

-Blow down strainer, -Look for other leaks

5 ~e~7;~~rP~;i;~h~d~~:cer ~ l/month most process

~ l/week critical process ~ and air heaters in winter ~ Daily-very critical process and b very cold exposure

~ ~ Blow down strainers each time g steam trap is checked.

SIGHT-Continuous Discharge of Steam, Blue-White, -No sign of liquid condensate.

-No intermittent discharge

SOUND-Continuous -Whistle like noise

TEMPERATURE -High inlet(pyrometer does not indicate cycling) -Return line indicates excessive pressure via high temperature.

Review trap sizing & selection. Oversized traps frequently wear faster than expected,producing leaks and defective linkage function. Most traps seldom fail full open, Failure toward open position is usually gradual unless water seal is lost or linkages suddenly fail.

-Check for leaking or open bypasses -Check down stream valve & check valveopen? OK? -Examine trap for dirt preventing valve closure.

-Blow down strainer to remove condensate, observe if trap closes.

-Repair trap -Add strainer with bov -Repair/replace leaking stop valves

-Review trap selection, & sizing

SIGHT - No Discharge . - Some discharge, but flow rate is low, or continuous and lit~le flash. i

SOUND - No flow or low gravel like noise level I

TEMPERATURE- Inlet temperature more than 15% less' than steam tempera] ture

i i

Review trap sizing. - Trap! may be backing condensate i due to changes in operating pressure or process requir~ments. Traps backing cond~nsate frequently produce corrosibn and corrosion products then prpduce fouled heat exchange surface and clogged screens.

-Drain strainer to s~e if condensate is backipg up and discharge is high v~locity.

-Blow down strainer, screen may be clogged -Steam supply on andi correct pressure an~ temp? -Put pressure gage a1l: strainer blow down and test tee valve to verify operating: pressures.

-Examine trap for di~t and plugging I -Trap air bound? I

-Select properly siz~d trap -Replace screen if clogged -Repair trap -Add strainer & bov -Repair/replace defective stop and check valves.

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CHART 2 Type of INDICATIONS OF CAUSES FOR INDICATIONS OF MALFUNCTION

Trap NORMAL OPERATION OPEN CLOSED

Any type of Trap

'Should observe relatively high trap inlet temperature,

'Excessive valve seat wear 'Dirt on trap seat

Temperature control valve throttled insufficient steam

but not superheat 'Open bypass constantly blowing pressure. 'Should observe flash on discharge to atmosphere & see

'Overload trap-discharging continuously.

. Overloaded trap, backing up cold condensate

normal characteristic discharge. Should hear normal,

'Clogged strainer 'Closed stop valve upstream

characteristic operation. 'Closed return line stop valve or check valve.

Float or 'Thermal element failed closed Float &

'Normal discharge-continuous 'Thermal element leaking but on light loads may be 'Mechanism worn, broken or held 'Float collapsed, main valve

Thermo intermittent. failed closed static

open due to dirt/or oxides Excessive pressure difference

'Should hear continuous dis'Should see flash 'Leaking internal seals or gaskets

across seat charge

'See above - Any type of Trap 'Worn oversized

'Should observe relatively 'See above - Any type of Trap high inlet temperature

Thermo . Thermal element failed closed static

'Normal discharge-intermit 'Thermal element failure(Some 'Excessive back pressure (some

ing on load pressure, or tent or continuous depend- types).

types) type .

'Excessive back pressure (some . See above-Any type of Traptypes)

Improper adjustment or setting justed for subcooled opera

Should see flash unless ad'Worn valve or seat

tion Leaking gaskets 'Should hear continuous or 'See above - Any type of Trap modulating flow

'Should observe temperature near rated discharge temperature.

'D1rt-plugged ventInverted 'Loss of prime(low load, fluctuat~'Normal discharge-intermit'Excessive differential pres-Bucket ing pressure differences)tent, can be continuous sure

. Worn mechanism, valve or seatunder some conditions of 'Worn, oversized seat

'Le aking internal seals/gasketspressure and load 'Body filled with dirt

.Bee above - Any type of Trap'Should see flash 'Air bound

'Should hear intermit'See above - Any type of Traptent discharge-possibly

rattle of bucket, or bubbling of vent flow.

'Should observe relatively high inlet temperature

. Installed backwardWorn seat, disc, or bonnetDisc . Normal discharge intermit'Air bound'Leaking internal seals/gasketstent 'See above - Any type of Trap'Excessive back pressure

. Should see flash 'See above - Any type of Trap

'Should hear intermittent discharge possibly click-u

H ing of disc on seat Should observe relatively~ high inlet temperatures>

CHART 3 \

SOUND (AUDIBLE ,AMPLIFIED ,ULTRASONIC) TEMfERATURE !SIGHT

-Can be used in open qr -No special tools -Can view discharge Audible

closed return -Can be used for both open &

-Can use in open or closed dis-Some devices can ind~cate

closed discharge_ Need test charges

off-on action of traps tee & extra valves for closed

-Can hear flaws and/or trap -Indicates cold or fa~led

returns_ valve & seat

closed traps 1-Tools low cost, no calibration -Indicates unusual or iunex

Ultrasonic pected temperature a~ trap -Similar to first two items inlet or outlet i above -Can be used 'to detec~ un

-Can hear small flow rates usual conditf0Us, e_~_ -Insensitive to ambient or back- clogged screens, open byground noise (see limitations) passes around failed ~losed

traps_

I -Does not quantify leak -Does not quantify le~ks -Need to understand trap opera-

Audible -Does not quantify leak -Need to understand t~ap opera

tion -Need to understand trap opera tion -Need to understand flash -Need to have an idea ~f ex-Discharge to atmosphere not

tion -Continuous flow noise may in pected temperatures I

the same as discharge into -Cycling control val~s inclosed return

dicate overloaded trap -Difficult to differentiate be fluence results i

-Possible hazard when used with tween steam and condensate -Cost of devices ranger' from

high capacity traps or on flow very small to very hi h high pressures -Operating frequency judge -Clean surfaces needed for

-Continuous (unexpected) dis contact Imental charge can be due to overloaded -Does not always detec~ failed trap or load from re turn system

-Background or ambient noise confusing open trap, especiallyl if

-Test tee & stop valves must be -Small leaks undetected condensate & steam arf being trap line size -Electrical safety-some discharged simultaneorsly

-Added cost of test tee,valves devices -Some devices need cal~bration en nipples, etc_ -Infra red devices nee~ cali-Z o

-Acceptable operating frequency Ultrasonic bration, consideratiop of H is judgemental -Same as first five items above target size and emiss~vity~ H

-Emphasis on steam loss may -Does not distinguish between of targetH allow traps failing or failed steam and condensate flow~'

H closed to be undetected -Not always insensitive to background or ambient noise

-Noise in electrical system if volume too high

-Head set quality important -Location of probe on trap, contact force, pressure drop in trap, wall thickness of trap and orifice size influence results observed

-Expensive & requires calibration

-Electrical safety-some devices

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Legend of Symbols

C = Quantity of condensate, lb

CR = Condensate Rate lb/hr

W = Weight of pipe, lb/ft

Cp = Specific heat, Btu/ lb (0.12 for steel)

hfg Latent heat of steam at final pressure, Btu/lb

L - Length of pipe, ft

T =Initial pipe temp. ,oFl Final pipe temp., of (Saturation for final pressure)

t Time for warm-up, hr

CL = Condensate load, lb/hr

U = Heat transfer coefficient Btu/hr/sq ft/oF temp. difference. (A value of U = 3 is frequently used.)

A External area of pipe, sq. ft/ft

L Length of pipe, ft

Tp Pipe temp. , of

T Ambient temp. , of a

hfg = latent heat of steam at operating pressure, Btu/lb

r, F Insulation factor, equal to 1 minus

efficiency

':~ ,~,

637

ESL-IE-82-04-119


1982 Proceedings Volume II.pdf

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ESL-IE-82-04-119-YARWAY