Steamtrap Module

8/16/2019 Steamtrap Module

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MechanicalIPCL – NC

TRAINING MODULEModule No.

IPCLDSMEC107

Prepared by: KGGRevision: 00

Reviewed by: SBDate:

Approved by: SBPage 1 of 17

INDIAN PETROCHEMICALS CORPORATION LTD.

MAHARASHTRA GAS CRACKER COMPLEX, NAGOTHANE

TRAINING MODULE

ON

STEAM TRAP

LEARNING CENTRE

IPCL- MGCC


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MODULE IMPLEMENTATION PLAN

TOPIC: Steam Traps CODE:

FOR: DATE:REV: 0 SITE:

Sr.

No

Contents Autho

r

Resources Availa

ble

(Y/N)

Learning Validation

1 Introduction KGG Experience

2 Purpose of steam traps KGG Internet Y

3 Types of traps KGG Internet Y4 Importance of Traps KGG Internet Y

5 Failed Traps -- Cause andEffect

KGG Internet Y ½hrs

6 Trap failure KGG Internet Y7 Testing Methods for

Steam Traps

KGG Internet Y

8 Application KGG Internet Y

9 Finding malfunctioning

traps

KGG Internet Y

10 Trap inspection methods KGG Internet Y

Selfstudy

8 hrs Quiz


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LIST OF CONTENTS

Sr.No. Descriptions Page No.

01. Introduction 3

02. Purpose of steam traps 3

03. Types of traps 4

04. Importance of Traps 9

05. Failed Traps -- Cause and Effect 10

06. Trap failure 10

07. Testing Methods for Steam Traps 11

08. Application 12

09. Finding malfunctioning traps 13

10. Trap inspection methods 14

11. Questionnaire 15


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01. Introduction:

Steam traps are automatic valves that release condensed steam (condensate) from a

steam space while preventing the loss of live steam. They also remove non-condensable

gases from the steam space. Steam traps are designed to maintain steam energy

efficiency for performing specific tasks such as heating a building or maintaining heat for

process use. Once steam has transferred heat through a process and becomes hot

water, it is removed by the trap from the steam side as condensate and either returned to

the boiler via condensate return lines or discharged to the atmosphere, which is a

wasteful practice

There are many different styles of steam traps but they all serve the same basic purpose:

to automatically allow condensate and non-condensable gases like air to escape while

maintaining an efficient thermal transfer process. Most traps function while remaining

closed to live steam but some use simple control valves to pass steam at a regulated

rate.

02. Purpose of steam traps

Steam traps serve two main purposes. First, they ensure efficient transfer of heat and

maximize the cost of creating the steam. Second, they reduce the possibility of damage

to the system from water hammer.

Processes using steam to produce high quality products depend on the good heat

transfer rates. Condensate and the presence of non-condensable gases adversely affect

the transfer of heat. To ensure maximum efficiency condensate must be removed from a

system as soon as it forms. Non-condensable gases such as air must be vented to

atmosphere at start up and on an on-going basis. When steam condenses in pipe work it

is crucial to purge it to prevent the potential catastrophe of water hammer.


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03. Types of traps

There are five types of traps.

Ø a. Inverted Bucket Steam Trap

Ø b. Float & thermostatic steam trap

Ø c. Disc steam trap

Ø d. Thermostatic steam traps

Ø e. Fixed orifice steam trap

The description of each trap is given below.

a. Inverted Bucket Steam Trap:

These types of steam traps have a “ bucket” that rises or falls as steam and/or

condensate enters the trap body. When steam is in the body, the bucket rises closing a

valve. As condensate enters, the bucket sinks down, opening a valve and allowing the

condensate to drain. Inverted bucket traps are ideally suited for water-hammer conditions

but may be subject to freezing in low temperature climates if not insulated. Usually, when

this trap fails, it fails open. Either the bucket loses its prime and sinks or impurities in the

system may prevent the valve from closing.


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Fig: Inverted Bucket Steam Trap

b. Float & thermostatic steam trap: In contrast to the inverted bucket trap, both

types of thermostatic traps allow rapid purging of air at startup. The inverted bucket trap

relies on fluid density differences to actuate its valve. Therefore, it cannot distinguish

between air and steam and must purge air (and some steam) through a small hole.

A thermostatic trap, on the other hand, relies on temperature differences to actuate itsvalve. Until warmed by steam, its valve will remain wide open, allowing the air to easily

leave. After the trap warms up, its valve will close, and no continuous loss of steam

through a purge hole occurs. Recognition of this deficiency with inverted bucket traps or

other simple mechanical traps led to the development of float and thermostatic traps.

The level of condensate inside the trap drives the condensate release valve, while the

temperature of the trap drives an air release valve. A float and thermostatic trap, shown

here (at left), has a float that controls the condensate valve and a thermostatic element.

When condensate enters the trap, the float raises allowing condensate to exit. The


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thermostatic element opens only if there is a temperature drop around the element

caused by air or other non-condensable gases.

c. Disc steam trap:

Thermodynamic trap valves are driven by differences in the pressure applied by steam

and condensate, with the presence of steam or condensate within the trap being affected

by the design of the trap and its impact on local flow velocity and pressure. Disc, piston,

and lever designs are three types of thermodynamic traps with similar operating principles

disc trap is used.


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When sub-cooled condensate enters the trap, the increase in pressure lifts the disc off its

valve seat and allows the condensate to flow into the chamber and out of the trap. The

narrow inlet port results in a localized increase in velocity and decrease in pressure as

the condensate flows through the trap, following the first law of thermodynamics and the

Bernoulli equation. As the condensate entering the trap increases in temperature, it will

eventually flash to steam because of the localized pressure drop just described. This

increases the velocity and decreases the pressure even further, causing the disc to snap

close against the seating surface. The moderate pressure of the flash steam on top of the

disc acts on the entire disc surface, creating a greater force than the higher-pressure

steam and condensate at the inlet, which acts on a much smaller portion on the opposite

side of the disc. Eventually, the disc chamber will cool, the flash steam will condense, and

inlet condensate will again have adequate pressure to lift the disc and repeat the cycle.

d. Thermostatic steam traps:


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As the name implies, the operation of a thermostatic steam trap is driven by the

difference in temperature between steam and sub-cooled condensate. Valve actuation is

achieved via expansion and contraction of a bimetallic element or a liquid-filled bellows.

Bimetallic and bellows thermostatic traps are shown here. Although both types of

thermostatic traps close when exposure to steam expands the bimetallic element or

bellows, there are important differences in design and operating characteristics.

Upstream pressure works to open the valve in a bimetallic trap, while expansion of the

bimetallic element works in the opposite direction. Note that changes in the downstream

pressure will affect the temperature at which the valve opens or closes.

In addition, the nonlinear relationship between steam pressure and temperature requires

careful design of the bimetallic element for proper response at different operating

pressures. Upstream and downstream pressures have the opposite affect in a bellows

trap; an increase in upstream pressure tends to close the valve and vice versa. While

higher temperatures still work to close the valve, the relationship between temperature

and bellows expansion can be made to vary significantly by changing the fluid inside the

bellows. Using water within the bellows results in nearly identical expansion as steam

temperature and pressure increase, because pressure inside and outside the bellows is

nearly balanced.


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e. Fixed orifice steam trap:

Another type of steam trap is the fixed orifice steam trap. Fixed orifice traps contain a set

orifice in the trap body and continually discharge condensate. They are said to be self-

regulating. As the rate of condensation decreases, the condensate temperature will

increase, causing a throttling in the orifice and reducing capacity due to steam flashing on

the downstream side. An increased load will decrease flashing and the orifice capacity

will become greater.

Orifice steam traps function best in situations with relatively constant steam loads. In


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situations where steam loads vary, the orifice trap is either allowing steam to escape or

condensate to back up into the system. Varying loads, such as those found in most steam

heating systems, are usually not good candidates for orifice steam traps. Before an orifice

trap is specified, a careful analysis of appropriateness is recommended.

04. Importance of Traps:

Steam is used both for process applications and to build heating spaces. Rising energy

costs make steam an expensive utility...too expensive to waste. Even if steam is a by-

product of what you make, conserving it can add dramatically to the bottom line.

A steam system can be a complex collection of pipes, valves and steam traps carrying

and regulating steam to countless areas within your facility. Traps are like stop signs at


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the end of the route. They keep the steam from blowing off to atmosphere, and purge it of

impurities that can make your system inefficient or cause damage.

Steam is hotter and lighter than water so it travels through the steam much faster. Water

or condensate forms in the pipe work and settles to the bottom. It tends to be pulled along

by the high velocity steam. If too much condensate collects in the pipe it can actually form

little waves. If the waves become large enough to touch the top of the pipe they cause a

momentary blockage. The force of steam behind the wave is still being forced through the

pipe. It will push the water forward with the force and velocity of a bullet. This

phenomenon is commonly referred to as water hammer. Its effects can be catastrophic to

pipe elbows, valves and even steam traps.

Removing condensate and air as soon as they form creates a more efficient transfer of

thermal energy throughout the steam system. More efficient is a synonym for more

profitable.

05. Failed Traps -- Cause and Effect:

Steam traps can fall open, fail shut, or in the case of mechanical thermodynamic and disk

styles they can continuously flutter between open and shut. When a trap fails open it isoften referred to as "blow-by". When a trap is blowing-by, it means that, in addition to

condensate and non-condensate gases, some steam is also being vented. If steam is a

commodity and it's being wasted by a faulty trap, then your facility is not running as

efficiently as it could. A typical failure rate for failed open steam traps is 15-30% of a

facility's steam trap population. A facility with 1000 steam traps may have 150 to 300

failed open traps. This translates into a loss of steam.

A trap that is failed open can also create downstream problems for other traps within thesystem. Steam traps, aside from purging unwanted condensate, also act as flow

regulators for the entire system. Like the locks in a canal, if one trap is failed open, the


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other traps in the system are subject to increased pressures. Certain traps may not

perform well with the added pressure and will have a shorter lifespan.

Traps that fail shut, due to corrosion from lime or other minerals, will allow condensate to

build-up in the system. The accumulation will follow the piping to low spots where enough

water will cause damaging water hammer. In colder climates there is also the threat of the

water freezing and bursting the pipe.

06. Trap failure:

Excluding design problems, two of the most common causes of trap failure are over

sizing and dirt.

• Over sizing causes traps to work too hard. In some cases, this can result in

blowing of live steam. As an example, an inverted bucket trap can lose its prime

due to an abrupt change in pressure. This will cause the bucket to sink, forcing the

valve open.

• Dirt is always being created in a steam system. Excessive build-up can cause

plugging or prevent a valve from closing. Dirt is generally produced from pipe scale

or from over-treating of chemicals in a boiler.

07. Testing Methods for Steam Traps:

With a fuller understanding of steam traps basics maintenance personnel are better

equipped to inspect traps throughout the facility using common methods.

1. VISUAL INSPECTION:

In a visual inspection the operator will check that the discharge valve is functioning.

This requires venting live steam to atmosphere and can pose safety issues. Because

it opens the closed portion of the system it is not a 100% reliable test. Visual


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inspection is important because a trained operator can look for potential problems in

engineering and design that can lead to trap failures.

2. THERMAL INSPECTION :

Another method for routine testing of traps is with contact or non-contact temperature

checks. Upstream and downstream temperature checks can reveal failed open traps.

But variables such as back pressure in the system can make temperature checks less

accurate. Thermal inspections are useful for identifying heat loss, overloads and

pressure build-ups.

3. ULTRASONIC INSPECTION :

Using both visual and thermal methods it is easy to spot traps that have completely

failed. But an ongoing predictive maintenance program involves looking for problems

before they become catastrophic so as to minimize system damage (water hammer),

minimize inefficiency (loss of heat transfer), and reduce the residual decline in product

quality.

Ultrasonic testing gives the inspector an "inside view" of the trap. A quality detector

translates high frequency ultrasonic noise to audible frequencies. These frequencies

are localized to the source of contact so the inspector will not be disturbed by ambient

parasite noise downstream. More sophisticated ultrasonic detectors are equipped with

digital measuring capabilities, internal data loggers that track all your steam system's

assets on board, and a direct PC interface for downloading collected data to an

organized filing system. Multi functional inspection tools combine both ultrasonic and

temperature measuring capabilities in one versatile device.

Inspectors using ultrasonic inspection methods as part of a regular predictive

maintenance schedule can accurately locate steam traps with full or partial fault

conditions.


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08. APPLICATION:

There are three primary categories of steam traps:

•

Mechanical

• Thermostatic

• Thermodynamic

Popular traps in these categories include the inverted bucket, the float, the

thermostatic and the thermodynamic disc types.

Which one to use depends on the application. The steam traps prime missions is to

remove condensate and air preventing the escape of live steam from the distribution

system.

The steam trap must adapt to the application. A disc thermodynamic steam trap

should never be used together with a modulating heat exchanger. Nor is it necessary

to overkill using floating ball steam traps for draining steam pipes.

The table below can be used as a short guide for the selection of steam traps:

OperationType of SteamTrap No or

little loadLight Load

NormalLoad

HeavyLoad

NormalFailureMode

Float &Thermostatic

No Action

Usuallycontinuous.May cycle.

Usuallycontinuous.May cycle.

ContinuousClosed A.V.open

Inverted BucketSmall

DribbleMay

dribbleIntermittent Continuous Variable

Bimetal

Thermostatic

No

Action

UsuallyDribble

Action

May blastat high

pressures

Continuous Open

ImpulseSmall

Dribble

Usuallycontinuouswith blast

Usuallycontinuouswith blast

Continuous Open


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at highloads

at highloads

Disc

Thermodynamic

No

Action

Intermittent Intermittent Continuous Open

09. Finding malfunctioning traps:

As with any mechanical device, a steam trap can malfunction. "If the steam trap fails

closed," the device that should be draining will flood and the heat transfer process will

stop, and whatever product is being produced ... will no longer be up to the required

quality standards. If the trap fails open, there will be a waste of energy, steam will not be

completely consumed or condensed in the exchanger and steam will blow through."

Banyacski notes that a plume of steam escaping from the condensate receiver or from

some part of the condensate return system signals such a condition.

He adds that it is difficult to determine whether a steam trap has failed just partially open,

indicating a slow leak and a developing failure. "Such a ... failure could persist for quite

some time without any outward sign. Therefore, a maintenance person should make

periodic surveys of the installed base of steam traps. Banyacski emphasizes that steam

blowing through a trap indicates that the trap needs to be repaired or replaced.

10. Trap inspection methods:

Oftentimes, a misapplied steam trap (too small, the wrong design) will malfunction.

Ultrasonic, infrared temperature measurements and visual inspection have proven usefulto maintenance personnel in checking for malfunctioning steam traps. Of the three,

ultrasound is the most reliable. Visual inspection requires an inspector to let a steam trap


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discharge to atmosphere. However, doing that changes the parameters of the closed

system and, therefore, can be unreliable.

There are enough variables in the system - backpressure, for example - so that

temperature is not the most reliable indicator either. Portable infrared thermometers

provide close estimations of pressures on valves, traps, and coil heaters. These devices

are also useful for spotting conditions such as heat loss, the need for insulation,

overheating, overloads, and cooling failures. Thus, an infrared thermometer be used

along with ultrasound.

Traps that have failed completely open are easy to detect, but the object is to find failing

traps before they fail completely. Ultrasonic testing can do that. In essence, using an

ultrasonic instrument is like putting the inspector inside the steam trap and piping system

allowing him to detect a leaking steam trap. Ultrasonic detectors translate ultrasonic

emissions ... into sounds the human ear can hear.

Technicians who use ultrasonic detectors on a daily basis can achieve accuracy that

exceeds 98%. And regarding frequency of inspections, process components of

equipment, as well as drip mainstream traps should be checked twice a year.

Heating steam traps (in facilities that use steam for space heating) should be tested

annually and instituting a reporting system to keep tabs on the location, type, size,

capacity and condition of all traps in a steam system is imperative.

Documents

Steamtrap Module