the powerful leak detector for all applications in power plants

THE POWERFUL LEAK DETECTOR FORALL APPLICATIONS IN POWER PLANTS

INTRODUCTION

Power plant turbines, regardless of the typeof fuel used to generate heat in the boilersystem, are turned by the steam generatedby these boilers. The boiler heats purewater and converts it to steam which flowsthrough the turbine in order to generaterotation of the power generator. Afterexiting the turbine, the steam is routedthrough a condenser which coolsthe steam to water. Thiswater is returned to theboiler to start the cycleagain. Typically the highpressure region of theturbine is working at apressure of about 200bar, while the lowpressure region isworking at a pressure of35 to 50 mbar. Because of the leaks thatare inherently present inthis type of system, avacuum pump (ejectorpump or water ring pump ora combination of the two) isused to maintain the lowpressure region at the requiredvalues.If a leak is being generated and causes anincrease of the pressure in the lowpressure region, it is absolutely important

to immediately locate it and repair it, sincea small increase of some millibars cancause a consistent loss in the efficiency ofthe plant.Various test methods have been used up tonow; they range from very crude andlow efficiency methods upto the use of

ultrasonicdetectors, which do not

fit well within a very noisy plantenvironment, or to the use of freondetectors, which require isolation of thepart under test from the system, and mustbe abandoned because of atmosphericpollution restrictions.

THE NEW TEST METHODRECOMMENDED BY VARIAN

Varian is proposing a method based onhelium as a tracer gas, which allows easy

and quick location of leaks, and istherefore the best method to

insure proper operation ofpower plants low pressure

steam systems.The use of helium is

advantageous because itis non-toxic, non

flammable, relativelyinexpensive, and quickly

diffuses through smallleaks. In addition, helium is

non reactive with otherchemicals and, because of its

low concentration in theatmosphere (only 5 ppm), very

small leaks can be detected withoutthe possibility of error.

This method allows the maintenanceengineer the flexibility to perform leak testswhile the plant is operational, without theneed to isolate the sections under test, anda single operator can perform the full test.The detector recommended for thisapplication is the Varian HeliTest GEN,derived from the basic HeliTest leak detector,used in many industrial applications, andwell known for its high sensitivity to heliumand its reliability in operation.

Use of Hel iTest GEN for locat ion of leaks on the steam circui t o f a turbine of a working power plant

VACUUMPUMPCONDENSER

HeliTest GEN

NOT CONDENSIBLE GASES OUTLET(AT ATMOSPHERIC PRESSURE)

H e l i T e s t G E N C o n n e c t i o n t o S y s t e m

Samho Syscom Ent. / www.vacuum.co.kr Varian, Inc. Vacuum Technologies

HeHe

BASIC UNIT PORTABLE LEAK INDICATOR

HeliTestDETECTOR

TRANSMITTER RECEIVER

H2OFILTERS

PROBE

LEAK L2

LEAK L1

SYSTEMREADY

SPRAYTIME

RESPONSETIME

H e l i Te s t G E N B e n e f i t s

The HeliTest GEN is a self-contained, rugged and easy-to-use leak detector, specifically designed to perform leak detection and leak locationin power plant applications.Most important benefits of this instrument are:

HIGH SENSITIVITYThe HeliTest GEN is sensitive to 2 ppm of helium, equivalent to 5 x 10-6 atm cc/sec.This roughly corresponds to one cubic centimeter of air escaping from the leak every week or to a bubble escaping every day.

HIGH SELECTIVITYThe HeliTest GEN is only sensitive to helium, therefore no false signals created by the presence of any other gases are possible.

SIMPLE OPERATIONNo specific operator training is required. The unit is designed to allow leak detection and leak location be performed by a single operator.

RUGGED CONSTRUCTIONDesigned for continuous operation in industrial areas.

HIGH RELIABILITYVarian long experience with HeliTest leak detector has allowed design of a very reliable instrument. Every time the unit is switched on, itautomatically performs an autocheck cycle to ensure proper operation.

AUTOZEROUse of automatic or manual zeroing system allows detection of leaks even in high helium backgroud environment.

H e l i T e s t G E N O p e r a t i o n


THE HELITEST GEN PRINCIPLE OF OPERATION

The HeliTest GEN is a leak detector basedon what is called “Selective Ion PumpDetector” (SIPD). The principle of operation of this newtechnology is based on a special silica

membrane which, if heated to a giventemperature, becomes permeable tohelium, because of its small molecule, butnot to other gases. An ion pump will detectand display a signal proportional to thequantity of helium that has permeatedthrough the silica membrane, and this

signal will be diplayed showing the heliumleak rate. This system of operation is highlysensitive, due to the very low pressure inthe ion pump (10-9 mbar), and very reliable,due to the absence of moving parts. In the HeliTest GEN a sample of the gas tobe tested is pulled from the pipe or otherobject under test towards the sensor froma sampling pump. If this gas samplecontains any helium, it will be detected bythe basic unit, and a “leak” signal will beshown, allowing not only to determine itsrelative size, but most importantly to locateits position. The Portable Leak Indicator,that can be carried up to 2,000’ (600 m)away from the basic unit, will show a signalindicating that a leak has been found. Theleak can be then rapidly repaired andequipment operation restaured in theshortest possible time.

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54321

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54321

1 – Sampling line2 – Power3 – Auxiliary pump switch

4 – Auxiliary pump power5 – Leak signal6 – Recorder output

7 – Bypass push-button8 – Leak signal transmitter

H e l i T e s t G E N B a s i c U n i t


6

5

4

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6

5

4

3211 – Receiver2 – Leak signal response

time display3 – Helium spray time

display4 – Helium spray pipe5 – Ready signal6 – Spray Helium button

H e l i T e s t G E N P o r t a b l e L e a k I n d i c a t o r

checking underground pressurized powercables. These cables can be generally easilytested even if placed underground, thanksto the high diffusivity of helium, which can

move upwards from the leak location,allowing its detection without need to digany holes on the ground.

HOW TO PERFORM A TEST IN A POWERPLANT USING THE HELITEST GEN

The HeliTest GEN allows performing leakdetection and the specific location of leaksin the shortest possible time, and can beoperated by a single person.In order to use this instrument, here is ashort description of the operations to beperformed.

1) The HeliTest GEN basic unit must beconnected to the system under test. It isenough to connect the outlet of the vacuumpump to the HeliTest GEN inlet port.

2) After having connected the HeliTest GENBasic Unit to the system to be checked, theoperator starts to inspect the system andcarries the HeliTest GEN Portable LeakIndicator. The indicator is then used by theoperator to spray helium to the suspectedareas, and to record the delay time for thehelium signal to appear in case of a leak.

3) When helium enters the system througha leak, it is detected by the HeliTest GENand the leak signal is shown both on thefront panel of the unit and on the HeliTestGEN Portable Leak Indicator, which acts asa radio signal receiver. This signal willindicate both the size and the location of theleak. The operator can continue the searchuntil all leaks are detected and located. The helium spray time and the responsetime are substantially dependent from theplant configuration and dimensions, andalso from the distance between the checkpoint to the place where the detector islocated. Typically the helium spray timeranges from 15 to 30 seconds, and theresponse time, that is the time necessary toget a leak signal, from 20 to 90 seconds. The spray time and response time are alsoshown on the Portable Leak Indicator.

OTHER APPLICATIONS OF THE HELITEST GEN IN POWER PLANTS

In a power plant other leak checking jobsare often required, and they can generallybe safely and easily performed using theHeliTest GEN.Besides leak checking the heat exchangers,we can mention the power transformersand related equipment, as well as leak


the powerful leak detector for all applications in power plants

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