DISHED END MAKING

CONTENTSCONTENTS

• Definition• Methods of SR• Terminology used in SR• Fuel used• Types of firing• Other Equipments used

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DEFINITIONDEFINITION

PWHTPWHT

• PWHT is done to relieve the stress generated in metal by tremendous heat input during welding operation.

• Therefore it is also called as “Stress Relieving”

METHODS OF SRMETHODS OF SR

METHODS OF PWHTMETHODS OF PWHT

• There are 2 ways of SR:1. SR in a furnace (Furnace firing)2. SR by using job as a furnace (Internal

firing)

FURNACE FIRINGFURNACE FIRING

• In this method job is placed inside the furnace.

• Furnace is closed & burners are used to increase the inside temperature of furnace by this inside pressure also increases , using air as a media heat is transferred to job this leads to raise the job temperature inside furnace.

Photograph showing Furnace Photograph showing Furnace firingfiring

INSIDE FIRINGINSIDE FIRING

• This method is selected generally when job cannot be placed under furnace due to any reason.

• In this the whole job is insulated from outside with specific thickness of insulating material.

• Burners are used from outside to maintain the inside & outside temp. of job this is measured on recorders by thermocouples tacked inside & outside the job.

Photograph showing internal Photograph showing internal firing arrangementfiring arrangement

TERMINOLOGY IN SRTERMINOLOGY IN SR

PWHT CYCLEPWHT CYCLE• Loading Temperature (max)• Rate of heating (max)• Soaking Temperature• Soaking Time • Rate of cooling (max)• Unloading Temperature• Variation in any 2 thermocouples not to exceed

_____/ hr during heating or cooling

LOADING TEMPLOADING TEMP

• At this temperature the job should be loaded in furnace I.e if the job is in furnace itself then the temperature recorder must be put on for recording & rate of heating is to be maintained as per given heat treatment request .

• Always “last in” thermocouple is referred.

RATE OF HEATINGRATE OF HEATING

• This is the rate of increase of temperature inside the furnace to achieve soaking temp. & to be maintained when the job is loaded in furnace I.e after loading temperature is achieved also called ROH , it is measured in deg. cel / hr. Always maximum value is given in request.

SOAKING TEMPERATURESOAKING TEMPERATURE

• To relieve the stress job needs to be kept at a particular temp. this is called soaking temp. where job is soaked at this temp. for specific period as per request.

SOAKING TIMESOAKING TIME

• For stress relieving job is soaked at certain temp. for certain time & this is called soaking time to ensure stresses are relieved.

RATE OF COOLINGRATE OF COOLING

• Temp. of job after keeping it in soaking temp. has to be cooled at a certain rate & this is to be maintained unless unloading temp is achieved & this cooling rate is called ROC & always max value is given in request.

UNLOADING TEMPUNLOADING TEMP

• The temperature at which job is taken out. After this temp further cooling to ambient temp is always mentioned in request.

• Always “last out” thermocouple is referred.

TEMP. VARIATIONTEMP. VARIATION

• The variation in temp. between any 2 thermocouples during heating/cooling should not be more than specified in request

FUELFUEL

FUELS USED FOR SRFUELS USED FOR SR

• Fuel is only a source for heat generation.• Generally following fuels are used :• Furnace Oil• HSD (high speed diesel)• LDO (light diesel oil)• LPG (liquefied petroleum gas)• NG (natural gas)

Fuel technical dataFuel technical dataS.No Fuel Calorific

value

FIRING METHODSFIRING METHODS

FIRING METHODSFIRING METHODS

• GAS FIRED• OIL FIRED

GAS FIREDGAS FIRED

• Gas Burners with sensors • Control Panel with FFD • Blowers• PRV (Pr. Regulating valve)• Gas Header (Solenoid Connection)• Gas Hoses

OIL FIREDOIL FIRED

• Oil pumping unit• Oil Burner with sensor• Control panel with FFD• Combustion air blowers• Air compressor & air manifold• Oil Header with Solenoid• Oil hoses

OTHER EQUIPMENTS USEDOTHER EQUIPMENTS USED

• TAU ( Thermocouple Attachment Unit ) • Thermocouples• Compensating Cables• Temperature Recorders