How to Read PWHT Chart

PWHT - [Part 1] HOW TO READ A PWHT CHART 11/30/2012 05:11:00 PM

Due to the advancement of metallurgy a lot many dierent materials are now used in mechanical construction industry !n this a few are heat treated to im"rove mechanical "ro"erties

#eat treatment is done $ecause of two reasons 1 % Process re&uirement 2% Material 'e&uirement

#eat treatment can $e done in many ways (urnace heating) *il +red heating) ,lectric resistance heating etc

 -here are dierent dierent ty"e of heat treatments treatments li.e li.e normaliing) annealing etc etc

#ere we are going to discuss a$out the gra"h which is generated in electric resistance heating for P#- Post eld #eat -reatment%

'eading a P#- chart is what is going to $e discussed here

elow is the gra"h of a "wht "rocess ets start reading it#ere i am discussing on the understanding that you are a little $it familiar with the "rocess%

!n this chart)

4a6is re"resents tem"erature and 7a6is re"resents -ime

!n 4a6is each line to line distance re"resents 10Deg 8 9ee it is written as 4 100 8)

that means in 4 a6is) 2 means 2 4 1008; 2008) 3 means 3 4 1008; 3008 etc%

!n 7a6is each line to line distance re"resents half an hour -hat means the time $etween 2 and 3 re"resents one hour

 -hese are the $asics

#ow to read the gra"h<

 -he gra"h contains several lines) =) 8) 8D) =, 1 % = is '=-, *( #,=-!>? curve

2% 8 is 9*=@!>? -,MP,'=-A',

3% 8D is '=-, *( 8**!>? curve

B% =, is '**M -,MP,'=-A', curve

hen you chec. the P9 you can see the re&uired values for each of these

1) AB: Rate of heating: !n P9 it is mentioned as a ma6imum value !n the gra"h the rate of heating is the slo"e of the curve = 9o the value of the slo"e should not $e more than the value in P9

#ow to calculate the slo"e: 9lo"e ; .l/lm >ow in the gra"h given a$ove) for = line) .l;C0Deg8 and lm;1/2 hr

slo"e ; C0 / 1/2% ; 10Deg8/hr E 9o in this gra"h the rate of heating is 10Deg8/hr

2) BC: Soaking Temperature: !n P9 it is mentioned as a single value with some "lus/minus allowance along with time it is to $e steadymentioned as minimum%

#ere in this gra"h it is F20Deg 'eading in 4a6is% and for a""ro6imate 2hr and 10minutethis is an a""ro6imation'eading in 7a6is %

3) CD: Rate of cooling: !n P9 it is mentioned as a ma6imum value !n the gra"h the rate of heating is the slo"e of the curve 8D 9o the value of the slo"e should not $e more than the value in P9

#ow to calculate the slo"e: 9lo"e ; &r/"& >ow in the gra"h given a$ove) for 8D line) &r;130Deg8 and "&;B5 Minthis is ta.en as an a""ro6imation from the gra"h%

slo"e ; 130 / B5 ; 2CGDeg8/Min E 9o in this gra"h the rate of heating is 1F3Deg8/hr

4) AE: Room Temperature: -his is the room tem"erature) here it is B0 deg 8

oa!ing Temperature: oading tem"erature is the tem"erature at which controlled heating maintaining the rate of heating in the P9% starts) u" to which there is no need for controlled heating

"nloa!ing Temperature: Anloading tem"erature is the tem"erature u" to which controlled cooling maintaining the rate of cooling in the P9% occurs) $elow which there is no need for controlled cooling>ormally the "ower connection is disconnected $elow the tem"erature) .ee"ing the insulation =fter getting cooled to the atmos"heric tem"erature the insulation is removed

>: Please chec. the s"eed of the chart movement in the P#- machine) >ormally it is 25mm/hr