PWHT Chart

Dear Mr. Raju Salvi,

Muthir Khabir replying to your question.

Question No: 1 The temperature variation depends on the spec. It may be + or - 20 degree celcius.

Question No: 2 Heating rate and cooling rate depends on the thickness of the material to be heat treated and metallurgy.

Question No: 3 In the PWHT chart the horizontal axis is time and the vertical axis shows temperature.

I hope you might have come across the equation of a straight line i.e,

y=mx+c Where 'm' is the slope and 'c' is the distance of intercept of the line in y-axis. To find m, follow this equation m=y2-y1/x2-x1. Where y2-y1 is the difference between two points in the in the line and x2-x1 is the difference between the two point in the line. Select two points in the temperature and find the difference between the two. you do the same for time. You have to divide the co-ordinates accordingly. Then divide the difference you will get the heating rate. You do the same for cooling rate.

NOTE: SLOPE IS CONSTANT FOR A STRAIGHT LINE.

you will get the slope as degree celcius per hour. The soaking time is constant for

1 hour or 2 hour depending on the thickness.

Note: During PWHT no welding should be carried out on the same spool. Because this will interfer with the chart and and the exact line cannot be achieved. In such case stop the welding because PWHT once started cannot be stopped.

- Vasanthakumar

Muthirkhabir

Qarn Alam steam project.