POST WELD HEAT TREATMENT (PWHT)
INTERVIEW QUESTIONS
PART TWO AND FINAL
CONTINUATION TO PART 1
The heating of the pipe is done by coils. The
principle of resistance heating method is used for heating with coils. The
coils are wrapped around the pipe or placed around a joint by bending the coils
back and forth. The ceramic beads avoid the touching of thermocouples with the
metal surface. The coils are available in different gauges.
The coils are heated by the heat input through
the control panel. The control panel contains PID controllers where the
requirements of heat input to the coils are manually entered.
The coils are covered with ceramic wool blankets
to avoid heat loss.
What is controlling thermocouple?
The thermocouple which is connected to the
control panel for the controlling of temperature to the coils is known as
controlling thermocouple.
There will be one controlling thermocouple for
each coil used. Depending on the size of the pipe there will be more
thermocouples around a joint. These thermocouples are known as monitoring
thermocouple. The location of the monitoring thermocouple is very important for
proper PWHT to take place.
For a horizontal joint, the controlling
thermocouple should be in the bottom. If it is on the top what will happen?
That thermocouple will detect the radiant energy also and thereby the actual
heating of the coil will be less.
The PWHT temperature range and holding time for
different materials are as below.
What are the other procedures follow after the completion of PWHT?
Remove the wool, Clean the area free from wool
and other discarded items. Remove the coil. Remove the thermocouple With a flat file, remove the spot where the
thermocouple is tacked. After thermocouples are removed, the areas shall
be visually examined for evidence of defects to be repaired
Make the report and submit the graph along with
the report.
Is hardness to be taken after PWHT?
As per ASME B31.3 Clause 341.5.2 edition 2019, it
is not required. Refer your construction code /procedure/contract documents for
the same. If it is there hardness to be taken.
PLEASE FEEL FREE TO ASK QUESTIONS IF ANY, THROUGH THE 'COMMENTS' SECTION IN THE BOTTOM OF THIS BLOG
FOLLOW ME ON TELEGRAM FOR UPDATES: @MechConstEngineer
END OF THIS SERIES
Disclaimer: Photos are taken from different websites. If this violates any copyright rules this will be removed. Please inform me if any of the photos or contents violate copyright rules. (through 13hareesh13@gmail.com). This blog is meant for educational purposes only. If it is used for any other means without the written consent from the author, the author will not be responsible. The author does not guarantee the accuracy of the data used in this blog. All the information, data, photo/image, calculations presented in this blog should be used at the sole risk of the user. The blogger is not liable or responsible in any way for any damage, losses or costs arising from the use of the blog for any purpose whatsoever or whosoever it may be. The blog is to be used at your sole risk and responsibility.
Summer Internship Training for Mechanical Engineering Students
ReplyDelete