Interpass temperature and where is it measured

[alvaro]

Could someone explain about the importance of interpass temperature and where should it be measured?

[balamuruganqaqc]

Hi Friends,
Interpass temperature is defined as "the temperature of the material in the weld area (in a multi-run weld) immediately prior to the application of the second pass and each subsequent pass". Normally it is expressed as a maximum but should not drop below the minimum preheat temperature. Both preheat and interpass temperatures are applied to slow down the cooling rate during welding avoiding the formation of brittle microstructure such as martensite and thus preventing cold cracking. Higher interpass temperatures (not more than 260°C) improve the impact properties of the weldment as a result of finer grain structure that is provided (it has been proved that above 260°C the impact values decrease as the temperature increase). In addition, interpass temperature affects the yield and tensile strengths of the weldment since they decrease with increasing interpass temperature.

Even though some codes specify that "minimum interpass temperature shall be maintained during the welding operation for a distance at least equal to the thickness of the thickest welded part (but not less than 75 mm) in all directions from the point of welding", the maximum interpass temperature shall be measured at a distance not more than 25 mm from the point of welding since measuring in a higher distance could result in significantly higher temperatures in the point of welding .

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M. BALAMURUGAN,
ASST. MANAGER - QA/QC,
L&T - MMH CONSTRUCTIN,
ODISHA,
PH- +91 8763569606,
Email - balamuruganqaqc@lntecc.com

[QCRobert]

What code are you quoting?

[wefel]

QCRobert,
I think that Balamuruganqaqc gives a general approach to such an issue so as to clarify the original query that was:

Could someone explain about the importance of interpass temperature and where should it be measured?

Regarding your query, the below statement:

minimum interpass temperature shall be maintained during the welding operation for a distance at least equal to the thickness of the thickest welded part (but not less than 75 mm) in all directions from the point of welding

specified in the AWS D1.1 and AWS D1.5 codes and it is a good practice for measuring minimum interpass temperature. Instead, if the maximum interpass temperature has to be controlled it is recommended the maximum interpass temperature to be measured on a distance not more than 25 mm from the weld toe so as to avoid the possibility the interpass temperature of the weldment to be higher than the maximum specified interpass temperature.
Could you please let us have your aspect
thanks,
wefel

[QCRobert]

The only reference to interpass temperature in AWS D1.1:2010 that I am aware of is 5.6 Preheat and Interpass Temperature that states, "This preheat and all subsequent minimum interpass temperatures shall be maintained during the welding operation for a distance at least equal to the thickness of the thickess welded part (but not less than 3 in. [75 mm] in all directions from the point of welding."

I am just asking in what code & paragraph is it stated that the maximum interpass temperature shall be measured at a distance not more than 25 mm from the point of welding ?

Regards,
QCRobert

[Ballbearing]

Gents,
Maximum Interpass temperature should be measured right in the middle of the weld, right where the next run is due to start - not 15, 20 or 25 mm away from the weld.

AWS A3.0
interpass temperature, welding. In a multipass weld,
the temperature of the weld area between weld passes.

ASME IX
interpass temperature: the highest temperature in the weld
joint immediately prior to welding, or in the case of multiple
pass welds, the highest temperature in the section of
the previously deposited weld metal, immediately before
the next pass is started.

Cheers,
BB

[QCRobert]

Ballbearing, I concur with your area of measurement.

I was just taking exception to the "shall" wording used by another poster.

Regards,
QCRobert

[GarthDennis]

so why you don't want shall word in posts??? i think you didn't justified it with the reason

[Ballbearing]

Garth,
When "shall" is used in codes or standards it makes something a mandatory requirement.
If it is a recommendation it will be "should" or "may".
Cheers,
BB