Stress relief of A106 at ambient conditions

[valero]

I have a piping system constructed of A106 carbon steel pipe. This piping is too constructed per ASME B31.1 piping code. The nominal thickness is greater than .750” thus requiring heat treatment per the code. This piping was constructed in the year 2000 and has not seen service. We have no record of heat treatment being performed. I have been told by a metallurgist that over time this material will stress relieve itself, and thus stress relief is not required on this particular piece of piping. Has anyone ever heard of natural stress relief at ambient conditions? The service of this piping will be 650# steam.. I am going to have this piping heat treated per the code for documentation and liability reasons, but I am curious if there is any merit to what I was told.

 

[metengr]

No. The carbon steel pipe welds will not be stress relieved at ambient temperature. It could be that the metallurgist was referring to stress relief in service if the steam temperature is at 700 deg F. Good call to have the welds stress relieved!

 

[valero]

Thanks metengr! When discussing this with the metallurgist I made sure he was implying that the stress relief has already occurred naturally over 4 years under ambient conditions. I have heard of certain situations were stress relief has been obtained during operation below the critical transformation temperature; however, as you stated that would be significantly higher than ambient conditions, and still not per applicable code.

 

[VeryPicky]

In addition to metengr posting: from code point of view if you don't PWHT the pipe than you have a non-compliant pipe. I assume your jurisdiction requires the piping in question to comply with the code, so the PWHT seems a necessity. The ASME code addresses time extension for lower PWHT temperatures but PWHT in room/ambient temp. is definitely not recognized by the Code.

Putting Human Factor Back in Engineering

 

[priyasachin]

Dear Friend,

For cast iron beds used for precision machinery like jig borers etc., it has been the practice to get the beds rough machined and leave it in the open atmosphere for 3-4 years for 'natural ageing' to take place. Such beds have been found to retain its accuracy and free of distortion for the life of the machine. Though modern tendency is for thermal stress relief of the beds, some manufacturers would go in for this tested path than turn modern.

Regards,
MRCN