Welding Q&T P1 Steels

[zakk]

We are manufacturing a vessel/pipe fitting from triple certified material, i.e. SA105 / SA350-LF2 Class 1 / ASTM A694 Grade F46. Our Regulatory Authority (R.A.) has stated that they will register the fitting in the Normalized only condition. Our Material Supplier says to consistently achieve the mechanical properties of all three material specifications, we should consider Quench and Temper heat treatment. Our R.A. says that if we go with Q&T, we must PWHT to the tempering temperature, paying close attention to our heat input, regardless of material thickness. We want to use Q&T material in the as-welded condition, per our WPS.

I talked to a couple of Welding Engineers and they said the requirement for heat treatment of P1 materials is based on material thickness, not the heat treatment condition of the base metal. Our WPS (P1 Group 1 & 2 to P1 Group 1 & 2) doesn't list base metal heat treatment as a variable.

I can't seem to get a satisfactory response from our R.A. as to the reason behind the PWHT requirement. As it is totally possible I'm missing something, does anyone know where, in any vessel/piping code, where PWHT is a requirement for Q&T P1 steels, regardless of thickness?

 

[weldstan]

Under the ASME Codes, it is not required to PWHT Q&T materials unless the thickness dictates to do so. You should not purchase this triple certified material. SA-105 is normally not made to a fine grain melting practice and will not have as desireable high temperatrure properties if so made. SA-350 LF2 must be made to a fine grain melting practice which provides its low temperature toughness properties.

yours,
stanweld

 

[metengr]

PWHT of quenched and tempered steels used by ASME Boiler and Pressure vessel Code are governed by thickness - Section VIII, Div 1 UHT-23 and Table UHT-56. In some cases, PWHT can be waived using control on interpass temperature. PWHT can result in a reduction of notch toughness. I would agree that using the normalized condition would be the better route.

 

[zakk]

Thanks for the replies.

Weldstan: The material is essentially SA350-LF2 Class 1 with 46 ksi minimum yield. That covers all three grades. The A105 will be manufactured to a fine grain practise to satisfy the requirements of SA350.

Metengr: I agree normalizing is a better way to go, but the higher yield requirements puts a little more pressure on the forging manufacturer to get the yields in the normalized condition - something I'm sure gets factored into the price. It's the PWHT requirement from our R.A. that's puzzling me and both responses help. Thanks.

 

[weldstan]

Then why not just purchase SA-350 LF2 since it is apparent low temp properties are what you are after? Having said that, the manufacturer's triple certification may not be of concern to you based on your low temp application needs. Still be aware that the "one-size-fits-all" steel manufacturing may well lead to the misapplication of materials for specific service conditions.

 

[wegm]

zakk,
Whenever you are to perform PWHT on welding that the base metal is in "quenched and tempered" condition you shall pay special attention since you may loose the "quenched-tempered" properties of the the base metal. As you know the quench-temper heat treatment is performed in order for the material to be done harder (first the material shall be heated above the upper critical temperature, then it is cooled rapidly and finally it is heated at about 600 deg C), so if you perform PWHT above the tempering temperature (about 600 deg C) you may loose the material's specific properties. Please have a look at these links that among others they clarify such an issue:

http://www.weldinguide.com/gdanastasiadis/viewtopic.php?f=5&t=413

http://www.weldinguide.com/gdanastasiadis/viewtopic.php?f=15&t=387

regards
wegm

 

[jamesl]

I see some confusions here between the Quench and Tempered materials covered under UHT section of the Code and regular P1 materials in Q&T condition. They are different. There are no special fabrication requirements for regular P1 materials (such as SA-105 or SA-350) in Q&T conditions. I think your AI was think about Table UHT-56, which is not applicable to your materials.