Temper Embrittlement of LAS pipes ?

[ATUL KHATRI]

API 934 A,B,C and D clarifies the impact and preventive actions for Temper Embrittlement for thick Low alloy steel (1.25Cr0.5Mo,2.25Cr0.5Mo etc..)vessels but i have never found anything for LAS pipes?

Does LAS pipes are not susceptible to Temper Embrittlement?

I believe "TE" is related to basic material of construction, temperature range and time. But no where any such damage mechanism is covered in any code for pipes.

Please share your views or any such issues you have come ac-crossed.

 

[metengr]

Low alloy steel pipe material can become thermally embrittled, similar to plate steels used in vessels. The only difference being thickness and metal temperature, where the pipe thickness can be much thinner in comparison to vessels, which does play a significant role in notch toughness behavior.

For pipe or even vessels operating at elevated temperature even thermally embrittled pipe or vessel material will most likely be in the upper shelf region and exhibit increased notch toughness. The concern is either pipe or vessel metal temperature near ambient where the embrittled material will be subjected to internal pressure. In this case, thick-walled vessels are at greater risk of brittle fracture rather than piping, when subjected to ambient temperature pressure.

 

[Chumpes]

Hello
what does "heavy wall" means ? can it be quantified in terms of thickness ?
thanks

 

[metengr]

If you mean thick walled vessels - greater than 3" thickness, typically.

 

[weldstan]

Those low alloy steels that are typically subject to temper embrittlement are Cr-Mo, Mn-Mo, and Ni-Mn-Mo alloys. Mn-Mo and Ni-Mn-Mo steels have been used in place of C-Mo alloys in heavier wall construction due to their increased tensile properties but one must take into account their embrittlement potential when operating at temperature between 700 F and 850 F and after PWHT.

 

[ATUL KHATRI]

@ metengr (Materials)
Thanks for your valuable response. I do agree that heavy wall thick vessels of Low alloy steels are more susceptible to "TE" as detailed in API 934 A,B &C. But from where this min thickness criteria( as you mentioned 3" and higher) comes from?

 

[Chumpes]

I was about to ask for the meaning of "thick wall" but i took the expression "heavy wall" from the title of API 934 =)

somme users use 50mm as a limit, but i found no definition in API 934.

1.25Cr-0.5Mo should not be selected for wall thickness above 3" due to difficulties in reaching required toughness for plates

Regards

 

[weldstan]

Heavy wall thickness is not defined in the ASME Codes. In the 1970s, most Owners and Engineers considered the need for enhancd construction and materials toughness requirements for 4" wall and greater. In the 1980s, most of the Petrochemical Owners and Engineers had lowered these added requirements for 3" thickness and over and some down to 2.5". The work of Puzak and Pullini (not sure of spelling) provided much of the basis for addded requirement for heavy wall construction.