Fatigue curves for 3Cr-1Mo at elevated temperature

[RVM21]

Hi Members,

As per ASME Sec VIII Div 2 Cl2, 3Cr-1Mo creep limit is below 475 degC. But fatigue curves are not available in Sec VIII div 2 or API 579 or in STP-PT-096 – 2022 for 3Cr-1Mo . Could someone advise how we can do a fatigue analysis with a cyclic operation between 430 degC to 470 degC ? Can we go for fatigue curves of a comparable material (if any) ? Whether it is allowed to extrapolate the values from available curve for low alloy in ASME Sec VIII Div 2 ?

Appreciate your support!

Thanks & Regards
RVM21

 

[GD2]

RMV21,
Not sure if I have understood your question right.
Creep and fatigue are two different things. Obviously, both can be combined but I don't think there is any design rule in BPVC due to its complexity with variable stress with time.

BPVC Section III provides rules for creep design.
Fatigue curves are given in BPVC Div 3
I would believe you can do a fatigue analysis for any temperature.
Div 2 Part 5 will give you the rule for fatigue analysis.

GDD
Canada

 

[RVM21]

Thank you for the response GDD.
ASME Sec VIII DIV2 part 5 allows usage of DBA procedures as long as allowable stress is governed by time independent properties. Time independent limit of 3Cr-1Mo materials for Div 2 Cl 2 is below 475 degC. This allows design of 3Cr-1Mo up to 474 degC using DBA procedures.

However as per Annex 3-F, for low alloy steel fatigue curves are available only upto 371 degC (I found the same temperature limit in Div 3 too). I have referred recent STP-PT-096 where 2 1/4 Cr-1Mo and 3Cr-1Mo fatigue data are listed separately and no data is given under the index for 3Cr-1Mo. Is there a way we can get the fatigue curves of 3Cr-1Mo for temperatures above 371 degC and below 475 degC. This will be useful for the cases where temperature cycles between 420C and 470C .

Besides, Can we extrapolate the curve given in Div 2 to a high temperature ? Or can we use same curve of 2 1/4 Cr at high temperature (from STP) , if it is conservative ?

Thanks & Regards
RVM21