Charpy Impact Properties for F11 CrMo Steel

[Guest102023]

I am looking for typical data for A182, F11, Class 1 forgings in about 4 inch section thickness. Anywhere in the temperature range -20F to +70F, or else a transition temperature. Thanks.

 

[metengr]

New or in-service?

 

[stanweld]

I have had no problem asking for and obtaining impact toughness testing at -20 F and meeting 15/12 ft-lbs absorbed energy criteria for F11, since about 1984.

This is based on test locations as specified in A182 for new forgings and does not imply that you will obtain same values on actual parts in any location, especially forging in use and never subject to testing.

 

[metengr]

Agree with stanweld. There is no specific requirement for impact testing this grade of steel because it is normally used in elevated temperature service, meaning grain size can be all over the map. Bottom line is minimum 15 ft-lb is met at -20 deg F, and that is it.

 

[Guest102023]

Looking for new values, but the part has been in service for decades and I need to interpret the Cv test results. I realize properties will be quite variable from one heat to the next and particularly with location within a large complex shape.

-20F sounds like a normal MDMT in my neighbourhood, but the part operates at up to 950F. I see some microstructural degradation in the hottest surfaces, but no difference in hardness between hottest and coldest regions. One set of impacts @ -20F are well below 15/12 ft-lb, but does that necessarily mean there may be some temper embrittlement?

 

[stanweld]

There is very little temper embrittlement with F11 unlike that of F22. Having said that, some embrittlement may be observed. How long ago was this put in service? Toughness in this grade is highly dependent on heat treatment and degree of hot work as well chemistry.

 

[Guest102023]

30-somthing years old. It has low phosphorus (0.005) but I didn't have other tramp elements tested.

 

[metengr]

brimstoner;
Why in heavens are you worried about interpreting notch toughness values with a component that was manufactured for elevated temperature service with no original notch toughness requirements in the material specification? The F11 and F22 (or P11 and P22) are supplied with no notch toughness requirements because they are operating well above the DBTT. Even if you have some manifestation of thermal embrittlement over the course of many thousands of hours of elevated temperature service, your main concern should be creep damage, not worrying about notch toughness. This is why ASME Section I components have no notch toughness requirements for application in elevated temperature service.

The above items are typically supplied as either annealed or normalized and tempered (N&T). Even a N&T thermal treatment is not going to improve notch toughness. When Section II endorsed this material for use in elevated temperature service back in the 1950’s, the concern was adequate creep strength not low temperature properties.

 

[Guest102023]

metengr,
I get all of that, except that one of the main concerns re:embrittlement is during a potential hydrotest at ambient temperature. And actually, the operating temperature cycles, so low temperature toughness might be of some concern. Having said that, however, I am sure this part was not ordered with impact requirements.

This is a post-mortem and I just want to be able to comment intelligently on Charpy results that were requested by the client. (I have already documented the creep damage that killed this component).

 

[metengr]

Hydrotest? If so, this is normally conducted at 60 deg F metal temperature by Code as a minimum requirement, or during commissioning, and not at -20 deg F. Second, for simple pressure testng for leak tightness of a boiler or pressure vessel, you should be using as low a test pressure as possible. There is no reason to repeat a code hydrotest on an operating vessel, even for an alteration.

There are ways around this. You can even use ASME Section VIII, Div 1 curve A and prewarm the water for pressure testing, if necessary.

 

[Guest102023]

I am not very familiar with hydrotest rules and just assumed worst-case conditions would apply. Anyway, the material I am examining is scrap, so its not a concern.

 

[stanweld]

Thirty years ago, we found it quite difficult to obtain 15/12 ft-lbs at -20F but not impossible. If the grain size is near 4 and the microstructure perlitic, the material is more than likely annealed; in which case, expect 15/12 absorbed energy at about 32 F or higher depending on long term high temperature exposure.