FFS Forum: When is a Brittle Fracture Assessment Needed?

Since about 1987, all of the major design codes have had a brittle fracture check as part of the original design. For pressure equipment designed after that, it would seem that a brittle fracture check would not be necessary. Well, not so fast! There are actually quite a few situations where a new brittle fracture assessment is very much necessary.

The joint ASME/API fitness-for-service (FFS) standard, API 579-1/ASME FFS-1, Fitness-for-Service (API 579), provides some guidance, to which I’ll add a few thoughts of my own, to come up with a list of reasons why you might need to perform a brittle fracture assessment (BFA) on an in-service pressure system.

The Two Most Obvious Reasons

Designed Before 1987

Around 1987, all of the major pressure system codes and standards introduced a brittle fracture check into the design procedure. ASME’s code for unfired pressure vessels (Section VIII, Division 1) introduced this check in the 1987 addenda. If your pressure vessel or piping system was designed before this, no such check was performed at the design stage. If you discover such a system, you should perform a BFA, in accordance with Part 3 of API 579, as soon as you become aware of this deficiency.

Required by Another Part of API 579

This one is pretty obvious too. Often, when performing an FFS assessment (by Parts other than Part 3), the procedure requires that you verify that the material has sufficient toughness. For example, Part 5 (Local Metal Loss) lists the conditions required for the use of Level 1 and 2 procedures, where Paragraph 5.2.5(b) says:

“The material is considered to have sufficient material toughness. If there is an uncertainty regarding the material toughness, then a Part 3 assessment should be performed.”