8 Damage Mechanisms and Failure Modes Flashcards
- 1 Introduction
- 1.1 General
- This section provides guidance in identifying credible damage mechanisms and failure modes of
pressure boundary metallic components that are included in an RBI analysis
- 1 Introduction
- 1.1 General
- Damage mechanisms include
corrosion, cracking, mechanical, and metallurgical damage
- 1 Introduction
- 1.1 General
- Failure modes identify how the damaged component
will fail (e.g. by leakage or by rupture)
- 1 Introduction
- 1.1 General
Understanding why damage
mechanisms is important
a) analysis of
the POF;
- 1 Introduction
- 1.1 General
Understanding why damage
mechanisms is important
b) selection of appropriate
inspection intervals/due dates, locations, and techniques;
- 1 Introduction
- 1.1 General
Understanding why damage
mechanisms is important
c) decision-making ability that can eliminate or reduce
the probability of a specific damage mechanism.
- 1 Introduction
- 1.1 General
Understanding why failure
modes is important
a) analysis
b) run-or-repair
c) selection of
a) of the COF,
b) decision-making,
c) repair techniques.
- 1 Introduction
- 1.2 Identification of Damage Mechanisms
- The RBI team shall consult with a corrosion specialist to define the
equipment damage mechanisms, damage modes (optional), and potential failure modes
- 1 Introduction
- 1.2 Identification of Damage Mechanisms
sequential approach
a) -Equipment design and
- Data used and assumptions made shall be
a) -current condition shall be considered.
- validated and documented.
- 1 Introduction
- 1.2 Identification of Damage Mechanisms
sequential approach
b) - All process conditions
- Identifying trace constituents (ppm) in addition to the
- shall be considered.
- primary constituents in a process can be very important.
- 1 Introduction
- 1.2 Identification of Damage Mechanisms
sequential approach
c) Considering the materials, methods, and details of fabrication, a list of
the credible damage mechanisms that may have been present in past operation, be presently active, or may become active shall be developed.
- 1 Introduction
- 1.2 Identification of Damage Mechanisms
sequential approach
d) - Under certain circumstances, it may be preferable to list a specific damage mechanism and
- All credible failure modes for each damage mechanism or
- then list the various damage modes or ways that the damage mechanism may manifest itself.
- damage mode should be considered.
- 1 Introduction
- 1.2 Identification of Damage Mechanisms
sequential approach
e) It is often possible to have two or more damage mechanisms at
work on the same piece of equipment at the same time.
- 2 Damage Mechanisms
1. Its vital the understanding equipment operation and
the interaction with the process environment (both internal and external) and mechanical environment
- 2 Damage Mechanisms
2. Process specialists can provide useful input to aid corrosion specialists in the
identification of credible damage mechanisms and rates
- 3 Failure Modes
1. Once a credible damage mechanism(s) has been identified,
the associated failure mode should also be identified
- 3 Failure Modes
2. The risk analysis may, at the discretion of the owner-user, also include failures other than
loss of containment, such as loss of function, tray damage, heat exchanger tube leaks, etc.
8.3 Failure Modes
Types of failure modes
a) pinhole
b) small to
c) large
d) ductile
e) brittle
a) leak,
b) moderate leak,
c) leak,
d) rupture,
e) fracture.
- 4 Accumulated Damage
1. Damage rates may vary as
damage mechanisms progress (i.e. various mechanisms may accelerate or slow or stop completely)
- 4 Accumulated Damage
2. An evaluation of damage mechanisms and failure modes should
include the cumulative effect of each mechanism and/or mode.
8.5 Tabulating Results
The results of a damage mechanisms and failure modes analysis for RBI should identify the following
a) Credible damage mechanism(s) list:
1) Example: external corrosion.
8.5 Tabulating Results
The results of a damage mechanisms and failure modes analysis for RBI should identify the following
b) Credible damage mode(s) list resulting from the damage mechanism(s) in 8.5:
1) Example 1: localized thinning,
2) Example 2: general thinning.
8.5 Tabulating Results
The results of a damage mechanisms and failure modes analysis for RBI should identify the following
c) Credible failure mode(s) ranking resulting from the damage mode(s) in 8.5 a) and 8.5 b):
1) Example 1: localized thinning:
— Failure mode 1: pinhole leak,
— Failure mode 2: small leak.
The results of a damage mechanisms and failure modes analysis for RBI should identify the following
c) Credible failure mode(s) ranking resulting from the damage mode(s) in 8.5 a) and 8.5 b):
2) Example 2: general thinning: — Failure mode 1: pinhole leak, — Failure mode 2: small leak, — Failure mode 3: large leak, — Failure mode 4: rupture.
