8 Damage Mechanisms and Failure Modes

Question 1

8. 1 Introduction
9. 1.1 General
10. This section provides guidance in identifying credible damage mechanisms and failure modes of

Answer 1

pressure boundary metallic components that are included in an RBI analysis

Question 2

8. 1 Introduction
9. 1.1 General
10. Damage mechanisms include

Answer 2

corrosion, cracking, mechanical, and metallurgical damage

Question 3

8. 1 Introduction
9. 1.1 General
10. Failure modes identify how the damaged component

Answer 3

will fail (e.g. by leakage or by rupture)

Question 4

8. 1 Introduction
9. 1.1 General

Understanding why damage
mechanisms is important

a) analysis of

Answer 4

the POF;

Question 5

8. 1 Introduction
9. 1.1 General

Understanding why damage
mechanisms is important

b) selection of appropriate

Answer 5

inspection intervals/due dates, locations, and techniques;

Question 6

8. 1 Introduction
9. 1.1 General

Understanding why damage
mechanisms is important

c) decision-making ability that can eliminate or reduce

Answer 6

the probability of a specific damage mechanism.

Question 7

8. 1 Introduction
9. 1.1 General

Understanding why failure
modes is important

a) analysis
b) run-or-repair
c) selection of

Answer 7

a) of the COF,
b) decision-making,
c) repair techniques.

Question 8

8. 1 Introduction
9. 1.2 Identification of Damage Mechanisms
10. The RBI team shall consult with a corrosion specialist to define the

Answer 8

equipment damage mechanisms, damage modes (optional), and potential failure modes

Question 9

8. 1 Introduction
9. 1.2 Identification of Damage Mechanisms

sequential approach

a) -Equipment design and
- Data used and assumptions made shall be

Answer 9

a) -current condition shall be considered.

- validated and documented.

Question 10

8. 1 Introduction
9. 1.2 Identification of Damage Mechanisms

sequential approach

b) - All process conditions
- Identifying trace constituents (ppm) in addition to the

Answer 10

• shall be considered.

- primary constituents in a process can be very important.

Question 11

8. 1 Introduction
9. 1.2 Identification of Damage Mechanisms

sequential approach

c) Considering the materials, methods, and details of fabrication, a list of

Answer 11

the credible damage mechanisms that may have been present in past operation, be presently active, or may become active shall be developed.

Question 12

8. 1 Introduction
9. 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

Answer 12

• then list the various damage modes or ways that the damage mechanism may manifest itself.
• damage mode should be considered.

Question 13

8. 1 Introduction
9. 1.2 Identification of Damage Mechanisms

sequential approach

e) It is often possible to have two or more damage mechanisms at

Answer 13

work on the same piece of equipment at the same time.

Question 14

8. 2 Damage Mechanisms

1. Its vital the understanding equipment operation and

Answer 14

the interaction with the process environment (both internal and external) and mechanical environment

Question 15

8. 2 Damage Mechanisms

2. Process specialists can provide useful input to aid corrosion specialists in the

Answer 15

identification of credible damage mechanisms and rates

Question 16

8. 3 Failure Modes

1. Once a credible damage mechanism(s) has been identified,

Answer 16

the associated failure mode should also be identified

Question 17

8. 3 Failure Modes

2. The risk analysis may, at the discretion of the owner-user, also include failures other than

Answer 17

loss of containment, such as loss of function, tray damage, heat exchanger tube leaks, etc.

Question 18

8.3 Failure Modes

Types of failure modes

a) pinhole
b) small to
c) large
d) ductile
e) brittle

Answer 18

a) leak,
b) moderate leak,
c) leak,
d) rupture,
e) fracture.

Question 19

8. 4 Accumulated Damage

1. Damage rates may vary as

Answer 19

damage mechanisms progress (i.e. various mechanisms may accelerate or slow or stop completely)

Question 20

8. 4 Accumulated Damage

2. An evaluation of damage mechanisms and failure modes should

Answer 20

include the cumulative effect of each mechanism and/or mode.

Question 21

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:

Answer 21

1) Example: external corrosion.

Question 22

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:

Answer 22

1) Example 1: localized thinning,

2) Example 2: general thinning.

Question 23

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):

Answer 23

1) Example 1: localized thinning:
— Failure mode 1: pinhole leak,
— Failure mode 2: small leak.

Question 24

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):

Answer 24

2) Example 2: general thinning:
— Failure mode 1: pinhole leak,
— Failure mode 2: small leak,
— Failure mode 3: large leak,
— Failure mode 4: rupture.