Part 8. Thinning Assessment - Further Considerations

SKG 12 Mechanical SKG 15 Materials, Corrosion & Inspection Engineering Level 3: Fitness-for-Service Part 8: Thinning assessment – further considerations CONFIDENTIAL © 2012 PETROLIAM NASIONAL BERHAD (PETRONAS) All rights reserved. No part of this document may be reproduced, stored in a retrieval system or transmitted in any form or by any means (electronic, mechanical, photocopying, recording or otherwise) without the permission of the copyright owner.

Outline 1.

Objectives

2.

Further considerations

3.

Does API 579 compromise on safety?

4.

Key lessons from Part 8

Objectives 1. To be aware of other additional considerations when performing thinning assessments

2. To have a feel of how much margin you actually have (Again….Yes!)
Most important objective of this course!!!

Outline 1.

Objectives

2.

Further considerations

3.

Does API 579 compromise on safety?

4.

Key lessons from Part 8

As usual, things always get more complicated……

Q – What if there are several flaws located close to one another – how to assess their interaction to estimate s & c? A – See Figures 4.7 & 4.8

And many other questions…. At the end of the day, you must know what you are analyzing for.

Outline 1.

Objectives

2.

Further considerations

3.

Does API 579 compromise on safety?

4.

Key lessons from Part 8

Does API 579 compromise on safety? • How far off are we from danger?

As implied in thickness calculation formulas used by API 579

• Example: SA 106 Grade B

σ

yield=

43 ksi,

σ

UTS

= 75 ksi

→ SE = ⅓

σ

UTS

= 25 ksi (piping)

Case 1: σflow = SE/0.9 = 28ksi → RSF=0.9 Case 2: σflow = 1.1σyield = 47.3ksi → RSF=0.528 Case 3: σflow = σyield+10ksi = 53ksi → RSF=0.47 Case 4:

σflow = ½ (σUTS+σyield)= 59ksi → RSF=0.42

Does API 579 compromise on safety?...cont Remaining thickness ratio

σ σ

UTS

RSF=0.9 As used by API 579

= 75ksi

σflow = 59ksi Case 3: σflow = 53ksi Case 2: σflow = 47.3ksi Case 4:

RSF=0.53

σ Case 1:

yield

σflow =

= 30ksi RSF=0.47

27.5ksi

SE = 25ksi RSF=0.42

ε

Outline 1.

Objectives

2.

Further considerations

3.

Does API 579 compromise on safety?

4.

Key lessons from Part 8

Key lessons from Part 8 When assessing thinning components, ask yourself the following questions: 1 - Have I taken enough thickness readings?

2 - Will the component rupture? (MOST DANGEROUS!!!!)
Flaw size is too large
Flaw had eaten up reinforcement at major structural discontinuities (MSD)

3 - Will the component will leak?
Remaining thickness is too thin

End of presentation Thank you