Risk-based Inspection Planning of Oil and Gas Pipes – The Fuzzy Logic Framework Figure 3: Simplified Fire Model for the Determination of Consequence of Failure Due to Ignition Event Parameters
Age of the installation (old, medium, new)
Safety condition of the installation (bad, medium, good)
Maintenance condition of the equipment
(bad, medium, good)
Amount of leakage (Small, medium, large)
Loss of containment
Characteristics of the leaking fluid (gas, liquid)
Manning (few, some, many) CoF
Environmental effect Air
Bad Medium Good Small Medium Large
(minor, significant, major) Water
Plant safety Affected section
(minor, significant, major) Land
(minor, significant, major) CoF = consequence of failure.
of a combination of several conditions (antecedents), all the conditions are aggregated using the ‘and’ fuzzy logic operator to determine the final degree of accomplishment.
Activation
In this work, the first-infer-then-aggregate (FITA) scheme has been adopted, in which the inferences are first made from individual rules and then these inferences are aggregated together. The degree of membership value of each rule is determined on the basis of the degree of accomplishment of the rule, and then the minimum of each element of the Cartesian product of the input and output sets is taken.
Accumulation
The results of all the rules are accumulated (combined) to give the overall result using the max algorithm.
Selection of Appropriate Defuzzification Process In the defuzzification process, a representation of the information contained in the output fuzzy set is obtained using an a ppropriate technique for defuzzification of the accumulated membership functions.
1. Det Norske Veritas (DNV), Risk-based Inspection of Offshore Topsides Static Mechanical Equipment, Recommended Practice DNV-RP-G101, April 2009.
2. Zadeh LA, From Computing with Numbers to Computing with Words – From Manipulation of Measurements to Manipulation of Perceptions, Int J Applied Math Computer Sci,
28 2002;12(3):307–24.
3. Ross TJ, Fuzzy Logic with Engineering Applications, John Wiley & Sons Ltd., Chichester, 2004.
4. Singh M, Markeset T, A Methodology for Risk-Based Inspection Planning of Oil and Gas Pipes Based on Fuzzy Logic Framework, Engineering Failure Analysis, 2009;16:
Conclusions
For the operation and maintenance of a plant, a reliable and robust mathematical tool for establishing an RBI programme can be a valuable asset. Such a tool can help a maintenance engineer to cut down on the expenditure arising from frequent inspections and unnecessary maintenance shutdowns and to take preventative maintenance action before an accident actually takes place.
This article presents an expert system based on the fuzzy logic framework for developing an RBI programme. The strengths of this model are:
• flexibility and easy calibration/modification of the input and o utput variables;
• the rule base may be modified by experts to reflect the actual plant data;
• it allows a better transparency of the model by giving the rules in the linguistic language as understood by the maintenance engineers; and
• it does not rely solely on complex first principles for the development of the model. It is based on a combination of expert knowledge, objective measurements and quantifiable objectives that are more easily available. n
2098–113.
5. IEC 1131 – Programmable Controllers, Part 7 – Fuzzy Control Programming, Technical Committee No. 65: Industrial Process Measurement and Control, Sub-Committee 65 B: Devices, International Electrotechnical Commission (IEC), 1997.
EXPLORATION & PRODUCTION – VOLUME 8 ISSUE 2 Environmental consequence
CoF (environment-fire/ explosion)
(small, medium, large)
Possibility if ignition (low, medium, high)
Affected section (small [equipment], medium [module], large [section])
Low Medium High Effective range Safety effect
Number of people injured (few, some, many)
Number of people killed (few, some, many)
Possibility of ignition Economic effect Repair (minor, significant, major) Production loss (minor, significant, major)
Damages/compensations (minor, significant, major)
Small Medium Large Safety consequence
CoF (safety-fire/explosion) (small, medium, large)
Possibility if ignition (Low, medium, high)
Economic consequence CoF
(economy-fire/explosion) (small, medium, large)
Membership
Membership
Membership
Membership
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72 |
Page 73 |
Page 74 |
Page 75 |
Page 76 |
Page 77 |
Page 78 |
Page 79 |
Page 80 |
Page 81 |
Page 82 |
Page 83 |
Page 84 |
Page 85 |
Page 86 |
Page 87 |
Page 88 |
Page 89 |
Page 90 |
Page 91 |
Page 92 |
Page 93 |
Page 94 |
Page 95 |
Page 96 |
Page 97 |
Page 98 |
Page 99 |
Page 100 |
Page 101 |
Page 102 |
Page 103 |
Page 104 |
Page 105 |
Page 106 |
Page 107 |
Page 108