Risk-based Inspection Planning of Oil and Gas Pipes – The Fuzzy Logic Framework
‘And’ maintenance_condition is good_maintenance_condition ‘And’ leakage_amount is small_leakage_amount ‘Then’ ignition_likelihood is low_ignition_likelihood.
The truth value of a linguistic statement (a real number between zero and one) depends upon the degree of match between the linguistic variable (installation age) and the linguistic term (new_installation_age).3–5 decided the structure of the rules, the next step is to generate the
Having Figure 2: Simplified Consequence of Failure Assessment Process Flammable?
Use Fire Model
Conseq.
Loss of containment
Toxic?
Use Toxicity Model
Conseq.
Max?
Conseq.
Physical state?
Each of the linguistic variables has a number of linguistic terms or fuzzy variables.
rules. The number of rules depends upon the number of linguistic variables and the number of linguistic terms in each variable.
In order to develop the rules for a fuzzy model, information can be collected in two ways: expert opinion of the responsible persons and measured data. In the first case, the expert knowledge is expressed as a set of linguistic if–then rules. These rules are then fine-tuned using the available input–output data. In the second case, the rules are formulated by clustering the input-output data by dividing the data into the required number of fuzzy partitions and then fine-tuning using the expert knowledge.
Use Physical State Model
Design of an Inference Engine
The inference engine relates the consequences of the linguistic rule base with membership function values to deduce the output for the corresponding input values. Depending upon the type of operator used in the individual step, different inference engines can be obtained.
This model works on the commonly used Mamdani inferencing scheme and uses the maximum–minimum (max–min) inference engine, which uses max for accumulation and min for activation. The inference engine consists of three sub-functions: aggregation, activation and accumulation.3–5
Aggregation
In this step, if a rule consists of only one condition (antecedent), then the condition is identical to the rule; however, if the rule consists
Conseq.
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