RAM Modelling using OptimiseModule 5 Conditional LogicOctober 28 2009R Briggs2Bureau Veritas AustraliaModule Roadmap1.Overview2.Logic Condition Definition3.Trigger Behaviour Definition4.ReferencesRAM Modelling using OptimiseModule 5 Conditional LogicOverview4Bureau Veritas Australia1. OverviewRepresentation of an operational condition or restrictionRules constructed to defined condition using Boolean LogicOften used to model:lsubsea / plant restarts, following failures;linterconnected / common equipment eg Heat Recovery Steam Generator with Steam Turbine;lequipment / system bypasses; andlvoting, 2oo3 not equal to 3 x 100%, 3 x 50% or 2 x 100%5Bureau Veritas Australia1. OverviewA Dependent failure distribution specifies:lA Logic Condition, which is an operational condition that must be met; andlA Trigger Condition, which specifies how and when to trigger based on the Logic ConditionRAM Modelling using OptimiseModule 5 Conditional LogicLogic Condition Definition7Bureau Veritas Australia2. Logic Condition Definition OperatorsConditional Logic = Boolean Logic, evaluating TRUE or FALSE conditionConditional Logic uses a number of comparison operators:lAB or AB (A is greater or less than B);lA|B (A OR B);lA&B (A AND B); lA!=B (A is NOT EQUAL to B);lA=B (A is EQUAL to B); andl(AC|B=B). (AB)|(A=B) (A greater than or equal to B)8Bureau Veritas Australia2. Logic Condition Definition VariablesConditional Logic in Optimise is used to represent specific operating conditions / scenarios based on the conditional state of equipment / system / linepackConditional Logic evaluates:lelement status;lvalue and capacity;lbuffer level / condition;linflow / outflow; andlcombination of any of the above.9Bureau Veritas Australia2. Logic Condition Definition Element StatusEvaluates the state of an element An element can be any of these:lfailed;lunder repair; andlfunctional10Bureau Veritas Australia2. Logic Condition Definition Element StatusExample Gas Turbine Waste Heat Recovery System2 x 70% LNG Liquefaction Compressor GTs, each with WHRUEach WHRU supplies supplementary heat to a hot oil systemGT provides heat to WHRU, GT fails, no heat provided11Bureau Veritas Australia2. Logic Condition Definition Value and CapacityEvaluates a capacity of a branch / group The Value and Capacity can be compared to another:lcurrent capacity (Branch or Group);lmaximum capacity (Branch or Group); orlvalue (a fixed number, compared to current capacity or maximum capacity).12Bureau Veritas Australia2. Logic Condition Definition Value and CapacityExample Distillation Column Maximum TurndownA distillation column has a minimum production rate of 70%Fed by 6 x 20% pumpsFailure of 3 pumps causes a total shut down13Bureau Veritas Australia2. Logic Condition Definition Buffer Level / ConditionEvaluates a branch buffer level / statuslBuffer Level (a numerical value)lBuffer Status (can be either Full / Empty / in between)Some examples are:lBuffer Volume a ValuelBuffer Status != Empty14Bureau Veritas AustraliaExample Pipeline linepack between Upstream and LNG PlantLinepack provides a buffer to allow LNG production to continue.Linepack is normally full (maintain near max operating pressure)Buffer provides 12 hours of full production:l24 hours at 50% LNG production2. Logic Condition Definition Buffer Level / Condition15Bureau Veritas Australia2. Logic Condition Definition Inflow / OutflowEvaluates a branch current throughput capacity and compares it with a valuelThe Inflow of a BranchlThe outflow of a BranchlValue (a fixed number)An example:lInflow Branch A Outflow Branch B16Bureau Veritas Australia2. Logic Condition Definition Inflow / OutflowExample Management of Pipeline linepack between Upstream and LNG PlantLinepack provides a buffer to allow LNG production to continue.Linepack is normally full (maintain near max operating pressure)Linepack usage is dependant on inflow into linepacklLinepack drawdown is reduced to 40% when the inflow is less than 50%17Bureau Veritas Australia2. Logic Condition Definition - Combinations of LogicA combination of the basic logical expressionExample: If a downstream element X is failed, and the upstream linepack volume is greater than 50%, and the level is rising, shut down the inflow to a branchThe logical expression:(X!=Functional) & (Linepack vol (50%*capacity) & (Linepack in Linepack out)RAM Modelling using OptimiseModule 5 Conditional LogicTrigger Behaviour Definition19Bureau Veritas AustraliaDefines when an effect should trigger and how long it should last for based on a Logic ConditionThe Logic Condition is used to evaluate the operational state, and at any time any given Logic Condition will be either TRUE or FALSEThree types of trigger behaviours are:lcommon;lindependent; andlsequential.3. Trigger Behaviour Definition Overview20Bureau Veritas AustraliaCommon behaviour is to mirror another condition in the modelElements governed by Common Logic change to the failed state when the condition defined by the logic string evaluates to true. It stays in the failed state until the logic condition becomes false. which means,lThe element fails when logic becomes true; andlThe element becomes functional when logic ceases to be true.3. Trigger Behaviour Definition Common21Bureau Veritas Australia3. Trigger Behaviour Definition CommonFalseFunctionalTrueFalseFailedFunctionalTimeLogic Condition StateThe Element StateTime22Bureau Veritas AustraliaIndependent behaviour is to trigger off another condition in the model, and then ignore that condition from there onElements governed by Independent Logic change to the failed state when the condition defined by the logic string evaluates to true. It stays in the failed state until the user defined repair length is completed, which means,lThe element fails when logic becomes true; andlThe element becomes functional based on the MTTR distribution.3. Trigger Behaviour Definition Independent23Bureau Veritas Australia3. Trigger Behaviour Definition IndependentFalseFunctionalTrueFalseFailedFunctionalTimeLogic Condition StateThe Element StateTimeUnder Repair24Bureau Veritas AustraliaSequential behaviour is to wait until another condition elapses, before the element failure is triggeredElements governed by Sequential Logic monitors the model to detect when the condition defined by the logic string is true. It then waits till the condition evaluates to false, at which point it changes to a failed statewhich means,lThe element fails when logic becomes false, having just been true; andlThe element becomes functional based on the MTTR distribution.3. Trigger Behaviour Definition Sequential25Bureau Veritas Australia3. Trigger Behaviour Definition SequentialFalseFunctionalTrueFalseFailedFunctionalTimeLogic Condition StateThe Element StateTimeUnder RepairCondition evaluates trueCondition evaluates falseRAM Modelling using OptimiseModule 5 Conditional LogicExamples27Bureau Veritas Australia4. Conditional Logic Examples1.Counters 2.Repair windows 3.Restarts after outages4.Common equipment sparing5.Voting6.Restarts after linepack empty7.Turndowns8.Deferred maintenance mobilisations28Bureau Veritas Australia4. Examples CountersUsed to monitor equipmentCount how often a state occursExample: Frequency and Duration of BOG gas compressors frequency and duration of flaring.29Bureau Veritas Australia4. Examples Repair WindowsIt is used to simulate a production buffer ie, a storage tank.This allows the downstream system to operate unaffected by a failure in the upstream system during the repair windowExample: a 48 hours repair window for a production buffer of a chemical injection system30Bureau Veritas Australia4. Examples Restarts After OutagesIt is used to simulate gradual ramp up of a process post shutdown.Linear ramp up is often assumed.An example:An LNG plant requires a 24 hours gradual restart following an equipment failure in the liquefaction circuit. It has been assumed that the gradual restart for 24 hours is only required if the LNG plant is down for more than 10 hours.31Bureau Veritas Australia4. Examples Common Equipment SparingCertain critical equipment may share spares.Conditional logic can be used to link these spares to the equipment that will use it.When the spare fails the equipment linked to it will be affected.Example:Loading arms and umbilical LP / HP coresReliability DataIn use?32Bureau Veritas Australia4. Examples VotingEquipment may be voted 2oo3Not 2 x 100%, 3 x 50%, 3 x 100%Conditional logic can be used represent this.Example:Pressure Detection33Bureau Veritas Australia4. Examples Restarts After Linepack EmptyLinepack is the ability to fill the export pipeline with additional gas.Linepack can be modelled in optimise.Linepack can be used to buffer upstream outages or to store production during downstream outage.Conditional logic is used to limit the linepack usage according to the clients needs. For example: linepack may only allow for a certain period of uninterrupted production until reduced production takes over.34Bureau Veritas Australia4. Examples TurndownsSome plants can not operate when the feed is less than 50% for example.Conditional logic can be used to shut the plant down when the capacity falls under a determined value.35Bureau Veritas Australia4. Examples Deferred Maintenance MobilisationsWhen an element (that has a maintenance utility assigned to it) fails in Optimise, the maintenance utility will immediately mobilise to repair.Conditional logic can be used to defer the mobilisation until the logic is satisfied.When mobilisation times are high, mobilisations are deferred until a group of non critical elements fail.36Bureau Veritas Australia4. Examples Deferred Maintenance MobilisationsRAM Modelling using OptimiseModule 5 Conditional LogicReferences38Bureau Veritas Australia7. References1.Optimise Software 3.00.239Bureau Veritas Australia