EvaluationEvaluation ofof PressurePressure andandEvaluationEvaluation of of PressurePressure and and ThermalThermal StressesStresses in in DissimilarDissimilar

WeldsWelds Pipe Pipe SpoolSpool RelatedRelated to to OTCOTCF ilF il A l iA l i dd D iD iFailureFailure AnalysisAnalysis and and DesignDesign

AnalysisAnalysis of Newof New SolutionSolutionAnalysisAnalysis of New of New SolutionSolution

š č ćš č ćMiša Jočić, PIPETECH JocicMiša Jočić, PIPETECH JocicZdravko Ivančić, NUMIKON d.o.o.Zdravko Ivančić, NUMIKON d.o.o.

OctoberOctober 20102010

Summary

Incident at the Combined Cycle Power Plant

Failure of a dissimilar (bi-metallic) weld seam at HP OTC (High PressureOnce Through Cooler) steam outlet

Aim to find possible design reasons for failure

Generate necessary corrective design actions

Produce a new solution ensuring future integrity of this type of pipingProduce a new solution ensuring future integrity of this type of pipingdesign

Analysis performed in accordance with method recommended in API 579Analysis performed in accordance with method recommended in API 579

Method has been combined with ASME B31.1 beam type CAESAR IIanal sis as ell as ith shell t pe elements FEM/FEPipe anal sisanalysis, as well as with shell type elements FEM/FEPipe analysis

FAILURE INVESTIGATION – Design Review

FAILURE INVESTIGATION – Design Review

FAILURE INVESTIGATION – Design Review

FAILURE INVESTIGATION – Design Review

FAILURE INVESTIGATION – Design Life Calc.

Calculation of design life using CAESAR II beam model analysis

Actual design life of the welded joint is approximately 18000 hrs (actualfailure occured after 16500 hrs)

DESIGN AND ANALYSIS OF NEW SOLUTION

First step was to find location with minimum stress (beam analysis)

DESIGN AND ANALYSIS OF NEW SOLUTION

DESIGN AND ANALYSIS OF NEW SOLUTION

Second step was to calculate stresses using shell type FE analysis

DESIGN AND ANALYSIS OF NEW SOLUTION

Third step was to calculate lifetime of welded connection

DESIGN AND ANALYSIS OF NEW SOLUTION

CONCLUSION

Within presented following was considered:

Location of the welded jointThermal expansion coeffiecient difference

The following was not explicitly taken into consideration but ratherimplicitly contained within the design procedure:

Residual stresses which have not been removed completely during heat treatmentResidual stresses, which are the consequence of existence of different micro structural components and phases, which in the zone of the welded joint have different propertiesStresses produced during transient processes of operation