Root Cause Failure Analysis of P91 HP Steam Pipe for an Asian Power Plant
Following a recent failure of a HP steam pipe, a client invited ETD to submit a proposal to carry out Remaining Life Assessment (RLA) of a HP bypass steam piping system and Root Cause Failure Analysis (RCA) of a failed pipe section. The work involved performing RLA and RCA study including recommendations to prevent any future failures based on data review, pipeline stress analysis, laboratory testing and assessment on the HP bypass steam piping system and the failed pipe section.
The objectives and scope of the work to be carried out was:
1. Perform metallurgical Assessment of the failed pipe section. This included the following tasks:
- Visual (macroscopic analysis) and dimensional/ thickness examination of the pipe sample including internal scale, external appearance and condition of the pipe inner surface;
- Chemical analysis of base material to determine the chemical composition of the pipe material to establish actual material constituents;
- Chemical analysis of filler material to determine the chemical composition of the filler to establish actual material constituents.
- Metallographic examination of the pipe sample using optical microscopy to assess the condition of internal and external surfaces, material degradation and also to identify the damage mechanism(s);
- Fractographic assessment of the fractured surface using SEM (Scanning Electron Microscope) to confirm the damage mechanism(s);
- Hardness testing and evaluation to determine the equivalent tensile strength values (using published hardness/UTS correlation tables) to assess the mechanical strength or softening of the tube materials or welds;
- Observation of sequence of the crack initiation and propagation;
- Assessment of the heat‐treatments (incl. PWHT) from microstructural examinations, quality of welds and fabrication defects in welds.
2. Perform pipeline stress analysis of HP bypass steam piping system. This included:
- Reviewing the design/ isometric drawings clearly showing all dimensions and piping connections of HP bypass steam piping system.
- Reviewing and analysing the inspection data/ information of hangers and supports collected during hot and cold condition inspection.
- Performing pipeline stress analysis of the piping system using CEASER II software.
3. Reviewing the design and operating parameters, previous failure and maintenance history;
4. Reviewing the existing welding & NDT records obtained from construction and during replacement of failed piping.
5. Root Cause Failure Analysis (RCA) based on the findings of above investigations to determine the actual causes of failure/ damage mechanism(s);
6. Performing life assessment of higher stress regions of the piping system based on the findings of pipeline stress analysis.
7. Submitting a report covering results of investigations, failure analysis, stress analysis, life assessment, detail explanation of root causes & recommendations for any further actions to be taken to prevent reoccurrence of failures and for safe operation of the component.
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