A reduction in the number of planned maintenance shutdowns of process plant is becoming one of the main objectives of plant operators. Not only does a reduction increase the amount of time available for production, but also, there is the embarrassing fact that most plant failures are a result of maintenance itself.
Inspection plays a major part in assessing the condition of plant and can even be used to predict when failure is likely to occur, so that replacement or repairs can be planned.
However, inspection is expensive and more inspection does not mean better plant condition. Inspection, particularly NDT must be applied effectively. This has given rise to methodologies such as risk based inspection. There is also the problem of selecting suitable NDT techniques, which can be both sensitive and reliable. Finally there is the problem of analysing NDT data. Too much useful data from NDT is lost, both by going unrecorded by the test operator and by being filed away in a manner that does not allow easy access and analysis.
TWI were faced with these inspection problems during the assessment of an ethylene plant. The solution was to use simple NDT techniques, to capture as much data as possible and to convert this into numerical form for filing in a spreadsheet.
Of course, assigning numbers to indications recorded by NDT can only be done after careful consideration of the sensitivity and reliability of the test, an understanding of the significance of flaws and knowledge about the operating conditions.
Spreadsheets offer greater flexibility over normal databases. They allow 'what if' procedures to be carried out on the data. For example, in-service flaws such as corrosion should be more heavily weighted than manufacturing flaws such as lack of weld fusion. This weighting can be changed to meet particular circumstances. Corrosion in more critical systems of pipework might be more heavily weighted than corrosion in other systems.
TWI was able to bring in its unique expertise in inspection, assessment and repair to derive the spreadsheet, so that the client could make informed decisions about the condition of the plant.