In Refining and Petrochemical Industries, the inspections are scheduled at calculated intervals, to determine the condition of equipment and to identify damage or deterioration. For this, unit shutdowns are planned to conduct inspections at specific time. Also the regular checks while equipment is in service help to provide useful information regarding mechanical and physical conditions. Sometimes due to operational/process failure or mechanical breakdown, unplanned shutdowns are carried out at time which is not expected. In such unexpected circumstances, opportunities can be availed to perform additional check-ups in order to;
- Distribute the workload
- Reduce the workload
- Reduce the duration of outage
This article involves all those conditions where opportunity to conduct inspection can be utilized.
1. When the equipment is out of service for cleaning
Normally when equipment is opened out of service for cleaning purposes, advantage can be taken to perform inspection on it. The collected data and information from such inspections can be useful to spot out repair requirements for next expected shutdown.
Examples: Heat Exchangers and Distillation Towers where equipment or parts of equipment are removed for cleaning.
2. Unexpected Operational Drop or Mechanical Break-down
As stated above unplanned shutdowns are placed due to unanticipated operational or mechanical problems. Such intervals can be utilized to inspect the equipment internally and the findings of which can be used to verify recent on-stream collected data. Moreover repairs and replacements can also be made if need be.
3. On-stream Inspection
It is a type inspection perform from the outside of an on-stream equipment (without shutting it down), using special non-destructive examination NDE techniques. The point of this inspection is to check and ensure the pressure boundaries of an equipment for continued safe service.
4. External Inspection while Equipment is in service
An external inspection can be performed during both when the equipment is or is not in service. Advantage should be taken to make external inspection of structural components, foundation, support, paint, insulation etc. while an equipment is in service. Moreover wall thickness for the calculation of corrosion and remaining life can also be evaluated using NDE techniques; ultrasonic testing and radiography.
5. Process Inefficiencies and Difficulties
When an operational group faces difficulties in operation/process, it is required to report the problem to inspection group. Inspection of such problems may reveal the indication of damage and associated deterioration.
- If the rate of heat exchange is reduced below the certain level, it’s more likely to expect the blockage of heat exchanger tubes by a considerable amount of corrosion deposits.
- Similarly the difficulty in taking out of distillation product in fractionation tower, may also point to damage of certain parts that ought to be repaired or replaced in order to avoid contamination of product.
These findings are quite helpful to provide worthwhile information for the next expected inspection.
Random Examinations during service or out-of-service for unanticipated reasons, play a vital role in lowering the work pressure, equipment downtime and equipment damage. Using them we can establish factors and recommendations beforehand, essential for upcoming scheduled inspections.
American Petroleum Institute API Recommended Practice, Inspection Practices for Pressure Vessel, In-service Inspection, Rating, Repair and Alteration.