Storage tanks require inspection at regular intervals to ensure deterioration is detected at an early stage. Effective inspection identifies the repairs required before the point where leakage or other failures occur, avoiding environmental contamination, product loss, or even catastrophic failure.
Degradation can be caused by environmental conditions such as weather and ground conditions, or by the contents stored, which may cause internal corrosion. It is often assumed that leakage will occur before a failure, highlighting thinned areas of shell. This, however, is not always the case and there are many instances where catastrophic failure occurred without any prior leakage. Inspection techniques and equipment should therefore be able to identify degradation and potential total failure, as well as the more likely corrosion that leads to leakage.
Objectives of Inspection Programs
- Identify areas of degradation before failure
- Provide trend information on deterioration so that life cycle and repair predictions can be made
- Minimize the out-of-service time to ensure maximum productivity of tanks
- Provide records of assessment that can be used to demonstrate operation standards and guidelines compliance such as EEMUA 159 and API 653
- Secure statutory operating license and negotiate lower TP insurance based on validation that plants are in good condition
Inspection Programs Typically Include
- Regular observations by the operating personnel
- Scheduled, in-service inspections by an inspection engineer, usually annually, which could include shell and roof NDT
- Out-of-service inspection when the tank is gas-free and cleaned for internal inspection and maintenance. This is carried out at much greater intervals (typically 5 to 10 years) in accordance with the suggested periods or as justified by a risk-based approach. A full floor (base) inspection and internal visual check should be carried out and preferably defect mapping and recording to provide information on corrosion rates
The Interval Between Inspections Should Consider
- Relevant mandatory regulations
- Company and industry experience of the type of tank
- Operating conditions of the tank
- Inspection and operating history of the tank
- Repair record
- Number of service years
- Climatic conditions
Out-of-service inspections are the prime means of confirming that tanks are fit for return to service and how long they can be used before being inspected again. Such inspections enables assessing the condition of tanks and ancillaries, measuring how they have performed under service conditions since the previous major out-of-service inspection, and determining the work necessary to bring tanks back to good condition.
The Eddyfi Technologies Silverwing range of test equipment and reporting tools play an important role in assessing the condition of storage tanks and recording of data for trending analysis. By having accurate, repeatable identification of corrosion, it is possible to elaborate a risk-based inspection program to maximize in-service time, while ensuring reliable and safe operation.