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 failure occurs, 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, however this not always the case and there are many instances where catastrophic failure has occurred without there being any prior leakage through the shell. 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 an inspection programme
- Identify areas of degradation before failure occurs
- Provide trend information on deterioration so that life time and repair predictions can be made
- Minimise the out-of-service time to ensure maximum productivity of the tank
- Provide records of assessment that can be used to demonstrate compliance with operation standards and guidelines such as EEMUA 159 and API 653 requirements
- Secure statutory operating licence and negotiate lower TP insurance based validation that plant is in good condition
An inspection programme will typically have:
- Regular observations made 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 freed and cleaned for internal inspection and maintenance. This is carried out at much greater intervals, typically 5 to 10 years either 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 for any particular tank should take into account:
- relevant mandatory regulations
- company and industry experience of the type of tank
- the operating conditions of the tank
- the inspection and operating history of the tank.
- repair records
- number of years in service
- Climatic conditions
Out-of-service inspections are the prime means of confirming that a tank is fit for return to service and how long it can be used before the next inspection. It allows the condition of the tank and ancillaries to be assessed, measuring how they have performed under service conditions since the previous major out-of-service inspection, and the work necessary to bring the tank back to good condition to be identified.
Silverwing’s range of test equipment and reporting tools play an important role in assessing the condition of a storage tank, and recording of data for trending analysis. By having accurate, repeatable identification of corrosion, a risk based inspection programme can be established to maximise in-service time, whilst ensuring reliable and safe operation.
For more information on the areas of inspection and tank inspection equipment please a select a category below