Question: This question relates to tank re-testing requirements. “How often and what are the procedures for retesting an ISO container. (Pressure and thickness)”
Tank Guru: Hazardous materials may only be carried in tank containers (ISO tanks) that have a valid, current 5-year or 2.5-year test certificate.
A 5-year periodic test is required 60 months after the date of the original hydrostatic test, or the most recent subsequent 5-year test. The scope of the test must include a hydrostatic pressure test at the tank’s full Test Pressure, usually 150% of the Maximum Allowable Working Pressure. It will also include a visual interior inspection of the tank barrel, and exterior inspection of the container to ensure structural integrity of the frame and safety items such as the catwalk. A bench test of the safety relief valve is required along with a final leakage test (after the water has been drained and the relief valve re-installed), to ensure satisfactory operation of all service valves and equipment. All of these tests are carried out under the witness of a surveyor/inspector for a third party agency or Class Society, which will issue the test certificate and stamp the new test date on the tank’s data plate.
A 5-year test is also required at any time when welding operations have been conducted on the shell.
At the midpoint between each 5-year test interval, a 2.5-year test is required 30 months after the most recent hydrostatic test. This will include the exact same scope of testing/inspection as the 5-year test, except that the tank will not be hydrostatically tested. Instead only the leakage test (pneumatic) is conducted at normal operating pressure. Again all testing is carried out under the witness of the third party surveyor, and after successful completion the data plate is stamped and a test certificate is issued by the Class Society or competent authority.
There are no specific requirements for checking the thickness of the tank shell. However, the thickness should be checked by using a UT meter whenever there is reason for concern that the thickness may have been compromised by corrosion, or repairs to the pitting such as excessive grinding, etc.