Category Archives: corrosion allowance

rubber linings

Posted on October 30, 2009 | 4 comments

Question:  “Do you have any idea what a rubber lined IMO 1 would have cost before 2000 ex USA?  Carbon steel, 4 bar MAWP, 20,000 liter, manufactured in 1992 by Zenith Engineering in Singapore.”

Tank Guru:  The best estimate that I can give you is somewhere between $35,000 – $50,000 USD.  It would depend on a number of factors, including the number and type of valves (lined?), the thickness and grade of rubber used in lining the tank interior, whether the tank also carried IM-101 (3/8″ wall thickness for AAR-600) approval, etc.  But it would have definitely been more expensive that a standard stainless steel IMO 1.   Hope this helps.

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Posted in corrosion allowance, tank linings, Zenith Engineering

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tank re-testing requirements

Posted on May 25, 2009 | 13 comments

Question:  “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. 

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Posted in corrosion allowance, tank testing

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corrosion allowance

Posted on February 21, 2009 | 2 comments

Question:  “I inspected a 1987 Consani tank.  I have a question about minimum thickness on IM-101 tank barrels.  The data plate said the thickness was 4.8mm (equivalent to 6.35mm steel).  I did not see a note that any corrosion allowance was built in.  What is the minimum thickness of this tank?  I took some readings and want to make sure the barrel is thick enough.  Any other items I should note about this 1987 Consani model?”

TankGuru:  In general, tank containers have very little corrosion allowance built in.  What the data plate is telling you is that the tank was built with shell material that was 4.8mm actual thickness (before forming), equating to a Mild Steel Equivalence of 6.35mm.  The head material will undoubtedly have a greater nominal thickness as this is likely a 4 bar MAWP tank, and the heads would have to be thicker in order to maintain the same MSE, not to mention in order to handle the 4 bar pressure rating, due to the thinning that occurs during head forming.

The latter number of 6.35mm is important because the IMDG regulations specified what MSE thickness was required for carriage of different products (for example: 6mm MSE, 8mm MSE, etc., depending on how hazardous the product is).  Most of the tanks of that vintage had a 6.35mm MSE and were constructed of 3/16″ shell material Type 316L or equivalent, with 1/4″ thick heads (again, nominal thickness prior to forming).

1987 Consani tanks were well-built in general, but considered heavy in terms of their tare weight as compared to other (newer) tank containers.  We have sold a number of these units, and my guess is that you are looking at a 23000 liter tank with a tare weight of approximately 10,000 lbs.  If the shell thickness readings are comparable to the original values and the tank passes a hydro test at its full Test Pressure of 6 bar, the only thing that I would be concerned about (if it is important to you) is having a working steam system in a tank that is 22 years old.

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Posted in Consani, corrosion allowance, Russell Harrison

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