Tag Archives: Russell Harrison

Changing the “T” code from T20 to T11 (or T12)

Posted on February 8, 2023 | Leave a comment

Question:  “We want to install a bottom discharge valve on our T20 tank container. What do we need to do to change from T20 to T12? Is a design certifying engineer needed?” 

Tank Guru:  No, you do not need a DCE. Although you will technically have to re-rate the vessel, you are down-rating the MAWP and Test Pressure rather than trying to increase the pressure ratings beyond what the original manufacturer certified.

The reason you will have to downrate the tank is because most bottom discharge valve assemblies commercially available for ISO tanks are only rated for 4 bar MAWP / 6 bar TP, so you will likewise need to downgrade the tank to 4 bar MAWP and then install a 4.4 bar PRV in place of the existing PRV that had a higher set-to-discharge pressure. This will make it a T11, or if a rupture disc is fitted, a T12.

With a change like this you are also supposed to request approval for the modification as per 49 CFR § 178.273 (e). The reason I say this is because the tank was originally designed with the relief valve(s) that is on it, and installing a PRV with a lower set pressure means that you now have less venting capacity than before. The approval agency should look at the specs for the new PRV to be used and confirm that the venting capacity is adequate. When we do modifications like this in our Houston shop, we take care of that paperwork on behalf of the customer.

Here is a link to the relevant section of 49 CFR: https://www.ecfr.gov/current/title-49/subtitle-B/chapter-I/subchapter-C/part-178/subpart-H/section-178.273

Leave a comment

Posted in Uncategorized

Tagged , , ,

food grade tanks

Posted on October 30, 2009 | Leave a comment

Question:  “Are food grade tanks exempt from hydro test, and are only leak tests required?”

Tank Guru:  This is an area of confusion for many people.  It always comes back to the product being shipped.  Since most edible products are non-hazardous, then a specification packaging is not required.  However, in the case of a tank container, then of course the requirements for CSC Safety Approval have to be met for the ‘container’ even if the tank itself is a non-Code vessel.  BUT, if shipping the non-hazardous material in a spec packaging such as an IMO 1, IMO 2, or UN Portable Tank; then the certifications (and associated testing requirements) should be maintained, or else the tank should be down-graded to a non-spec packaging.  In the case of a non-spec tank, obviously there would be no requirement for a hydro test.

Keep in mind that some food grade products are still considered hazmat (certain alcoholic beverages might ship as a Class 3 flammable liquid, for instance); and in that case one would need to refer to the MSDS for details on the authorized packagings.

Leave a comment

Posted in food grade, tank specifications, tank testing

Tagged , ,

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. 

13 Comments

Posted in corrosion allowance, tank testing

Tagged , ,