Tag Archives: ISO tank

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

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Video

TC Impact Approval

Question:  “I was wondering if you knew anything about the TC impact approved spec I saw recently stamped on tank containers?  I am trying to design into our new tracking device an impact monitoring capability.” 

Tank Guru:  Quoting from the UN Sub-Committee of Experts on the Transport of Dangerous Goods, the TC Impact Approved mark is “used to identify tank containers that are in compliance with a design that has been successfully tested at a test facility approved by the Canadian competent authority.”

What that means is that the tank container you saw (or more specifically, the prototype unit for that series of containers) was tested by the tank’s manufacturer for use on Canadian railroads, by virtue of completing of a rail impact test like this:  https://www.youtube.com/watch?v=yWeDwE_7gNU.

Once testing is completed successfully, the Class Society issuing the design approval on behalf of the manufacturer will send to Transport Canada (http://www.tc.gc.ca/) a “pre-notification of intent to mark portable tanks” which outlines the tank numbers for the entire series of tanks to be marked with the TC Impact Approved marking.  Tank containers are not allowed to be transported on Canadian railroads unless their capability to withstand impacts has been proven by this testing, and they must be marked accordingly.

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Posted on January 8, 2015 in Russell Harrison, tank testing

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cladding for insulation required under Special Provision TP38

Posted on April 15, 2009 | 3 comments

Question:  “Do we need to use stainless steel cladding when insulating tanks with 4″ insulation (as required for PIH products)?”

Tank Guru:  The insulation requirement for toxic products which are considered an inhalation hazard (special provision TP38) is as follows:  “Each portable tank must be insulated with an insulating material so that the overall thermal conductance at 15.5 °C (60 °F) is no more than 1.5333 kilojoules per hour per square meter per degree Celsius (0.075 Btu per hour per square foot per degree Fahrenheit) temperature differential. Insulating materials may not promote corrosion to steel when wet.”

In the simplest terms, 100mm (4″) of any of the normal insulating materials used on tank containers (mineral wool, fiberglass, polyurethane, etc.) more than meets the requirement.  And while it is most common to see tanks carrying PIH products with SS cladding, this is not required and any jacketing material will work.

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Posted in cladding, insulation, insulation and cladding, jacketing, Russell Harrison

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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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