Recently couple of shippers, looking for T14 and higher tanks, asked me why T11 tanks are more in the fleets and what is the advantage of T11 UN Portable Tank for an operator?. After looking into the IMDG Code entries which are permitted in tanks and talking to some tank operators I am sharing my view why T11 tanks are more in the fleets and what advantage it has.

Below is the difference between T1 to T22 tanks in IMDG code (T23 is for Self Reactive substances and Organic Peroxides, T50 and T75 are for gas)

Permitted Tanks and Options

T code assigned to the entries in column 13 of Dangerous Goods List in Chapter 3.2 of IMDG Code determines which tank is authorized to carry the specific entry.

Further section 4.2.5.2.5 of IMDG Code, ‘Determination of the appropriate portable tank instructions’, gives option to use a different tank than the one assigned in column 13 of Dangerous Goods List which possess higher test pressures, greater shell thicknesses, more stringent bottom opening and pressure relief device arrangements.

According to section 4.2.5.2.5 T11 Tank may be used for Dangerous Goods Entries assigned with T Codes T1, T2, T3, T4, T6,  and T7.

T11 tank with bottom opening and minimum test pressure 6 bar becomes more suitable to carry a large range of dangerous goods than any other tank.

To know the advantages of operating T11 tanks let us look at the number of dangerous goods entries and permitted Tank Codes in IMDG Code.

Above table lists number of UN Numbers in each class assigned with specific Tank Codes (excluding, Class 1 Explosives, Class 2 Gases, Class 4.1 Self-Reactive Substances, Class 5.2 Organic Peroxides, Class 6.2 Infectious Substances, and Class 7 Radioactive Materials) (Manually calculated from IMDG Code, variation in packing groups are also taken into account, figures may slightly vary).

As dangerous goods assigned with T Codes T1, T2, T3, T4, T6, T7 are also permitted in T11 tanks  we can see a total of 1562 dangerous goods entries can be carried in T11 tanks!

Certain advantages of T11 Tanks

• Cargo can be loaded/discharged from top as well as from the bottom.
• Tank material SS316L is compatible with most chemicals transported.
• Thickness of the shell of the tank is 5-6mm, most tanks above T11 have shell thickness more than that of T11, hence the cost of T11 is cheaper.   
• T11 tanks can be operated from ground level during discharge, T13, T14 and T19 to T 22 bottom opening is prohibited hence discharging is from top which is not convenient.  
• A T20 or T22 tank if converted to T11 is acceptable.
• T11 tank converted to T20 or T22 not acceptable due to shell thickness.
• If Cargo solidify in transit, during discharge, it is easier to discharge from bottom valve, as the steam coils are up to half the tank and touching the shell of tank. The first parts to melt will be the bottom half.
• For bottom discharge, if Cargo is less viscous then no need for pump, discharge can be done with gravity, in top discharge need a pump for pressure.
• For shippers T11 tanks are easily available, hence can be used for spot business, while T14 or higher are usually available for dedicated cargo moves.

Conclusion

With average life span of 25 years, T11 tank is more advantages to a tank operator than other tanks. Of course too many tanks in the global fleet will definitely bring down the demand and thus effect the business

Further Readings

Bulk Liquids – Think Tank, do the Math!

https://www.shashikallada.com/imdg-code-38-16-changes-tank-provisions/

Nitrogen Blanketing – Tanks