cleaning T50 (IMO-5) gas tanks

Question:  “Our office in Japan will be sending a gas tank to the USA with class 2.2 Non-toxic/Non-flammable. The tank will be gas free when offhire. Does the tank needs to be cleaned in order to prep the tank for the next loading?” 

Tank Guru:  I suppose it depends on what mean when you say ‘gas free’ and also what you mean by ‘next loading.’  

In my mind, gas-free means ‘safe for fire, safe for man,’ or in other words, the tank is safe to enter when you check the LEL and O2 levels and there is no risk of fire.  This definition of gas-free also includes nitrogen as a gas, meaning that the O2 level is high enough that a worker entering the tank can safely breathe without special PPE. 

If the tank is truly gas-free to this standard, then it should be good enough to meet the offhire requirements of most lessors since an interior inspection would normally be performed in the process of writing the offhire estimate. 

But if by ‘next loading’ you mean that it is going to be reloaded immediately upon arrival to the U.S. instead of off-hired and then loaded at some future date, then I don’t think the tank would necessarily need to be safe to enter.  So long as all residue of the previous gas has been purged from the tank and the atmosphere inside is completely inert (for example a nitrogen atmosphere), then I think that is normally more than good enough for loading the next cargo.

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

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

Tank Container numbering system

Question:  “ISO Tanks are assigned a six-digit serial numbers by an international body. Can we label a tank with a different serial number?  The six-digit serial number remains on the tank.  For example, we have a tank with a serial number 117003.  We labeled the tank as AH-1.  This is how the tank is identified on a BOL.  Is this authorized?  Can we do this legally?” 

Tank Guru:  Absolutely, provided you are talking about transportation domestically.  If the tank were traveling internationally and going on a container ship, you would want to refer to it by the container number (the six digits you refer to above, preceded by the 4 alpha characters and then followed by the check-digit).  For more information on that numbering system, please see this link:  https://www.bic-code.org/bic-codes/

But if the tank stays on a chassis and you’re just referring to trucking the tank container from A to B, then you can call it whatever you want on the BOL.  Hope that helps.  Great question!

How old is too old?

Question:  “My company wants to send a hazardous cargo (Toxic & Corrosive liquid) to the USA. Currently we are using old IMO 101 (US DOT) tank containers for non-USA destinations. 
  1. In specific reference to the USA, are there any regulations (US DOT or otherwise) which specifies the age of tank container beyond which the tanks are not allowed to enter the USA?
  2. In general reference, for how many years a portable tank container can be kept in service for our type of cargo?”

 

Tank Guru:  There are no regulations which specify the age of tank containers.  And when properly maintained, tank containers can last indefinitely.  

We have refurbished tanks that were built in the 1960’s and they were as good as new once complete.  But we have also seen brand new tanks which were completely destroyed because of corrosive products.  It has everything to do with how well you maintain your equipment.  If you transport a product that is corrosive to stainless steel, then obviously the tank and its valves needs to need to be lined.  Regular inspections should be carried out to ensure that the lining is not compromised.

Data Plates for UN Portable tanks (T11, T20, T22, T50)

Question:  “My tank is missing the data plate. What do I need to do in order to get another one?” 

Tank Guru: 

Each tank container used in international service needs to have the data plate that was affixed by the original manufacturer (or a replacement copy), a CSC Safety Approval plate, and a TIR/Customs plate.  The manufacturer’s plate includes key information regarding the design pressure and temperature, shell thickness, original hydro test date and last test date, and the approvals to which the tank was designed and constructed.  Additionally, for certain high-pressure tanks there might also be an ASME Code plate or a product plate that shows the list of substances approved for transport in the tank.

Most newer ISO tanks have a consolidated data plate that includes all of the manufacturer’s details as well as the CSC and TIR approvals.  If the data plate is lost or damaged in such a way that it’s not legible, you should affix a replacement plate that has been engraved with the original information — and then reviewed and stamped by the class society surveyor who carried out the last periodic test.  Replacement plates are available through tank container repair facilities or select parts suppliers:

http://www.perolousa.net/Combination_Replacement_Plate_for_MFG_DataCSCCustoms_-_8__x_20__Stainless_Steel/p733948_3684161.aspx

http://www.perolousa.net/Replacement_Plate_for_Manufacturers_Data_-_8__x_12__Stainless_Steel/p733948_3684051.aspx

http://www.perolousa.net/Replacement_Plate_for_TIRCustoms_-_4__x_8__Stainless_Steel/p733948_3684133.aspx

http://www.perolousa.net/Replacement_Plate_for_CSC_Safety_Approval_-_4__x_8__Stainless_Steel/p733948_3684080.aspx

 

tank linings

Question:  “Is there anything in CFR about pressure-testing lined tanks?” 

Tank Guru:  Not that I’m aware of. All tanks have to be pressure tested, regardless of whether they are lined.  Additionally, the lining should be inspected visually as you would perform an interior inspection at the 2.5 and 5-year periodic anyway; and if the visual raises cause for concern then a spark test (or other type of additional inspection) may be warranted.

There is the IMDG language about waiver of the interior inspection during 2.5 year test for tanks in dedicated service (as I suppose that many lined tanks are), but as a tank owner you certainly wouldn’t want to skip something so important as a chance to ensure that your lining is holding up against the cargo!

container weights

Question:  “We mounted a mixer and some other equipment to our tank container.  This added equipment also added weight, so now the markings on the tank are incorrect.  What should I do?” 

Tank Guru:  Now that the International Maritime Organization (IMO) has introduced the Safety Of Life At Sea (SOLAS) regulations for Verified Gross Mass (VGM) of containers, there will continue to be increased scrutiny of container weights — especially when loaded, but also when empty.

It is key to have an accurate starting point, knowing what the empty weight of the container is before cargo is added.  If you have reason to believe that the actual weight of the container doesn’t match the tare (empty) weight that is stenciled on the tank, then we recommend re-weighing the tank.  First ensure that it is completely emptied of product, then have it weighed at a certified truck scale or comparable.  Once you know the weight, grind and re-stamp the data plate to correct both the tare weight and net payload, and replace any corresponding decal markings as well.

There are a lot of reasons that the tare weight on a tank container can change from its originally declared weight.  More common reasons include the installation of baffles, or the addition (or removal) of insulation and jacketing.  It is important that when changes are made, the markings are also updated accordingly.  People will make assumptions based on a container’s markings, and  improperly declared weights have been a factor in previous incidents involving ship safety.

Thanks for the question!

ISO dimensions

Question:  “We are going to set a concrete foundation for our tank container which we will use for storage purposes.  Is a 20′ ISO tank exactly 20′ long?  And what is the exact width?” 

Tank Guru:  Please see attached chart of ISO tank container dimensions.  You will note that a 20′ tank container is actually 19′-10.5″ long from end-to-end (6058 mm).  The overall width is 8′ (2438 mm) and both of these dimensions refer to the distance from the outside faces of the corner castings.

A standard tank container is considered a “1CC” shipping container as defined by ISO 668 (https://en.wikipedia.org/wiki/ISO_668).  Center-to-center of the holes in the bottom castings are 5853mm and 2259mm, respectively for length and width.

Good luck!  We sell a lot of these portable tanks into storage service, because it’s hard to find the same value for a stainless steel, pressure-rated tank.

2015 in review

The WordPress.com stats helper monkeys prepared a 2015 annual report for this blog.

Here’s an excerpt:

A San Francisco cable car holds 60 people. This blog was viewed about 2,000 times in 2015. If it were a cable car, it would take about 33 trips to carry that many people.

Click here to see the complete report.

PRV Set-to-Discharge Above MAWP

Question:  “Is our tank’s MAWP defined in units of PSIG or PSIA?  Can we adjust the PRV set pressure to match MAWP (or lower), instead of 10% higher?” 

Tank Guru:  It’s definitely PSIG (gauge), not absolute.  And in the case of tank containers with a working pressure higher than 3 bar, the set-to-discharge pressure of the PRV (also called SRV) will generally be set at 10% above MAWP.

Relief valve pressure settings are specified in 49CFR Sec. 178.275 (g) 6.  For a link directly to the regulations, click here:  http://www.gpo.gov/fdsys/pkg/CFR-2010-title49-vol2/pdf/CFR-2010-title49-vol2-sec178-275.pdf.  In summary, tanks with an MAWP higher than 3 bar have the “set-to-discharge” pressure of the PRV set at 10% above the MAWP (110% of two-thirds of the Test Pressure).  This applies to tanks conforming to Tank Instruction T11, which make up the majority of the world’s fleet of chemical tank containers.

However, once you get up to an MAWP of 6.89 bar or higher (such as with T20 or T22 tanks) it’s not uncommon to have the safety relief valve set right at the MAWP (instead of 10% above MAWP) on certain tanks, like older DOT-51 tanks. With ASME vessels, sometimes the tank manufacturer followed ASME rules versus DOT — and they don’t align perfectly, as relief valves on ASME vessels are generally set at MAWP instead of higher.

With that being said, it’s hard to argue with wanting a high-pressure tank to start venting excess pressure as soon as it reaches MAWP, rather than allowing the internal pressure to exceed MAWP by 10% first.  Therefore when you have tanks with a working pressure of 6.89 bar (100 psig), for instance, sometimes you will see the SRV’s set at 100 psig and sometimes you will see them set at 110 psig.

It’s important to note that these valves are purely emergency venting devices; spring-loaded to discharge excess pressure in order to protect the tank from exploding.  Leave them set exactly as the manufacturer intended (the tank’s manufacturer will have performed venting calculations and submitted them to the Class Society as part of the tank’s initial approvals), and ensure that PRV’s are serviced regularly.

Also, some valves are dual-acting and provide vacuum relief in addition to relief from over-pressurization.  Again, it’s important that the relief valves are checked regularly to ensure proper function.   https://www.youtube.com/watch?v=fIWDzp03_qo

Be safe!

relief valve