grace period on 2.5-year (midpoint) inspection

Question:  “Is there a grace period on the 2.5 year test?”

Tank Guru:  Yes there is a grace period of 90 days before or after the test due-date for the 2.5-year periodic test.  For instance, if the last 5-year hydro test was performed in Jun-2008 and the 2.5-year test should have been performed in Dec-2010, you still have until Mar-2011 to carry out the periodic test.  This does not change the next test due-date, which will still be Jun-2013 (5 years after the last hydro test). If the 2.5-year test is not carried out by Mar-2011, then you would have to perform a full 5-year test to get the tank back into compliance.  Thanks for a great question.

box tanks and removable linings

Question:  “Have you ever heard of installing a flexible lining in a tank container?  I can think of reasons why this isn’t a particularly good idea.  I’ve also been asked recently why box tanks, like those made years ago by Hoyer and Hugonnet, couldn’t carry more cargo than a standard liquid tank.” 

Tank Guru:  I have indeed heard of installing a disposable liner inside of a tank container, but never seen it done.  One company I know tried it several years ago and ultimately determined that it wasn’t an effective solution, either because of installation difficulties or cost-effectiveness.  The reasons to install would be either to protect the tank from the cargo in the case of chemicals corrosive to stainless steel, or to protect the cargo from the tank such as shipping edibles as a backhaul in a chemical tank.

Box tanks were limited in capacity because most of the older 20′ boxes had a MGW of only 24000 KG to begin with, and additionally there is no point carrying a load larger than you could legally transport over the road without being overweight.

level gauges for portable tanks

Question:  “What are the possible alternatives of level gauges we could install on our T11 24000 liter tanks.  Would a Scully system work for this?”

Tank Guru:  Scully systems are mainly intended just as overfill protection (high-level alarm) and do not provide a continuous indication of the product level.  When considering level gauges, the options are somewhat limited on portable tanks because of the lack of electrical power, and the need to have something that will hold up to the rigors of transportation service (shock, vibration, etc.).  Not to mention that in a stainless steel chemical tank, most customers are going to want a gauge with all SS wetted parts.  

So there are basically 2 practical options: float gauges, and ultrasonic or radar technology.  There are a handful of float gauges available for transport tanks that vary from basic mechanical devices which have a long arm inside the tank with a stainless steel float that magnetically operates a simple dial (indicates percentage of tank volume); to a precision gauge where the float travels up and down a sender bar which is calibrated to display the actual volume of liquid inside the tank (either liters or U.S. gallons).   

Another option is the radar gauge, and as with the float gauge there are a couple of different ways you can go – either guided wave radar or microwave loop (non-contact).  There are pros and cons of one technology versus the other, and a lot of it depends on what will be transported in the tank and whether you have the ability to anchor the probe used in a guided wave system to the bottom of the tank; but in general one big advantage of radar systems over the float gauges is that there are no moving parts.  The disadvantage is that these systems typically cost more than a float gauge.

stress corrosion cracking

Question:  “Please see attached pictures of the inside of my tanks.  What is causing the pitting in this area?”

Tank Guru:  I suspect that the reason for this damage may be chloride stress corrosion.  Chlorides are a problem for 300 series grades of stainless steel, such as 304 or 316 (most common in tank containers), and stress corrosion cracking can occur when you have the simultaneous presence of tensile stresses along with specific environmental factors such as having a steam-heated/insulated tank.  Most insulation contains chlorides, especially polyurethane, and so it is usually advisable to not have this type of insulation in direct contact with the barrel when the tanks are going to be steam-heated.  Chloride stress corrosion is an increased risk with temperatures above 125° F.  The tensile stresses could be the result of certain operations to the tank, or due to residual stress from the fabrication process such as bending and/or welding.  I think this is why you are seeing the corrosion problem between the head seam and knuckle radius.

painting tank frames and barrels

Question:  “What types of paint coatings should we put on our tank containers?”

Tank Guru:  The industry standard for ocean-going containers is a zinc-rich epoxy primer on any steel surfaces, like the framework on a tank container, followed by a top coat.  It goes without saying that surface preparation is everything, so first the steel surfaces must be abrasive-blasted or otherwise suitable prepared to receive the primer coat.  Follow the coating manufacturer’s instructions for thinning (if necessary), application thicknesses, re-coat times, etc.

A good acrylic enamel top coat, compatible with the primer coat and applied to customer color, should be all that is needed afterward.  These provide the best corrosion resistance in general and are used througout the conainer industry and available in a variety of colors.  A polyurethane top coat can also be used providing acceptable corrosion resistance and much better gloss retention.

A link to the RAL color codes is provided below.  If painting frame and barrel (stainless steel), then a different procedure would be used.  You are welcome to contact me with any further questions.

http://www.ralcolor.com/

decals

Question:  “Can I install new decals on top of old decals?”

Tank Guru:  When it comes to the regulatory markings on a container, what is typically specified in various regulations is the size of the required markings and their location; NOT the manner in which they are installed.  There is no rule stating that one cannot install a new decal on top of an old decal.   That said, there is no reason that it wouldn’t be better to first remove the old decal. 

But, if for example the old decal is faded or illegible due to years of sun exposure and likewise adhered to the cladding because of being baked on by the sun and therefore difficult to remove; then I suppose you could install the new decal on top of the old one.  Just make sure that the new decal is securely affixed and easy to read (old decal does not show through).  Thanks for the question.

gaskets

Question:  “What measurments do you need to make gaskets?  Is it just the diagonal bolt pattern and the size of the opening?”

Tank Guru:  Usually what we need to make gaskets is the Outside Diameter, Inside Diameter, and thickness of the gasketing material regardless of whether it is a ring gasket or a full-face gasket.  Then for full-face gaskets we also need to know the number and size of the bolt holes, and the Bolt Circle Diameter.  For instance, we might spec out a 3” ANSI 150# gasket this way: 

7.5” OD x 3.5” ID x 1/8” thick full-face gasket with 4x ¾” holes, equally-spaced on a 6” BCD.

more on food-grade tanks…

I had another question today about used food-grade tanks.  Now, “food-grade” can mean different things to different people — from sanitary tanks (with a polished interior) for milk or like products where bacteria is a concern, to tanks for ‘food-grade’ phosphoric acid or some other hazmat material.

But generally speaking in the intermodal tank world, a food-grade tank is simply a stainless steel tank container with a factory 2B finish that has never carried any chemical product, only edibles such as wine and spirits, corn syrup, etc. (not fish oil).

The issue is that if you want to purchase a food-grade tank, normally you will be buying a new tank rather than a used tank.  Reason being that at some point in the life cycle of a typical used tank, it was introduced into chemical service, especially here in the United States (transport of food products in tank containers is much more common in Europe) and therefore can no longer be considered food-grade.

So the question I got today was whether there are any options besides buying a new tank, and the answer is YES.  We have a process where we can take an ex-chemical tank, strip it of all valves and fittings and thermally clean it (heating interior to bake out impurities), then sandblast the interior and coat all wetted surfaces with a lining that is FDA approved for direct food contact.  Lastly we replace all valves with new stainless steel so that any wetted part is a virgin surface. 

This is a fairly expensive process, but still usually cheaper than purchasing a new tank, and of course involves less lead time than building a new tank.  So there you have it, “food” for thought!

food grade tanks

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.

rubber linings

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.