The prairie provinces may still have anhydrous ammonia nurse tanks imported from the United States years ago without Canadian approval or inspection.
“These tanks do not have a Canadian Registration Number (CRN),” said Terry Rieger, manager of boiler and pressure vessel inspection for Manitoba. “This is not a grey area. It is illegal to put anhydrous ammonia into any tank that does not have a CRN.”
Rieger said the designs of these non-certified tanks have never been approved by Transport Canada, nor have they been inspected by provincial authorities. The tanks may not be safe.
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Over the years, some of the illegally imported tanks have been pressure tested and their ancestry documented, said Rieger. If such a tank can meet the Canadian criteria, it gets a special CRN and it can go back into service. If not, it is scrapped.
“If you’re in doubt, always look for a CRN,” said Rieger.
There are a number of tests for weld integrity including ultrasonic, mag particle or magnaflux and X-ray. But the cost of these tests is prohibitive for large scale testing. An anhydrous tank X-ray costs about $2,500. The hydrostatic pressure test costs $400.
Consequently, hydrostatic pressure testing remains the most cost-effective technology for detecting structural flaws in an anhydrous tank. All photos on pages 67 and 68 were taken in 2004 when Agricore United was performing hydrostatic pressure tests on some of its nurse tanks as well as tanks belonging to customers.
“We only had two or three tanks that actually failed the pressure test, but several of them creaked and groaned,” said Glenn Dickson, AU manager of equipment and facilities.
He was observing the tests when one of the suspect tanks began making ominous noises.
“It started creaking and groaning at 375 psi, so we knew there were structural defects inside which had not been detected by the exterior visual inspection. In fact, this tank had already passed visual inspections in previous years.(See photo above, right.)
“We decided to cut it open to investigate. It had been built in the United States in 1977 or 1978. It would not likely have passed had it ever been inspected by a boiler and pressure vessel inspector,” said Dickson, who served for several years on the Anhydrous Safety Council and is now on the Canadian Standards Association safety council.
The tanks that failed the hydrostatic test were all from the same defunct manufacturer. The data plate on the tanks gave the name of the company, date of fabrication and type of material used. ChemiTrol, the firm that built the tanks, disappeared in the late 1970s. None of the ChemiTrol tanks located had a CRN.
“If you have a ChemiTrol tank, look to see if there’s a CRN on the data plate,” said Dickson.
“A number of these tanks somehow got into Canada without going through the approval process. Nobody knows how many or how they got here.
“We had two of them X-rayed. The X-ray technician reported that every circumferential weld on both tanks would have failed a Canadian inspection because of insufficient weld penetration.” (See photos below)
Rieger said a weld on an anhydrous ammonia tank must have 100 percent penetration along the entire length of the seam to be legal. The slightest flaw is an automatic rejection.
Pat Beavis at the Dyterra Corp. in Oak Bluff, Man., agreed. Dyterra specializes in testing and repairing all types of pressure equipment.
“There’s no question about 100 percent penetration in this business,” said Beavis.
“We have to be able to prove 100 percent penetration for every weld on every anhydrous tank we repair. Every seam has to be able to stand up to a complete X-ray or any other kind of test.”
But that’s not what Dickson found when the ChemiTrol tank was cut apart.
“The X-rays showed cracks up to 14 inches (35 centimetres) long on the horizontal welds and insufficient penetration on the circumferential welds. In some spots, the weld only penetrated 25 percent and in the best spots it was still only 75 percent. It was just plain bad welding along with poor quality control. It looked like a stick weld with no robotics. I doubt they were ever inspected during fabrication.”
Dickson said on the first search, only two or three of the ChemiTrol tanks were this bad, and were immediately taken out of service.
“We decided we’d better search our database to find all similar tanks we owned and we did the full hydrostatic test on each and every ChemiTrol tank in our fleet. As a result of inadequate performance in the tests and the fact that we could find little or no documentation, we scrapped them all,” said Dickson.
AU also notified anhydrous customers who had their own ChemiTrol tanks on the farm, and every farmer took his tank out of service voluntarily. In all, several dozen ChemiTrol anhydrous tanks were scrapped.
In 1995, when the Anhydrous Safety Council standards were being developed, the fertilizer industry randomly selected 18 anhydrous tanks from across Canada to be shipped to the Sheritt Gordon facility in Fort Saskatchewan, Alta. They were all hydrostatically pressure tested, then cut open, mag particle tested, X-rayed and intensely studied with the goal of learning more about what constitutes a safe anhydrous tank.
Reiger said two major changes came out of the 1995 test.
“The first thing we documented was that a fine grain steel performs better in these conditions than a more coarse grain steel. All Canadian anhydrous ammonia tanks since 1995 must be fabricated with fine grain steel.
“The second major discovery is stress relief to prevent metal fatigue. Every anhydrous ammonia tank sold in Canada must be treated in an oven at about 1,000 degrees.”
Although AU takes the CSA position that all anhydrous tanks should be pressure tested once every five years, Dickson clarifies that the age of the tank may be less critical than the original design, materials, fabrication and maintenance.
“The highest rated tank in that 1995 study was also the oldest one, built in Quebec in 1966. When we opened it up, you could still read the inspector’s chalk marks on the inside walls. The welds were near perfect. It ranked far better than some tanks that were 20 years newer.
“Somebody knew how to take care of that anhydrous tank. It’s all a matter of keeping moisture and oxygen out. Never leave any valve or fitting open to the atmosphere. Before a tank goes into storage, you should purge it with anhydrous ammonia to get rid of all water and air. Just before you close it up, put in enough fresh anhydrous ammonia so the vapours fill the tank.
“The main thing is to keep the atmosphere out of the tank. Obviously, that’s how the Quebec tank had been treated for 29 years.”
The worst tank in that 1995 study was built in Canada. It was constructed of spiral wound pipeline that had the weld seams wrapping around the cylinder like the cardboard tube in a roll of toilet paper. As the cylinder was subjected to stress, the welded seams began to unwind.
There are more than 12,000 anhydrous nurse tanks in Canada, including a few built in the 1950s. Dickson said these tanks might be in top condition, but like all tanks, he recommends they be tested.
A qualified technician, registered with Transport Canada, conducts the hydro test. In the case of AU, the inspections were contracted out to independent third party companies that specialize in performing such tests.
Rieger said the tank is brought to a test site, usually the fertilizer dealer’s yard, where it gets a complete exterior visual inspection.
“Then it’s filled with water and pressurized to 1.5 times its maximum rated pressure. For example, a 250 psi rated tank is brought to 375 psi and held there for about 10 minutes. The manual doesn’t specify a time, but 10 minutes is usually more than enough time to identify a leak.”
He said it’s important that water be used to fill the tank because water does not compress. Pressurizing a tank to 375 psi with air alone would create an extreme safety hazard because air does compress.
A tank failure with only air could send shrapnel flying in all directions. With water in the tank, everything just falls to the ground.
During the pressure period, the entire external surface is scrutinized for water droplets that would indicate a leak. The pressure reading is also documented to see if it holds. If there is a problem, it must be repaired before the tank can go back into service.
Beavis said the procedure must be strictly followed, even for a pinhole leak.
“Once we’ve identified the problem, we submit a plan for the repair. We don’t do further work until a plan is approved. The boiler and pressure vessel office has experience with every imaginable kind of problem, so if they know of a better way to fix it, they give us the alternate plan. Or they may decide our plan is the best.
“When a plan is approved, we go ahead with the repair. All corroded and damaged material must be removed before we start welding. We often do a lot of drilling and grinding before we get rid of all the bad stuff. When we’re done, our job is inspected and the tank gets the full hydrostatic pressure test.”
In the 2004 hydro tests, AU found just such a pinhole flaw on one of its tanks that had a legitimate CRN. The tank had developed a leak on a circumferential weld. It was brought to an authorized repair facility and brought back up to the standard. (See photo above, left.)
“It was the kind of leak where you might just barely detect a whiff of anhydrous if you stood next to it,” said Dickson.
“In the test, it gave off just a few small droplets of water, but that’s all the inspectors need to identify a problem.”
Another tank in 2004 was found to have a pinhole leak from a simple threaded coupling at the top of the tank.
“This was a tank that was fully approved for use in Canada and fully documented. But at 375 psi, the inspectors noticed a few small drops of water below the coupling. They wiped it away, but the drops came back. It was a leak, no question,” said Dickson. (See photo above, right.)
“It looks like the weld didn’t quite go around the full 360 degrees, more like 359 degrees. The end of the weld bead didn’t fully meet the beginning of the bead. When filled, the tank would have emitted a very small amount of anhydrous. The old coupling was cut out, a new one installed and it was pressure checked.”
If a problem cannot be fixed according to standards, said Rieger, the tank is scrapped. There is no argument.
The idea of full hydro pressure tests every five years dates back to the mid-1980s when Transport Canada introduced its Transportation of Dangerous Goods, or TDG, regulations.
United Grain Growers was one of the first fertilizer retailers to initiate hydrostatic pressure testing on its own, before regulations required it.
“Sheritt Gordon approached us in 1991 to see about pressure testing our nurse tanks,” Dickson said.
“They already knew the stricter regulations were coming by 1995. Working with them, we began testing 20 percent of our tanks each year. By the summer of 1994, we had pressure tested nearly 80 percent of our entire fleet.”
Anhydrous is classified as a dangerous good. Any company setting out to build a tank to transport these products must have the design approved by Transport Canada. This includes all highway, rail or local delivery tanks for products like gasoline, diesel, propane, sulfuric acid, anhydrous ammonia or any other dangerous substance on the TDG list.
Stationary storage tanks for these products fall under jurisdiction of provincial boiler and pressure vessel inspectors.
“If there is no design approval, along with the appropriate inspections during fabrication and after completion, the tank is not legal for anhydrous ammonia in Canada and dealers should not fill it,” Rieger said.
Once a new design is approved and on the market, it’s up to owners to make sure the inspections remain current and legal. The data file that follows the life of every tank, from factory to scrap yard, must be kept up to date. If documentation is not complete, the dealer doesn’t fill and the tank may take a premature trip to the scrap yard.
For example, the CSA inspection program requires the pressure relief valve to be replaced every five years and a visual inspection every two and a half years. The hydrostatic pressure test must be done once every five years.
An alternate inspection program is in effect. In 1996, the Canadian Association of Ag Retailers along with the Canadian Fertilizer Institute approached Transport Canada to ask for a visual inspection program instead of a full hydrostatic test required by CSA. This is strictly an external check that does not put a tank under stress to identify flaws.
When the new CSA standards go into effect within the coming year, they will incorporate a number of changes, including annual hose inspection.
Dickson said it’s important to ensure maximum safety in storage and transport tanks, but one of the greatest risk factors remains the human one.
“We certainly want to locate every weak tank and take it out of service, but the tank itself is probably the safest component. We took one of those condemned ChemiTrol tanks and hydro tested it up over 1,000 psi before it sprung a leak.
“In an on-farm situation, an anhydrous tank that’s 85 percent full might reach 150 psi on a hot, sunny day. The pressure relief valve triggers at 250 psi or 265 psi. I can’t think of any way nurse tank pressure can possibly get up into a danger zone.”
The danger in handling anhydrous is not being careful when working with hoses, couplers and plugged openers. Nearly all accidents happen when people don’t follow the correct procedures.
“The hose and quick coupler are the two most likely things to fail because they can be inadvertently left dragging on the ground or on a tire. The hose is constantly being flexed. The ultraviolet radiation from the sun breaks down the rubber.”
Dickson said components like hoses, couplers and openers involve human factors and people have the option of treating them with respect or paying the price.
