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ILTA study to aid storage tank design and repair

Sept. 6, 2016
Find how to make better decisions on construction and maintenance of storage tanks and to serve as a resource to companies evaluating tank design and repair.

THIRTY-FIVE percent of storage tanks have some form of cathodic protection, and there is a lower rate of bottom replacements in those tanks.

That’s one of the preliminary findings from the International Liquid Terminals Association’s new study on tank bottoms and foundations, according to Tyler Ley, professor of civil engineering at Oklahoma State University. He said the final report should be submitted by September. The goal is to help the industry to make better decisions on construction and maintenance of storage tanks and to serve as a valuable resource to companies evaluating tank design and repair.

“I am not a tank expert,” Ley said during the ILTA’s 36th Annual International Operating Conference in Houston, Texas. “However, I have spent a lot of time and been involved in many research projects studying other infrastructure systems: roads, bridges, buildings, parking garages, and airports. There are a lot of lessons we can learn from those sectors and apply to your industry. There are a lot of concerns those industries have in common with yours: ‘We have this big infrastructure investment. We need to make decisions today to make them last as long as possible. How can we keep a storage tank going?’

“We need to know how our infrastructure performs. We need to have great data so when regulators want to come in and tell us how to handle our systems, we can say, ‘We have the data and are doing the best we can.’

“It’s kind of like studying humans. On average in the United States, the human life span is 76 years. It’s different in Texas than it is in Florida than it is in New York City. Why? Lots of reasons. Doctors tell us what to do and not to do: eat right, don’t smoke. That advice is given to us to help us live longer and have a better life. We’re going to try to give you those exact same recommendations for your tanks and infrastructures. That is the goal of the study.”

Some questions that will be analyzed:

Do all tank foundations perform the same?

Do certain tank foundations perform better in different environments?

How should storage tank designs change with size?

How long do tank foundation repairs last?

Is cathodic protection helpful?

If we heat the product in a tank, does that shorten the lifespan?

How do different products impact the lifespan of a tank?

Can we do things better to make our tanks last longer?

“We need more information,” he said. “We need more data. This study will give us insights into the best practices on how to manage our storage tank infrastructure. This will help companies make wise decisions with their dollars and also justify industry actions to regulators. If you don’t generate the data, someone else will make the decision for you.

“How are we going to do this? It sounds really hard. We need real performance. We’re going to gather case studies from ILTA and American Petroleum Institute (API) members of tank performance from many different locations. We’ll statistically analyze these records to find insights into the data. Then we’re going to go back and discuss our findings with our oversight committee. We are not doing this study in a vacuum. I am not a tank expert, but I need tank experts. These are helpful people. Let me bring them something and say, ‘You know what? Look at that data again. Maybe there’s more to the story.’ We’re going to make recommendations on best practices for first design and repairs and publish this information in a report that all ILTA members will get for free, and also in peer-reviewed journal papers, so it will be maintained and available for future generations.”

He said the focus is on performance of newly constructed tank foundations and their resistance to corrosion; performance of newly constructed tank foundations to settlement; and the effectiveness of different repair methods for corrosion.

The study will look at construction variables: location, year constructed, foundation type, product type, API design standard, capacity, seismic zone, roof type, fill material and preparation, initial bottom, thickness, and type of floor. Is the tank heated? Is it insulated? Does it have an annular ring?

Performance information includes: current plate thickness, patch information, bottom replacement, repair type, and settlement events. Is the tank in service?

Ley said 5,707 tank records were provided, with 4,667 having enough critical data. All tanks are from seven different countries in North and South America. The construction years are between 1906 and 2016, with the majority of tanks from 1950 to 1960. About 5% have had a bottom replacement.

Next, they will analyze the data, work with panel of experts to discuss the results, and prepare reports.

Other preliminary findings:

•  “We found that tanks are taken out of service on average after 50 years of service. You might want to think of that as death. It’s not really death, though. It’s more like retirement. How many people are taken out of service but then come back? That happens with tanks, too. You take a tank out of service because it’s not economical to run now, but you know what? It might come back. And that’s an average number. There are some that will be 70 years old, some that will be 50, some that will be 30.”

•  “The lifespan in the United States seems to be longer than in other countries. But it’s still early in the study.”

•  “Fifteen percent of tank floors have some kind of replacement. That’s reported replacement. Other tanks may have had floor replacements, but if we don’t have the information, we can’t say anything.”

•  The average age for tank floor replacement is 25 years.”

•  “Twenty-five percent of tanks reportedly have settlement. Have important settlement, we’ll call it. But we’re still going through that data and trying to get a better understanding.”

Mark Kelley, vice-president of Kelley Construction, provided a look at tank foundation and underside corrosion from an owner’s perspective.

He asked these questions: Is this asset going to perform as intended during its life expectancy? What is going to be the return on our investment?

“When we start the thought process of building the new asset or tank, how often do we think about the foundation first? Or do we really go directly into the tank itself?” he asked. “I would venture to say a lot of times we go into the development of a tank before we think about the foundation.

“When we do start thinking about the foundation, we need to ask: Is it going to sit on a stand? What material will be choose? Will it have earth-bearing to it? What is the moisture content of the ground? Is water going to pond around it?

“We may not know the exact effects that could come about from that, but we know that they’re not good. A lot of times we put common sense into our practices that we’ve done in the past because that’s really all we have to go by. Most of the time, we look at our own tanks, our own assets, and say, ‘What works? What doesn’t work?’ There are other factors: Excessive tank settlement. Is it due to the ground? Due to the style of the foundation we actually used?”

He showed a photo of underside corrosion, saying: “This has come into the study because it’s impossible not to look at the corrosion portion of the underside as being one of biggest costs effects to whether a foundation works or not. Because we’ve defined foundation as whatever this tank actually sits upon, that brings this factor into it. I’d venture to say that’s probably one of our biggest expenses to a foundation repair than anything else. A lot of times that’s not really known until that asset is taken out of production.

He outlined various foundation types:

•  Earthen. “We still see quite a few of those. I’d venture to say most of the tanks we see are on ground, especially in other countries. Maybe not as much in the United States, but definitely in other countries. And we are doing the study worldwide.”

•  Asphalt. “We see this more in asphalt tanks themselves.”

•  Stone. “These seem to go away and all of a sudden come back. I belief that’s due to cost. Does the stone really give us what we need? Can we get it to the elevation we need? Does it cause corrosion to the bottom of the tank? I’ve been in many discussions where they’re trying to weigh out that. We see it more on smaller tanks than larger tanks.”

•  Concrete ring wall. “That seems to be the most used at this point. It’s a cost-effective way. When using concrete ring wall, it seems to be, what is out on the inside? What are the properties of the sand? We can see where the cost of the sand fill material is exceeding the cost of the ring wall itself. In my opinion, that’s something that the study can really help us out with because that cost is astronomical in some states.”   ♦

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