Floating roof storage tanks have become an integral part of the storage terminal industry by reducing losses from evaporated, stored product. They also are essential to maintaining environmental compliance, by reducing potential emissions caused by evaporation. However, they can come with their own set of maintenance challenges.
Common issues include roofs sinking causing product contamination and weather conditions. Accumulated snow and rainwater can cause roofs to tilt compromising their overall effectiveness. Facility managers can mitigate these challenges with thorough and regular check-ups which now can be done remotely with wirelessly captured, floating roof monitoring.
In this storage terminal safety podcast series podcast, we are joined by Emerson’s Per Skogberg and Christoffer Hoffmann. We discuss how predictable tank incidents can become preventable with Remote and Continuous Floating Roof Monitoring.
To learn more about how to ensure the safety of your storage terminal facilities, please visit: www.emerson.com/terminal-safety. For specific product information, please visit: www.emerson.com/rosemount-tankgauging.
Jim: Hi, everyone. This is Jim Cahill from the “Emerson Automation Experts Blog.” And today, we have a podcast, part of the “Enabling Storage Terminal Safety” podcast series. And today, we’re going to talk about mitigating tank damage with floating roof monitoring. And I’m joined by Per Skogberg and Christoffer Hoffmann. And I guess to get started, why don’t we start with you, Per? Could you give us a little bit, introduce yourself, tell us a little bit about what’s your title, and your education, and background?
Per: Yeah, sure. I’m a solutions manager at Emerson, working with our tank gauging system. I studied Industrial Engineering and Management at university and have a Master of Science in Management and Economics of Innovation. I’ve been with Emerson now for six years, just about, in a few different roles but actually always working with our tank gauging business.
Jim: That’s great. And Chris, could you tell us a little bit about yourself?
Christoffer: Absolutely, Jim. I’ve been working with Emerson for approximately 10 years now. I have a multitude of roles just like Per. My current role is business development manager, primarily focusing on Latin American for tank gauging. My background actually comes from more of an IT world rather than the industrial world. So I’m bringing that into the picture.
Jim: Okay. That’s great. I guess let’s start out for our listeners, can you share a little history of floating roof monitoring technology and why it’s important for, you know, some of our customers with storage tanks?
Christoffer: Well, the existence of floating roof tank was more or less unknown to most people outside of the industry. That said, before Hurricane Harvey swept across the U.S. in 2017 causing a lot of damage, and that you heard a lot of media reports about the damages that occurred for several storage terminals and refineries. We had tank failures, product spills, and a lot of release of hydrocarbon vapors and volatile organic compounds or VOCs into the atmosphere. And since then, safety of oil storage and floating roof tanks especially has become a much more widely discussed topic. And according to the International Association of Oil & Gas Producers, the IOGP, the incidence frequency of floating roof tanks per year is 1 in 625 tanks will have liquid spilled onto the floating roof. One in 900 floating roofs will actually sink into the product, in the tank. One in 8,300 tanks will develop a full surface fire, which is the extreme case.
Per: And an interesting thing here you might say is that many of these incidents are actually…they’re considered when they happen to be sort of one-offs or just, you know, fluke accidents. But instead of… If you were to consider them as predictable events, you know, it would be possible to prevent and mitigate this in a whole different way. And that’s why it should be made a part of the systemic safety work to monitor the roofs. And that’s where we now have an option to use automatic monitoring in order to be able to see when an issue is first arising. Previously, if you compare, then a tank could fail suddenly without notice, but now you would have a means to continuously monitor the status of the roof and to get early notice that when something is amiss here and you should take action.
Jim: Yeah, sounds like monitoring from a safety perspective is critical. Chris, what are some common issues you see in storage tanks without floating roofs, I guess some of the fixed tank roof? What are the disadvantages of those types of tanks?
Christoffer: Well, before the invention of floating roof storage tanks, these tanks were often without any cover or top at all. So it was leaving the product exposed to the elements and that, of course, comes with numerous disadvantages. You have evaporation of the product, so product loss, you have increased risk of ignition since there’s no protection, and you also had the risk of product contamination. So the roof storage tank can be… The easiest, the best analogy I find is to compare it to a swimming pool and the swimming pool cover because they basically do a lot of the same things.
And the main reasons you started using floating roofs in the first place were to reduce evaporation from the stored product, which in turn has several benefits. You reduce the risk of igniting the volatile vapors. You reduce the product evaporation losses, of course, that has a significant impact on the economics on your operation. You reduce emissions released into the atmosphere. This is a big talking point, it’s becoming more and more brought up because stricter and stricter regulations for product emissions allowed into the atmosphere and you need to regulate them. You need to keep them under control as much as you can. And lastly, you protect the product from contamination like precipitation and debris depending on where you are in the world, we’re talking about rain, or snow, or sand, or whatever that you’d want to keep out of your tanks.
Jim: Well, that sounds like a lot of good reasons for floating roofs and why you see them more widely in use today. Per, what are some important considerations or advantages and disadvantages when investing in floating roof tank storage?
Per: Well, you know, there are some disadvantages as you said, and mainly it’s because the floating roof, really, it’s like this really big moving part which then has wear and tear and requires maintenance. Of course, any failure of that roof, as Christoffer mentioned, can have quite severe impacts. You know, in worst case, a fire, or and otherwise injuries, or tank downtime, or a number of different…or other issues. To add on top of that, I mean, there are both internal and external floating roof tanks. On the external tanks, they are exposed to the elements which, of course, can’t be controlled. So and that’s what we saw in the case of Hurricane Harvey, that that caused a lot of problems.
But then, due to all of this, it’s practiced that, of course, the roof should be inspected regularly, but that requires a lot of effort. And it’s not always that such inspections are performed as they should be. And that could be for a number of reasons. I mean, first of all, it’s a safety hazard for operators to climb down to the tank and climb down to the actual roof of the tank. And there’s typically a permit process involved there that you need to go through to gain access to the tank and that could be cumbersome. And the operating parameters might simply not be right for inspection when the need arises. For example, if the tank is in service you would prefer to enter the roof when the tank is full, and the roof is at the top position. But that, of course, isn’t always the case. And it may also be that management simply doesn’t understand the likelihood or the consequences of an incident occurring or there might not just be enough operators to prioritize this particular job against all of the other things that you need to do in your tank farm.
Jim: Yeah, it sounds like there’s no perfect solution on the type of tanks there. So for these floating roof tanks, what are some signs of what a damaged floating roof looks like, Chris? And how easy is it to detect this damage?
Christoffer: Well, there are numerous failure modes and types of damage that can occur. Some are easier to spot than others. An easy indication that there is an issue is you can see product, the tank product on the top of the tank roof where it’s not supposed to be. That’s one of the easy indications, but this could indicate roof leakage which could in the end could lead to the roofs sinking completely. Another sign is that the roof is tilting, it’s not floating level. It should always be as level as possible on the product and follow the product it’s floating on. However, if you’re standing there, these are big structures. Spotting a tilting roof just by visual inspection alone can be difficult because it looks level when you’re close up, up-close to it.
If you have a tilting roof, that could in turn indicate numerous different problems. You could have leaking roof pontoons enabling the roof to float on the product. And these can sometimes be easy to spot, sometimes not. You can have a leaking center deck, which is the inner portion of the roof where you can have a puncture. Leaking roof rim seals, the seals around the roof towards the tank walls. You could also have buckling of the tank shell or rough spots where the roof seal binds to the tank shell when it moves up and down. So all of these are different indicators of different problems, but all of them can have severe effects.
Per: And there are also a number of other failure modes. For example, the roof might sink or start tilting from heavy rain, or snow, or even sand from sandstorms in that part of the world. If that happens, that typically often is connected to the roof drain being clogged, or under-dimensioned, or maybe the valve just happened to be closed so it hasn’t let the water out as it should. Another thing that can cause tilt actually is strong winds. And, of course, if that happens in combination with rain or snow, that could lead to the roof tilting rather severely. And then also it may be that the rolling ladder that normally you would use to gain access to the roof, that can get stuck and prevent the roof from floating freely and following the liquid level up and down as it falls or rises.
Christoffer: And regardless of the cause, an incident involving a floating roof impacts operations to some extent and requires a number of measures to be taken before the situation is back to normal. The specific measures needed will, of course, depend on the type of the incident, but effects of a floating roof failure can be a lot of different things. For example, you need to take the tank out of service. You need to clean up spills, worst case, if you have an incident, you have incident reporting to the proper authorities, which in turn can have consequences on their own. You need to monitor the air quality for any pollution as a result from the evaporating product. You need to clean the product if you have product contamination from any water, or any dirt, or any…for example, in case of a fire, we have to put it out using foam or anything like that. You need to clean up everything.
Then you have the repair costs of the tank and/or the floating roof which is no small task. You have cause and effects related to the emergency responder or fire brigade actions taken. And, of course, you have interruption to your normal production under normal operations. In case of an accident, you suffer damage in the public perception, the public eye, and your reputation from shelter-in-place orders as a norm. And all of these consequences aside, it’s not even considering the potentially disastrous effects of a full tank fire. So all these are just the minor effects of a tank roof failure. But certainly, all these effects have a significant financial impact as well as putting the well-being of your employees at risk. So it’s definitely not a problem to be ignored.
Per: Indeed. And I mean, so the standard way to reduce the risk of incidents then would be to, you know, routinely and thoroughly inspect the roof. And that would include maybe, you know, climbing down to the roof, opening the manways into the pontoon compartments to inspect them on the inside, to inspect the roof legs and vacuum breakers, and ensure that the rolling ladder is functioning properly. And checking or testing the parts of the seal that you can reach, and checking for corrosions, and many other tasks. So it’s an extensive job to be carrying out these inspections. And you need to do it regularly, of course, according to whatever safety guidelines and directives you have in place for the facility. But unfortunately, as we mentioned earlier, it’s not always the case that these are carried out as they should be.
Christoffer: And not performing inspections routinely will cause problems at a later stage. So, when inspections are not carried out, you have less critical faults that could’ve been repaired not discovered. And as time passes, these escalate into, or these could escalate into more serious events. So in the end, this leads to operators being caught offguard by a sudden emergency like Per talked about in the beginning. Instead of having solved the issue by the repair as part of routine maintenance, we mean that it’s not a sudden occurrence. These all can be, or many of these failure modes can be detected early on. It’s actually, in fact, rare for serious incidents to happen suddenly out of the blue without any warning signs that could’ve been discovered earlier. And using automation technology to continuously monitor the behavior of the floating roof then becomes a way to predict when a tank needs maintenance. So it’s a way to improve routine practices and make sure you can focus your attention where it’s needed the most.
Jim: I think you’ve really talked about a lot of the issues that can come up, both minor and major, and routine maintenance, and everything. And let’s drill in a little bit about the automation technology. So, Per, how has the Emerson team worked help to help solve these problems?
Per: Well, I would say that adding automatic monitoring to the floating roof is a reliable way to be able to predict and mitigate roof failures. Using radar level gauges, this can be done, in fact, without making any modifications to the tank, and then combined with our TankMaster software, which we use in the control room, you get an overview of the status of all your floating roofs. And then you can also get the history of roof movements which can then be used to create a baseline for how the roof of each specific tank should be moving or is normally moving during operation. And then from that baseline you can set up alarms to quickly identify abnormal behavior before any kind of serious incident would occur. And we use radar gauges since, really, it’s the standard instrument you can even say for level measurement in box storage tanks. And it’s a proven technology. It’s been used for decades in terminals and tank farms all over the world and it’s very suitable for this application as well.
Christoffer: Depending on the tank type and the existing conditions, the solution can be implemented in several ways. But the basic principle of operation is the same for all of these. You have three or more, you can have up to six level gauges, are installed to monitor the position on the floating roof. So it’s measured to the roof. And then it’s measuring these values and comparing them against each other and against a primary level device to detect any anomaly such as roof tilting or sinking. So it’s basically calculating the difference between the different level points. You can also add drain sump monitoring, for example, in combination with this. So you can use a level switch to detect a clogged or a closed drain like Per mentioned before. And in addition to this extra device, you can also add hydrocarbon detectors to integrate into this monitoring software to detect any product leaks onto the tank roof.
Jim: So, Per, can you give our listeners a picture of the process of what it takes to set up these monitoring solutions?
Per: Yeah, sure. I mean, there are two basic principles here. There’s shell mounted installation and there is roof mounted installation. And in the case of shell mounted, you would use non-contacting radar, specifically the Rosemount 5408 Radar Level Transmitter or the 5900C Radar Level Gauge. And you would use, as Christoff has said, minimum three of these and they are installed at equal distances from each other on the tank wall at the very top of the tank.
Directly below each radar, you place reflector plates to enable measurements without disturbances even if the surface is uneven, or if there are object protruding from the roof, or if there happens to be a heavy snowfall, or anything like that. And then the tilt of the roof is tracked simply by comparing the distance from each gauge down to the floating roof or the reflector. That’s the non-contacting solution. It’s very accurate. It’s very, very reliable. It can be retrofitted to existing tanks without taking the tank top out of operation. If you add the ordinary level measurement as a reference to the system, you can also monitor the buoyancy of the roof to see if it’s floating higher or lower than it should be or than it normally does.
Christoffer: And then we have the second type of installation which is the roof mounted installation using a guided wave radar gauge. So this is an alternative solution where you can use up to six guided wave radar transmitters, between three and six, directly on the floating roof itself. You’re using a rigid probe penetrating through the roof and into the liquid, and then you track the roof tilt by comparing the distance from the floating roof down to the product surface, and you will also track the roof buoyancy with this solution. So it’s almost working in an inverted way from the non-contacting version, but the result is the same. And one major advantage you get with this on-roof configuration is that it’s 100% wireless. It’s a battery-powered solution where we use the Rosemount 3308 Wireless Guided Wave Radar, so no strings at all attached.
Jim: So I can visualize both ways. One, you’re kind of fixing it on the tank itself measuring down to where the roof position is, non-contacting radar. The other, you’re actually mounting the instruments on the roof itself into the liquid down to compare between those. That makes sense. So, Per, what does a fully automated approach look like?
Per: Well, so beyond the level gauges on the tank, the data can be transmitted either wired or through wireless communication to the control room, where an operator can monitor the roof status. And you can also add more instruments to the tank for more extensive monitoring as we’ve maybe mentioned a bit earlier, I think. For example, you can monitor the drain sump to make sure it isn’t clogged or it’s not overflowing. Or you could monitor for water gathering on the roof itself. For that we would use the Rosemount 2160 Wireless Vibrating Fork Switch. But you could also detect if there are hydrocarbons that are accumulating or pooling on the roof itself by using a Rosemount 702 Wireless Transmitter with Liquid Hydrocarbon Detection attached to that. So there’s really much useful data that you could gather from up there on the tank. And then with the software in the control room, you would get automatic alarms for, you know, roof tilts, buoyancy, roof sticking, as well then as for drain sump blockage, or hydrocarbon detection.
Jim: Yeah, that sounds like you have a really good picture remotely there of what’s going on with the tank. So I guess, Chris, what are some common concerns about adapting to an automated approach as opposed to what’s historically been done through a manual approach?
Christoffer: Well, if the question is should I go for a roof mounted installation with guided wave radar, or should I go for the shell mount version using non-contacting radar, it [inaudible 00:21:19] really possible to give any general recommendations like that because all tanks are different. They have different characteristics. I mean, it’s like when you go to a terminal, every tank has its own personality almost. It all depends on what suits best for each particular tank. It’s going to depend on things like what kind of tank openings and nozzles are available on the roof. What kind of infrastructure is already in place such as when it comes to power and communication cabling or if you have any existing wireless networks already on the site, and also what kind of instrumentation you already have installed on the tank itself. So there’s no really hard rules. There is one recommendation for best practice is if you’re using an internal roof tank, there are external and internal floating roof tanks. So if you’re using the internal floating roof tank, it needs a shell mounted installation using non-contacting radar.
Per: I think the beauty of the system that we have is that you’re entirely free to combine the two technologies. You can have roof mounted monitoring on some of the tanks and then use shell mounted on some of the other ones. And you can have wireless data transfer for one tank and wired communication to all the others. And in the end, it’s all integrated into the same system. So there’s a large degree of freedom there in regards of installation.
Jim: So, Chris, let me ask, how would you sum up performance gains by using these automatic floating roof monitoring solutions?
Christoffer: Well, in short, installing automatic floating roof monitoring is all about increasing reliability and safety by moving from being reactive to being proactive. Whereas previously, floating roofs could suddenly fail without notice, and now, if you automate it, you can have means to continuously monitor the health, if you will, of the roof. You get early indications if the roof is not behaving as normal. You can send personnel out to properly inspect it when needed. Based on the findings, you will be able to schedule and plan repairs and maintenance. This, as opposed to discovering a problem only after an incident has occurred and then having to deal with all of the consequences we mentioned before like fire prevention measures, cleaning up, reporting missions, regulation violations, potentially having to take the tank out of service, and not to mention, damage to people or property, and many other…
Per: And in addition to this, there’s just the fact that there is less need to send personnel out into the field into the hazardous area for routine inspection rounds potentially in bad or even dangerous weather conditions.
Jim: Well, it sounds like this automatic monitoring can provide a lot of information and help people better understand when there’s a problem early and be able to go deal with it for safer and more reliable operations for the tank farms. So where can our listeners go to learn more? And if they have specific questions coming out of this podcast, how can they get a hold of y’all?
Christoffer: For more information, you can go to our webpage for tank gauging which is located at emerson.com/rosemount-tankgauging. And you can also visit our other website for the overall terminal safety initiative which is emerson.com/terminal-safety. When it comes to contact, you can always contact us on LinkedIn.
Jim: I know you guys are active in LinkedIn, so that’s a great way to get a hold of you. All right, well, I know I’ve learned a tremendous amount about the different types of tanks and the different types of ways that we can make sure things are operating correctly. So I want to thank you both, Per and Chris, for joining us today and sharing your knowledge and experience with our listeners. Thank you very much.
Christoffer: Thank you for having us.
Per: Thank you for having us.