The safety of our drinking water supply is a serious matter. By now everyone is familiar with the tragic situation in Flint, Michigan, where a decision to switch the municipal water system led to massive lead contamination in the drinking water. The Flint tragedy had numerous causes, but one lesson to be learned is that regular inspection of the physical water system is critically important. If the infrastructure of the Flint system had been adequately inspected, it is possible that officials would have been aware of the problem at an earlier date. When it comes time to inspect a water system – whether a giant municipal potable water supply or a small private tank like a facility storage tank – remote operated vehicles (ROVs) offer a number of advantages over other methods.
In the pre-ROV era, tank inspections meant either sending a human diver into the tank (posing risks to the safety of both the water supply and the human diver) or draining the whole tank and inspecting it dry. Both of these approaches have serious drawbacks. Using ROVs as the centerpiece for a tank inspection strategy has some enormous advantages over the older method.
The Tank Doesn’t Need to be Drained
Draining a water tank is a wasteful and expensive process. A municipal potable water supply tank can be millions of gallons of water – even tens of millions of gallons. It’s rare for there to be any productive use for all that water being drained at once – it literally flows out into the sewers and is gone. Not only that, but the water system the tank was supporting is then left high and dry while the inspection takes place. ROVs permit the tank to be left filled and in service while the inspection is taking place, saving both time and money.
No Risk to Human Divers or the Water System
Human divers cost a lot of money. Training, equipment, insurance – the list goes on. If there’s a safety incident, the financial cost alone can be huge, to say nothing of the human cost. In addition, to send a human diver into a potable water system, the diver must be sterilized – a difficult, unwieldy and unpleasant process, and one which if done improperly can compromise the safety of the entire water system.
ROVs, on the other hand, are relatively inexpensive and, compared to a human life, completely expendable. Because they are small and mechanical, they are much easier to sterilize for use in a potable water environment. Best of all, ROVs don’t charge extra for working a long shift!
Low Barrier to Entry
Certified divers are skilled professionals and scarce in some locales. By comparison, becoming proficient in operation of the Aquabotix ROV is a matter of three days of practice with the vehicle. Divers require support teams, so a minimum of two people are going to be on the job site, but an ROV is a one-person operation. Aquabotix ROVs come complete with recording capability (allowing the operator to take video footage, snap photographs, and record data from onboard instrumentation) and can operate on battery power alone.
Built-In Data Gathering
Every measurement a human diver takes requires them to carry (and learn the operation of) another sensor or instrument. ROVs, on the other hand, can carry built-in sensor suites that have all of the needed data-gathering equipment for any given inspection mission. For example, thermal stratification (water forming temperature layers or clines) can prevent mixing of water in a tank, which can reduce the efficacy of chlorine or chloramines in disinfecting the water. ROVs carry temperature and depth sensors which will automatically record and report the temperature and depth throughout the vehicle’s inspection cruise, automatically producing an easily-read report showing problem areas. There are many other environmental sensors available for ROVs which can quickly collect enormous amounts of data that would take a human diver multiple dives, at great expense, to gather. For example, ROVs can carry a Cygnus NDT metal thickness gauge, allowing the vehicle to test the thickness of the tank wall at hundreds or even thousands of points during an inspection.
Increased Frequency of Monitoring
As become sadly evident in the case of Flint, a water system can develop problems very quickly. Because ROV-based inspections are so much less expensive and so much more convenient than diver or draining inspections, they can be performed at much shorter intervals. That means, for example, that a problem like Flint’s (which is expected to cost hundreds of millions of dollars to fix) might instead have been caught when it could have been fixed for a few million. Frequent inspections greatly increase the chance of catching minor problems while they are still minor.
ROV-based inspections of water systems, particularly water tanks, save water and money, reduce the risk to human life, increase the safety of the water supply, are easier for small municipalities and operations to do for themselves, and collect valuable data at a lower cost than other options. There will continue to be need for human divers in some applications, but ROVs greatly expand our ability to inspect, and to keep safe, our water systems.
Fire tanks are an important part of the infrastructure that supports firefighters around the globe. These tanks are found at residential, commercial, industrial and institutional sites. Some fire tanks are used to supplement a building’s available standard water pressure during a fire emergency, while others provide the direct water supply for a building’s internal sprinkler system. Obviously, the condition of these tanks is a major part of a building’s fire safety plan.
There are a number of industry and regulatory standards for fire tank construction, installation, and inspection. In the United States, the National Fire Protection Agency has two important standards: NFPA 22, which establishes the requirements for the design, construction, installation, and maintenance of tanks and accessory equipment that supply water for private fire protection, and NFPA 25, which sets standards for the inspection, testing, and maintenance of water-based fire protection tanks and systems. Other industry standards include the Factory Manual (FM) standard and American Water Works Association (AWWA) standard.
These standards exist in a patchwork system of governmental, insurance, and industry mandates and policies, so it is difficult to make general statements about which regulations are going to apply to which facilities. As in real estate, a great deal boils down to “location, location, location” – where you are and what your facilities does will control what regulatory regime(s) you are subject to. However, probably the single most widespread requirement is also the most onerous for tank owners, and that is the requirement for periodic inspections of the inside of the tank.
Inspections look at a wide variety of tank conditions, including (but not limited to) internal corrosion, the condition of suction inlets and vortex inhibitors, roof supports, vermin infestation, the condition of tie rods and liners, ultrasonic or electronic testing of tank wall thickness, dry film thickness testing, paint adhesion, and more. In addition, inspections are often also combined with repair work to fix problems that the inspection uncovers.
How often are tanks required to be inspected? In the United States, NFPA 25 sets a requirement for a complete internal inspection every five years, a fairly typical value. Each country has its own legal requirements, however, and it is important to check your own local laws and regulations to know the inspection interval.
Rules and regulations can change, sometimes very quickly, and those changes can have enormous impacts. For example, in Australia, the regulatory standard is known as AS1851, and it recently changed the inspection interval for fire tanks from every ten years to every year – a tenfold increase in required inspections! Given that Australia has approximately 20,000 water tanks, this is a massive increase in the inspection workload. Fortunately, the standard also permits the use of ROVs as an alternative to human divers for inspections, meaning that Australian tank inspection companies can now leverage their human divers with an ROV fleet. This will permit them to greatly increase the efficiency and decrease the cost of tank inspections. Aquabotix ROVs make an excellent addition to any tank inspection service, providing new capabilities, reducing the cost of existing capabilities, and increasing the reach and flexibility of human divers.
Thank you to Unmanned Systems and author Marc Selinger for their coverage of Aquabotix in the February edition of the magazine.
To learn more about Unmanned Systems, please visit http://www.auvsi.org/publications/unmannedsystemsmagazine.
Thank you to Aquaculture North America for the coverage of the HydroView pro 7M/AQ in the Jan/Feb 2016 edition. The HydroView Pro 7M/AQ is configured specifically to address the needs of aquaculture applications and includes options most requested by fish farm operators.
To learn more about Aquaculture North America, visit their website at www.aquaculturenorthamerica.com.
The problem of seeing things underwater is one that has vexed divers and others who work in the water since time immemorial. Ordinary vision works OK, in the daytime or with artificial light, in shallow water, in good conditions – but fails spectacularly in poor light or when water conditions are murky or worse. The modern electronic marvel that let us “see” for thousands or even millions of miles through air and space – radar – is completely useless underwater; water is effectively a brick wall to the short electromagnetic wavelengths that radar employs. Yet it is extremely important that underwater craft be able to sense their surroundings; if your craft is unable to see what is around it, you will pay the price for your lack of vision. Around the beginning of the 20th century, researchers realized that they could use sound waves to “see” underwater.
Unlike radar, sound waves propagate just fine underwater – in fact, they propagate underwater better than they propagate through the air. The first sonar-like devices were used to listen for icebergs; sonar technology advanced enormously during the First World War as a tool to listen for enemy submarines. Sonar still has extensive military uses, but today civilian sonar is the primary area of development.
Although in this post we will talk about “seeing” it should be noted that sonar does not actually produce a direct visual image. Many sonar control suites will translate the sonar data into a visual picture, and high-end sonars actually can produced simulated images that look very much like you are “seeing” what is out there – but the actual data is sound pulses being reflected back. Computers do much of the interpreting of that data stream, making it more accessible to people without advanced training in sonar interpretation.
Most remote-operated vehicles have the ability to carry sonar sets as optional equipment.ROVs use sonar for a variety of purposes, from mapping the bottom of bodies of water to searching for items in the water.
There are three basic types of sonar available for deployment on an ROV:
Scanning sonar operates in a way that will be familiar to anyone who has ever seen a radar dish turning at an airport. The sonar emitter physically rotates, sending out a pulse of sound as it does so, and simultaneously listens for the echoes returning from any objects in the water. The rotational speed of a scanning sonar balances out the time between pulses and the time it takes for a returning pulse to come back to the sonar.
Scanning sonars do not provide a high degree of resolution. They are able to detect large objects (for example, pilings or ships) but lack the discrimination necessary to spot smaller objects, particularly when those objects are on the bottom or next to another object. Because there is only one beam, scanning sonars have no ability to see behind objects; if one object is behind another object in a line to the scanning sonar, the scanning sonar can see only the closer of the two. The strength of the scanning sonar is that it does cover an area of 360 degrees, although only from 10 to 20 degrees above and below the plane of the sonar.
Multibeam sonars (often referred to as “hydrophones”) are significantly more capable. A multibeam array has multiple sonar emitters, which are all digitally rather than manually moved, allowing for a much higher rate of scanning. A combination of hardware and software allows the multibeam sonar to sweep a wider area of the water – about 120 degrees in all directions. Multibeam sonars do not cover a 360 degree arc, however. They make up for this by having a higher degree of resolution than scanning sonars – at a hundred meters, a multibeam sonar can spot a diver in the water. At 10 meters it can distinguish arms and legs. Multibeam sonars are extremely good at looking in one direction at a time.
Side-Scanning sonars have two arrays, each of which has a sonar beam that traverses a 90-degree arc, one horizontally and one vertically. This means that they can see in almost every direction, except for straight up and down. Side-scanning sonars are used to collect data as an ROV moves through the water; unlike scanning and multibeam sonars, they do not provide information in real-time. Instead, they provide a “historical” view of what was there when the ROV was moving past a certain point. The advantage of side-scanning sonars is that they “see” almost everything, providing great resolution and covering an enormous area. Side-scanning sonars are suitable for wide-area searches for stationary objects (such as bodies or objects on the bottom of the body of water), surveying, and environmental monitoring.
The right type of sonar for your ROV will depend on the missions for that ROV. Each sonar type has advantages and disadvantages for various kinds of work. Aquabotix ROVs can be configured with any of these sonar types. As with other accessories, choosing the right tools for the job will go a long way towards ensuring that you get the best possible results.