One of the most common uses for commercial underwater remote-operated vehicles (ROVs) is in conducting inspections of water tanks, ship hulls, and submerged infrastructure such as bridge components or dams. A critical element of these inspections is measuring the thickness of metal components like hulls or girders. How do ROVs conduct this type of measurement?
On the Aquabotix Endura line of high-performance commercial ROVs, we offer the Cygnus NDT Metal Thickness gauge as an optional accessory. These gauges use ultrasound technology to measure the thickness of metal objects underwater. By emitting an ultrasonic beam into the surface of the metal and analyzing the return sound, the Cygnus NDT can measure metal of thicknesses up to 10”, even through coatings such as paint up to 0.787” thick.
The Cygnus NDT is extremely easy to use. The included CygLink software allows the ROV operator to visualize the tool’s measurements remotely on the video feed. To make things even easier, the optional Cygnus Probe Handler automatically aligns the probe to the wall or item being measured, with 15 degrees of movement, even if the operator has not perfectly approached the measurement subject.
Tools like the Cygnus greatly enhance the utility of our Endura ROVs. As ROVs take on more responsible roles in things like underwater inspections, the need for tools such as the Cygnus will continue to grow.
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.
Check out the HydroView Pro inspecting a separation tank. The walls, pipes and sediment levels were observed. Pay close attention to the end of the video where the bottom skids of the HydroView were used to evaluate the depth of the sediment - just another example of an innovative way to use an ROV.
Thermal stratification in potable water storage tanks poses risks for system operators and their customers. Water treated with chlorine or chloramines generally remains stable for a few days. Thermal stratification can hamper passive mixing or cycling of the water resulting in the potential for limit aging or deterioration of the disinfectant chemicals. Drops in residual chlorine can lead to growth of bacteria often requiring the draining and flushing of the tank.
Thermal stratification can also promote the formation of nitrates and other disinfection byproducts, allow for the formation of ice endangering coatings and tank walls and allow headspace temperatures to rise above recommended levels.
The HydroView Pro 5MWI is equipped with depth and temperature sensors. Data from these sensors is recorded during tank inspections and downloaded following the inspection in an easy to read/report format. Additional water chemistry sensors are available and can be integrated with the vehicle and the data reporting module.