Maintaining Storage Tanks
Preventative care keeps water safe.
An integral ingredient in maintaining the health of a water supply tank is a good inspection according to tank manufacturers and consultants. In the words of George Mead, municipal sales director with Tank Connection in Parsons, KS, “Nothing fabricated and installed will continue to operate without inspections.”
Some states have created regulations requiring water tanks to be inspected periodically, some yearly, or in one case—the state of Connecticut—a minimum of every 10 years. The specificity of the inspections varies from state to state. The American Water Works Association (AWWA) has developed inspection plans for finished water storage tanks modeled after a regulation the state of Colorado approved in 2015. AWWA recommends water tanks be inspected every three to five years.
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Colorado requires that suppliers must develop and maintain a written plan for finished water storage tank inspections to include an inventory of information for each finished water storage tank, a schedule for performing inspections, and treatment technique requirements. Other requirements include responses to violations of the storage tank rule and record-keeping requirements.
Connecticut provides guidelines that specify what a qualified inspector should inspect on both the exterior and interior of the tank, foundation condition, water volume and detention time of the tank, an analysis of water quality, assessment of any cathodic protection system, vulnerability to tampering or terrorism, among many other specifications. Connecticut’s guidelines also define a “qualified inspector.” The guidelines are available at the Connecticut Department of Public Health Drinking Water Section, “10 year Atmospheric Storage Tank Inspection Guidelines.”
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The State of Texas has created a 10-item checklist for annual evaluations, according to Chip Stein, with Tank Industry Consultants, headquartered in Indianapolis, IN. Stein is chairman of AWWA’s Revision Task Force, which has been working for about three years to rewrite the inspection standard D-101, he says. The task force hopes to submit a draft in the next 18 months. AWWA also has standards for coating steel water storage tanks (D102-14) and factory coated bolted carbon steel tanks (D103-09).
What follows is advice from four manufacturers of water storage tanks and two tank consultants whose job it is to independently inspect water tanks as they are being built, repaired, or recoated.
IT BEGINS WITH DESIGN
Designing and constructing water storage tanks has evolved over the past twenty years. Technologies and designs to accommodate environmental and building regulations have driven the developments, according to Stein. He says the materials and connectivity methods in the tank fabrication industry have also evolved. Owners want them to be more hurricane and earthquake resistant.
Twenty years ago, Stein says, engineers didn’t understand how a tank structure would react to abnormal environmental loading stresses as well as they do today. For example, historically the country was divided into “seismic zones” and building codes for tanks were written for those zones. Now, design parameters are site-specific, says Stein. Design criteria must anticipate site-specific loadings such as high winds, seismic events, soil type, snow loads, etc. Also, the strength of materials being used must be evaluated. Additionally, tank and site security is now important.
Water quality issues are now impacting tank use, says Stein. Tanks need to turn water over quickly. With passive mixing, water is mixed using the pumped inflow. As water is fed into the tank, it stirs the water. Then there are active systems using an external power source, such as solar energy, to mix the water. New systems are coming on the market every year, he says.
Andy Mumford, vice president at Mumford Bjorkman Associates (MBA) tank consultants headquartered in Wilmington, DE, agrees that tank roof designs can be the source of a majority of problems. Those problems arise around the vapor zone on the roof and anything above the water line, like rafters with ninety-degree angles supporting the roof. These angles make painting properly difficult and corrosion can start there. There is the potential to spot the beginnings of corrosion during the first year inspection.
Currently, all manufacturers have increased the efficiency of their designs, says Mumford. They have reduced roof support structures such as I beams of angle iron. Rolled steel is often used to form a roof. If you have a tank with a flat roof, you need to be concerned about inspecting the rafters regularly. For example, he describes a four-million-gallon ground storage tank that was being repainted. Once drained, corrosion in the rafters was discovered. It cost $275,000 to replace the rafters. The metal loss drove replacement costs, he says.
Credit: INDURON PROTECTIVE COATINGS
A 100% solids epoxy (solvents free) lining is being applied to the interior of a new concrete basin at the Sandy Hook, NJ,
Water Treatment Facility. The epoxy is being applied to reduce corrosion inside concrete vessels which could lead to leaking or a shortened life span of the structure.
TYPES OF TANKS
Water storage tanks can be constructed of steel, fiberglass, or concrete. Wooden water tanks—while some are still standing—are historical artifacts, like horse-drawn buggies.
Matthew Tasch, with Superior Tanks in Rancho Cucamonga, CA, explains the differences between welded steel tanks and bolted steel tanks. The latter are designed, then steel fabricated, sandblasted, and fusion bonded with powdered coatings in the factory. Bolts are located on the inside of the tank and are in contact with water. That’s why they are encapsulated with a compliant plastic or rubber. He says he has seen no deterioration around these bolts and explains the lifetime of this material will exceed the lifetime of coatings. Historically, galvanized nuts and bolts were used and did cause corrosion.
On the other hand, welded steel tanks, where the steel is rolled to the configuration of the design, are brought to the location in pieces where they are to be assembled and welded, sandblasted, and coated. Tasch says there are welded steel tanks that have been in service for over 100 years. They have survived, not because of maintenance, but because of the good non-corrosive water stored in them, and the fact that no chemicals like chlorine have been added to the water.
Tasch says these welded steel tanks are more expensive due to labor costs associated with welding and coating the steel in the field. He says the choice of which type of tank to go with is left to the preferences of the client but that welded steel is the most common type of tank, then bolted steel, then concrete.
Containment Solutions, headquartered in Conroe, TX, has been manufacturing fiberglass tanks for petroleum storage since it pioneered the technology in 1965. Some 300,000 are in service, according to Pete Young, vice president, Flowtite Water Products, the trademark name for Containment Solutions’ fiberglass water tanks.
The company entered the water tank market recently, and Young says the use of fiberglass for water tanks has been increasing over the past 10 to 20 years.
Flowtite fiberglass tanks are non-corrosive, watertight, lightweight, and do not require cleaning, resurfacing, or internal inspection. If sludge or slurry develops in a tank, or if settlement appears in a tank where water has been stored in it for use in peak periods, a vacuum truck can vacuum the tank out.
Young says fiberglass tanks are a competitor to concrete tanks and have been replacing them. A 20,000 gallon fiberglass tank will cost between $30,000 and $40,000, while an equivalent stainless steel tank will cost perhaps as much as 50% more and requires inspections and maintenance.
Young says fiberglass water tanks have a design life of 30 years, maintenance free. “The oldest tank we have is a 45-year-old gas tank,” he says, adding that there are over 10,000 gas tanks over 40 years old. He expects no less from fiberglass water tanks.
Davies Hood, president of Induron Coatings in Birmingham, AL, explains shelf life and costs of the various types of tanks. Welded steel tanks utilizing modern construction methods have no predetermined “shelf life,” he says. Reinforced concrete and welded steel tanks will literally last through generations, as long as the coatings are maintained to keep corrosion at bay. Hood has seen this in the form of tanks which were constructed in the early 20th century, reaching the milestone of 100 years in continuous service. Because finance departments usually don’t like open ended asset life expectancy, he says, many owners chose this 100-year timeline to evaluate total cost of ownership of the asset.
Credit: INDURON PROTECTIVE COATINGS
Hood explains that costs can vary dramatically depending on tank size, style, and the foundation required by the soil conditions. “To give some context, a short 50,000-gallon elevated tank may cost as little as $200,000, whereas a 2-million-gallon tank will stretch upwards of $1 million in most cases. Cost is also greatly impacted by the specific requirements included in the contract. The allotted duration, the ancillary equipment and infrastructure included, plus site conditions, etc., will all have a large impact on the final cost.”
Hood further explains that fiberglass tank styles, which do not offer the opportunity for future maintenance, are dramatically cheaper to construct, perhaps by as much as 50% in some cases. However, it is noteworthy that because they are generally not elevated, they require additional pumping capacity to create the pressure otherwise offered by a gravity-driven elevated tank. When they reach the end of their life, after roughly 25 to 35 years, they are simply taken down and replaced. Therefore, on the same 100-year timeline, you would plan to go through three to four tanks, he explains.
Hood estimates, based on the Steel Tank Institute and Steel Plate Fabricators Association’s total cost of ownership tool, that a 1-million-gallon welded steel ground tank would cost $626,750, a bolted steel tank of the same size would cost $1.14 million, and the same size concrete tank would cost $2.14 million. The life span of each type of tank, taken from the same source, would be 100 years, 50 years, and 60 years, respectively.
WHAT COATINGS DO
The major shift in the coatings industry is the phase-out of solvents, says Tasch. In California, the phase-out is due to air quality regulations in favor of 100% solid coatings.
Solid coatings are not new and have been used in other industries including by the Navy on ships. The tank industry is only now adopting them, says Tasch. Solid coatings are thicker and more durable and last longer, he says, adding that a safe lifetime estimate for solid coatings is 20 to 30 years. Also, the chemicals in today’s water affect the coatings.
“Each tank type will have its own problems,” says Tasch. Look for things that lead to contamination, Tasch recommends. Sanitation-based issues include the unprotected opening of roof vents without screens and roof hatch lids that are left open. Holes have been drilled in the roof to run chemical inspection lines or probes for liquid level indicators and never properly sealed. Holes are drilled in the roof to hang cathodic protection units from rafters to allow anodes to reach the water. This invites corrosion.
Stein agrees that coatings have come a long way in the last 20 years. Environmental regulations, including those for volatile organic compounds (VOCs), have also pushed along coating development, Stein says. Acceptable application conditions for the newer coatings are more restrictive—pushed by technology.
Older coatings were more user-friendly and environmentally harmful, Stein adds. Those with higher VOCs dried more quickly in cases with vinyl coatings, which are heavily regulated in some areas of the country.
Now there are coatings that cure quickly and are VOC regulation compliant—for example 100% solids polyurea coatings for interior tank walls. The technology and restrictive applications have increased the costs of manufacturing coatings, while also increasing their life expectancy. An interior tank coating should last 12 to 15 years, excluding isolated spot features that may need to be treated separately.
George Mead, municipal sales director with Tank Connection, explains there are two categories of coatings: those that can be applied at the job site, or those applied at the manufacturing plant. Epoxy or glass coatings are the most common for steel storage tanks. Inspections of all coatings are necessary to ensure the integrity of the tank.
Tank coatings can break down for numerous reasons. Mead has seen a bullet hole in a tank, which subsequently led to coating failure inside the tank, which in turn led to development of rust. In colder climates, ice can form inside the tank, which can harm the coatings on the internal sidewall. If the water is “turned over,” or used at a rate that minimizes ice buildup, the water should not freeze inside the tank. The design should suit the needs of the population being served, but should also allow the water to circulate through cold seasons, he says.
The inside of a water tank is the most important part to maintain properly, says Hood. The atmosphere inside is more hospitable to corrosion—it’s damp, wet, and because the water is always fluctuating, is dry in some areas. The moisture and chemicals in the water like chlorine increase the likelihood of corrosion.
The first area that corrodes is the roof, Hood explains. Above the water line, the tank walls are exposed to oxygen, creating an opportunity for corrosion. Ladders, angles, and edges are the most difficult to paint and the first to rust.
Hood says the industry standard to address this issue is a brush-applied seam coat—a coat of paint and the mechanical action of the paintbrush gets paint into the seams and protects them. An additional coat should go over the seam coat.
Epoxy linings with no VOCs or hazardous air pollutants (HAPs) are excellent barrier coatings for steel. “The thicker the materials the longer they last,” says Hood.
Induron is promoting materials that are 100% solids which do not evaporate and give 100% edge protection, says Hood. The company’s products are solvent-free, have no VOCs, or HAPs. Paint flow is provided by new technology resins and application equipment such as spray rigs, which heat paint to 110°F to improve paint flow.
When repainting, the client needs educated third-party inspectors to be in attendance during and after painting, says Hood, to make sure specifications are being followed and good painting practices prevail.
Hood recommends a fluorourethane coating as an exterior finish for tanks after fully blasting and repainting them and he recommends specifying it when designing systems to protect new tanks. The added years of service make the increased cost worthwhile, he says.
A one-year warranty is standard for a newly painted tank, Hood says. The application and quality of material will manifest itself and any problem can be seen within 11 to 12 months, when an inspection should be conducted to correct any minor deficiencies before the warranty expires. He estimates coating jobs should last 20 to 25 years.
Which type of coating to use, depends on several factors—usually the tank’s intended use. To extend the lifetime of an in-use water tank, Mumford recommends removing the existing interior coating by sandblasting or abrasive blasting to take it down to the bare steel. Use high-performance coatings, such as polyurethane or 100% solids epoxies that will provide a long service life to capitalize on the expense of the abrasive blasting operations performed.
On the other hand, if the exterior of a water tank is being coated to look nice, two coats of acrylics could be appropriate. Mumford recommends not spending the extra money for the high-performance coatings if a significant investment is not being made for the surface preparation.
For example, the University of Delaware acquired the nearby Chrysler facility and left its tank standing. It wanted to repaint it with school colors, and the recommendation by MBA was to pressure wash and paint the tank with two coats of acrylic coating. These coatings have been applied for five years, and the University’s tank still looks good, says Mumford.
WHY INSPECTIONS ARE NECESSARY
“Each tank type will have its own problems,” says Tasch. Look for things that lead to contamination, he recommends. Sanitation-based issues include unprotected opening of roof vents without screens and roof hatch lids left open. Holes have been drilled in the roof to run chemical inspection lines or probes for liquid level indicators and never properly sealed. Holes are drilled in the roof to hang cathodic protection units from rafters to allow anodes to reach the water. This invites contamination.
Unprotected openings can allow birds and animals to get inside the tank, which Tasch has found. He has also found beer bottles inside (teens have launched inflatable rafts for parties inside tanks!). He says protections to avoid these problems are regulated by the AWWA or the Occupational Safety and Health Administration.
Also, be aware that deterioration of cover plates and gaskets with clamps used to cover cathodic protection units create gaps allowing detritus from owls, rats and birds on the roof to be emulsified by rain and washed into the water below the roof, Tasch says.
As others have recommended, Mumford says that if the tank is in good condition it can be given a full comprehensive inspection every five years. However, if any problems like delamination of layers of coatings appears, inspections should be carried out every three years or even once a year.
Using divers or remotely operated vehicles can be a cost effective alternative to draining a tank for the five-year inspection, Mumford says. Draining means taking the tank out of service for a week and then cleaning and disinfecting the tank following repairs, if they are needed, before it is refilled. On the other hand, using a diver or remotely operated vehicle (ROV) to inspect the filled tank will take about two hours, Mumford explains. Either a diver or an ROV can record all video in real time while the customer or inspector is viewing the screen. The ROV can also be moved to investigate a potential problem further. Both can communicate in real time.
Mumford says MBA uses an ROV as a preliminary option to identify problems for 95% of its inspections. Draining the tank covers the remaining 5%.
Daily inspections during construction and repainting are the major parts of MBA’s business. The inspector gives the utility a fresh set of eyes during the work. For example, says Mumford, six welders working six days a week accomplish a lot of work. During that time, they can become distracted or blowing wind can affect the work. “We can recognize deficiencies and get them corrected before they become problems, he says.
Other advice Mumford has includes sampling soil before and after a tank is repainted to check for lead levels in the soil. The before sample serves as the baseline and a sample of the soil is tested after the job is completed. If the lead level in the sample increased it means some materials from the coating escaped the containment curtain and contaminated the area.
A containment structure is erected around the tank before it is sandblasted and painted either by welding outriggers to the roof of the tank, which holds the containment tarpaulins over the tank, or scaffolding can also be built around the tank, and the tarps wrapped around the scaffolding. Which method is used depends on the contractor’s preferences, the type of tank, and its location.
Mumford says fiberglass tanks can be inspected at the end of their planned lifetimes and in the meantime, their replacements can be budgeted. Events such as wind, lightening, and snow can affect any vessel, he says.
Mumford recommends that security inspections be done yearly given the potential for vandalism and trespassing. These inspections are not comprehensive and are limited to security issues. They should include making sure ladders are locked and that the roof vent screen is in place and locked. Check inside the roof manhole and verify it and other entryways are locked. And, it is wise to take pictures.
This year has seen a number of incidents with PokemonGo gyms located at water tank locations, Mumford says, reinforcing the need for security. Recently, a 13-year-old boy got inside the perimeter of a tank and when he couldn’t get out, he had to be rescued.
Most, if not all, tank manufacturers recommend tanks be inspected one year after being painted for the first time or repainted. Then they can be inspected every three to five years, Stein says.
During the first one-year inspection, Stein says to look for premature failures. But before any significant corrosion can occur, spot clean the areas that have failed, then apply a coating to that area. Stein says it is important to spot these problems early in the corrosion state when it is more cost effective to repair.
However, if the failure becomes more widespread than just isolated spots, the economics flip and repairs become much more expensive, Stein says. As coatings near the end of their lives, he recommends speeding up inspections to every three years.
If you don’t inspect a tank on a regular basis, any coating could be jeopardized says Mead. In Kentucky, he says, a glass-lined bolted steel tank failed because of lack of maintenance. Welded and bolted tanks have had catastrophic failures, he adds. He recommends that all owners and utilities should drain the tank and physically inspect it inside after the first year, and again every three to five years.
Normally, the independent engineer overseeing the design of the tank will specify that the tank should be inspected 12 to 14 months after installation. Performing inspections also aids in maintaining the warranty, which could range from one to five years, depending on the specifications requirements.
Water utilities typically have other tanks onsite, enabling them to continue serving customers while the tank to be replaced or repaired is taken offline. The best inspections occur when the tank is empty, Mead says. At the end of the day it is the responsibility of the owner or utility to inspect their tanks regularly, Mead concludes.
Maintenance contracts have distinct advantages for utilities if done right, says Stein. Smaller utilities that may not have the staff to oversee tank maintenance can benefit from contractors to do that work. But the utility needs to have the discipline to budget the work over the long term.
A disadvantage is that some maintenance contractors won’t let the owner or utility specify the work, when inspections are to be done, or if third-party inspections will be done. And some contractors rely heavily on subcontractors, leading to the owner or utility not knowing them or their safety records.
Stein says the best way is to write a good scope of work and specifications following a good inspection. The structure and coatings are specified along with a list of deficiencies. Vendors are asked to bid on the work to get the best price for the work specified. This type of contract will be under the owner’s or utility’s full control.
Mumford says, as independent inspectors, MBA does not offer maintenance contracts. A conflict of interest arises when a company doing maintenance also provides inspections and makes recommendations for the immediate and long-term maintenance.
MBA establishes maintenance programs for utilities and every utility should have one, says Mumford. This can take the form of a program document that establishes when inspections will be done and a budget for future repairs. “We’ve had success with programs that project out to the next five years and budgets accordingly for the work to be performed. This provides the utility with the most control over its capital spending,” concludes Mumford.
Superior Tank Solutions does offer maintenance contracts, Tasch says. “When structured properly, they can be a good tool for the industry. Most entities want their infrastructure to be inspected but things fall through the cracks and they go for five to six years without maintenance.”
Having a company come every year to do an inspection and every two to three years do an in-depth inspection and repair will extend lifetimes of the coating system and improves water quality, according to Tasch. Tanks are getting more expensive to replace and taking care of them is less expensive.