When you want to purchase an above ground storage tank (AST), size and location aren't the only things to consider. The material is another important factor. As a professional stainless steel storage tank manufacturer, I will tell you five advantages of the tanks.
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1. Longevity
Stainless steel also remains ductile through all temperature ranges, is fire resistant, and is unaffected by exposure to UV light, which can damage paint and other coatings. That being said, properly maintained welded steel ASTs can have an expected lifespan of over 100 years, whereas bolted steel tanks only survive around 30.
2. Durability
Bolted steel tanks also pose a danger, as every bolt on the tank represents a potential point of weakness. With welded steel, tanks are stronger, maintenance is lower, and repairs are easier.
3. Cost
With welded steel tanks having a longer life cycle and requiring much less maintenance, the total cost of ownership (TCO) of a welded steel AST is often lower than its bolted steel and concrete counterparts over the long term. Don't just take our word for it though, check out the Steel Tank Institute's TCO tool, and see for yourself.
4. Customization
With different jobs requiring tanks in different shapes and sizes, wouldn&#;t it make sense to build a tank to your own needs, rather than buy one pre-fabricated to someone else&#;s? With welded steel tanks, you can design ASTs to be virtually any height or diameter, with multiple roof styles, paint schemes, and other architectural elements to choose from as well.
5. Hygienic and Eco-Friendly
Not only is stainless steel 100% recyclable, but over 50% of new stainless steel comes from re-melted stainless steel scrap, greatly reducing the environmental footprint left behind.
Before you buy your next AST, you can view www.dfc-tank.com, a special website for storage tank.
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.
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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
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.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.
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