An international oil and gas company that operates a liquid natural gas (LNG) terminal on Italy’s Adriatic Sea coast recently encountered a...
Tips for staying on top of water tank repairs
All water tanks eventually will require maintenance and some repairs. Some of these fixes may be minor and require very little preparation and downtime, but others may be major and require extensive preparation. A great deal of time and money can be spent trying to find a reliable and experienced tank company capable of performing repairs correctly. A water tank owner, however, can remain a step ahead by establishing a relationship with a desirable professional tank company before repairs are needed. The desired company should be experienced and reliable, and possess necessary equipment to perform repairs in accordance with all applicable codes and safety requirements. Establishing a relationship with an expert in the field can increase reliability and communication when repairs are needed.
One of the first steps in establishing this relationship could be hiring experts to perform an inspection of the water tank. Regular and routine inspections can be the determining factor in having only minor repairs or developing major repairs. According to the National Fire Protection Assn. (NFPA) 25 standard, “The interior of steel tanks without corrosion protection shall be inspected every three years, and the interior of all other types of tanks shall be inspected every five years.” Many tank owners, however, prefer yearly inspections to help eliminate surprises in the future.
All aspects of the tank should be inspected for structural, safety, sanitation and coating conditions in accordance with the American Water Works Assn. (AWWA), NFPA, U.S. Occupational Safety and Health Administration (OSHA), and U.S. Environmental Protection Agency standards. These standards should be notated in the written report along with deficiencies, photographs, recommendations and test results. Special attention should be given to the foundation condition as well as evidence of leaks, corrosion and other damage that could result in future repairs. Tank inspections and tests are designed to find these needed repairs, and it is the inspection company’s responsibility to bring them to the tank owner’s attention.
Some inspections can be performed using a robot. This method eliminates the need to drain the tank, and does not require lockout/tag out procedures because no one enters the tank. Live viewing of the inspection takes place via monitor as the inspection is performed, and a DVD recording of the inspection is included with the report.
Cleaning & Washout
During the inspection, it may be apparent that the tank contains excess sedimentation and requires cleaning. Great risk and damage can occur if sedimentation is not cleaned out regularly. Pipe can become clogged, creating another list of deficiencies and expenses. AWWA states, “Tanks should be washed out and inspected at least once every three years, and where water supplies have sediment problems, annual washouts are recommended.”
In the past, tanks had to be drained in order to be cleaned. Today, however, technology has allowed the creation of a robot that not only can inspect tanks, but also clean tanks without draining them. The robot is a convenient, cost-effective and safe option for tank cleaning without taking the tank out of service.
Codes and standards change regularly and updates may be needed or recommended for a tank to remain in compliance. One of the most commonly found violations is improper ventilation. Improper ventilation can include anything from missing screens on vents and overflow pipe to improper drain valves and vortex plates. Improper ventilation can create pressure build-up, causing a tank to rupture if left uncorrected. A defective screen can allow birds, insects and other animals to enter the tank and contaminate the water. Waterborne disease could result from the contaminants and obstructions could develop in the pipe, hindering the effectiveness of the entire fire protection system.
Ladders, handrails, safety cages and safety climbs are other items commonly notated in a detailed inspection report. These types of violations could create dangerous environments for crew members to work properly and safely and could be subject to heavy fines if discovered by OSHA.
Corrosion is the leading cause of repairs and often is noticed during an inspection. Corrosion that goes unnoticed or unaddressed can lead to pitting, thinning metal, holes, leaks, structural instability and even tank failure. A tank’s interior is especially vulnerable to pitting corrosion, which begins as a microscopic defect on the metal surface. After an extended period of neglect, the corrosion eats away the metal shell, which can lead to reduced metal thickness or, in extreme cases, holes. Metal loss can compromise the structural stability of the tank. Additionally, interior ladders, safety gratings, vents, piping and other attachments that are seriously corroded can detach from the tank and more damage can be created when these pieces fall from the structure.
Protective coatings such as paint and galvanized coatings can be used to prevent or limit the level of corrosion on a steel tank; however, coatings must be monitored and reapplied when necessary with the proper mil thickness for each area of the tank. Maintaining the interior coating of a tank can help prevent major repairs in the future.
One of the most vulnerable areas for leaks and cracked welds is the tank bottom plates. These plates are subjected to internal corrosion and bottom-side corrosion. Bottom-side corrosion can occur more rapidly if rainwater reaches and ponds under or around the tank often. When water gets under the tank, the foundation can settle and floor weld seams can crack. NFPA 25 states, “Tanks on ring-type foundations with sand in the middle shall be inspected for evidence of voids beneath the floor ... Voids discovered beneath the floors of tanks shall be filled by pumping in grout or accessing the sand and replenishing.”
Water tanks demand not only routine inspections and regular cleanings, but also routine maintenance and repairs. Major damage and even tank failures can occur if deficiencies are not noticed and addressed in a timely fashion.
Therefore, a dependable and reliable relationship between the tank owner and an experienced tank company should be established early in the tank’s life. Accurate information should be collected and maintained on the history and life of the tank, and this information must be easy to locate to be useful. All correspondences, documents and drawings should be kept. A copy of every inspection, and all repairs and modifications made throughout the life of a tank should be saved. Past repairs and areas of concern can be monitored more closely if a tank’s history is known, and predictions about the paint system can be determined more accurately.
The information gathered and the relationship between the tank company and tank owner should enable a deeper level of understanding to create more effective strategies for preventing and limiting tank repairs.