Maintenance History of Four Steel Water Tanks
A survey looked the maintenance painting costs for four large-capacity steel water tanksDetermining real maintenance costs associated with protecting large-capacity steel water tanks from corrosion has been a topic of discussion for years among specifiers, manufacturers, contractors and owners of water storage systems.
Because of the need for a comprehensive, fact-based, long-term examination of costs, we studied four all-steel, fluted-column elevated tanks which have been in place and operational for more than two decades in the variable climate of Northern Illinois. Our purpose is to bring into a clear, unambiguous focus the costs incurred in maintaining these large steel structures. Details will include actual costs, materials specifications, and a chronology of maintenance activities on these four tanks which have been subjected in their lifetime to the full gamut of weather conditions-from an Arctic chill of -27 F to searing temperatures above 100 F.
The all-steel, fluted-column water tank came to prominence in the early 1960s as municipalities across America encountered continuous population increases during the last few years of the Baby Boom. Fast-growing suburbs, in particular, needed to upgrade water service to handle the influx of new residents and businesses.
Steel water tanks-then and now-have been designed in a wide variety of configurations to suit the needs of municipal and corporate customers. Examples of innovative structural engineering and creative paint designs are visible in many communities. The fluted-column style offered the advantage of usable space within the support column. Some uses have been for fire stations, pumping facilities, municipal offices and storage areas.
There are many popular water tank designs, but the fluted-column style was selected for this study because of its unique painting needs. Some of these may have led to misunderstandings about the actual long-term maintenance requirements. For example, there appears to be an opinion that the periodic need for maintenance on steel water tanks means each repainting will require complete sandblasting and recoating of all surfaces-an expensive proposition. This examination of the histories of the four selected tanks shows that only certain portions of them have needed attention.
The examination of the record of each of the tanks in the study includes a discussion of the surface blasting and coating requirements for
- the wet interior (the actual water-holding vessel),
- the exterior,
- the dry interior (inside the support column).
The chart on page 26 represents the cumulative painted surface area of the four tanks, and shows a breakdown into three categories of the total. These structures are all within a 90-minute drive of downtown Chicago. Two are in Alsip, an industrial southwest suburb; one is in DeKalb, a more rural university town west of the city; the fourth is in the northern suburb of Glenview.
Northern Illinois' climate offers challenges to painting contractors who must account for potentially wild fluctuations in weather conditions that truly reflect all four seasons. For instance, National Weather Service data show that for March 16, the record high in Chicago was 78 F, while the record low was -1 F. Daily temperature variations (based upon 30-year averages) during the painting season in the region are shown in Table 1.
Because of such variations, coating application must take into account the development of condensation on external surfaces of the water-bearing portions of a tank. Some alkyd paints will blister under these conditions, but examination of these four tanks provides no evidence of such reaction.
Future maintenance with the new generation of epoxy and urethane coatings commonly used today will demonstrate enhanced protective properties compared to the paint formulations of the original coatings used on the subject tanks. Besides combating condensation, the newer coatings provide UV resistance to counteract sunlight-induced cracking.
A key concern in future painting projects will be the removal of lead-based primers. Although this task will incur significant expense, it will be a one-time cost.
All four of the study tanks were built and painted to standards of the American Water Works Association (AWWA). The AWWA tank construction standard is D100, and the painting standard is D102. AWWA develops consensus standards that have been adopted by the American National Standards Institute (ANSI). The D102 standard, however, is not currently an ANSI standard because more than 10 years have passed since its last review.
The dry surfaces of all four tanks were originally painted at the tank fabricators' shops with an alkyd red-lead primer, as specified in AWWA D102-64 (updated in 1978). All other painting was done in the field by Neumann Company Contractors, Inc., which supplied cost and specification data from corporate records.
As noted above, lead-paint products were used in the original specifications for all four tanks. Because of environmental-safety and health concerns, lead paint has fallen from grace during the last decade.
Alsip Tanks No. 1 and 2
These tanks were built in 1967 by the Village of Alsip. The original field-painting contract cost for coating all surfaces was $12,500 per vessel. Each has a storage capacity of one million gallons. The height of Alsip's Tank No. 1 is 94 ft to the bottom, while No. 2 is 125 ft to the bottom. The stated height is the distance from the lowest level of usable water to the ground. Surface areas for No. 1 are approximately 18,500 sq ft for the interior wet surface, 32,500 sq ft for the exterior, and 31,000 sq ft for the interior dry. Since it has the same capacity, No. 2 also has 18,500 sq ft of interior wet surfaces. However, due to its greater height, the exterior surface is 37,900 sq ft and the interior dry area is 39,000 square feet.
The original paint specifications for the tanks were identical. Interior wet surfaces were painted with a three-coat zinc dust, zinc oxide phenolic paint system to AWWA D102-64 (Inside System No. 3) standards. The same materials, applied to a dry-film thickness of at least 4 mils, were used for both primer and finish.
Exterior surfaces received three coats-one of primer and two coats of alkyd enamel to a final thickness of 4 mils. Exterior coatings conformed with AWWA D102-64 (Outside System No. 1). Interior dry surfaces were painted to AWWA D102-64 (Outside System No. 1), which called for one coat of primer and two coats of alkyd aluminum. Dry-film thickness also was 4 mils.
Though the 1967 paint job was supposed to have a design life of 5 to 7 years, local officials didn't see a need to repaint these tanks until the late spring of 1976. In November, 1975, village staff had requested bids on spot sandblasting, spot priming and applying two complete exterior coats for the tanks. The village wanted new exterior paint on the tanks to mark the nation's Bicentennial. The new red, white and blue motif-prepared with a spot coat of alkyd primer and two coats of alkyd enamel finish-cost $16,500 per tank. No wet or dry interior work was carried out at that time.
The next painting was bid in 1985, and scheduled for completion during the spring and fall of '86. This project called for a complete blast clean of the interior wet surfaces, using a Steel Structures Painting Council standard-(SSPC SP-10). Coating for the interior wet area was a three-coat epoxy system to a 10-mil thickness, in accordance with AWWA D102-78 (Inside System No. 1).
The exterior was spot cleaned to standard SSPC SP-6 (commercial blast quality), spot primed with a non-lead alkyd primer and a following spot intermediate coat of straight alkyd enamel, then a finish coat of silicone alkyd enamel. This work was specified in accordance with AWWA D102-78 (Outside System No. 3). Total cost of the '86 work on the two tanks was $124,800.
No work was requested in 1985p;86 for the interior dry section of either tank. This means that, as of the summer of 1994, over 70,000 sq ft of combined surface area inside the two tanks had gone without painting maintenance or steel repairs for nearly 27 years.
The DeKalb Tank
This structure was built by the City of DeKalb during 1966 and 1967, and painted for $12,800 in 1967. The one million gallon elevated fluted-column tank has an inside wet surface area of 18,500 sq ft, an exterior of 31,600 sq ft and inside dry surface of 34,200 sq ft. Various girders and stiffeners inside the fluted column, as well as a condensate ceiling (painted on both sides) to protect elements at the lower levels from dripping water, explain the larger interior dry surface area compared to the exterior. Height to the lowest level of usable water is 91.5 ft.
As a contemporary of the Alsip tanks, the original coatings for the DeKalb structure exactly matched their material specifications. The tank became a prominent billboard to alert passersby that the city was home to a major university.
The first repainting of this tank occurred during the spring and fall of 1976. City staff were concerned about some loose, scaling paint on the exterior. They commissioned $9,800 of work to spot blast the trouble spots to SSPC SP-6 quality, and in addition to apply an alkyd primer and two coats of alkyd enamel. The work was done to AWWA D102-64 (Outside System No. 1). No interior work was required at the time of this project.
Eleven years later, the DeKalb tank was scheduled for its next coating maintenance. In 1987, a $25,000 project for interior wet surface work was completed. This included a full blast cleaning to SSPC SP-10, and the application of a two-coat catalyzed epoxy system to a dry film thickness of 8 mils. The work was done in accordance with AWWA D102-78 (Inside System No. 1).
The project also called for $60,000 worth of exterior work. The cost covered a complete blast of all exterior tank surfaces to SSPC SP-6, and spot blasting of failing areas on the fluted column to SSPC SP-6. Coating included two coats of alkyd primer for all areas blasted. Exterior surfaces received two coats of modified acrylic (or dry fall) enamel to a dry film thickness of 6 mils in accordance with AWWA D102-78 (Outside System No. 1).
Spot blasting of certain inside dry surface areas to SSPC SP-6, and spot painting with two coats of an aluminum-pigmented urethane to 4 mils thickness, also carried out in the '87 project, cost $10,000.
The Glenview Tank
Built in 1971 by Domestic Utility Service Co., this 750,000-gal, 100-ft-high tank has since been sold to the North Suburban Public Utility Co. The first painting of the tank and its fluted column cost $15,000. Surface areas are 13,800 sq ft for the interior wet, 26,000 sq ft for the exterior, and 20,000 sq ft for the interior dry.
The original inside dry specifications were almost the same as those used for the Alsip and DeKalb tanks. The inside dry surface received one coat of alkyd primer and one coat of alkyd aluminum applied to a 2-2.5 mils combined dry film thickness-per AWWA D102-64 (Outside System No. 1). Exterior finishing used one coat of alkyd primer and two coats of alkyd enamel to 4 mils dry-film thickness. This conformed with AWWA D102-64 (Outside System No. 1). However, the inside wet surface treatment was completely different from the other three tanks. That area was coated three times with a single-component epoxy ester to a 5 mil thickness.
The paint-maintenance history of this tank includes the addition of two coats of alkyd enamel in June of 1973-only two years after the vessel was put into service. However, this paint job stemmed from a rental agreement between Domestic Utility Service Co. and the management of a new Glenview apartment complex known as Triumvera. The maintenance project was instigated by the need to market apartments, rather than to carry out normal water storage tank upkeep. Painting the tower with the Triumvera logo for $8,000 gave the management group a huge billboard easily spotted from a nearby tollway and other major thoroughfares.
Eight years later the highly visible logo was no longer needed. It was removed when the exterior was hand-tool cleaned, spot primed and repainted with two coats of modified acrylic (dry fall) enamel. Cost for the 1981 exterior work-which complied with AWWA D102-78 (Outside System No. 1)-was about $24,500.
Interior work was carried out the same year. The inside wet surface was spot sandblasted, spot primed and covered with one coat of epoxy ester. The interior dry was spot primed and received one finish coat of alkyd aluminum, which brought the total thickness up to 4 mils-as originally specified for the other three tanks discussed above. This work cost just over $16,280.
What Can Be Concluded
The observations made on the experience of these four elevated steel tanks demonstrate that there is not necessarily a need for complete blasting and recoating on every maintenance painting project. Table 2 shows the aggregate painting expenditures for original work and subsequent maintenance to date on all four tanks. Also shown are the amortized annual painting costs, excluding the original coating work.
Any painted structure subjected to extreme heat or cold will need periodic maintenance. The coefficient of expansion for coating products cannot exactly match the coefficient of expansion for the surface to be painted. After time any structure will require at least partial maintenance. The key questions become: How often will work be needed and what will it cost?
As a result of recent enhancements in coating technologies, today's paint products are expected to provide even longer service lives than the coatings used in the 1960s and 1970s. Certainly the maintenance record of these Northern Illinois water tanks suggests that specifiers should take into account realistic assessments of periodic maintenance needs along with initial costs, no matter what material of construction is used.