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Minnesota Rural Water Association "Today Magazine"
Painting for Antenna Installations on Water Storage Facilities
February 11, 2003

By Dan Zienty and Lee Dornbusch

This is the second article in a two part series, the first titled; "They're Water Storage Tanks?" covering issues related to the installation of wireless communications equipment on water towers. (Go to Part 1)

The attachment of various coaxial cables, brackets, structural members, and the cutting penetrations, for sometimes numerous providers, can have an effect on the overall performance of the original paint system. As with most projects, there is usually more than one way to skin a cat. From a coatings perspective, the installation of telecommunications equipment may include variations in:

• Method of attachment
• Surface preparation
• Coating selection
• Material selection

With the proper attention, conflicts can be avoided. A winning situation can be achieved for both the owner and the contractor representing the telecommunications provider.

Different tank configurations, ground storage and standpipes, pedestals, fluted column, and legged design's lend themselves to varying types of installation concepts. Depending on provider need, installations may be on the shell or tank roof (Ground reservoirs), roof and riser (pedestals/fluted column), roof, catwalk and support column (legged). In each situation it is important that any attachment is structurally sound, visually unobtrusive and minimizes the impact to the existing structure.

Field painting with coax cables.

Method of Attachment

Attachments to the tank support antennas and coaxial cables. The cutting in and welding of penetrations to allow cables to pass through also has an impact. Generally, three methods of attachment may be incorporated in any design; seal welding, stud welding, or bolted connection.

Seal welding, while providing the strongest means of connection, has the greatest negative impact on an existing coating system. Existing coatings need to be removed to avoid weld contamination. In addition, heat transfer can damage the paint system on the backside. For tank surfaces in immersion service, the potential for damage is greater as corrosion can be accelerated both above and below the waterline.

Stud welding, depending on type (Standard Welded Studs or Discharge Capacitor Studs), can cause less damage to the existing finished surface, but may not provide adequate structural integrity (discharge capacitor studies). Studs of either type typically require coating removal in a much smaller area when compared to seal welding. In the case of Standard Stud application, there is still the potential for damage to the paint system, on the backside, due to heat transfer.

Bolted or screwed connections are normally associated with the placement of antennas attached to the riser portion of pedestal or fluted column style tanks. Though connection devices involving screws such as C-Clamps can be incorporated into design details for any tank style, this type of connection comes with a few drawbacks. Often the owner just does not want additional holes made. From a coating standpoint these types of connections, if not designed and finished properly create the potential for spot rusting. This can be the result of improper material selection, rusting at edges, or the fastener (C-Clamp) penetrating and damaging the coating system.

Surface Preparation

Surface preparation plays an essential role in the surface protection of new attachments, and maintaining the integrity of the coating system for the rest of the tank. Whenever possible or when project scheduling is an issue, shop preparation and painting should be considered. In any case, specific procedures should be followed that are applicable to the materials being painted, and or to the type of repair needed. Procedures should include:

• Cleaning of surfaces in accordance with SSPC SP-1 Solvent Cleaning to remove grease, oil, or other surface contaminants prior to abrasive blasting, or hand or power-tool cleaning.
• Scarification of non-ferrous material, if being painted.
• Protection of areas affected by welding to prevent damage from heat and or paint removal to adjacent areas. (Hot grindings/filings can become embedded into the existing finish coat and cause unsightly surface rust within a short period).
• Removing all surface imperfections such as sharp fins and weld spatter.
• Feathering all edges (repair areas) to provide a smooth transition for paint application.
• Abrading by sanding painted surfaces to scarify and de-gloss the existing finish.

Field grinding to remove sharp edges around attached base plates. Care should be taken to protect adjacent surfaces from grindings.

The application of all coatings should be in accordance with Manufacturer's requirements.

Coating Selection

Coating selection is primarily based on three factors:

• The existing system on the tank
• The type of material being painted
• Ambient conditions.
  

During the summer months, cold water entering the tank can cause condensation to occur. This can produce application problems depending on water tower design. Seasonal conditions may also result in application difficulties associated with high humidity levels or low temperatures.

Alkyd-based systems may exist on older tanks. Many, if not most, water tower exteriors today are painted with organic zinc or epoxy primers and top coated with acrylic polyurethane. It is essential, to ensure coating integrity, that the repair paint is compatible to the existing system. The size of the repair area, tank location and or the condition of the existing coating(s) systems should also be considered in coating system selection.

Coatings of a different generic type may be chosen for shop coated components. Some providers require a non-metallic paint system over their antenna covers to prevent signal problems.Most coaxial cables are manufactured with a flexible black plastic casing. On an interior installation, painting would normally not be required. On many exterior-exposed installations, providers are requested to paint the cables to match the exterior finish coat.

The selection of this finish coating should be based on its ability to adhere to the plastic substrate and offer color/UV stability similar to the existing tank coating. The polyurethane coatings commonly used on tank exteriors have not demonstrated adequate adhesion to the coaxial cable. Water-based Acrylics seem to offer improved adhesion and flexibility when applied to the properly prepared (scarified)surface.

Shop masking (prior to painting) of surfaces affected by field welding.

Application of the coating is typically achieved by brush and roller. Spray application may be allowed if the coating offers "dry fall" capabilities.

Depending on the type, age and condition of the existing coating, an exact color match may be difficult. Depending on the degree of chalking, selecting colors 1-2 shades lighter than the original finish may offer an adequate match. Masking (squaring up) the area to be coated will provide a cleaner appearance.

The owner should provide the following information to the contractor:

• Product manufacturer's name
• Paint system series and product name(s)
• Color of finish coat, interior/exterior (as applicable)

The contractor should be responsible for the following:

• Supplying manufacturer's product material safety data sheets (MSDS)
• Certification that materials used are lead/chromate free
• Certification that the applicator is knowledgeable on procedures for proper preparation, mixing, and application of the coatings to be applied

Material Selection

Material selection refers to the altering of installation design details and/or usage of alternative materials. The purpose is to reduce the possibility for corrosion, expedite project scheduling, and reduce cost.

Tank design can place limits on or dictate material selection. For example, owners concerned with direct visibility of attached components such as galvanized cluster mounts may require a coating system to match the existing tank color. However, the use of the same mounts in routing coaxial cables through a fluted column style tank may allow for deletion of the coating system.

As a design alternative for legged tanks, one consideration would be to route cables on the inner face of the support column and horizontal braces. Still, another solution would be to specify the use of manufactured colored coax cable. Manufactured colored cable provides for a uniform finish, eliminates the need for field painting and the need for future maintenance by the provider.

As discussed earlier, bolted attachments are an alternative to welding and can prove less damaging to the existing painted surface. Care is necessary to provide proper film thickness around the edges of the drilled hole. Additionally, care must be given in selecting the type of fastener used. The introduction of dissimilar metals can accelerate corrosion at the point of contact.

For smaller penetrations, such as that utilized for 7/8", jumper cables, drilled holes incorporating firewall grommets (metal edges prime coated prior to installation) can eliminate the need for welding a larger penetration.

Attaching with what are referred to as C-Clamps can damage the paint down to the substrate. This situation can also result when using stainless steel straps. Damage can be reduced and/or eliminated by placing neoprene strips between the screw or strap and the painted surface.

Coax cables snapped into galvanized cluster amounts and attached to the tanks overflow pipe with
stainless steel banding with a neoprene strip underneath.

Summary

Wireless communications impacts all of us in our daily lives. The use of water towers to facilitate these services creates a number of issues outside the communications service being provided. Special consideration must be taken that integrates the original use of the facility as a water tower and its added function. Careful consideration during planning should be given to the routing of coaxial cables and the attachment of antenna brackets for future maintenance of the structure. Just as important is the attention paid to surface preparation, applied coatings and the selection of materials used for the installation of this equipment. Finally, it is important that applicators involved with these types of projects be aware of the potential safety hazards from radiation exposure (RF) when there are existing providers on the tank, or when retro-fitting equipment.

Biography

Daniel J. Zienty is an Associate/ Project Coordinator—Protective Coatings in the Water/Wastewater Practice Center for SEH. He has a Bachelor of Science Degree in Construction Technology from Purdue University, and is a participating member of the
National Association of Corrosion Engineers International (NACE) and Society for Protective Coatings (SSPC).

He is also certified as a Protective Coatings Specialist with SSPC, Coating Inspector with the National Association of Corrosion Engineers (NACE International) and as an Associate Welding Inspector with the American Welding Society (AWS).

Lee Dornbusch has over 25 years
of experience on both municipal and industrial coatings related projects
including water/wastewater, petrochemical, pulp and paper, transportation, and mining. Since joining SEH, he has specialized in plant surveys, failure analysis, specification development, training and site inspection.

He is a member of the National Association of Corrosion Engineers (NACE International) and is certified as a Protective Coating Specialist with the Society for Protective Coatings (SSPC).