Finishing Transformer Tanks: Blast, Paint and Cure

Moving a Heavy Tank Through Blast, Paint and Cure

Most transformer plants handle tanks with overhead bridge cranes, heavy transfer carts on rails, or a combination of both. The finishing layout has to respect whichever method the shop already uses. If the crane is the primary mover, the blast room and paint booth either need roof openings with crane slots and closures, or the tank has to be set on a cart outside the enclosure and rolled in. Crane slots save floor handling but complicate the enclosure: the slot needs a seal that keeps blast media and overspray inside while letting the hook travel. Rail carts keep the enclosure roof solid and simplify airflow, but they require embedded rails, a pit or flush track at each doorway, and doors that close tightly over the track.

• Map the hook height and crane travel path before sizing any enclosure door or roof.
• Decide whether the tank stays on one cart from blast through cure, which avoids extra lifts on fresh coating.
• Plan where the tank sits between steps so primer is not handled before it is ready.
• Leave space at each end of the enclosure for the cart, the operator and the door swing.

Blast Room Layout for Radiators, Fins and Weld Seams

Surface preparation is where tank coatings succeed or fail. A blast room for tanks is normally a large, fully enclosed room with a dust collector, a media recovery floor and lighting that lets the blaster see into corners and around stiffeners. Media recovery can be a full floor system, partial floor sweeps feeding a recovery trench, or manual sweep-in on smaller rooms. On tanks, full or partial floor recovery is common because the volume of spent media is large and the operator should be blasting, not shoveling. Radiator banks and cooling fins are often blasted separately before assembly because the tight spacing is difficult to reach once they are mounted. The dust collector and recovery equipment need clear access for filter changes and bucket elevator service, which usually means a mezzanine or a dedicated service corridor outside the room.

• Confirm compressed air capacity and air drying before the blast pots arrive.
• Specify lighting fixtures rated for an abrasive environment and positioned to light vertical tank walls.
• Route the dust collector exhaust and plan the collector pad, ductwork and fan location early.

Paint Booth Airflow Around a Tall Workpiece

Liquid coatings remain the norm for transformer tanks because the parts are too large and heavy for most powder lines, and the coating systems specified by utilities are typically multi-coat liquid systems. The booth style follows from the tank size and the building. Crossdraft booths are the simplest and fit buildings without pits, moving air from the door end to an exhaust filter wall. Side downdraft and semi downdraft designs pull overspray down and away from the painter along the length of a tall tank, which helps keep the breathing zone and the upper surfaces cleaner. A full downdraft booth with a floor pit gives the most even airflow but requires concrete work that may not be practical in an existing plant. Whichever style is chosen, the painter needs safe access to the top of the tank, so plan for lifts, platforms or man baskets and make sure their clearances fit inside the booth with the tank in place.

Curing, Make-Up Air and Exhaust Connections

Many tank coatings will air dry, but the time a tank sits waiting ties up floor space and crane capacity. Plants that want faster turns often add a heated cure cycle, either by using a combination spray and bake booth or by moving the tank into a separate batch cure oven sized for the largest tank. Either way, the heat source, burner controls and fuel train need to be planned along with the make-up air unit, because a booth exhausting large volumes of air has to replace it with tempered, filtered air or the building goes negative and doors become hard to open. The exhaust stack, the make-up air intake and the gas or electrical service usually run through the roof or an exterior wall, so structural support, roof penetrations and weather sealing are part of the mechanical scope. Fire suppression for the booth, interlocks between the spray equipment and the exhaust fan, and electrical classification of the spray area all have to be coordinated with your local fire code authority and your insurer before the system is turned on.

Getting the Site Ready Before the First Walkthrough

A site visit goes faster and produces a better scope when the plant has a few things gathered ahead of time. The goal is to understand the largest tank, the path it travels and what utilities are already nearby, so the blast room, booth and cure equipment can be sized and placed once instead of redesigned after the fact.

• Drawings or dimensions of the largest and most common tanks, including radiators if they are finished attached.
• Building drawings showing columns, crane rails, roof structure and floor conditions.
• Location and capacity of existing gas service, electrical service and compressed air.
• The coating system data sheets, so cure and ventilation needs are understood.
• Any existing booth or blast equipment that will be reused, removed or relocated.