We line tanks over clean blasted steel

A frac tank needs two different coatings

A frac tank is a big steel storage tank on wheels. It gets hauled from one job to the next. It holds whatever that job produces, from water pumped out of a construction dig to wastewater from a plant. The inside and the outside of that tank face very different problems. That is why they get two different coatings, and treating the whole tank as one paint job is where a lot of tanks start to fail.

The lining on the inside keeps the liquid off the steel. Whatever the tank holds sits against that lining for weeks at a time, and some of it is salty or acidic. If the lining has one thin spot or a pinhole, the liquid reaches bare steel there. Rust starts under the coating where nobody can see it. By the time a stain shows up, it has usually spread well past where it began.

The outside coating has a different job. It sits in the sun and rain for months at a time. Road salt hits it on every trip between sites, and it gets scraped each time the tank is loaded or dragged into place. A good exterior coating keeps rust from starting at those scrapes and creeping under the paint around them. Done right, the outside still looks like one solid surface after a hard season of moving around.

• Tank washed out before any blasting starts
• Interior blasted down to clean bare steel
• Welds and seams coated by brush first
• Lining sprayed with plural component equipment
• Exterior coated to hold off rust

The lining only holds on blasted steel

Before anything else, the tank has to be empty and washed out. Old product left in the corners, or soaked into rust on the floor, will ruin a new lining. So the inside gets power washed or water jetted until it runs clean. Then we look over the steel inside for pits and cracked welds. Those spots get repaired before any coating goes on, because a lining will not hold a bad weld together.

Next the inside is abrasive blasted down to clean, bare steel. The blast takes off every trace of old lining and rust, and it leaves the steel with a rough surface the new lining can grip. Smooth steel gives a lining nothing to hold, and so does steel with a thin film of rust left on it. A lining over either one can look fine the day it goes on and then peel away in sheets once the tank is filled.

Blasted steel does not stay clean for long. On a humid Illinois summer day, bare steel can start to flash rust within hours if moisture settles on it. So the blast dust gets blown and vacuumed out, and the lining goes on while the steel is still clean and gray. If a light orange haze shows up first, that area gets blasted again. Coating over it would seal fresh rust under the new lining.

The welds get coated before the walls

Coatings fail first at edges and seams, and a frac tank is full of both. Sprayed coating pulls thin as it dries over a sharp corner or a rough weld bead. So before the main coat, every weld seam and corner gets an extra layer brushed on by hand. Painters call this a stripe coat. It is slow work, and it is the reason a lining holds at the seams instead of rusting along every weld line.

Most tank linings are two part coatings, a resin and a hardener that start to cure the moment they are mixed. We spray them with plural component equipment, which keeps the two parts apart and mixes them right at the spray gun. That means the lining goes on thick and even without the batch hardening halfway through the job. It also keeps the mix the same from the first wall to the last.

A finished lining is smooth and even, with no runs and no bare spots along the seams. It gets checked for thickness across the walls and floor, and any thin area gets another coat. Then the lining needs time to cure hard before liquid goes in. Fill a tank too early and the lining can soften or blister, and that damage shows up months later when it is much harder to fix.

Illinois winters are hard on tank steel

Frac tanks around here spend the winter outside, on a job site or parked in a yard. Water gets into every chip and seam and freezes overnight. Each freeze pushes the gap a little wider, and the next thaw lets more water in. Road salt thrown up on the drive between sites makes the rust move faster at those same spots. A small chip in the fall can be a patch of flaking rust by spring.

Summer brings a different problem. Central Illinois gets hot and sticky, and humid air leaves a film of moisture on cool steel, most of all early in the morning. A lining sprayed over that film will not bond the way it should. So field work gets timed around the weather, and the steel temperature is checked against the dew point before anything is sprayed. Work that can come to Fillmore goes into our temperature controlled paint shop instead.

The farm buildings around Fillmore and Nokomis show the same pattern. Steel pole barns and grain bins rust first along the bottom edge and around each bolt, where water sits the longest. A frac tank rusts the same way, along the floor seams inside and the bottom rails outside. Those spots get the closest look before the blast and the heaviest brush coat before the spray. That is where a tank usually gives out first.