A clear protective coating on a production line has to do three things at once and gets credit for none of them. It has to go on thin, because film costs money and the customer wants to see the steel. It has to dry fast enough to stencil and stack a few minutes later. And it has to hold up outdoors for however long the product sits before it is used, while staying inside whatever VOC limit the region has set this year. Solvent-borne clears do the first two and fail the third; most water-based clears do the third and struggle with the first two.
Two Cortec case histories show a water-based acrylic clear doing all three: a Texas tube mill that ran four production trials on EcoShield 386 and left several hundred pipes in a Gulf Coast yard for a year, and an Illinois refrigeration-coil maker that replaced a solvent-borne paint with a VpCI-386 dip tank.
Four trials at a Gulf Coast pipe mill
Cortec Case History #783 (2020 to 2022) describes a large tube-steel manufacturer in Texas that was looking for a new coating supplier for the outside diameter of pipe sold into oil and gas. The specification was strict: water-based, clear, applied at 1 mil (25 µm), meeting the regional zero-VOC requirement, force-dried quickly and completely so the pipe could be electronically stenciled, and protective enough to keep the OD rust-free until the end user commissioned it.
Between October 2020 and June 2022 the mill ran four separate trials of EcoShield 386 FD, the fast-dry grade of the coating. The process is simple to describe. After hydrotest, the coating is applied automatically to the OD at 1.0 to 1.2 mils. The pipe goes through an oven at 140 °F (60 °C) for 22 minutes, is stenciled, and is shipped, or occasionally left in the yard for a few weeks. For the first trial, several hundred coated pipes were deliberately left in the yard for a full year.
| Requirement | Result after one year in the yard |
|---|---|
| Film thickness | 1.0 to 1.2 mils dry, applied automatically |
| Dry time | 22 minutes at 140 °F, ready for electronic stenciling |
| Adhesion | 5B, the top rating on the cross-hatch scale |
| Corrosion | No rust on the OD after a year near the Gulf of Mexico |
| VOC | 0.04 lb/gal (5 g/L), meeting the local zero-VOC rule |
The other three trials matched. The VOC figure was decisive, because a competitor’s coating could not meet the same rule. The mill also reported that it was using less paint than before while getting longer protection, and it is planning to roll the coating out to its other mills. Note what the yard test really measured: an acrylic film one mil thick, on hydrotested pipe, in salt air, for twelve months. That is a harder test than most fabricated steel will ever see between the paint booth and the customer’s site.
A dip tank instead of a solvent paint in Illinois
Cortec Case History #616 (2018) is a smaller shop and a different application method. A small Illinois manufacturer of refrigeration coils was coating its coils with a solvent-based paint. The operators disliked the smell and the health exposure, and the paint was not delivering the long-term corrosion resistance the coils needed in service.
The shop switched to VpCI-386 applied by dip. Coils are lowered into a large tank of the coating, which is circulated to keep it uniformly mixed and covered when the line is idle. The case reports better corrosion performance than the solvent paint, lower VOC emissions, and a safer shop, because the solvent-borne product is gone. For a small manufacturer, the dip tank is the point: no spray booth, no overspray, no filter changes, and a coating that stays usable in the tank between shifts if it is kept covered and agitated.
What the two cases have in common
Both shops replaced a solvent-borne clear with a water-based acrylic that is applied direct to metal, dries fast, can be welded through, and carries a blend of organic corrosion inhibitors in the film. The difference between the two products is mostly paperwork. Standard VpCI-386 is the clear the coil maker dips, at 0.7 lb/gal VOC; EcoShield 386 is the lower-VOC grade at 0.6 lb/gal with its own data sheet and an NSN, and the FD version the mill uses is a force-dry variant of it. Cortec’s consultation guide rates the whole 386 family for outside, uncovered service, which is what the one-year yard test confirmed at 1 mil.
How to do this in your plant
- Get the steel clean. The 386 data sheet asks for a surface free of oil, drawing compound and rust inhibitors, with a phosphatizing pretreatment on a production line or a commercial blast on structural steel. A blast room for weldments, a Build-All or Magido washer for machined parts.
- Choose the grade. EcoShield 386 when a VOC limit or a military spec is in play; VpCI-386 clear for a general-purpose dip or spray line. Ask us about the FD grade if you force-dry.
- Prime aluminum, galvanized or plated parts with VpCI-373 at 0.5 to 1 mil and run an adhesion test before full production. Carbon steel needs no primer.
- Set the film. The mill ran 1.0 to 1.2 mils; the data sheet range is 1.5 to 3 mils dry for harsh outdoor service. Thin coats need the force-dry step the mill used, 140 °F for about 22 minutes, or a longer ambient dry. Full spray and dip settings are in our coatings application guides.
- For a dip tank, keep the coating circulating and cover the tank when idle, as the coil maker does. Thin with water up to 10 percent to hold viscosity.
- Prove it the way the mill did: coat a batch, leave some of it outside for a season, and check adhesion with a cross-hatch kit before you change the spec.
Which Cortec products
- EcoShield 386, clear 5-gallon pail: the lower-VOC clear in the pipe-mill case; NSN listed; about 165 to 330 sq ft per pail at spec film.
- VpCI-386 clear, 5-gallon pail: the standard clear grade for dip tanks and spray lines; weldable; the product in the Illinois coil case.
- VpCI-386 clear, 55-gallon drum: for charging a dip tank or running a production line.
- VpCI-373 wash primer: half-mil adhesion primer under 386 on aluminum, galvanized and plated parts.
We stock EcoShield 386, VpCI-386 and VpCI-373 in Elmhurst, Illinois, and we can supply the blast room or washer that gets the steel ready for them. If you have a solvent-borne clear that is about to fall outside a VOC limit, or a yard full of product that is rusting between shipment and install, contact us for a sample pail and we will help you set up a trial batch and a yard test of your own.
Sources: Cortec Case History #783 (2020 to 2022), Cortec Case History #616 (2018); Cortec product data sheets for EcoShield 386, VpCI-386 and VpCI-373.
