Pull the inspection cover on a gearbox that has sat idle through a wet season and you can see it: a rust bloom on the gear faces above the oil line, orange streaks down the case walls, a film on the bearing housings. The gearbox is not worn out. Nothing needs replacing. But putting it back into service like that means grinding rust into the oil, and the alternative, a full teardown, is days of millwright time and a crane, on a unit that may never have been apart.
A construction and engineering company in Virginia had exactly this on a gantry-crane gearbox, and in December 2021 it de-rusted and preserved the unit in place, in an afternoon, with three Cortec liquids and a borescope. Cortec Case History #828 is the source, and the procedure is simple enough to write on the side of the drum.
The problem: rust inside, no teardown allowed
The gearbox had corroded internally and had to be brought back to a clean condition and then preserved for a long idle period. Disassembly was off the table. Whatever was done had to be done through the fill and drain ports, using the gearbox’s own rotation to move fluid over every surface.
What they did: soak, rotate, neutralize, inspect, oil
With the oil drained, the crew worked through four fills:
- Fill the empty gearbox to capacity with VpCI-422, an organic biobased rust remover, used as supplied. Soak 20 minutes.
- Rotate the gearbox for 5 minutes to sweep the remover across the gear teeth and case. Let it soak again. Repeat the soak-and-rotate cycle three times in total.
- Drain the VpCI-422 and refill with a 1 to 1 mix of VpCI-414 alkaline cleaner and water. Rotate for about 30 minutes to neutralize every internal surface the remover touched, then drain.
- One hour later, put a borescope through the inspection port and photograph the internals. The crew found that all the corrosion visible in the before pictures was gone.
- Fill with oil to the operating level, add M-531, a corrosion-inhibiting oil additive, close the gearbox, and run it at low speed for 5 minutes to disperse the inhibitor through the sump, bearings and case.
| Step | Fluid | Ratio | Dwell | Rotation |
|---|---|---|---|---|
| De-rust | VpCI-422 | As supplied, box full | 20 min, 3 cycles | 5 min per cycle |
| Neutralize | VpCI-414 in water | 1 to 1 | About 30 min | |
| Verify | 1 hour after drain | Borescope | ||
| Preserve | Oil plus M-531 | Data sheet: 3 to 5 percent | 5 min at low speed |
The result was a gearbox set up for two years of preservation, with photographs to show management that the inside was clean. Cortec’s field services group guided the customer through the work on site, but every step was done by the customer’s own crew with the gearbox in place.
Why each product
VpCI-422 is the remover because it can sit inside a closed steel casing for an hour of soaking without attacking the base metal. It is 92 percent biobased, non-flammable, passes hydrogen embrittlement testing, and is rated for carbon steel, stainless, cast iron, copper and brass, which covers a gearbox’s gears, shafts, case and bronze bushings. It is not rated for aluminum, so check the case material and any aluminum bearing carriers first.
VpCI-414 is the neutralizer because Cortec specifies it as the follow-up to VpCI-422, and because it strips the remover residue and any remaining oil film at the same time. The case used 1 to 1; the VpCI-414 data sheet gives 5 to 10 percent for neutralizing in a dip tank, so the strong mix reflects the short 30-minute contact and the fact that the crew wanted a single pass. Freshly de-rusted steel flash rusts quickly, and the alkaline cleaner leaves a flash-rust inhibiting film that bought the crew the hour before the borescope and the oil fill.
M-531 is the preservation step. It is Cortec’s corrosion inhibitor package for petroleum and synthetic lubricants, dosed at 3 to 5 percent of the oil, and it protects carbon steel, stainless, copper, brass and aluminum. It sheds water rather than emulsifying it and does not stain, which is why Cortec’s turbine and gearbox lay-up procedures use it. In a gearbox that will sit idle, the vapor-phase component protects the surfaces above the oil line, which is where the rust in this case started. Check the Cortec compatibility charts before dosing: M-531 is compatible with most turbine, gear and hydraulic oils but not with several polyglycol synthetics.
How to do this in your plant
- Confirm the case and internals. Steel and cast iron cases with bronze bushings are fine for VpCI-422. If there is aluminum inside, ask us; VpCI-426 is the aluminum-safe remover.
- Drain the oil and measure the fill volume. You need enough VpCI-422 to fill the box to capacity, then the same volume of the 1 to 1 VpCI-414 mix. For a 20-gallon sump that is one drum of VpCI-422 with plenty to spare and two pails of VpCI-414.
- Soak 20 minutes, rotate 5, three times. On a gearbox you cannot rotate under power, bar it over by hand or use a drive motor on the input shaft.
- Drain, neutralize with the VpCI-414 mix for 30 minutes of rotation, drain again. Both fluids are water-based and biodegradable, but the drained VpCI-422 carries dissolved iron, so handle it as process wastewater.
- Borescope and photograph before you close it. The photographs are the record that the work was done and the baseline for the next inspection.
- Fill with oil, add M-531 at 3 to 5 percent, run 5 minutes at low speed. If the unit will be idle for more than a season, close all breathers, and consider a VpCI-111 emitter in the inspection cover and a VpCI-126 bag or MilCorr shrink wrap over the whole unit.
- Use the same remover for the parts you can take out. Removable covers, couplings and small components go through a VpCI-422 dip tank and a parts washer running VpCI-414, and come out ready to reinstall.
Which Cortec products
- VpCI-422, 5-gallon pail: rust remover for small gearboxes, dip tanks and sprayer work.
- VpCI-422, 55-gallon drum: for a gearbox sump over about 15 gallons, or a shop that will do this more than once.
- VpCI-414, 5-gallon pail: alkaline cleaner and neutralizer; also the stripper for Cortec temporary coatings.
- M-531, 5-gallon pail: oil additive at 3 to 5 percent; treats about 100 gallons of oil at 5 percent.
- M-531, 55-gallon drum: for plant-wide lube system lay-up.
- VpCI-111 emitter: for the headspace of a gearbox that will sit idle for months.
We keep VpCI-422, VpCI-414 and M-531 in stock in Elmhurst, Illinois, so a crew that finds rust on a Monday inspection can have the fluids on site the same week. Contact Solvent Recycling Systems with the gearbox sump volume and oil type and we will size the fluids, check M-531 compatibility with your oil, and send samples if you want to test on a small unit first.
Sources: Cortec Case History #828 (2021); Cortec product data sheets for VpCI-422, VpCI-414 and M-531; Cortec oil compatibility chart.
