What Happens When You Don’t Drain Water From Your Compressed Air Tank

Alternate title: I looked inside a corroded air tank and now I kind of wish I hadn’t.

During the disassembly of our thermoforming machine, we noted with worry that the compressor doesn’t have an air dryer between it and the tank, and that the tank is installed in such a way that the water drain valve is basically inaccessible. So any water in the compressed-air system (and due to basic physics, there definitely will be some) would have accumulated in the tank over its years of service.

A short while ago we got far enough in the rebuild to test the compressed air subsystem. Not surprisingly, the compressed air tank leaked and could not hold pressure. Upon closer inspection the leak appears to be rust perforation implying the inside is pretty rusty. So we replaced the tank instead of trying to patch it.

10 - Rusted hole

But I was curious: OK, it’s rusty. But how rusty? During a lull in projects (waiting for some parts to arrive) I pulled out the angle grinder, attached the cutting wheel, and merrily started making sparks.

20 - Grinder

As I made progress cutting, I noticed chunks of degraded metal were falling out of the gap I had cut. Not flakes of rust – chunks of varying color and texture. This is my first hint things are about to get ugly. Once I cut enough to pull away the end of the tank, we can see inside.

30 - Cut open

That’s far more corrosion than I had expected. And while most of the inside surface qualifies as “rusty” the bottom part deserves a stronger word. I can think of a few, but the only one I am willing to put in print is “Yuck”.

40 - Closeup

This sight is something I might expect to see in a home plumbing project fixing the sewer pipe. And this stuff has the soft squishy consistency of… well, the kind buildup you’d find in a sewer drain. This is not something I expected to see inside a piece of industrial equipment.

50 - Full Length

This layer has built up across the entire bottom part of the air tank.

I had originally thought it’d be neat to find the other side of the perforated hole but I was not in the mood to dig through this muck. Even while wearing gloves.

So let this be a lesson to everybody: If you have a compressed air tank, be sure to drain the water out of it regularly, or this might happen to you!

(Cross-posted to Hackaday.io)

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