Cleaning Ideas for engine oil testing machine

[humax300]

I've got a job testing engine oils that involves running it through a capillary tube for a time related test. I am having problems cleaning the deposits that are being left on the inside of the glass tube,I've tried nitric acid,sulphuric acid,caustic soda solution and hydrogen peroxide along with a heptane type solution but to no avail. The oil would contain carbon type impurities and that is probable what is being left behind. The capillary tubing is small so I can't get any pipe like cleaners into it,so does any one know what would be another way of cleaning the film off.

[SystemRat]

I've worked on a system that accepted oil samples in plastic bottles these where robotically uncapped diluted with avgas and placed in an elliptical shaker to make sure any particles where suspended in the solution then a small amount was then drawn off via a Teflon tube and burnt in a gas chromatograph. From memory the tube was then flushed with avgas and the cycle repeated with typically 3000 tests per day. The robotics where made by Zymark I had a look on their site to see if the system was list but could not find it and my involvement in that stuff was a long time ago.

Perhaps the dilution with avgas reduced the viscosity of the oil and the Teflon did not easily allow particles to remain on the walls of the tube. The avgas could be ignored in the test results. Not much I can think of will dissolve carbon so perhaps the answer is to help it not to stick.

I've seen aqua regia used to clean some lab gear but I am not sure about the safety of using that or if it would clean carbon.

[trash]

You're basically looking for a solvent of oil.
Chemically, it's pretty stable. Nitric and Sulphuric acid, I hope not together ?
I hope you don't live close to me ! No, wait, I hope you live close enough that I can see the mushroom cloud from my kitchen window !

Solvents. Well, the lighter petroleum fuels are a start.
I'd consider several runs through. Kerosene, Petrol, Acetone.

A chemical solvent that should do well is Potassium Hydroxide. That will turn the longer hydrocarbons into soaps. Sodium hydroxide (draino) is not suitable as the soaps formed tend to be solids. KOH forms liquid soaps.

Carbon itself isn't know for being soluble.
I'd consider, liquid oxygen, Carbon tetrachloride or Carbon itself in the form of very fine diamond dust in a very light solvent like methanol or liquid nitrogen.
Pumping it through the tube to effectively sandblast it on a microscopic scale.

If you had a capillary to sacrifice, putting it under an electron microscope might provide some clues as to the nature of the deposits.

[humax300]

thanks,I could try the carbon tet and acetone,no chance of nuclear reacion btw as its all done very carefully using a small dropper of individual cleaner solutions followed by a cleaning solution and vaccum backflush to move the debris back up out of the tube. I've tried using a heavy detergent oil as a backflush but that didn't help so will see how the other 2 will perform.
btw,thanks on info about the hydoxide as I did seem to get a few solids.

[Godzilla]

Caustic soda AKA sodium hydroxide...hot.

It works for my parts washing.

I Use draino from my local supermarket.

[Tradesman]

would an ultrasonic cleaner work on those small capilleries ?

[fandtm666]

i use a chemical called GREASOL for commercial cleaning works in kitchens and
and alike

[humax300]

thanks for all that replied,borrowed the wife nail cleaning stuff (acetone),hitithe deposits with that,flushed with solvent then a quick flush with caustic soda solution,now its better then new. I think the acetone did the real damage,glad I dont have to use it on my nails like the ladies do,seems to be quite nasty stuff.

[SystemRat]

At least acetone in the form of nail cleaner smells nicer. Xylene might might be worth a try too.

[Arbiter]

I believe acetone is a by-product made from the production of sugar.
It is one of the few chemicals that can dissolve polyester resins used in the fibreglass industry. Polyester resins are also a derivative from oil.
I also know it will destroy an internal combustion engine if used as a fuel because it leaves lots of carbon ( I had a nasty neighbour who found this out the hard way).
It certainly dissolves oil-based chemicals, and will literally suck the oils out of your skin - split fingertips being commonplace after repeated excessive exposure.
NOTE: Keep the ignition sources away because it has a flash point of about 17 degrees.