Can acrylic tube hold fuel? What PMMA survives, and what it does not

That gap is not a trick of wording, and we are not claiming the charts are wrong. The charts are right. They are answering a narrower question than the one most people are actually asking — and the difference between the two questions is where nearly every field failure lives.

A compatibility chart rates a material against a liquid. Your problem is a part, at a temperature, under a load, with an edge finish, for a duration. Four of those five variables never appear on the chart — and in our experience they decide the outcome more often than the liquid does.

What actually attacks acrylic

PMMA is not attacked by "chemicals" in general. It is attacked by specific families, and once you know the families you can predict most of the chart without looking at it.

• Ketones — acetone, MEK. These dissolve PMMA outright.
• Esters — ethyl acetate, many lacquer thinners and nail-polish removers.
• Chlorinated solvents — dichloromethane, chloroform. These are not a hazard so much as a tool: dichloromethane is acrylic solvent cement.
• Aromatic hydrocarbons — benzene, toluene, xylene.
• Concentrated alcohols — ethanol and isopropanol, where the effect climbs steeply with both concentration and temperature.
• Ammonia — which is the active ingredient in a great many blue glass cleaners, and the single most common way a finished acrylic part gets destroyed after it leaves the factory.

And what it shrugs off: water, brine, dilute acids and alkalis, aqueous ethylene glycol, glycerine, most neutral detergents, mineral oils, and — this is the interesting one — straight aliphatic hydrocarbons at room temperature.

Kerosene and petrol are not the same problem

People group them as "fuel" and expect one answer. Chemically they are barely related.

Kerosene is predominantly aliphatic — straight and branched carbon chains, C9 to C16. Aliphatics are poor solvents for PMMA. The published rating for kerosene at 20 °C is A, excellent.

Petrol is not a compound, it is a blend, and it is the minority components that matter. Depending on grade and region it carries up to roughly a third aromatics — toluene and xylene, added as octane boosters — plus, in most markets now, ethanol. Both of those attack PMMA. The aliphatic majority is harmless; the blend is not. That is the entire reason petrol rates D while kerosene rates A.

The column nobody reads

Every serious compatibility chart has two temperature columns, and almost everyone reads the first one. Look at what happens in the second.

Kerosene goes A → C. Fuel oil #1 goes A → D. Diesel goes B → D. Isopropyl alcohol goes A → D. Ethanol at E10 concentration goes A → D. A material that looked entirely suitable at 20 °C is, at 50 °C, not recommended at all.

50 °C is not exotic. It is a generator set after an hour's running. It is an engine bay. It is a sealed enclosure in summer sun. It is a sight tube on a machine that has been working all day. If your test was done cold on the bench and your part lives warm, the chart you consulted answered a question you did not ask.

Why the same liquid gives two different answers

Here is the mechanism the chart cannot show you, and it is the link back to the residual stress we wrote about last time.

Most acrylic failures in contact with a mild medium are not chemical attack in the sense of the polymer dissolving. They are environmental stress cracking — a liquid that on its own would do very little, acting on a surface that is already under tension. The liquid does not need to dissolve the material. It only needs to soften the surface enough, and reduce the surface energy enough, that stress which was already there can open a crack it could not open in air.

This is exactly what the ten-minute and one-week results are showing. The petrol is identical in both jars. What differs is how much tension the surface was already carrying when the petrol reached it — and that was decided at the die, months earlier.

It is also why two parts cut from the same tube, wiped with the same cleaner, can behave completely differently. One was machined with a sharp tool and sits loose in its mounting. The other has a chipped edge and was pulled into a frame 0.4 mm too narrow. The liquid is a constant. The stress is not.

It also explains the failure mode people find most unfair: nothing happens on the day. The part is wiped, it looks perfect, it goes out. Three weeks later a fine spider-web of crazing has appeared across the surface. Stress cracking is a slow process at the margin, and the margin is exactly where most real parts sit.

What we have tested, and what that does and does not mean

We ran our own extruded acrylic round tube against both fuels, at ambient temperature and with no pressure, and we ran unannealed tube of the same material alongside it. The difference was not marginal.

Ten minutes against one week, from the same resin, the same die and the same wall thickness. The only variable is twenty hours in an oven.

Tube we have supplied for fuel contact has been in service without a reported failure. The applications we know about are petrol at car dealership service centres, display and demonstration stands, and kerosene collection tubes — all of them ambient, unpressurised, and none of them a sealed fuel tank.

What the result does not mean

We would rather set the limits ourselves than have you find them.

• It is a week. A week is not a year, and it is not the ten-year life of a fuel system. We have no data past that and we are not going to imply we do.
• It is ambient and unpressurised. Look again at the 50 °C column above: kerosene drops to C and fuel oil to D. We have not validated anything warm, and pressure is a variable we have not tested at all.
• It is our material in our stress state. It says nothing about how your part will be cut, drilled, mounted or torqued — and those decide as much as the liquid does.
• Petrol is not a fixed formulation. Aromatic and ethanol content vary by market and by season. A higher-aromatic or higher-ethanol blend is a different liquid from the one we tested.
• It does not overturn the published D rating as a general statement about acrylic, and we are not asking you to read it that way.

What the result properly supports is the narrower claim: annealed tube has a great deal more margin against stress cracking than unannealed tube, and against a medium this aggressive that margin is the difference between ten minutes and a week. That is a statement about our process. It is not a certification of your application.

Where we will tell you to use something else

We sell tube. We would still rather lose the order than have a part fail in a fuel application, so these are the cases where we will say so:

• Permanent immersion in petrol — a fuel tank, a bowl, a reservoir that is full for years. The published rating is D and we are not going to argue with it for a safety-critical, long-duration, uncontrolled-formulation case.
• Anything pressurised. Pressure is applied stress, continuously, exactly where the medium is. This is the worst possible combination and it is not an acrylic job.
• Fuel above ambient — heated lines, engine-bay mounting, anything that sees 50 °C in service. Look at the second column again.
• E85 or high-ethanol fuel, at any temperature.
• Ketone, ester or chlorinated solvent contact of any duration.
• Highly polar oils and greases. Non-polar mineral oils are generally fine; the more polar the fluid, the less we will commit to it. We do not yet have a tested list here, so rather than guess we will ask you for a sample of the actual fluid and run it.
• Ammonia-based cleaning on a finished part. This one is worth writing into your assembly instructions, because it is usually not the designer who does it.

For permanent fuel containment the sensible materials are borosilicate glass, PTFE or FEP, or polyamide for lines — and that is a conversation to have with a fuel-system supplier, not with us. Where acrylic does earn its place is intermittent or low-duration contact at ambient: level windows, indicator tubes, demonstration and training rigs, display and test equipment, short-contact sight sections. Clear, machinable, a tenth the weight of glass, and it does not shatter.

How to test it properly yourself

If your medium is anything other than water, do not take our word or the chart's. The test is cheap and it takes a month.

1. Use your real liquid. Not "petrol" — the petrol you will actually have, from the market you will sell into. Not "cleaner" — the bottle that is actually on the line.
2. Use your real temperature. If the part runs warm, run the sample warm. This single step catches more problems than everything else combined.
3. Put the sample under the stress the part will see. This is the step everyone skips. A loose offcut in a jar is not a test. Clamp it, bend it into the radius it will be held at, torque a fastener through it — reproduce the mounting. An unstressed coupon will pass tests your part will fail.
4. Include a deliberately bad sample. One with a rough saw cut, one with a hole drilled near the edge. You are looking for the margin, not a pass.
5. Wait 30 days minimum, and look with a light behind it. Crazing is far easier to see in transmitted light at a low angle than head-on. Most stress cracking does not show in the first 48 hours.

Run that on our sample and on your current supply at the same time. If ours is not better we would rather you found out on a bench than on a production run.

What we do

Every acrylic tube we ship is annealed, and the material carries UV and anti-ageing additives as standard rather than as an upcharge. Both of those exist for the same reason: the failures that damage a customer relationship are the ones that appear months after delivery, when nobody can prove whose fault it was.

What we will not do is tell you acrylic is fuel-proof, because it is not, and a supplier who tells you it is has either not tested it or is hoping you will not.

Tell us the medium, the temperature, how long the contact lasts and how the part is held, and we will tell you before you order whether our tube is the right answer — including when it is not. The stock sizes are here: round tube from Ø4 to Ø400 mm, and the inspection plan behind them is written out too.