Lexan (electric meter covers) Pressure Vessel Limit

Did you mean 140-150 mm i.d.? (I'm not visualizing 14-15 as realistic.)

Any flat surfaces might be an issue if the contained pressure is significant.

Doh! yes, 140-150. On the top flat part, I see the thrusting force as 129.8 lbs. (58.9 Kg) at 5 psig. Multiply by appropriate factors for 10, 15 psig - gives me 259.6 lbs. (117.7 Kg), and 389.5 lbs. (176.7 Kg).

I'm assuming that you'll be hydrostatic pressure testing.

Be sure to check your medical insurance limits ahead of time.

And while you're at it, check your life insurance limits. For your wife's sake.

This will be done MythBuster style out in the country behind some panels, with a long air hose.

So you want to repurpose some Lexan meter covers because you figure they have high strength, impact resistance, and you can use the flange to provide a secure clamping means.

I'll leave the mechanical strength calculations to the mechanical engineers here, but I suggest that you do some research on the suitability of Lexan for resisting the chemical and heat effects that can cause embrittlement and subsequent early life failures. As good as the material is under the mechanical stresses and water exposure that a meter cover is exposed to, it may not retain those properties very long under chemical and high temperature fluid attack.

From this monograph: "...While Lexan resin generally displays good property retention when exposed to water, mineral acids and organic acids, crazing and/or embrittlement may occur if the Lexan resin part is highly stressed and exposed to hot water or a humid environment.

Lexan resin is insoluble in aliphatic hydrocarbons, ethers and alcohols. It is partly soluble in aromatic hydrocarbons, soluble in chlorinated hydrocarbons and will slowly decompose in strong alkaline solutions..."

While Lexan may stop a speeding bullet, it won't resist a Sodium Hydroxide 10% solution. Check out the table on page 38-39 for more info.

Quite right, and the main concern in my case is the increasing alkalinity of electrolysis where sodium bicarbonate is the added electrolyte. Over time, this electrolyte will drift toward an alkaline pH. Although our group already has experience with this in polycarbonate containers (not this thick, I believe) at atmospheric pressure for up to two weeks at 80 C. If I operate 20 C higher (100 C), there can be issues. The reactor will be in containment (a large beer cooler - no ice, no beer, that is for another cooler.)

As most trials in Texas go, the famous quote will be: "Hold my beer and watch this!"

Sounds familiar. Didn't you already do this?

I seriously doubt anybody would pressure test a cove that is not sealed. Maybe test the compression strength in case a truck runs over them.

Your joint will no doubt fail first anyway. How will you seal/clamp them and why not use a clamp that exerts pressure on the entire top and bottom. Two round plates with a bolt pattern around the outside. A circle cut out of each disk for a view port.

Send a picture, please.

Well Lyn, here is what I have done:

Two each plywood rings constructed from 4 plywood rings, where two each are glued up cross grain, so yes, about the same strength as 1" plywood. Hexagonal bolt pattern, 6 each 6" 1/4-20 carriage bolts with hardware. The upper (and lower) meter covers are partially covered, and pressure is "evenly" distributed over the flanges. There are two high temperature red silicone gaskets supporting a metal ring of 3" height, whose diameter is appropriate to match with the meter cover flange faces. The plywood rings were carefully routed with Roman Ogee router bit to have approximately the same radius of curvature as the plastic as it transitions from the side wall of the covers to the flanges. I have done about all I can to distribute stresses, without entirely sheathing the vessel in steel, but if I would go to that trouble, I would totally re-design, and line the vessel with an alkaline resistant finish to avoid shorting out (vacations in the coating would be a catastrophic failure waiting to happen).

http://www.amazon.com/Contained-Electrolysis-Science-Teaching-Apparatus/dp/B00N2Y021S

Solar Eagle: As always, you come through for the group! I will have to get one of these test vessels for $24.95 as shown below the ad you linked. I already have a (non-adjustable) power supply, but have plans to use an H-drive (square wave). For gas testing purposes, I will replace the gas collection tubes with polycarbonate tubing.

Gas testing may consist of a combination electrochemical cell having a silver billet oxidation-reduction potential response, along with pH, under very weakly buffered conditions. Hydrogen containing gas would cause a decrease in pH (and a general lowering of the ORP, hopefully), whilst oxygen would cause ORP to increase along with pH increase. Not that hard to set up preamps for these, and then log them on an

Arduino. Another gas testing cell involves oxidation-reduction of methylene blue dye, a trustworthy redox indicator. Physical testing involves buoyancy tests of known volumes of gas.

So, yes, thank you for pointing that out.

It would be great if you could post some video cataloging your procedures and findings...

https://www.youtube.com/watch?v=T-OwWOYHhMI

Plasma electrolysis...?

https://www.youtube.com/watch?v=ALFYm_6IlX8

Hydrogen balloons...

https://www.youtube.com/watch?v=gZJEDe_HUcw

Posting on You Tube depends on two things: (1) results that are worth mentioning, and (2) permission from the senior members of our group to do so.

Our plan: As I understand it, nothing we are doing right now is patent worthy. If we produce useful energy from the devices, the plans will be put out there as open-source documents available for (safe) public use. That is as short as I can state it.

Still working on fundamental aspects as we transition from ambient pressure to pressurized work.

We ran pressure tests (hydrostatic tests also) this last weekend, at my friend's place in the country.

1) the red molding silicone is simply not up to the task as a high stress gasket material.

2) as flexible as this silicone is and deformed by pressure, we could not get a good seal even at 5 psig until we sanded the gasket flat using a grinding wheel (that was available).

3) we observed about 1 psig per minute leak rate at 5, 10, 15 psig, then slightly less at 20 psig, then about 2 psig/min at 25 psig. At 30 psig, the gasket shifted and the assembly was leaking loudly.

Back to the drawing board as to the seals. The Lexan did just fine (with air). Not sure what will happen as RAMConsult pointed out with alkaline electrolysis bath. Probably bad things.

At some point, I will make a totally steel vessel for this (or purchase a pressure tank I can sacrifice), then flange up a large window on top, as that is the only place that needs to be transparent. I have more research to do on alkaline resistant coatings, but there are some epoxies out there used around chemical treatment pumps that leak that should work just fine. No vacations or fish-eyes allowed, though.

You might try using a meter ring for a better seal, they come in different types but most of them have a wrap around flange that will grip both of the cover flanges and pull them together. You know they're the right size, but I don't know if they'll accommodate the double thickness. As far as a sealant goes, you might try a preformed silicon gasket rather using instead of RTV, and the meter ring will prevent it from creeping out or lifting under pressure.

Have you considered using an old propane tank. I used to use the tall Bernzomatics, they come complete with a fitting and a pressure relief valve, although viewing what's going on inside could be problematic.

I think the propane tank is a good idea. the Mr. Heater Buddy tanks are about the right size for this, but one thing has to happen. I must find a material to coat the inside of the tank that will not fail at say 125 C and 2 bar, and insulate the metal of the vessel from electric current, otherwise, I would have to use the vessel itself as the cathode (or lined with lead as cathode, or other metal electroplated on. Even that would not be insurmountable. One end (or the other) could be cut away, and have a flange welded on for the transparent port. This sort of avoids issues with corrosion induced failure of polycarbonate that is in fact of considerable concern to me when operating at pressure.

Preformed gaskets or even O-rings will work under confined, and properly aligned conditions.

I have a bit more tinkering around to do before I totally abandon what I have to this point, probably some measuring (for a change), experimenting with sleeve materials to help keep things in place, and a bit of luck.

"I read somewhere that plastic beverage bottles (for carbonated soft drinks) can hold 50 psig (345 kPa), under normal circumstances, and supposedly withstand 100 psig (689 kPa) during impact testing. While this might be true, I am sure that bending stresses at a flange does not exist within these bottles, which are not far different in size (diameter) from the electric meter covers. Thus hoop stresses might be similar, but thicker material for the meter covers."

Personal hands on testing I have done with soda bottles has shown that they can take well over 200 PSI before they rupture. The better ones past 300!

As for your lexan covers as with your other thread on the same subject as this one the laws of physics and chemistry have yet to change so once again the primary problem will be the seal blowing out before the lexan gives up.

Personally If I was you I would be looking at getting a stainless steel fire extinguisher for your experiment. To get one cheap stop by any local fire extinguisher testing and sale place and ask about buying a used one.

I got one once for free and in good shape that had a busted bracket for hanging it on a wall just because I gave them a good story about what I was going to do with it and it was the same thing you are trying to do.

Even with extreme abuse and hydrogen embrittlement you will likely never blow one up in your life time running it at 10 PSI.

Thank you for the reassurance. I appreciate you extensive experience with "popping" vessels under pressure. This is worthwhile information. I also found the same information on 2 L soda bottles.

Now that I have witnessed at some considerable personal expense how house drain gut lines of cast iron are cleaned and lined with plastic using epoxy, I think I have a plan on how to proceed with a steel vessel if these Lexan covers can't work for me (but you and I "know" they will). I think they might well take 10 psig at temperature, and with sodium carbonate present, just not sure how other oxygen species as peroxides and superoxide may attack, but other materials present should react with these first anyway. The other material is a granulated substance that has proven useful in other hydrogen production apparatus, and has been tested by our group over the past few years as reliably in production of hydrogen by various means (applied electrical power, or by the use of active metals).

I would love to operate the LER-1 reactor at 10 psig, because it should be much easier to reach a safety margin on gas velocity in a premixed burner at that pressure than with 5 psig. I have a contact with a ceramics fabrication company that makes finely machined ceramics for everything from electronic components to aerospace. I plan a premixed burner head with a ceramic (sapphire?) disc with a number of tiny drill holes no larger than 0.05 mm each. Obviously the gas will have to pass through a filtration frit rated lower than 50 microns. Even with that, the burn velocity of the gas mixture coming off this electrolysis (driven far from equilibrium) will be expected to be well in excess of "normal" burn velocity for stoichiometric hydrogen-oxygen. I have found conflicting papers on the effects of water vapor on the 2:1 gas mixture laminar flame velocity, although the apparently more authoritative paper (done with more sophisticated measuring apparatus and high speed camera), reports clear decrease in flame velocity as water vapor is added. Thus if that holds true (we shall see), saturation at 10 psig will be better than at 5 psig as to flame stabilization, and less action at the flash arrestors, which will be the best ones I can lay hands on, and more than one.

Standard schedule 80 PVC water pipe will easily handle 10 PSI at 100 C.

So will black HDPE pipe. I ran 1 1/4" black poly for my boiler lines from my shop to my house for over a decade where they endured 190 F water at 15 - 20 PSI continuously with occasional periods of ~215 F when the boiler overheated and steamed out.

The pipe I used was standard 160 PSI @ 80F rated commercial pipe which if you find the temperature/pressure derating specs for it still has a rating of ~30 PSI at 100 C which is similar to what PVC pipe comes out at as well.

Plastic soda bottles make great rockets...

https://www.youtube.com/watch?v=0qzOzjRJpaU

http://www.aircommandrockets.com/construction.htm

I ran a quick and dirty stress analysis (not some sophisticated model, more back-of-the-spreadsheet), and hot this: