Small scale pipe connections (Need Input/Insight) 1

[twl724]

Without any preface here is the problem...

I have a 1" dia. stainless steel (for lack of better words) tank. There is a 0.25" dia. hole located on its side. The tank has an approximate wall thickness of 3/32". A fitting is needed to connect the 0.25" dia. hole to any standard NPT thread size, preferably 0.25". The quarter inch hole cannot be threaded because the wall thickness of the cylinder/tank (~3/32") is too small, even for fine thread. I have looked into various 0.25" bulkheads. However, all bulkheads of an appropriate size have criteria that prevent them from working. The first criterion for small bulkheads is that the tank size must be sufficiently large as to allow the bulkhead to seat properly against the tank's curvature. The second criterion for bulk heads pertains to the hole size. A quarter inch bulkhead generally requires a hole size of 7/8". The hole is located such that it can not be modified. One other possibility that I have contemplated is welding... this is a last resort.

In the exploded view provided, the leftmost piece is in question.
Please ignore the other excess.

What do you guys think? Any input would be much appreciated.




T.W. Lewis - Mechanical Engineer
Virginia Commonwealth University

 

[pennpiper]

I have attached a link to a possible solution idea. The view you will see is for a much larger and cruder application. What I am trying to convey the concept.
You may not be able to find one in the size or material you need but you could use this image as a model or basis to have one made to meet your requirements.

http://www.anvilintl.com/SharedContent/Pdf/TechnicalData_AnvilProductInstallation/DS_045.pdf

 

[racookpe1978]

What pressure will be aopplied to the tank and fittings?

What fluid? What are your safety criteria? (If it breaks, what is your hazard or liability?

How long does the application need to work? Is a test rig that will be used in only place for a little while? Or some commercial fitting that you need make work thousands of times a day?

 

[CRG]

silver solder?

 

[Duwe6]

Call over to the Boilermaker Union hall. They will have several Tube Welders [who make jewelery on the side] that can make your weld. Just takes finding that 1 in 1000 welder.

 

[twl724]

Thank you all for your input.

NOTE: The pressure is roughly 60psi and currently the design is for a test rig.

For anyone who is interested, the design is for my senior capstone project, a needle-less injection device, where the cylinder in question will contain medicine (for the time being water). The closed end of the cylinder is a thin plate of Iron-Gallium which is a magnetostrictive material. Under an applied magnetic field the FeGa expands. Being confined by the walls of the cylinder it will buckle, creating a displacement. This displacement will be ejected through a nozzle (~50um) in which it will have enough velocity to penetrate skin. The smaller, quarter inch hole will be used to pressurize the chamber. Everything on this end is worked out aside from the final connection which is the basis of this thread. The entire concept is synonymous with inkjet printing except that they use piezoelectric material to create the displacement. Currently we are trying to get a working model built in order to test the nozzle and enhance its geometry.

...Boiler Maker Union Hall? I'll give it a shot

 

[racookpe1978]

OK. Low pressure and a safe fluid in a test situation.

Real world, for a fabricated part (medical quality and cleanliness) I'd machine a cylinder of the required ID and length, but with a variable diameter OD (so the single small section of greater wall thickness for the threaded fitting's female threads is thick enough to screw in securely. Obviously, a machined single piece of metal will have no "slots" or traps to catch material or cause sterility concerns.

For a test fitting with filled with only water, I'd make a thick-walled "outer" cylinder to slip around the tube you have now. Silver solder (or even fillet weld) the thick outer cylinder around the thin-walled tube you have now, and screw the fitting into a threaded hole in the outer cylinder. The outside tube (which could be a saddle-shape tube) has to be thick enough for the threaded fitting - a little over a 1/4 thick, probably better at 5/16 to 3/8)

Remember, you're testing the injection method of the inside tube with sterile water into a test fleshy item (pig skin carcass maybe), not how you got low-pressure pure water into the injection tube.

 

[twl724]

We've decided on machinig and welding a .25" OD x .125" ID to the hole. Opposed to threading the rod we will use a Swagelok fitting.

Thanks again, all of your inputs were appreciated.

 

[MiketheEngineer]

Epoxy or Super Glue??

 

[HazGas]

Too late now, but another (good) way to do it would be to take a piece of round stock, maybe 5/8" thick or a little larger. Turn it off to about 1" long in a lathe, then bore a 1/4" ID hole in it. Then tap a female pipe thread (or an SAE straight thread port - easier to clean) in the hole. On the other end you need to cut a weld prep bevel and then "saddle" it for the 1" diameter of the tube. Now you can get a full penetration weld on it and it will not only be easy to clean but it will actually be durable, last, and be very strong.

Yes that is a real PITA. That's why real companies have machine shops, welders, and pipefitters on hand. It's a shame nowdays that many organizations have gotten rid of that capability in favor of buying "off the shelf" items that are never available and often won't work.

 

[HazGas]

I should also say that what I've suggested is essentialy a homemade Thread o Let/"Boss o Let". They aren't very easy to find in tube sizes (1" OD is a standard tube size... 1" pipes aren't 1" OD.) so thats why I suggested making them instead of buying them. Additionally, the 1/4" inside hole may turn out to be an issue if the commercial product has a different ID, which it probably does. When tapping or porting you may be left with a sharp edge or step on the ID. Boring it to form a smooth radius at the diameter change will improve flow characteristics and ease of cleaning.