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To Pressurize 6063 Aluminum Tubing Or Not

03/13/2018 2:49 AM

Im working on a pneumatic dry bulk tank trailer. I am a welder by trade and we have a few trucks an trailers pulling dry bulks. We're having some trouble with a trailer of a different manufacture from the others over heating the trucks blower. The piping on this trailer has a different configuration in the used 3 90 degree elbows to get the pipe to the 1 st hopper. That being said I think by the use of those tight radius bends so close to each other is causing a restriction in airflow. I can eliminate the existing and use just two bends with one of them being bent on a 12" radius. My question is I have a piece of 6063 aluminum tubing 3.5 OD x 11 GA. Would this be suitable running a pressure of about 20 psi? This piece of tubing will have about an 8" tangent on both sides of the bend. Thanks for any help

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#1

Re: To pressurize 6063 aluminum tubing or not

03/13/2018 4:00 AM

Carry out a force balance calculation on a theoretical longitudinal section of the material, if a pressure rating for it is not otherwise available from the manufacturer. The tensile strength of materials at various temperatures can be had from a number of sources, among them being Kempe's Engineers' Yearbook, any edition.

The alternative is to substitute piping material with a known pressure rating.

Bear in mind that if the stored energy in the structure exceeds 215bar-litres, the thing classes as a pressure vessel for insurance purposes and will be subject to periodic assessment by the facility's burst/collapse indemnity insurance company.

The length of the pipe has been withheld from the forum, which doesn't help.

The pressure drop caused by a 90deg bend is the equivalent to 30 diameters of straight pipe whereas a swept bend is around 12 diameters. The geometry of the arrangement, which the forum cannot see, will determine whether substitution is worth considering; the figures given suggest, at first glance, that substitution may not be worth it.

It's time to do some Engineering before carrying out any more Welding.

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#2
In reply to #1

Re: To pressurize 6063 aluminum tubing or not

03/13/2018 9:24 AM

The pressure drop caused by a 90deg bend is the equivalent to 30 diameters of straight pipe whereas a swept bend is around 12 diameters.

Nice rule of thumb.... is there a standard radius for a 90 deg bend and a swept bend for aluminum?

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#3
In reply to #2

Re: To pressurize 6063 aluminum tubing or not

03/13/2018 10:29 AM
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#4

Re: To Pressurize 6063 Aluminum Tubing Or Not

03/13/2018 7:29 PM

If this is really 1/8" wall tubing, think about it. That's trivial.

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#5
In reply to #4

Re: To Pressurize 6063 Aluminum Tubing Or Not

03/14/2018 5:21 AM

Agreed, at the sort of wall stress at 20psi I wouldn't worry, just get on with it.

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#6

Re: To Pressurize 6063 Aluminum Tubing Or Not

03/14/2018 9:08 AM

Q: "Is 5psi dangerous?"

A: "It is, if it is propelling a cast iron surface drain access cover in your direction!"

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#8
In reply to #6

Re: To Pressurize 6063 Aluminum Tubing Or Not

03/14/2018 5:59 PM

I guess we don't call them manhole covers anymore.

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#7

Re: To Pressurize 6063 Aluminum Tubing Or Not

03/14/2018 11:19 AM

The hoop stress in the pipe tube for 20 psi will only be about 300psi, a safety factor of about 200 for pressure only.

Any strength issues in the pipe will come from other sources, such as end loading conditions and weld residual strength. BTW, unless you re-heat treat after welding, the tensile strength of the material will be degraded from the 60,000 psi yield to less than 20,000 psi due to welding heat affected zone and over-aging of the material near the weld. You might as well use non-precipitation hardening material for the tube, but since you have it, might as well use the 6061. A fellow once told me that the reason he used a particular piece of really obsolete equipment was that it was already paid for.

Reducing the number of bends and increasing the bend radius is a good idea, but isn't really associated with the tube strength unless it changes the end loading conditions.

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#9
In reply to #7

Re: To Pressurize 6063 Aluminum Tubing Or Not

03/14/2018 8:08 PM

Thank you for your response, deep down I feel confident with using this tubing, but when it’s boiled down I am not an engineer. What spooked me was I noticed that the manufacturer used sch40 aluminum pipe with stamped weld together fittings. I think they did this to save time and money since that would save the time they would have messing with bends. I did a formula for burst pressure and came up with 2,400 psi. We’ll be nowhere near that. Thank you again, never hurts to ask. I’ve learned a lot that way.

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