[TowerTalk] Choice of material for Mast

[npalex at aol.com]

The question was asked about the differences in Aluminum tubing and aluminum pipe.  The answers that followed in some cases indirectly answered the question and in other cases also illuminated other differences between "tubing" and "pipe", two things that are often confused by many.  

With respect to the original question, Tubing may be extruded and essentially seamless, or it may also be rolled and have a welded seam.  Pipe is almost always rolled and welded.  The bright shiney aluminum tubing used in many antennas is run through a die twice to get that mirror finish (also makes it more expensive then "mill finish material").  

Next is dimensional considerations - Tubing is measured OD, and various wall thicknesses reduce the diamater accordingly.  Pipe is dimensioned nominally on the ID as it is used to compute fluid flow characteristics.  There are various wall thicknesses that impact the inside diameter, but not the Outside diameter as that must be held to a standard so as to interface with thread dies, and associated fittings.  A schedule 40, 2" pipe will have a ID of about 2.060 (nice slip fit for 2" TUBING) and an OD of 2.375".    An often used substitute for a 2" mast is 1-1/2" PIPE whose OD is around 1.9" making it a sloppy fit inside of a 2" thrust bearing, but that can be shimmed to compensate.  

When choosing a material for MAST applications there are many other factors to be considered then just Pipe or Tubing.  Probably to most important is what is the Wind load of the antennas to be attached?  From that info and how much exposed mast (distance above the top bearing) there is, the stress can be calculated which leads to the strength of materials, diameter and wall thickness computations.  Selection of materal (aluminum or steel), diameter (2" for tubing, 1.90" for pipe), wall thickness (lots of choices in tubing, schd 40 or 80 for pipe).  The "strength of material number" will vary over a wide range depending on the type choosen.

But back to what most hams do, and that is find the cheapest or most available.  If it bends in the first wind storm then that becomes the time of regret in your choice.  Depending on where it bent, you will likely cut it there and reuse what is left only now not as long.  Ten or twenty-one foot lengths of  galvanized "PIPE" are readily available at home improvement stores or local plumbing outlet.  Aluminum pipe may be available at a large electrical supply house as it is often used as rigid conduit (pipe sizes) and 10 ft lengths.  Or you can find both steel and aluminum tubing at a metals distributor, who may or may not supply to a retail market.  Or you can buy super quality chromaloy masts from various tower and ham supply outlets.  

I would stick to tubing for a mast application, and choose the appropriate material (steel or aluminum), and wall thickness to achieve the necessary strengh needed. 

Norm W4QN

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Message: 8
Date: Thu, 31 May 2007 20:35:06 -0500
From: <jacobsen_5 at msn.com>
Subject: [TowerTalk] tubing vs pipe
To: "towertalk" <towertalk at contesting.com>
Message-ID: <BAY111-DAV1597E7095AC1E110413AD7B22C0 at phx.gbl>
Content-Type: text/plain;   charset="iso-8859-1"

Hello all.  I've tried to check the archives but don't seem to find an answer. 
Just what is the difference between aluminum  TUBING  and aluminum  PIPE.  My 
"gut" (and poor memory) says tubing is extruded and pipe has a welded seam.  
TIA

73
K9WN  Jake

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Message: 9
Date: Thu, 31 May 2007 20:39:34 -0500
From: "Clint Talmadge" <unclebudd at bellsouth.net>
Firstly:
Pipe is measured inside and tubing is measured outside.
Secondly:
Pipe is meant to carry pressure on the inside and tubing caries stress on the 
outside.

Clint - W5CPT
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Message: 10
Date: Thu, 31 May 2007 19:08:26 -0700
From: "Richard (Rick) Karlquist" <richard at karlquist.com>

Correction:

Pipe is also measured outside.  For example, all
so-called "2 inch" (Iron Pipe Size) pipe is 2 3/8 inch O.D.,
regardless of wall thickness.  The I.D. varies
from below 2 inches to above 2 inches, depending
on wall thickness.  It also varies depending on the material
the pipe is made out of.

Rick N6RK

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Message: 11
Date: Thu, 31 May 2007 22:55:04 -0400
From: "Bert Almemo" <balmemo at sympatico.ca>
Subject: Re: [TowerTalk] tubing vs pipe
To: "'Richard (Rick) Karlquist'" <richard at karlquist.com>,   "'Clint
    Talmadge'" <unclebudd at bellsouth.net>, <jacobsen_5 at msn.com>,
   
This is the first time I've heard anything to be defined the way you measure
it!! The difference between pipe and tube is how it's made - not how you
measure it or what you use it for.

Pipe is made of cast iron or other metal and tube is made of sheet metal
that's folded and welded or drawn from a blank through a die, cold or hot.

73 Bert, VE3OBU

 -----Original Message-----
[mailto:towertalk-bounces at contesting.com] On Behalf Of Richard (Rick)
Karlquist
Sent: Thursday, May 31, 2007 10:08 PM
To: Clint Talmadge; jacobsen_5 at msn.com; towertalk
Subject: Re: [TowerTalk] tubing vs pipe

Correction:

Pipe is also measured outside.  For example, all so-called "2 inch" (Iron
Pipe Size) pipe is 2 3/8 inch O.D., regardless of wall thickness.  The I.D.
varies from below 2 inches to above 2 inches, depending on wall thickness.
It also varies depending on the material the pipe is made out of.

Rick N6RK


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