[TowerTalk] [Bulk] Re: Mast Material

[Grant Saviers]

"Regular" sch40 pipe is often specified as 30kpsi yield strength, but 
schxx IPS is available to 70kpsi.  The example fence folks are 
specifying 50kpsi and a non-standard wall thickness of 0.120" which is 
in between sch20 and sch40 normal pipe sizes, 0.105" and 0.145" 
respectively.  If I calculated correctly, the radius of gyration/section 
moment of inertia is 0.423/0.495 = 0.85 for fence "high strength" vs 
sch40.  Given the yield stress ratio is 50k/30k = 1.67 then the relative 
bending yield is 1.67 x .85 or 1.42x better for the 0.120" wall "high 
strength" fence pipe.  It's an interesting result to trade the amount of 
steel for better steel to yield higher bending yield stress.

Here is one fence pipe manufacturer's brochure with what they call W40, 
W30, W20, and W15 grades, with varying wall thickness, usually not the 
same as IPS sch40, 20, or 10.  Note the W30 which seems to be the pipe 
mentioned earlier in the post is hot dip galvanized on the outside, but 
something different inside and also has additional polymer coatings.  
The W15 goes down to 0.047 wall.
http://www.wheatland.com/images/fence_framework/Fence_Framework_Brochure.pdf

if you want to see all of the choices in "standard" pipe here is the USS 
pipe brochure
http://usstubular.com/resources/library/brochures-and-catalogs/u-s-steel-tubular-products-standard-and-line-pipe

Yield strength is not the only variable in pipe performance.  High 
strength tube (not pipe) is Drawn Over Mandrel (DOM) to insure 
uniformity of wall and strength.  It may have been seam welded or 
pierced bar to make the rough shape.  Then there may be heat treating to 
a specific hardness/strength.

Using fence pipe for gin poles which have a significant risk of life 
hazard, is a risk I would not take.  Rather, a DOM structural tube in an 
appropriate wall thickness.

Using EMT with a 0.065" wall for a tribander on tower mast, welded seam 
and electro-galvanized only on the outside is just plain nuts. There are 
NO specs for the steel properties.

YMMV,

Grant KZ1W


On 3/13/2016 18:27 PM, Steve Maki wrote:
> On 3/13/2016 9:01 PM, Richard (Rick) Karlquist wrote:
>
>>> A good alternative to schedule 40 pipe is the tubing used nowadays for
>>> fence top rails, known as SS40. It's lighter (thinner wall) but 
>>> stronger
>>> and actually less expensive than galvanized sch. 40 pipe if purchased
>>> from the right place.
>>>
>>> We routinely use it on cell sites for antenna masts in place of sch. 
>>> 40.
>>>
>>> Here are the specs:
>>>
>>> http://www.hooverfence.com/catalog/chart.htm
>>>
>>> -Steve K8LX
>
>> Note that the outer diameter of fence tubing will always
>> be the same as the outer diameter of some standard water
>> pipe size.  E.G. Both "1 7/8 inch" fence tubing
>> and "1 1/2 inch" water pipe (any schedule) actually
>> have an outer diameter of 1.900 inch.  Either can be
>> shimmed with standard 2" OD aluminum irrigation pipe with
>> 0.050 inch wall to fit standard 2.000" mast clamps
>> or bearings.
>>
>> I don't know why they make fence tubing and pipes the
>> same size.  One theory is that you if you want to build
>> a fence on steroids, water pipe can be substituted for
>> fence tubing very easily.  (Attention:  Donald Trump :-)
>> Or maybe they make both of them on the same equipment.
>> (Obviously, I have spent way too much time loitering
>> in hardware stores.)
>
> Hehe.
>
> But I'm not sure why substituting schedule 40 for SS40 in fence 
> applications or any other (except plumbing perhaps) would be an 
> *upgrade*. A quick search didn't yield specs for sch. 40 that would 
> lend itself to an applicable comparison, but the fence people claim 
> that SS40 is *stronger* than sch. 40.
>
> In the fence business there are numerous tee couplers, etc. already 
> sized for stand sch 40 OD's, which probably drove the size constraints 
> for SS40.
>
> -Steve K8LX
>
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