I think, meaning I don't know for sure, but I have the background to
make an educated guess, when comparing tubing and pipe, particularly
water pipe they are two different animals. The difference in alloy and
hardness is substantial.
If you take one leg of a 25G, I see it comparable to thin wall conduit
(not the same, but comparable). It's fragile, easily bent, or crushed.
The tower gains the majority of its strength from the construction.
Water pipe OTOH is "relatively" soft like rigid conduit and easily
bent. Compared to a 25G tower leg it's very heavy, so I'd expect a 10'
section to be notably heavier than a 10' section of 25G. Per size, or
length, I'd expect such a tower to be as durable as a 25G up to 40
feet. BUT...
The idea of using 1" pipe as a sleeve coupling is a sound one I'd make
them about 6 or 8 inches long with 6 being the absolute minimum. Use 2
bolts per section, or 4 bolts per coupling as ROHN does.
Bear in mind, this is not an engineered tower that "MIGHT" be similar in
strength to the 25G. It's built of a material not designed to support
a load. Based on that I'd be very hesitant to climb one.
As for corrosion, as long as it's well coated with a rust preventative
paint ( Cold Galvanizing, or zinc based paint) at sufficient intervals I
would expect it to hold up.
As I mentioned earlier, water pipe is relatively soft and bolt holes are
prone to "egging out" (holes get larger from wind induced tower
movement). A good reason for tight/snug fitting bolts.
For my own comfort, I'd make the "water pipe" tower with the leg spacing
of a 45G, rather than 25G and I would definitely refrain from climbing
it. Using the falling derrick to raise and lower it for maintenance
would be my preference. I think a tower made 3 lengths of 3/4" water
pipe 40 feet long plus bracing. antenna and rotator might be a bit
heavy for two to "walk" it up. Again, the falling derrick sounds good
to me.
I have never painted a tower that needed it. I have painted a couple of
the old American Steel as they were beginning to look pretty rough with
the original paint peeling off after 20 to 30 some years, or wearing off
from me climbing it. I had 25 to 30 years on a 25G and about 15 on a
45G that never needed painting. However, I'm in Michigan, about 25
miles W of Saginaw bay and over 700 miles from salt water unless you dig
a hole. Then it's 200 to 300 feet down.
OTOH Acid rain keeps removing the solder joints from antenna connections
around here. Every C3i antenna I own ( 5 of them) has had the coax come
off. So I resolder the connections and apply several liberal coats of
liquid tape which seems to work. The clear Krylon paint (which is
recommended) is completely gone in just a year or two.
With plenty of paint, I think your tower will stand up well. Don't
neglect the inside of the pipe.
73 and good luck,
Roger (K8RI)
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