Date: Tue, 06 Dec 2011 21:44:17 -0500
From: K8RI <K8RI-on-TowerTalk@tm.net>
Subject: Re: [TowerTalk] Tower Leg Maintenance
On 12/6/2011 4:39 PM, Frederick Vobbe wrote:
> I think most of us with older towers have, at one time or another,
> painted or at least removed rust starting on the outside leg of a tower,
> and repainted it.
> Has anyone done anything to the inside of the leg?
Pouring sealant in from the top is a bit "after the fact", BUT the old
aircraft construction sprayed linseed oil for rustproofing into the
steel tubes that made up the strength of the fuselage.
Were I going to recondition an old tower like the 25G or American Steel
(BTW the American Steel towers of which I have used many) are no where
near as strong as the 25G. I don't know what they are coated with but
it's definitely not hot dipped galvanized. I would get some of the
steel brushes used to clean the inside of copper pipe joints before they
are soldered. Use brushes of a size that are a snug fit in the tower
legs. Using a 1/4" to 3/8" rod at least as long as the tower section
drill a hole at least a half inch deep into the end of the rod. 1/4",
5/16", or 3/8" steel tube might work. Half as long will work and might
be easier for some to handle. Cut the handle off the brush leaving
enough of the twisted wire to fit into the end of the rod and using
either a set screw or solder...or brazing, fasten the brush to the end
of the rod. Chuck the rod up in a variable speed drill and run the
brush up and down through the tower leg as many times as it takes to get
it clean. This may help to spot any rust that might be in there. If
you get a lot of rust out, it'd probably be best to just pitch the section.
Once the legs are clean inside, a flashlight should reflect off the
inside making them look almost like the inside of a shotgun barrel.
I'd then use a sprayer with Linseed oil or a spray can of LPS2 to coat
the inside of the tower legs thoroughly. This will be messy. LPS 2
has enough solvent in it to penetrate into tight places but will leave a
grease like coating for protection. I've seen it used to
rustproof/corosion proof portions of cars or aircraft.
A pump up sprayer could be adapted with a tube to run the spray nozzle
through the length of the leg getting a much better coating. OTOH the
sprayer probably will not be good for much else afterwards.
I'd be more inclined to clean the tower legs and then give them a good
coating of the cold galvanizing inside and out with the rustproofing
internally a few days later. What ever you put in there is likely to
eventually wash out.
Just remember that reconditioned old towers may have some weak spots
that don't show. There is a tool (Ultrasonic) for checking leg
thickness. I don't know where you'd borrow one and they are most likely
expensive. We used to use them to measure tank and pipe wall thickness
down to a few thousandths of an inch IIRC.
and good Luck
## U could also,[ if the tower is all in sections], stuff the TV camera into
each leg, like the
plumbers all do, and see the inside of the legs... in colour. Dunno how small
an ID those things
will fit into though. IF it's not that bad inside, you might be able to hit it
with a pressure washer,
or fabricate something that will fit inside each leg...and fit onto a pressure
washer. IF you use
the rotating brush, you may just tear off zinc left and right, and make things
worse in the process.
Then pour in a ton of cold galvanizing from a 1 gal container. If you capped
off the bottom legs
1st, then poured it in the top legs, then capped off the top legs, then
balanced it on a single
saw horse, you could pivot it like a teeter-totter..and get it fully coated
really good. Then
roll the tower onto another face, then repeat.
Then open off the 3 x caps on the bottom, one at a time, and let any excess
drain into a container.
Now I can see why solid legs are popular. Pi-rod uses em.
Trylon also makes a 10' tower section,
18" wide, but 129 lbs per section, solid legs, and stronger than 65G. 7/8"
solid legs..and 1/2"
solid bracing. Not cheap though. I have never seen one. The way the
connections bolt together
looks slick though. A single 5/8" A-325 bolt [6" long] for each leg, via a
welded spigot. Just
2 x hollow tubes welded to the tower legs, one at the bottom of the upper
section....and the 2nd one
is at the top of the lower section. 6" bolt just drops in. The solid legs
butt against each other. I have seen
that exact splicing technique years ago, at one of our telco sites, on a 26"
wide tower. It makes
for a fast assy.
I have also see towers, like rohm 65G, where square plates are welded to the
bottom of each leg, and
4 x bolts join the 2 x plates. A drain hole is on each leg, facing the inside
of the tower. Seen these things
get plugged up, fill with water, then split wide open when it freezes, what a
mess.... with a 16" rip right
up the leg. The tower engs finally said screw it, and went to solid legs...or
angle legs. Angle leg towers
were either 60/90 deg..and of course either 3 or 4 sided. On 4 x sided towers,
8 x guy wires were used per level,
2 x per face. They don't budge, and no star [TQ] bracket required. Some of
these installs are on mtn tops,
or way out in the bush, or on small islands etc. They only get inspected 1-2
per year, wx permitting. That
orange/white paint only last so long too.
later.... Jim VE7RF
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