[TowerTalk] how much rust is too much?

Matthew Kaufman matthew at matthew.at
Thu Oct 16 21:17:43 EDT 2014

On 10/14/2014 1:40 AM, Roger (K8RI) on TT wrote:
> On 10/13/2014 11:45 PM, Matthew Kaufman wrote:
>> On 10/13/2014 8:37 PM, Tim Duffy wrote:
>>> Hello Matthew:
>>> What is the center to center distance of the legs? It could be Rohn 
>>> 25 - not
>>> model 45 from the photos.
>> If my notes are right, I measured it at about 17 inches, and the 
>> joints are like Rohn 45 joints, not swaged joints.
> I installed 100' of 45GT. It used swedged joints, just like the 25G 
> only larger.  The solid leg 45Gs use a circular flat plate joint. It's 
> about 3" in diameter IIRC, but it's been a long time since I saw one.

Went and re-measured. Almost certainly is Rohn 55. 17 inch faces, 1-1/2" 
legs, welded sleeves and bolted.

> Look for pits after removing the rust.  Be extra cautious if there are 
> any pits large enough to notice.  There are ultrasonic thickness 
> gauges for measuring the tube thickness.    I used to measure a lot of 
> pipes and tanks, even with epoxy paint on them. If there are ANY pin 
> holes in the tube or welds, you will need an auxiliary base to hold 
> the tower, or a big crane.. A job for professionals.

It is starting to clean up pretty well, but there's a bit of pitting 
where the worst of the rust was... no pinholes and nothing deeper than 
this though. Photo of a mostly cleaned section here: 

Except for the pitting, the diameter is within 0.2mm of the non-rusted 
(and still galvanized) diameter after cleaning according to my caliper.

Matthew Kaufman

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