[TowerTalk] galvaniizing heat treated steel

[Jim Lux]

On 12/28/12 10:28 AM, SPWoo wrote:
> Good questions Jim.  I called the tube supplier and they told me the
> tube is stress relieved but not quenched as in traditional heat
> treatment.  The 'SR' designation in the description denotes stress
> relieve.  I did a google on 4130 stress relieve and it appears it's done
> at about 1200F.  Hot dipped galvanizing is done at 830F.  I did some
> research on galvanization of high strength steel and it appears that the
> process is highly dependent on the chemical composition of the steel.
> Steels with yield strength higher than 150ksi encounters
> 'hydrogenembrittlement'.  To get an answer on this from an expert I sent
> an e-mail to a person at the American Galvanizers Associastion at the
> recommendation of my galvanizing supplier.  My galvanizing supplier uses
> the same process for all steels with yield strength less than 150ksi.
> For steels more than 150ksi they use a different process.
>


Very interesting.. so it's very much a matter of making sure that 
everyone involved knows what's going on.  That is, you wouldn't want to 
take that tubing down to Bob's Corner Galvanizing and tell them "throw 
it in the tank with the rest of the stuff"


> You are correct if some of this is overkill.  In my case I do get a lot
> of wind here and I'd rather be safe than sorry.  Another local ham lost
> an antenna with the same mast that the 4130 replaced. That mast is the
> M15R sold by US Towers.  The material for that mast is low carbon
> structural steel with a yield strength of only 36kpsi.  For me it's
> better safe than sorry.  73.


Exactly... for a few hundred dollars on a $10,000 installation, it might 
not be worth agonizing..

And, going to 120ksi from 30ksi would double the "wind speed rating" of 
the system.  I'm not sure, in fact, that you could even get the same 
failure load on a solid 2" bar of 30ksi as you could with 1/4" walls of 
120ksi: the middle just doesn't carry that much of the load.

In fact, I just ran a simple calculation.. a solid 2" bar is only about 
bit more than twice the strength of a 2" OD tube with 1/8" walls of the 
same material.  For 1/4" walls, you only pick up 60% by going to solid.

There's more to be gained by going bigger in diameter and thinner walls.