[TowerTalk] A near imminent TX-455 failure (Bob Shauger)

K8RI on Tower talk k8ri-tower at charter.net
Mon Nov 14 15:40:53 EST 2005

> I guess I have a different take - looking at the pictures and having
> reviewed these sorts of failures for years in the aerospace industry.

You 're dealing with different materials and much lower grades though.

> The legs (not the welds) have broken at the point where the side plates

I'd really need to have the piece in hand to inspect, but to me (and I've 
seen this in towers and tube welds before) that is the end of the leg, not a 
break.  The weld was stuck to the bottom piece, but only formed a barrier 
around the leg.

It appears to me that basically those legs were never welded to the base 
with much more than a tack, if that.

This is an easy weld to make, but a novice will usually be afraid to apply 
enough heat to the thin tube.  They get a tad gunshy after bloing holes 
through thin stuff and this is old enough it may have been stick welded.

Today's MIG and TIG welders make welding thin stuff a breeze, but it still 
takes skill to weld thin tube to 1/4" stock at those hinges. I regularly 
weld 16 ga sheet steel as well as relatively thin wall tuve with a MIG. 
With a TIG it's fairly easy to even weld thin Aluminum

> are welded to the legs.  Also, the failures show no sign of ductile
> deformation - note how sharp the cracks are.  Also, the failures have
> occurred at the point of maximum applied tensile stress to the leg
> members.
> This looks like a classic hydrogen embrittlement failure of the legs.
> http://www.corrosion-doctors.org/Forms/embrittlement.htm
It still looks like a poor weld job to me.

Roger Halstead (K8RI and ARRL 40 year Life Member)
N833R - World's oldest Debonair CD-2

> A few thoughts:
> - The third leg will likely fail the same way, at any time.
> - This is fixable - the legs need to be realigned and backing stock
> welded in place by a professional.  All three legs!
> - The rest of the tower is suspect, but the failures have occurred at
> the point of maximum applied tensile stress - as you move up the tower
> the loads get smaller and the chances of a hydrogen embrittlement
> failure go down.  The rest of the tower may be okay.  It should be
> THROUGHLY inspected - every leg and tubing weld as a bare minimum.
> - It is difficult to detect cracks with the eye and impossible to detect
> hydrogen embrittlement without very sophisticated equipment.  Applying
> some side force with a pry bar may be the best you can do
> inspection-wise.
> - It is quite possible the manufacturer has seen this before.  Get them
> to talk to you - if they will.
> Good luck -
> Hal
> N4GG
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