Need a book? Engineering books recommendations...

Return to index: [Subject] [Thread] [Date] [Author]

Re: SE Grassroots Effort at Change (WAS: Field welding)

[Subject Prev][Subject Next][Thread Prev][Thread Next]
Ah, yes.

But the problem was that I didn't know anything about these kinds of special steels in 1966.   I was so naive that I thought the only steels available were the one's in the steel handbook!   It wasn't until later when I had to make things out of T-1 that I started really looking at pre-heat, delamination and other steel problems.

My first real brush with a failure using an "exotic" steel was the design of a C-clamp fixture for lifting curve precast girders for the freeway overpass near 6th street in San Francisco.  My employer had farmed out the design  to a very reputable civil/mechanical engineer.   There was a long rod called out on the drawings and it was to be A325.  A325 doesn't come in rods (didn't know that then) and the fabricator up in a little northern California town substituted Stressproof, which included welding a clip to the rod, without telling anyone.

Subsequently during the actual use of these C-clamps (one crane at each end of the curved girder to make the pick and set the girder), one of the C-fixtures broke and the curved girder rolled over into a "horizontal" or weak axis attitude.  I'm in the office in Oakland and the phone call comes through to me asking what to do?

My response:  "Put it on the ground".   Of course this breaks the girder.  But the alternative is for the girder to break in the air and the booms on both machines come flying back into the operators cabs.  You know, those little boom stops are not really worth anything for really stopping the boom.

This experience started my delving into all the other steels available and the pluses and minus of which steel to use in the different situations.  What inspections are required?  Heat treating? What welding procedures are required?"   Certification of the welders, i.e. materials, pre-heat, positions, mill certificates, material identifications, etc.   One important thing, being able to inspect the connections at any time; remember, some pin and shaft connections for some structures might be hidden and no one knows it condition until it breaks.  A certain hydraulic crane manufacturer made thousands of these cranes until at one of them killed a worker in San Jose when it came flying apart!

I still don't know all about the hundreds of different steels available - it wasn't until about two years ago that I learned about A354 bolts when I was in a quandry to make flanges connections work on a 426 foot free standing flagpole.   Harold Sprague came to my rescue on that one.  

Enough.  I still don't like field welding unless I have special inspection, I know the actual welder is certified for the actual welding he is doing, that I have the mill certificates and somebody else signs off on the whole thing!

Neil Moore, S.E.


At 12:15 PM 9/9/2005, you wrote:

On Sep 9, 2005, at 1:49 PM, Neil Moore wrote:

Part of the problem was that the mast was made of "spun" steel and had a yield around 130 ksi.  (Probably Stressproof).  No one checked the chemistry.
You don't need to check chemistry with 'Stressproof.' The trade name means 'not weldable.' You can melt the edges and they'll stick for a while, but it only takes a few load cycles to unstick them. I used to get the 'we weld it all the time and we've never had any problems' argument, which was true only if a problem means something that happens before shipping.

Within about two weeks, I was working in another S.F. office and my old employer is no longer in business.
That happens to us troublemakers, doesn't it?

Christopher Wright P.E. |"They couldn't hit an elephant at
chrisw(--nospam--at)skypoint.com   | this distance" (last words of Gen.
.......................................| John Sedgwick, Spotsylvania 1864)
http://www.skypoint.com/~chrisw/


******* ****** ******* ******** ******* ******* ******* ***
*   Read list FAQ at: http://www.seaint.org/list_FAQ.asp
* *   This email was sent to you via Structural Engineers *   Association of Southern California (SEAOSC) server. To *   subscribe (no fee) or UnSubscribe, please go to:
*
*   http://www.seaint.org/sealist1.asp
*
*   Questions to seaint-ad(--nospam--at)seaint.org. Remember, any email you *   send to the list is public domain and may be re-posted *   without your permission. Make sure you visit our web *   site at: http://www.seaint.org ******* ****** ****** ****** ******* ****** ****** ********