Need a book? Engineering books recommendations...

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

Re: Welds

[Subject Prev][Subject Next][Thread Prev][Thread Next]
On 12/30 Tom Harris wrote:

>      There is an interesting L.A. Times article on welds today ( Mon,
> 12-30-96) on the front page and two other pages ( 2 1/2 page article ). It
> says Mr. Fisher warned against using E70T-4 electrodes at a L.A. seaoc
> conference in Sept. '94 but i can't remember it. If E70T-4 is what has mainly
> been used in the past and is not recommended, then what is recommended in its
> place?

Engineers should not call out specific electrodes for their projects. 
The selection of an electrode is really the fabricator/erector's 
responsibilty.  Selection depends on the weld process to be utilized 
(e.g. SMAW, FCAW, SAW, etc.), the  procution conditions, the 
position that welding will be done in, the materials being welded, 
and the qualifications of the welders who will do the work.  Much of 
this information is available to the engineer.

Instead, the engineer should specify welds on a performance basis.  
Specifically, strength (as given by the ultimate tensile of the 
deposited metal - 70ksi is usually specified for building structural 
purposes), toughness (if required) in terms of a rated Charpy V-notch 
value for the deposited metal at a specified temperature (20 ft-bl at 
0 deg. F should be considered for critical applications in most 
building applications).  

The engineer should require that the Fabricator/Erector provide a 
Welding Procedure Specification for approval, prior to performing any 
work.  The WPS will call out the electrode type, as well as the 
various welding variables including - position, voltage, current, 
interpass temperature, preheat temperature, etc. required to acheive 
the requried performance.  The WPS should be accompanied by the 
product data for the proposed electrode, which will indicate the 
rated performance of the deposited material, and the variables for 
which this performance can be obtained.

For more information on this please refer to the SAC-FEMA-267 Interim 
Guidelines document.  You will find Chapter 8 particularly helpful.  
Also, SAC is about to publish a volume of Background Reports that 
includes a 120 page paper on structural welding.  It will tell you 
all you wanted to know about welding, but were afraid to ask.

By the way, there is currently ongoing litigation, pertaining to  use 
of E70T4 electrodes.  The L.A. times article was spurred on by this 
litigation and an attempt by one side in the case to press its point. 
All "technical" information presented in the article should be read 
with that knowledge in mind.

However, the fact is that E70T4 material does typically result in 
very low toughness.  The use of low toughness metal is not 
recommended by SAC for welds subjected to large cyclic demands, such 
as the full penetration welds of moment connections.

 
Ronald O. Hamburger
Project Director for Product Development
SAC Joint Venture