single vs double v-weld

huangyhg

single vs double v-weld
we have a fabricator welding a short girder.  while the designer had indicated a single v-weld, the fabricator wants to do double v.  pros and cons??  help would be appreciated.
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double v's sometimes have more weld material required to be deposited - look at the cross sectional areas to verify ...this adds to the number of passes required and the associated costs of the weld go up.
the single v will generate a larger mass (generally) of weld (i.e. more passes will likely be required).  the larger the mass of weld, the greater the chance for poor weld quality, rework, slag clean up, and everything else associated with multiple passes.  
perhaps the fabricator thinks they can achieve the weld with say two passes (one on either side of the v), as opposed to maybe 3-5 if its one large mass from one side?
prep work should be close to the same for either method.
i try use single v myself unless the pl thickness goes past say about +10mm, then i try to stick with double v if possible.
anyone else with comments?
drw
the issues are axial shrinkage, residual stress, prep time, weld time, and amount of filler metals.  i agree with drw75, thicker sections are more economical with the double -v.  the axial shrinkage, filler metal used, weld time, prep time and residual stress created by the larger number of passes in the single-v weld  is much greater than in the double-v weld in thicker sections.  the shop is trying to minimize the amount of filler metal to be used and weld time to give you their most economic design.  
both joints can be 100% penetration connections and are interchangeable.
thanks so far - the plate is definitely thicker than 10mm.
bigh,
my dime is to remind you of the changes of the metal structure in the heat affected zone. what thickness of plate are you trying to weld?  you say that it is thicker than 10mm, anything beyond one inch (sorry i'm an imperial system user), may require preheating (something else to add to your costs) in order to minimise residual stresses due to welding.
i agree with the statement that the shop is trying to give you their most economical, yet efficient design.
double-v is a preferred choice both from the view of economy as well as structural. i specifically re  
as follow up - the plates are 32mm and 50mm thick.  
all the more reason to go for double-v. it is economical. for 50mm plates, some people even go for j-weld. that is a u like groove in place of v.
ciao.
for plates that thick you should definitely use double-v.