the first pass in a joint is called the root pass and is typically the most difficult to make. Subsequent passes are called fill passes. Final passes are called cover passes and determine the profile of the weld face.
Designing larger welds will result in more passes, as will the use of smaller weld electrodes.
The greater the number of passes, the more heat is put into the metal, resulting in increased distortion, residual stresses, and a possible loss of strength in the base metal.
Use of larger electrodes will decrease number of passes, but also requires a welding machine with enough output capacity.
