The definition of a weld defect is "Any weld irregularity that measures beyond the acceptable limits of a defined criteria".
As an OEM, you have the option of writing your own criteria, or adopting other standards.
Other standards come in a myriad of different requirements meant to adapt to a myriad of differing circumstances.
So, on size does not fit all. GMAW weld quality standards for building fences are much different than those for building submarines, etc.
As you're making agricultural sprayers, I recommend taking a look at AWS D14.3 -
Specification for Earthmoving, Construction and Agricultural Equipment.
http://pubs.aws.org/p/1039/d143d143m2010-amd1-specification-for-welding-earthmoving-construction-and-agricultural-equipmentThis will provide weld criteria applicable to your product.
Tim