Yes there are. For example in spanish code NBE EA-95 presently vigent for steel structures table 5.2.3.A lists maximum and minimum values of throat (derive multiplying ·sqrt(2) leg size for orthogonal welds) for fillet welds depending upon thicknesses of parts being joined. Not complete for jumbo plate (goes to 36 mm plate thicknesses) but good for common and proportional or so sizes can be inferred for thicker.

US minimum size limits upon thickness I have for example in Table 2.17 of Gaylord, Gaylord and Stallmeyer's Design of steel structures 3d ed, p. 85. Other codes (AWS?)may be providing the maximum value you are searching for.

From the ref above GGS maximum size of fillet weld per AWS along edges of material 1/4 in or more thick is 1/16 in less than the thickness, and even the thickness is permitted if required by strength.

For material less than 1/4 in thick, the thickness is the maximum size.

I would simply call one of my local steel fabricators and speak to one of their engineers or welding superintendants.  They usually have a wealth of experience in these matters.

I agree with JAE, call the local fabricator.  In the end he's the one who will have to deal with it.  Also keep in mind that some welding features are also constrained by inspection methods.  And the larger the weld the less can be discerned in earlier weld passes.  Anyway, you might wish to bring this up as well.

In the absence of any rules or regulations, it depends entirely on the load the weld is to carry.  

www.gowelding.com ; contains lots of useful information on calculating the strength of fillet weld attachments.

There is a recent newsletter article on welded girders on
http://www.topica.com/lists/Structuraldzine/read

This might answer some of your questions.