I'm not sure of what you mean by "open butt with inside splice plate".

The standard details for some of the state DOT's is to provide a single bevel (45 deg), welded from both sides with backgouge (B-U4b).

E6010, E6011, and E7018 separately or in combinations, are often used. Self shielded FCAW is also used for field splices.

I have also seen piles spliced using backing bars on the inside profile
(B-u4a) Sometimes the backing bar is fillet welded to prevent peel back

Sometimes a rat hole at the web/flange intersection is needed, but very often the rat hole is not required.

Another common method is to use commercially available pile splicing shoes, similar to pile tips, that only require square ends and are joined by fillet welds.

Most jobs specify what is needed. I would check out the contract specs to make sure your method is in compliance. It could be a bugger to rework a splice on a driven pile.

Chet Guilford

A word of warning.
Apart from the welding specification (position, electrodes, preparation etc.) you should take also into careful consideration the welding sequence, in order to prevent warpage of the pile.
Giovanni S. Crisi
Sao Paulo - Brazil