The state DOT's that I have worked with in the past few years typically specify 12-inch or 14-inch nominal diameters. Wall thickness will vary, depending on load and anticipated driving stresses, but usually 1/4 to 1/2 inch.
I was involved with a project up until about a year ago where they were planning to use 18-inch pipe piles for bridge foundation elements in sand (under the Mississippi River).
