Pipe pile caps have been around as long as pipe piles, but mating them to a pile hammer via a pipe cap may be new to some users. The diagram above (which, as you can see, dates from 1931) shows how this is done.
The cross-section shows three diameters of pipe piles mating with a pipe cap. Pipe caps typically have steps to mate with more than one size of pipe pile. It’s also possible to drive pipe caps “flat face” (with no steps) but you lose the alignment assistance of the cap when you do.
The outer two pipes mate with “male steps,” those which face the inside diameter of the pipe. It’s necessary thus to know the ID of the pile, which usually means the OD and the wall thickness. A little clearance is allowed to make mating simpler and to take into account the fact that pipe pile isn’t always perfectly round (especially at the ends, where it gets bent.)
On the small onshore caps, the steps are typically straight. On the offshore caps, Vulcan typically put in a draft angle to make stabbing the pile easier.
With caps with multiple steps, it’s possible for the steps to interfere with each other because the diameter of one step is too small to accommodate the OD of the pile below it. To avoid this problem requires some layout before the cap is machined.
Male pipe caps can be used with wall thicknesses thinner than originally intended with the use of welded shims.
The inner pile mates with the “female” portion of the cap, i.e., the OD of the pile. This eliminates the ID mating problem but requires a completely different cap design.
Some other information is shown below.