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If you've looked at a conventional Vulcan, Conmaco or Menck air/steam hammer package for offshore use, you've noticed the hammer is surrounded by the leaders, which align the hammer to the pile. But what if the hammer could be self-aligning?
In 1968 offshore contractor McDermott Inc. wanted to find out just that, and commissioned Vulcan to develop the Internal Pile Hammer. The prototype (shown at right, in Vulcan's Chattanooga facility) was relatively small, with only a 16.7 kip ram in an era when 40 and 60 kip rams were becoming commonplace offshore.
In addition to simplifying the hammer assembly, eliminating the leaders reduced the weight at the top of the pile. Since most offshore piles were on a batter (angled,) this would reduce the cantilever bending moment the hammer assembly induced in the pile, thus allowing for longer add-on sections and less welding in the field. (This is the rationale behind Offshore Tip 22, which locates the centre of gravity for the hammer assembly.)
The hammer (which looked suspiciously like the automatic drafting erasers in use at Vulcan during the era) used a stabbing cone at the bottom of the hammer, which could be fitted with cones of various diameters to mate with the inside diameter of the pile. Also mating with the inside diameter of the pile were the steps, at the top of the white area of the hammer. The pile top seated at the horizontal faces of these steps and the two points of contact with the I.D. of the pile aligned the hammer, thus eliminating the need for leaders.
The concept was great, but the hammer's downfall in actual use was the division at the bottom of the black portion of the hammer. (Click here for the field service manual for the IPH-16, which shows this and the hammer construction in more detail.) Originally Vulcan wanted to use a one-piece cylinder, but foundry limitations forced the two-piece configuration. The uncushioned blow (another step from a conventional Vulcan hammer) insured that the two pieces would not stay together.
Vulcan obtained a patent on the design, although McDermott never pursued the concept further after the unsuccessful field trials. The alignment concept would reappear on the Sea Water Hammer, whose own patent ran into the IPH's patent.
Today most of the hydraulic hammers used offshore use an external guide and dispense with the leaders in this way. Had the IPH succeeded, it would have revolutionised (for McDermott at least) the Vulcan product line and lengthened the undisputed reign of steam hammers offshore.