The alignment of boiler should incorporate provisions for thermal expansion at the boiler feet (saddles) when the boiler is in hot operating condition. Expansion may be in the order of 10mm. Assuming a fourpoint support; one foot will be bolted down hard to the foundation, while the other three feet will be bolted down so as to permit the feet to slide. Holes for the fixed bolts will be reamed in place. The foundation bolts in way of the sliding feet must be accurately located with respect to the elongated holes in the boiler feet to enable the feet to slide clear of the bolts. The pipe sleeves prevent the bolts from tightening down on the sliding feet. A brass liner or a lubricant such as molybdenum disulfide is normally used to facilitate the sliding action. In some cases, the pipe sleeves
are not used. Instead, the bolts are tightened only slightly so that the boiler foot can slide.
