Four basic phenomena (or characteristics of operation) are predictable, and influence the radial and axial clearances throughout the steam path. These phenomena will affect the total alignment within the stages, and at any location where stationary and rotating surfaces are close. The extent to which these phenomena influence the steam path design can be established (or predicted) by calculation and taken into consideration during the design phase when selecting and arranging "cold stationary clearances" and bearing elevations for the unit at initial assembly and subsequent alignment.

While the designer can calculate the "hot" running relationships between the stationary and rotating parts, he or she can only meaningfully define to the manufacturing and installation departments the spatial relationships, clearances, and setting requirements as they can be measured and set in the cold stationary condition. Therefore, it is necessary first to consider the types of modifying effects that need be evaluated, and then the degree to which they will influence the cold stationary arrangement of the unit. There are four predictable (and always present) phenomena, whose evaluation remains part of the mechanical design, and therefore always considered in determining the initial settings.

The influence of these four phenomena must be predicted by design, and their total effects compared on some form of clearance chart. These values must then be used to select the optimum cold setting at the various locations throughout the steam path with the final cold settings selected to help ensure "rubs" do not occur,...