Boiler plates are ordered from the rolling mill as flat plates. Their dimensions are determined from the drawing of the boiler, and the plates ordered should be near their finished dimensions, leaving a margin of about once the thickness of the plate to be trimmed off around the edges. The trimming of this margin by chipping or planing removes the strained metal along the edges caused by shearing the plate at the mill.

A few days before a plate is needed for laying out, it is selected from stock and pickled to loosen scale and to expose the clean surface of the steel. Pickling is done by immersing the plate on edge for about 24 hours in a wooden vat containing about 5% of hydrochloric acid in fresh water. When lifted out the plate is scrubbed and rinsed with clean water made slightly alkaline with lime to remove all acid.

A careful record of each plate, giving dimensions, weight, and data of its manufacture and tests, is furnished the master boilermaker. This record enables the selection of the particular plate intended for a certain place in the boiler.

Laying out consists of transferring to the clean surface of a plate the dimensions and lines shown by the laying-out diagrams and the original drawings. The location of lines and boundaries is marked on a plate by scribed lines and by center-punch marks.