FOREWORD: These specifications were prepared by the Committee on the Standardization of Oil Field Boilers. The Committee@ in formulating these specifications@ has endeavored to reduce the number of sizes of boilers now in use and to provide for interchangeability of the necessary fittings on boilers of equal horsepower. It will be noted that these specifications provide for the following: 1. A. P. I. Standard Boilers must meet the A. P. I. Specifications and must also be built in accordance with the A. S. M. E. Boiler Code. 2. The chemical and physical properties of materials used in the manufacture of A. P. I. Boilers are the same as specified for A. S. M. E. Boilers. 3. These specifications provide a standard method for computing the horsepower rating@ which enables the purchaser to make comparisons on a uniform basis. 4. Complete interchangeability is provided for stacks and fittings. Purchasers are urged in their purchase orders to specify that their boilers be manufactured in accordance with A. P. I. specifications.