Specifies requirements and criteria for the periodic inspection, repair and alteration of in-service boilers, unfired pressure vessels, associated control and safety equipment, and piping. Criteria are given for the selection of intervals between internal and external inspection of boilers, pressure vessels, and piping. Criteria for the assessment of defects and deterioration are included. Guidance on repairs, modifications, and re-rating are given. Provision is made for owners to carry out statutory inspections.