PREFACE This chapter is one of a series which make up the manual@ Guide for Inspection of Refinery Equipment.It is-based on the accumulated knowledge and experience of engineers of the petroleum industry. All users are invited to submit suggested revisions to the Director of the Division of Refining@ American Petroleum Institute@1271Avenue of the Americas@ New York@ N. Y.10020. The information contained in this publication has been arranged in its present form as a means of facilitating continuity of presentation and convenience of reference. It does not constitute@ and should not be construed to be@ a code of rules@ regulations@ or minimum safe practices. It is not intended that the practices described in this publication supplant practices that have been proven satisfactory. Nor is it intended that this publication discourage innovation and originality in the inspection of refineries. Users of the publication are reminded that no book or manual is a substitute for the judgment of a responsible engineer.