Analysis of Corrosion Pitting by Extreme-Value Statistics And Its Application to Oil Well Tubing Caliper Surveys

Abstract

A detailed account is given of how extreme-value statistics can be applied to the analysis of depths of corrosion pits. Particular attention is given in this connection to pitting in oil well tubing as measured by caliper surveys. It is shown how pit depth data may be sampled and abstracted to give predictions of the expectation of deep pits and of perforation. The methods are illustrated by evaluation of the effect on pit depths of certain factors (i.e., upset ends and depth in well). A special graphical method has been developed for analysis of tubing caliper surveys and related pit depth surveys; this is known as the Pit Depth Rank Chart. Detailed directions are given for its use. This chart takes into account the normal occurrence of the deepest attack toward the top of the tubing strings, but is also suitable if this does not occur. 2.1.1