Inspectioneering
Inspectioneering Journal

Portable Pipe Wall Thickness Measuring Technique

"CUI Exposed"

By Joseph E. Pascente at Lixi, Inc.. This article appears in the January/February 1999 issue of Inspectioneering Journal

Introduction

One of the greatest challenges facing many of the process industries, namely the petrochemical, refining, fossil power, and pulp and paper industries is how to effectively examine their insulated piping.

While there are a number of failure mechanisms involved in various process piping systems, piping degradation through corrosion and erosion are by far the most prevalent. This degradation can be in the form of external corrosion under insulation (CUI), internal corrosion through a variety of mechanisms, and internal erosion caused by the flow of the product through the pipe.

Refineries, chemical plants, and electrical power plants have MANY thousands of miles of pipe that are insulated to prevent heat loss or heat absorption. This insulation is often made up of several materials, with the calcium-based material being the densest. The insulating material is usually wrapped with an aluminum or stainless steel outer wrap.

What is CUI?

The increase in corrosion failures under thermal insulation has made this topic a major concern for petroleum, chemical, food processing and many other types of industrial operations. Energy conservation has expanded the use of thermal insulation to reduce energy loss and associated costs in applications involving heating and cooling of process equipment. Since insulation covers the metal surface it can allow degradation to proceed, unseen, which unfortunately in many occasions results in serious consequences.

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