Abstract:
INSPECTION TECHNIQUES FOR DETECTING CORROSION UNDER INSULATION

by Michael Twomey
CONAM Inspection Inc

TABLE OF CONTENTS

Introduction When does Corrosion Under Insulation occur? Systems susceptible to CUI Alternative Inspection Methods Profile Radiography, Ultrasonic Thickness Measurement, Insulation Removal, Infrared, Neutron Backscatter Real-Time Radiography Performing the Inspection Results Limitations Real Time Radiography uses to Locate Piping Components for Positive Materials Identification Programs References

INTRODUCTION

Corrosion under insulation (CUI) is real threat to the on stream reliability of many of today's plants. This type of corrosion can cause failures in areas that are not normally of a primary concern to an inspection program. The failures are often the result of localized corrosion and not general wasting over a large area. These failures can tee catastrophic in nature or at least have an adverse economic effect in terms of downtime and repairs. The American Petroleum Institute code, API 570, Inspection, Repair, Alteration and iterating of In-service Piping Systems, the piping code first published in June 1993, identifies CUI as a special concern. Typically, as happened with API 653 and the Clean Water Act, the API codes become an industry standard, and theregulations demand that organizations maintain a program to meet that standard. OSHA 1910 is the rule with the teeth in this case.

CUI is difficult to find because of the insulation cover that masks the corrosion problem until it is too late. It is expensive to remove the insulation, particularly if asbestos is involved. There are a number of methods used today to inspect for corrosion under insulation. The main ones are profile radiography, ultrasonic spot readings, and insulation removal. The other method now available is real-time X-ray. Real-time X-ray has proven to be a safe, fast and effective method of inspecting pipe in plant operations.