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Inspectioneering Journal

Managing the Integrity of Insulated Equipment: The Right Non-Destructive Examinations

By Ana Benz at IRISNDT, Michael Townsend at IRISNDT, and Fadi Basma at IRISNDT. This article appears in the September/October 2018 issue of Inspectioneering Journal

Introduction

Corrosion under Insulation (CUI) has been occurring since we started insulating equipment.  However, most of the CUI reported until the ‘70s developed in stainless-steel due to stress corrosion cracking. At that time, with limited insulation, carbon steel equipment did not develop significant CUI.[1] Since then, carbon steel piping, tanks and vessels have been more frequently insulated to save energy costs and add personal protection, leading to more opportunities for CUI to develop.

CUI is a common problem for refineries, petrochemical, offshore and onshore facilities, power plants, chemical plants, and fertilizer plants.  One might think of CUI as mainly a problem next to a marine environment, but this is not always the case. CUI can happen in dry industrial sites as far away from the sea as the Canadian prairies (see Figures 1 and 2).  Once equipment is insulated, the location of cooling towers, leaking heat tracing, rain, atmospheric humidity, moisture from melting snow that saturates insulation, and other leaks/steam impact CUI.

Figure 1. Horizontal Coated NPS 14 0.375-inch-Thick Pipe Which Leaked Due to CUI after 4 years of service.
Figure 1. Horizontal Coated NPS 14 0.375-inch-Thick Pipe Which Leaked Due to CUI after 4 years of service.

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