Corrosion Under Insulation : Management Using Risk-Based Inspection Approach

Corrosion under insulation is the cause of many of the process industry’s most pressing problems. These problems include forced shutdowns, lost productions, early repair and replacements, and other safety and environmental consequences – resulting in billion dollars worth of capital loss and additional money which could be spent productively elsewhere.

The US Chemical Safety Board (2008) reported that “The highest incidence of reported leaks in refining and chemical industries are due to CUI and not to internal process corrosion.” This means that there is a higher chance of piping leaks due to localized, external corrosion within the piping insulation in comparison to the inner piping. Industry data suggests that 60% of pipe leaks are caused by CUI– with 81% of pipe leaks occur within pipes smaller than 4 inches. With the cost of CUI is 40%-60% of the maintenance budget.

It is critical to note that corrosion under insulation is responsible for up to 60% of incidents, and the amount to which CUI has cost industries is an estimation of $276 billion in 2005.

Besides the cost of correcting CUI, this would lead to questions of why is it a growing problem within the industry? And what are the challenges that businesses face with CUI?

1. Challenging to detect

Generally, corrosion-under-insulation tends to remain undetected until the insulation and cladding are removed for inspection, or when leaks occur- such visually, this cannot be detected during routine inspection.

2. No published performance data for new coating and insulation innovations

CUI failure patterns can generally take 10 to 20 years for it to emerge on facilities and nurtures confidence to reduce inspection costs significantly.

3. Difficult to confidently predict CUI

This type of corrosion is often difficult to predict. It is noted as even more challenging without the removal of insulation. Such, there is no sure-fire way to be able to provide a confident prediction or forecast on when CUI will occur with an asset.

4. Removal of insulation is still considered as the most reliable method

It is still widely believed that the removal of the asset’s insulation or visual inspection is still the best way to detect CUI as the entire surface is inspected. However, this can be very expensive as it requires plant shutdown, insulation would need to be replaced, it is quite time consuming, and relatively intrusive.

5. NII techniques may not be reliable and as cost-effective

Non-Intrusive inspection allows for the examination of assets with little interruption to the processes. Despite this, however, several Non-Intrusive Inspection techniques and technologies may not be considered as reliable or cost-effective as the removal of the insulation.

So what is the solution?

A Risk-Based Inspection (RBI) approach is used to identify highly vulnerable equipment that may be subjected to CUI, manage critical inspections, and generate an inspection plan to mitigate risks. This is integrated when developing your asset’s CUI inspection plan.

Step 1: Review of current plant status

This step is essential for any CUI or external corrosion program. It is necessary to execute a rigorous review of the plant’s current conditions to identify factors such as incident rate, potential incident rate, possible impact(s), and financial performance of the plant. One of the critical drivers of ensuring continuous management support is to showcase the essential benefit of this process and investment of this program into the facility.

Step 2: Screening

Due to the dramatic increase in energy costs, it has been encouraged for industries to conserve process energy and reduce excessive unnecessary? use of thermal insulation to fight against CUI.

There is a four-phase process that allows users to determine the continued use of thermal insulation on the process equipment vulnerable to CUI. This includes (1) determining the material type and operating temperature range, (2) evaluating the purpose of the insulation system, (3) understanding the process environment, and (4) ascertaining the consequences and probability of removing the thermal insulation system.

Step 3: Executing the Risk-Based Approach

This methodology engages in the use of consequences of failure and the probability of failure to estimate the overall risk of failure. Traditionally, the likelihood of failure is extracted from the corrosion rates. However, the probability of failure for CUI is challenging to determine due to unspecified corrosion rates. Factors such as operating temperature and external environment (wetting extent and frequency) are essential and should be taken into consideration. A number of approaches can be done in order to perform these assessments (see European Federation of Corrosion Publications Number 55, DNVGL­RP­G109, and API RP 583).

Steps such as assessing the consequence and probability of CUI failure and susceptibility factors will lead to the overall risk of CUI failure.

Step 4: Develop Inspection Plan

The final step is to link the determined risk class to the necessary and appropriate inspection and maintenance strategy.

Here at Cygnus Asset Solutions, we provide asset integrity services through the use of several assessments, such as the RBI Approach, to mitigate CUI. Our RBI approach is based on the methodology and recommended practice of API RP 583.

We also proudly present AXIS – the ultimate asset management software that provides automated live reports allows ease in asset data collection, and analyses asset conditions and risks, all in one database.

References

Winnik, S.. European Federation of Corrosion Publications Number 55, Corrosion Under Insulation (CUI) Guidelines. Cambridge: Woodhead Publishing Limited

DNVGL­RP­G109. “Risk based management of corrosion under insulation.” Recommended Practice.

API RP 583. “Corrosion Under Insulation and Fireproofing.”

Technology Leadership Board. 2016. Asset Integrity Theme Landscaping Study. United Kingdom: Technology Leadership Board.