Updated: Jun 29, 2022
Corrosion Under Insulation or CUI is one of the common problems across the industry. CUI is known to be a hidden enemy and is the result of poor design and maintenance of the insulation system. It is also a fact that CUI cannot be eliminated, but can only be minimized through effective implementation of insulation design, installation, and maintenance.
Insulation system design is one of the important considerations that minimize almost half of the CUI possibilities. This article is helpful in understanding the basic strategies that may be followed to design and maintain the insulation system to reduce the risk of CUI.
Purpose of Insulation
Insulation, or rather thermal insulation, is a term for a variety of materials used to reduce the transfer of heat. Thermal insulation is used everywhere from crude oil extraction, transportation, and storage to refining.
While there are a number of reasons for using thermal insulation, some of the most common are listed below:
Process control, since insulation can provide more accurate control of process temperature
Saving energy by restricting or resisting the heat transfer.
Inhibiting freezing, where the insulation prevents the freezing of unheated surfaces.
Reducing noise to prevent noise pollution
Protecting personnel from injury through contact with hot or cold surfaces.
Preventing condensation on surfaces conveying fluids at low temperatures
The 4 Parameters to Design and Maintain the Insulation System
For a thermal insulation system to work effectively, the system must have the following 4 insulation system design and maintenance parameters:
Proper designing of the insulation system and the insulating item
Well-written insulation specification
Skilled craftsmanship for the insulation installation
Inspection and maintenance program during plant construction and operation
Specify the Right Insulation Material When Designing the Insulation System
A refinery or industrial process plant requires its mechanical systems to insulate for several reasons like heat conversation, process or condensation control, and more. However, the insulation system designer and/or specifier must be able to determine the right insulation material for the system to fulfill the desired requirements.
Common Problems that Come from Piping and Equipment Design
Protrusions—which are often a result of poor designs of piping or equipment—are one of the major causes of corrosion under insulation (CUI). These protrusions break the jacketing continuity and provide a path to ingress the water or moisture into the installed insulation system.
We often seal the breaks in the jacketing with the use of caulking or mastic, but remember that the caulking is made of organic materials, and are subjected to a harsh environment. Over a period of time, the caulking breaks and the water gets its path to the installed insulation.
For the best results, what the designers can do here is minimize such protrusions for the sake of CUI prevention.
Responsibilities of the Specification Writer (Specifier) and/or Insulation System Designer
A project’s insulation specification must be complete and detailed. Improperly or poorly written specifications with insufficient or incomplete descriptions of materials and application requirements may have adverse effects.
Specifically, poorly written specifications may result in expensive repairs during construction and/or after the plant is operational.
The specifier must understand the thermal insulation requirements of every mechanical system (piping or equipment) in the project, and consult the insulation manufacturers to decide on the insulation materials to be used for the project.
The specifier must write the specification with all the necessary information and requirements to carry out the insulation installation and quality control/assurance tasks following the manufacturer's instructions and the industry's best practices.
Importance of Hiring Skilled Workforce
Insulation installation in accordance with the project insulation specification is essential. An unskilled workforce can install the insulation system that can have gaps between the insulation joints allowing heat to easily pass through.
Similarly, improper water-shedding and sealing during jacketing installation are one of the key problems that cause Corrosion Under Insulation (CUI). There are instances where the unskilled workforce used screws for the jacketing securement of cold insulation systems, that punctured the vapor barrier and caused condensation to start.
So to carry out the insulation installation and maintenance work and/or to get rid of the above problems, the insulation specification must include hiring an experienced and skilled workforce who have been trained to the tradesmen level. The workforce must have sufficient education to read and understand the specification and relevant drawings, and are familiar with the insulation systems, materials, and their proper installation/use.
Don't Let the Insulation Inspection Carried Out by an Untrained Inspector
For the insulation inspection and quality control/assurance work, a project insulation specification must clearly include hiring trained and certified insulation inspectors. The inspector must have sufficient training and qualifications to ensure the thermal insulation and accessory materials used for the work meet the specifications.
The certified insulation inspectors acquire the inspection skills specifically in the thermal insulation work field and carry out the insulation inspection work systematically. The inspectors verify and confirm that the insulation installation complies with the specification by inspecting each phase of the insulation work according to the project's ITP.
Importance of Periodic Maintenance of the Installed Insulation System
An installed insulation system must have a maintenance program. It is necessary to appoint a dedicated team of skilled professionals for regular inspection and monitoring of the insulation system installed on the piping or equipment.
A periodic and regular inspection helps identify problems and early signs of failure due to CUI. This is the duty of the maintenance professionals to account for any staining on the jacketing immediately, as this can suggest moisture under the jacket.
The maintenance professionals are responsible for reporting all identified problems for repair. The reposted problems must be addressed as soon as possible in order to determine the appropriate repair method. All damaged insulation that was reported must be repaired as quickly as possible to reduce the CUI spread and/or possibilities.
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