ARE CORRECT CLADDING SYSTEMS THE KEY TO REDUCING CORROSION UNDER INSULATION (CUI)?
Exploring the benefits of UV-Cured GRP as an alternative to metal cladding systems
Corrosion under insulation (CUI) refers to the external corrosion of piping and vessels that occurs underneath externally clad/jacketed insulation as a result of the penetration of water. By its very nature, CUI tends to remain undetected until the insulation and cladding/jacketing is removed to allow inspection or when leaks occur.
CUI is a common problem shared by the refining, petrochemical, and power industries. CUI typically occurs on the external surfaces of insulated systems operating in a temperature range from -4° to 150°C.
This is a growing concern among facility owners and is estimated to be a $300 Billion per year problem in the United States alone and over a trillion dollars on a global scale.
There are three key components to a good CUI risk minimization program.
One component in this equation is to have the correct and suitable coating on the insulated surface.
The second component of the equation is to have an insulation system that minimizes the intake of moisture like a closed-cell foam or hydrophobic type material.
The third component of this equation, for which this paper is written, is to have a cladding system that minimizes ingress of moisture and has high resistance to mechanical damage.
Current issues with metallic cladding systems
Metals such as aluminum, stainless steel, or aluminized steel have been used as the cladding of choice over mechanical insulation systems for many years. They have provided an adequate barrier to weather, have been key components in fire protection systems, and can offer some chemical resistance in certain atmospheres. There are, however, a number of growing concerns over the use of metal as a cladding over mechanical insulation.
The biggest concern from a CUI point of view is the mechanical means by which the metal has to be attached. Typically, self-tapping screws or rivets are used to tie the metal together. At each of these points, the vapour barrier can be compromised and each penetration requires sealant, though properly addressed in most specifications, in practice this is very hard to accomplish and inspect.
Another issue with the metal jacketing is that it often relies on the strength of the insulation underneath to give it rigidity. If the insulation is fibrous or if the contour of the metal doesn’t exactly match the form of the insulation underneath, as is often the case at elbows or transitions, then metal cladding can be highly susceptible to mechanical abuse which can open up the joints.
Metal cladding systems are not ideal for dress up, pre-insulated systems or for modular designs. This is because of the tendency of the metal to easily dent or open up at the joints when transported.
Benefits of UV-Cured GRP for reducing CUI
UV-Cured GRP’s have many benefits over traditional metal cladding systems. UV-Cured GRP is a non-metallic cladding system that is a composite laminate based upon high-grade isophthalic polyester resins and chopped glass fibers.
The UV-Cured GRP arrives pre-formed and pliable for easy installation. When installed with correct adhesives the UV-Cured GRP provides an instantly tough and durable cladding system.
No mechanical attachments like screws or rivets are required to hold UV-Cured GRP in place.
UV-Cured GRP is easily modified on-site, it can be cut using standard metal cutting tools, this allows correct fitment at terminations.
High-risk water ingress points can be sealed using the un-cured GRP roll, which once cured in situ, has high adhesion strength to coated metal substrates. This provides a truly long-lasting and watertight seal.
Overlap joints are fully waterproof and can pass wash down tests from high-pressure washing or deluge system testing.
UV-Cured GRP has excellent resistance to chemical attack and when compared to most metallic cladding systems is highly chemical resistant in comparison
Fire Performance
UV-Cured GRP is ideal for fire rated areas. These systems do not drip like aluminum, and are self-extinguishing with low smoke production. UV-Cured GRP’s have been tested and have passed a variety of fire tests. Even Jet Fire ratings can be achieved when combined with products like Chartek or Favuseal
ASTM E-84 CLASS A
IMO RESOLUTION MSC307 (2010FTP CODE) ANNEX 1: PART 2 & PART 5
NFPA 274
UL – 1709 (Combination of UV-Cured GRP + Chartek or Favuseal )
ASTM E-1317
BS 476 pt 7 CLASS 1
Markets Served
These qualities make UV-Cured GRP ideal for use in harsh industrial and offshore environments such as:
LNG Plants
Refineries
FPSO
Power Plants
FLNG
Food processing plants
Chemical facilities
Mineral processing plants
Pre-insulation with UV-cured GRP
Another important area where UV-Cured GRP can help is the constructability for pre-insulated systems.
Due to its nature of being high strength, an owner can take comfort knowing that a vessel or pipeline pre-insulated and clad with UV-Cured GRP will have a lower risk of damage due to mechanical means and/or water ingress.
This is a key concern when the growing trend for today’s megaprojects is to build prefabricated modules in overseas construction yards and then ship them, often thousands of miles, to the job site. This is sure to continue as energy companies build new projects in increasingly remote destinations.
The strength and flexibility of the UV-Cured GRP is ideal for withstanding the mechanical abuse that inevitably occurs during handling, shipping, and installation of these modules. The full sealing and joint integrity is also critical as often imported modules will be quarantined and subjected to wash down procedures, this is the norm for modules imported into environmentally sensitive regions.
These two key points are integral for a pre-fabricated system which reduces CUI risk and has the included benefits to provide better schedule control and lower scaffolding costs.
Conclusions
CUI is a major long term maintenance issue that must be addressed by owners. Using the correct products at the build stage of a project would possibly increase cap-ex but could greatly reduce ongoing op-ex later in the assets life.
A key component to reducing CUI is having a cladding system that is strong enough to handle the mechanical abuse that inevitably occurs in an industrial environment.
A good cladding system also maintains tight seals at overlaps and terminations and fully protects the integrity of the vapor barrier and insulation systems underneath. Though metallic cladding has been the choice of many specifiers and owners, there are some fundamental problems with these systems that have contributed to the CUI problem we now face on a global scale.
A good alternative in the CUI process range is to use a UV cured GRP system. These systems exhibit superior resistance to mechanical damage as compared to metal and also offer greater potential to seal the overlap and termination joints.
A UV cured GRP can also offer superior fire resistance and chemical resistance as compared to a typical metal cladding.
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