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Companies Turn to TSA Coating Due to its Recognized Corrosion Under Insulation Mitigation Properties

Published on 2011-09-26. Author : SpecialChem

Bill Jordan, General Manager, MTM Metalizing, Singapore

Globally, companies such as ExxonMobil and Shell are turning to Thermal Spray Aluminum (TSA) as the solution to CUI. The technology, which is more than a hundred years old, has proven itself as a corrosion under insulation (CUI) mitigation coating.

Simple to apply, cheap, and robust, these coatings provide a 20-year CUI inspection cycle at ExxonMobil, and 40 years at Shell. TSA is unaffected by CUI conditions, even in severe cyclic operation with mineral wool. ExxonMobil has a vessel operating in these conditions for over 50 years and it still has its original 1958 TSA coating on it, without any maintenance or touch-up done. It is pretty impressive, and a good reason to look at TSA. Shell has launched a global TSA implementation program to mitigate the damage caused by CUI.

It is simply aluminum wire that is heated, atomized, and sprayed onto the blasted surface until the correct thickness is achieved. It is an old, simple solution without many opportunities for people to make money on it; besides the applicators, the owners also save due to reduced maintenance costs.

It has been part of "NACE SP0-198-2010 Control of Corrosion under Insulation and Fireproofing" for years and peers from all industries (insulation, paint, cladding, applicators, owners, etc.) who have reviewed this document all agree that TSA is an important CUI mitigation technology. TSA is also an important part of "EFC WP 13 and WP15 Corrosion in the Refinery Industry CORROSION UNDER INSULATION (CUI) GUIDELINE". The people at ExxonMobil were very much involved with this document, especially the TSA parts. Overall, both ExxonMobil and Shell consider TSA a CUI mitigation method and freely say so.

In 2011, at the Houston coating society, Shell Global Solutions reaffirmed their global commitment to TSA and presented ~4 years worth of lab testing with TSA under all common insulations in constant wet/dry cycling and in boiling saltwater. TSA (1100 alloy) was not affected by mineral wool, pearlite, or any other insulation. Shell also presented this data and reaffirmation, and had their global CUI manger there to say that under all CUI conditions, TSA coated equipment will have a 40-year inspection cycle. Shell bases this time-frame on lab data and actual historical performance, like ExxonMobil's 50-year old mineral wool insulated vessel.

One thing to understand that while TSA is anodic to carbon steel, it is also a huge anode as compared to any holidays that might be present (excellent anode to cathode ratio). Due to this, and the inert, firmly adhered oxide layer that forms on the surface and in any pores in the TSA (1100 alloy!), the coating is considered first and foremost a barrier to electrolytes (water) thus removing one part of the corrosion cell. To make certain that the TSA is a barrier, it is applied 2x thicker for use in CUI conditions than normally required (most specifications are looking for around 12 mils/300 microns for CUI mitigation). It is a very effective barrier at this thickness, especially when the correct aluminum alloy is chosen and any porosity inherent in TSA is closed up by oxides (this happens when the TSA gets wet).

The second way it protects is by being an anode. The entire carbon steel surface coated is now cathodic to the entire TSA coating, therefore removing the possibility of carbon steel corrosion cells until the TSA is all consumed. With such a huge anode to cathode ratio, the expected holidays in the coating would take an incalculably long time to consume. Also, the aluminum ions that transfer to the holidays tend to passivate the uncoated carbon steel surfaces, slowing down the corrosion process to almost a standstill.

This has all been proven out time and time again in tremendous amounts of testing done and real world use over the last 100 years or so. Shell did intentional TSA holiday testing under various insulations with wet cycling, saw how well it performed, and concluded that 40 years would be a good time to strip insulation and inspect. If it did not work so well, I do not think companies like Shell and ExxonMobil would be using it. The 40-year inspection cycle (not 40-year life, as TSA users feel that after 40 years the coating will still be corrosion-free) is based on actual experience with TSA/CUI coatings applied for more than 40 years in the field. For Shell, it is also based on their own internal lab tests.

The surface does not have to be too perfect. Some petrochemical company written specs are "near-white", others are "white", most are in the 3mil/75micron range. Residual chlorides are not much of an issue with TSA. Like any other process, the applicator needs to know how to do it.

Once the surface is blasted clean (which realistically needs to be done when applying any good CUI coating system) and we look at the costs of the actual coatings, TSA is not really that expensive. Figure on the application speed to be in the 100 square foot per hour range. Slower than paint for sure (but it is a low-build system (12mil/350 micron range) that is fully applied in one pass with no drying time.

About MTM Metalizing

MTM Metalizing is a joint venture set up with International Metalizing & Coating Inc. (IMC) of the U.S.A. who have been in Thermal Spray Application business since 1995. The IMC patented technology used by MTM Metalizing is the current state of the art system for corrosion prevention.

With the latest advancements of the IMC patented application technology, MTM Metalizing process can be conducted on site, and not just confined to blasting and spraying chambers. Their metalizing machines are compact and mobile, designed to do applications in difficult-to-reach areas. The fast application rate of their equipment enables them to complete large area jobs within tight schedules. They provide customized solutions to corrosion problems for Marine, Petrochemical, Structural steel, Rail and Infrastructure industries. Their technology has been approved and used in a variety of corrosion prevention projects of high-profile clients, including; Panama Canal Authority, NASA, United States Navy, New Jersey Department of Transportation, American Bureau of Shipping (ABS) and Major Oil Companies. Since MTM Metalizing is conveniently located in Singapore which is a major transit hub in Asia, MTM Metalizing can swiftly deploy mobile teams to undertake jobs within Singapore, Malaysia, Indonesia, Korea, India, Philippines, Japan, Thailand, China and Taiwan.

Source: MTM Metalizing


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