The role of atmospheric corrosion test methods in specifying CUI coatings
A discussion with a client last week highlighted to me that the role of simulated atmospheric corrosion testing in determining a coatings suitability for use in an insulated environment is at best not fully understood and potentially a little misleading.
A new standard on the block. With the introduction of ISO 19277 in 2018 there was for the first time a standard which provided guidance on testing for coatings which intended to be used to combat corrosion under insulation (CUI).. Additionally in that year the more well known ISO 12944 standard - which has long been used to determine the suitability of coatings subjected to atmospheric corrosion - was also revised. This included the incorporation of a section dedicated to use in a CX environmen,t which had previously been covered by ISO 20340 (now withdrawn).
Atmospheric corrosion protection prior to entering service. Turning first to ISO 19277. This standard was introduced to provide guidance and test criteria which should used when specifying coatings intended for insulated service, a problem which costs industry billions of dollars per annum. As such the need for testing in "atmospheric" corrosion is not immediately apparent. During the transportation, construction and installation phases of any project, pipes and equipment will be un-insulated for lengthy periods and as such it is essential that this is captured in any standard for this type of service. ISO 19277 includes salt spray testing (ISO 9227) and water immersion (ISO 2812-2) as a measure of performance in this area. The duration of the test varies between 480 and 3000 hours dependent upon the test and whether the panel has been exposed to heat or not. Annex A in ISO 19277 explains the rationale behind this selection of test criteria in more detail.
Dual use. Beyond this, additional pipe intended to be covered by the same specification my be subjected to atmospheric corrosion for much more extended periods of time, or even indefinitely, where it is used without insulation or where the insulation is subsequently removed, for example to assist in mitigating CUI risk. Here it could be argued that the traditional "atmospheric" testing such as found in ISO 12944-6 (for corrosion categories C2-C5) and ISO 12944 - 9 (CX) is more relevant. Both of the above test methods include salt spray testing to ISO 9227 in various forms but are not directly comparable with the relevant section of ISO 19277.
Need for clarity. As such it is easy to see how a specification which quotes ISO 19277 and ISO 12944 requires further clarification or at the very least includes an element of precedence to be applied.
Summary. Whilst the introduction of ISO 19277 adds an element of clarity to the testing required for coatings intended to be used in an insulated environment, there is an element of potential conflict which requires to be managed in specifications which also quote more traditional "atmospheric" corrosion test methods.
If you have any comments on this topic please don't hesitate to add them. I'd love to hear what you think.
Thermal Insulation Engineer
4 年Working as a contractor for Dow Corning we did an inspection on a pair of their columns 189ft tall , They were insulated on the floor and lifted into place with cranes , While being lifted even with support rings the weight of the insulation and cladding shifted increasing the chance of CIU , But they never took into account the sun revolving around the columns and creating hot and cold spots and creating condensation on the inside of the cladding which then poured down the cladding and rested on support rings , man doors and brackets , In the nights as the cladding cooled down this condensation just got sucked into the Rockwool and caused huge areas of CIU . The scaffolding alone cost ￡1 million and Dow did not want to pay for that every few years , So we devised a system of insulation that created an airflow between the cladding and insulation , We fitted a 50mm plastic egg box a 100mm wide and banded to the vessel at 1 metre intervals and then we insulated with 50mm Rockwool Lags , On the support rings we fitted boxes with mesh bottoms so that warm air would flow up through the sections of columns and dry out any moisture or condensation within the cladding , Took a year to strip , blast ,re-insulate and clad , But it stopped all CIU on columns , Bit long winded but hope it helps anyone in future works .
#Mechanical Engineer #Reliability and Integrity Consultant #Trainer #Materials Researcher #Passionate for development and implementation of new products and technologies for safe operation of processing plants
4 年Coatings can be definitely a good solution as barrier protection. The problem again is similar to CUI. We cannot monitor the health of coating. Zinc coatings have given good life but they have issue of reverse polarity with temperature and they have issues in cyclic service. I have not gone thru the standard but a careful and conservative life assessment of prevailing coatings could be a good information. Amine adduct cured epoxies have performed well but they should be procured from a reputed and qualified manufacturer. Secondly, dry heat resistance or maximum temperature should not be more focused. The focus should be on cyclic heat and sweating resistance. Some specialized composite liners have performed well in sweating conditions. Some researchers have advocated Polysiloxane coatings. My experience of Polysiloxane is limited to bare surfaces, so I can not comment here.
I think ISO-19277 is wat it is. It describes various test methods for coatings. Whether these test methods reflect the actual conditions under insulation, remains to be seen.?Because it clearly rules out possible detrimental chemicals from insulation materials. Also specific (often unique) site related conditions are not part of scope. From a practical point of view this is understandable. This is a good method to compare coatings. But in the end these conditions can have an effect on durability or life –cycle.
Chief Technology Officer & Co-Founder, CorrosionRADAR
4 年Very insightful. Thank you