Service Requirements & Environmental Factors for Coatings
Defining environmental factors and services requirements during the design phase helps to ensure selected coating systems meet the owner's expected service life expectations.
Coating and insulation engineering expert, Mark Davidson, just completed two new-build projects for a major oil company involving two bridge-linked platforms and a new floating production storage and offloading (FPSO) vessel. The first of the platforms has been installed and the second will be installed in 2016. The FPSO replaces an existing FPSO that reached the end of its service life. Those projects are located northwest of Scotland, west of the Shetland Islands in the North Sea. Major construction and coating was completed in Korea. Below he shares some thoughts on service requirements and environmental factors.
Using Standards to Define "Durability"
I’ve found it is very important to define environmental factors and service requirements early in a project. Unless everything is documented and the owner defines what durability they require for their coatings system, then there’s no real reference point for the future and it’s difficult to have a basis around which you select your coatings systems for the required durability.
The most important thing is for the owner of a structure to define what durability they expect from their coating system, and I’m a great believer in using recognized standards for that. (For more on the importance of standards and specifications, see Problems Caused by the Lack of Clarity & Definition in Coating Specifications.)
The standard that I use is the ISO 12944 series of standards. Part 1, clause 3.5 defines durability as “…the expected life of a particular paint system to the first major maintenance painting”.
This standard then refers you to clause 4.4, which provides some guidelines: “The level of coating failure before the first major maintenance painting shall be agreed by the interested parties and shall be assessed in accordance with ISO 4628 Part 1 to Part 5.” This standard allows you to assess the degradation of a coating during its life, decide when the first major maintenance painting will be due, and plan accordingly.
In ISO 12944 Part 1, durability is expressed in terms of three ranges: low (2–5 years), medium (5–15 years), and high (>15 years). It further clarifies the term durability by saying, “Durability is a technical consideration that can help the owner develop a maintenance program.” Once the owner has defined the durability, they then know what their maintenance program is.
Defining the Environment
Next is to define what the owner requires in a coating system for the particular environment, because the environment will affect the durability of the coating system.
For this I use another standard, ISO 9223 “Corrosivity of Atmospheres – Classification, Determination, and Estimation.” This standard allows the owner to determine what the atmospheric classification of the environment is. It defines categories of corrosivity of atmospheres starting at C-1, which is very low going up to C-5, which is very high and CX, which is extremely corrosive. This is important because this standard not only helps to define the corrosivity of atmospheres, but it also provides related standards on determining what the corrosion rates might be, and how this category is defined.
This is all very well laid out based on scientific principles, and it’s all valid and traceable. This traceability is very important for the owner, or owners in the case of a joint venture. The JV operating company is usually responsible for engineering design and therefore needs to be able to show the joint venture partners that as far as coatings, maintenance and future coatings requirements are concerned, the durability and the future coatings requirements are being determined through the use of these ISO standards. So it’s all traceable and therefore valid.
Determining the Coating System: Onshore or Offshore
Once the owner identifies what the corrosivity of the atmosphere is, they can then go back to ISO 12944 series of standards. Part 5 of this series provides example generic coating systems based on the durability and corrosivity categories. For example, you’ve identified that you have a C5 environment and you want 15 years to first major maintenance; Part 5 of ISO 12944 will tell you that you need this type of system, which comprises these number of coats of this particular generic type of coating to give you an overall system. The types of coatings systems listed in Part 5 of the standard have been based on expected performance.
When high durability coating systems are required, such as offshore where minimization of maintenance is paramount, there’s a newer standard, ISO 20340, which deals specifically with offshore environments such as the Gulf of Mexico, the North Sea or anywhere in the world offshore. That standard provides a testing regime for determining the durability of particular coating systems.
What the owner is then able to do is to identify the coating system based on these (sample) factors:
- We have a corrosivity category of C-5M (Corrosion Factor 5 Marine Atmosphere).
- We require that the time to first major maintenance painting be minimum of 15 years.
Based on the testing that has been and continues to be undertaken by the majority of global coating manufacturers under ISO 20340, the generic coating system type that we require for the particular environment is, say, a three-coat system, which might comprise two coats of an anti-corrosion coating with a suitable top coat.
What the owner can then do is write into his/her specification:
- This is our environment, all related to these ISO standards.
- Therefore you, Mr. Coating Contractor, or you, Mr. Fabricator, must supply the equipment or the steel work, coated with coating systems in accordance with these standards.
The fabricator and/or coating applicator then go to their coating suppliers, for example Carboline, Hempel, International, Jotun, PPG, Sherwin Williams or any of the various major coating manufacturers. So they have already done testing on coating systems according to ISO 20340, and they are able to say, “Right, here we go, this is our set of coatings systems that will meet your durability requirements and this is what we recommend you apply.”
So the whole coating selection and application process is valid and it’s traceable. And that’s really the best way for it to be done.
Determining Environmental Factors at Existing Facilities
If this is a refurbishment project, an engineer consultant must go to the plant or facility, and using the ISO standards, they would assess what the macro and micro environments are within that facility. They would spend time with the maintenance engineer and look at their records, and inspect various locations around the facility.
So determinations must be made for the macro environment generally and then for the specific micro environments within the whole. Say it’s a processing plant where they have various equipment, which runs at high temperature and low temperature, as opposed to the majority structural steel, which is only subject to the ambient conditions. It’s important to identify those micro environments for specific equipment. If all of that is documented, coating manufacturers can provide coating systems to meet those service requirements, and they will be able to provide the testing data to verify and demonstrate that their coating system has passed certain testing requirements. Plus they should be able to provide a track record of successful service of coating systems in the same or similar environments. (Read Lessons Learned from 50 Years of Coatings Testing at SA Water for insights on coating testing.)
The important thing about the track record is this: Some coating manufacturers think that a coating track record is merely a list of the projects where they have supplied their products. But a track record really needs to include results of inspection of equipment. Sometimes that type of data isn’t easy for coating manufacturers to assemble. But if, for example, a coating company has a long ongoing relationship with a plant operator, they would be able to talk to that operator and get the inspection data.
For instance, if there’s going to be a shutdown or an inspection, ideally the coating manufacturer’s representative would ask to attend that so they can see how well their coating systems have actually functioned in that situation. From that they would create a dossier of the performance of their particular coating systems.
Shared Learnings from the Field
What my long experience has been, and certainly on the most recent project, is that durability has not been considered formally in the early stages of the project and documented in the design basis or similar document. That is usually because there’s a lack of awareness within the project team about the importance of defining coating system durability. This occurs because they don’t have a knowledgeable coating engineer on the team early in the project, or the owner’s corporate standards don’t include requirements on durability.
One of the good things about the company I worked for until recently is that they have a formalized feedback system—an intranet site where the team can provide shared learnings. From the two projects I was on, I was able to provide multiple shared learnings, which then went through to the technical authorities for the particular disciplines. I dealt with the coatings TA, the process TA, and the instrumentation/piping design TA.
One of shared learnings I provided included: a recommendation that the requirement for selection of coating system durability be included in the fundamental corporate standards, rolled out at the very early stages of the project and documented in the project-specific basis of design.
This is important because it assists the operations team to be able to state particular maintenance requirements. For example, for reasons of cost in the case of these particular projects in the North Sea, we only have about a three-month weather window for coating maintenance. And, because coating application is such an expensive type of project, they want to maximize the periods between coating maintenance activities.
The maintenance team also wants to ensure that whatever maintenance they do has minimum environmental impact and requires minimum surface preparation.
However, in this project, it didn’t occur to the project team to define durability in terms of these ISO standards. So they didn’t have the advantage of being able to write into the coating specification the durability requirements in accordance with ISO 9223 and ISO 12944—all coating systems must meet this durability requirement. They didn’t have that opportunity.
Therefore, they got a mix of coating systems. We had a very big team on site and all different parts of the company were represented, from engineering and construction through to operations. The operations people regularly used to say to me: “How many years are we going to get out of this coating system?”
And I said, “What do you mean?”
Their response was, “When is it going to fall off?”
I told them that this isn’t the right consideration. You need to be talking about durability in terms of these ISO standards, which define “time to first major maintenance”.
So another shared learning I sent back to the TA was this: When this corporate standard is next revised, include a requirement for the project team, at a very early stage when the design basis is being prepared, to define durability in terms of the ISO standards.
This way, there is always a reference. People can look back and say, “The coating system needs to meet a high durability of 15 years+.” There it all is. It’s a reference that is useful from then on.
Written by Mark Davidson, Eng.