Tightrope: Identifying Limiting Conditions for Coatings Specification
In places where preventive coatings are left to degrade in challenging environments, as sometimes happens with offshore oil platforms, the asset owner/operator and coating specification writer must incorporate maintenance painting requirements into the design.
In writing coating specifications, it is essential to understand and include all of the limiting conditions at a specific site where maintenance painting is to be done.
The Ideal: Maintenance Painting at the First Signs of Degradation
In considering the requirements of equipment and the constraints of maintenance painting, for example in an operating refinery or a pulp and paper mill, the selection of the coating system at the time it is newly installed is extremely important. This is where the importance of having the design basis document really comes into its own. If the design engineers or the persons working with the specification are aware of all limiting conditions when the specification is written at new-build, it makes for far easier maintenance painting later on.
This comes down to how all of the elements of a good coating specification are interconnected. So in an ideal world, the coating specification should recognize all of the maintenance requirements and limiting conditions when maintenance painting is to be done.
Assuming that all of the requirements have been addressed in the coating of new equipment and structural steel, the maintenance painting should ideally not be difficult. But having a knowledgeable coating engineer or a long-term relationship with a skilled coating manufacturer is essential.
Many articles discuss when you should do maintenance painting and they often state that that owners should never allow the coating to break down to the point that abrasive blasting is necessary.
Ideally you should be doing maintenance painting as soon as finish coats begin showing signs of weathering and deterioration—before you have to do full surface preparation and abrasive blasting that requires large-scale containment of blast media. This scenario causes major impacts on the operation and also creates major health and safety impacts.
So that is an ideal situation and that’s really what an aware facility owner should be aiming for. Ideally, if the coating engineer has a design basis that recognizes all these factors, he/she would be able to say to management, “It is well understood that if you do your maintenance painting fairly early in the life of a coating system, when you first begin seeing signs of deterioration in the top coat, then the scope of surface preparation and access—the major cost and the major facility impact—will be much lower than if you leave it untouched for another 5 or 10 years. If you wait, you’ll have major coating degradation and corrosion occurring in the substrate.” So these are very important considerations for all stakeholders.
The Reality: Overdue Maintenance Painting
If maintenance has not been done, or a premature coating degradation has occurred, full-scale surface preparation may be required. This is where limiting conditions come into play. Here are some examples:
- Can equipment be taken out of service?
- Is there a time limit on the painting project to be done?
- Is blast surface preparation practical?
- Is blast media containment required?
- What other restrictions will impact coating application?
Can equipment be taken out of service? Again, that requirement would ideally be contained in and recognized by the design basis. (See Defining Client Objectives for Coatings Specification for more information.) But if limiting conditions are not documented in the design basis or in the maintenance philosophy, then it’s a whole different ball game.
Health, safety and local/national regulatory requirements must also be recognized in the coating specification. And this is where the coating engineer or the consultant who writes the coating specification must spend a lot of time with the facility owner or the maintenance engineer who is responsible for the maintenance painting and for health and safety. These meetings will help the specification writer understand all pertinent limitations at that particular facility. (Safety aspects are covered in more detail in the article Writing Safety Into Your Coating Specification.)
Ideally, the coatings engineer or consultant would be engaged by the facility owner and together they would inspect the plant with the painting contractor, covering all of the areas where painting is to done. They would look at the pressure vessels, the structural steel—all of the areas that require painting, and they would document:
- Access issues and solutions
- Which equipment can be taken out of service, if any
- What factors will affect the type of surface preparation that can be done
- Hot and cold surfaces
Once the coating engineer understands all of the limitations that will affect surface preparation and painting, then they can sit down and discuss limitations with the maintenance painting contractor—ideally a contractor who has experience with that particular plant. What methods have been used previously? What limitations does the contractor see for different surface preparation methods and the equipment and structures?
At this point, the coating specification can be drafted. Then the coating engineer will spend time with the facility owner and with the coating contractor, going through that first draft to include all the various practical requirements for containment, surface prep cleanup, and other restrictions that will impact coating application.
These are all of the special things that need to be incorporated into the coating specification. And, of course, the coating manufacturer who will supply the coatings must attend those meetings. Ideally, this would be a manufacturer who has supported that refinery or pulp and paper facility since newly built.
The combined experience of all these stakeholders should go into the maintenance painting specification.
A Recent Field Case in the North Sea
Take for example a company that has many offshore facilities in the North Sea and around the United Kingdom. The company embarked on a major maintenance painting program on one of their offshore platforms. The coatings on this offshore rig had been left untouched to the point where there was extensive coating breakdown and some corrosion of the substrate.
This oil company has maintenance painting contractors present on all of their offshore facilities, so the contractor and the operations maintenance engineers were asked to come up with a maintenance program.
Bear in mind that in the North Sea environment there is only about a three-month window optimum over the summer when maintenance painting can be done. On offshore platforms, the size of the accommodation, and hence the number of beds that are available is limited, so accommodations are planned in detail during the design stage. That’s where the operations team has a major impact on the overall specification. It’s envisioned that during maintenance painting, so many personnel will be needed onboard, and therefore so many beds are incorporated into the design of the accommodation.
However, with this platform, the maintenance painting scope required so many painting personnel that they had to bring in a floating hotel, or "floatel", at a cost of hundreds of thousands of dollars per day. The floatel had to be brought alongside the platform and connected by a special bridge to the offshore platform. And that’s where all personnel lived, and where all the coatings materials and equipment were stored.
This scenario is not uncommon for offshore platforms, where the operator will leave maintenance painting undone a long, long time before he/she decides to do any work.
Surveys of Offshore Platforms in the North Sea/UK Sector
Recently, there was a survey carried out in the United Kingdom by the statutory body, the Health and Safety Executive (HSE). That agency visited and surveyed a number of offshore platforms within the North Sea/UK sector. They identified where coating breakdown had occurred and how it was affecting the various systems on the platforms. (Related reading: Case Study: Offshore Platform Implements Faster, Safer Corrosion Monitoring Tools.)
There are also safety critical service valves for ensuring that in the event of a leak or emergency, the facility can be shut down quickly. These systems include many safety critical valves that have to operate reliably in an emergency in order to shut off the flow of gas and oil.
Many valves are remotely operated using instrument gas, which is a whole piping system reticulated around the facility.
The HSE surveys found some of this instrument gas piping, a mix of carbon steel and stainless, in very poor condition. Had it been left any longer, there may have been failures. The agency found coating deterioration so advanced in some instances that it could have an impact on the reliable operation of safety facilities, and their ability to shut off hydrocarbons flow in an emergency.
These are extreme examples of how long the responsible parties had left the coatings to degrade. There were various other examples of safety components degradation, such as steel grating that had been allowed to corrode to the point where it was no longer safe for personnel to use. Walkways and escape routes weren’t safe. Cable supports were corroded, and cable ladder and cable racks coatings had all degraded, affecting the structural integrity of those supports.
When structural degradation reaches that point, then structural replacement is required, and this involves welding of new structural steel and additional cost. This is a poor reflection on the facility owner who allows deterioration to get to the point where it jeopardizes safety. None of this was unusual in the survey that was carried out in the North Sea/UK sector.
When writing a coating specification for maintenance painting, agree to and document the required coating system durability in the facility design basis, and incorporate maintenance painting requirements into the design basis. For new-build coating specifications, ensure that the specification includes maintenance painting systems. In all cases, adhere to the design basis during facility operation.
And always include the facility owner/operator, the painting contractor and the coating manufacturer in preparation of the maintenance painting specification.
Written by Mark Davidson, Eng.