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Lifecycle cost - a philosophy

13th November 2012

This paper considers the various parameters that relate to the costs and consequences and simplifying of this process guiding us to the right choices, both in the maintenance and new construction process, whilst not making it complicated.

Lifecycle cost - a philosophy
One of the last considerations when designing and building a plant whether it be a refinery, petrochemical or for that sake any industrial complex is the corrosion protection

Paint and corrosion protection does not create the largest cost or complexity during the build stage of an industrial plant, engineering and design is much more costly and consequential. Yet during operation corrosion will simply create mayhem if not controlled properly and the cost of this is exorbitant in comparison to the original investment to limit the corrosion. So whether we make the calculation of life cycle cost complicated or simple the result is usually the same, a quality paint system with properly prepared surfaces, will cost a small amount more at the new construction phase and save the asset owner considerably over the life cycle of the structure. Notably the same philosophy can be applied during maintenance as well as new construction and pay dividends.

Paint and corrosion protection does not create the largest cost or complexity during the build stage of an industrial plant, engineering and design is much more costly and consequential. There can be many reasons for this. For example, design life may well be 30 years plus, but this includes maintenance. What does maintenance mean? Full repainting every second year or never? During operation corrosion will simply create mayhem if not controlled properly and the cost of this is exorbitant in comparison to the original investment to limit the corrosion.

Discussion

One of the last considerations when designing and building a plant whether it be a refinery, petrochemical or for that sake any industrial complex is the corrosion protection. It may well be that there is a paint specification in place, but has it been well thought through? In fact in most cases we can say yes, it is a well thought through specification. It will include products and systems in line with good practice and surface preparation and cleanliness as requirements. But note that we refer to ‘in line with good practice’. So what does that mean? Usually it means no better or worse than previously achieved.

That is in most cases fine if you are the engineering or design company. But if you are the asset owner, would it not be prudent to target better than previously achieved, or even the best that can be done with today’s knowledge and competence?

From the writer’s point of view the latter is beneficial and although a small extra cost would be involved, it is manageable and the cost should be borne by the asset owner, who will gain tremendous benefit.

So in our Philosophy, it is not about special solutions but rather tacking each detail and component of the whole painting process and doing it a little better.

To start with a huge cost is incurred by the need for massive amounts of staging. This is an unavoidable cost; one has to reach safely the structure for preparation and painting. This is perhaps obvious at maintenance, but even at new construction there is a need to access the joints, and often the staging must remain for some days or weeks after build to allow for joint coatings.

It is a well-known fact that the surface cleaning and preparation has a great deal to say for the performance of the coating and these count for a large proportion of the cost of a coating process. If money is invested here then the largest chunk of the out lay has been invested for the whole coating process. Normally this is well specified for example stating a standard like Swedish Standard Sa 2,5. However take care; this has not covered the cleanliness or the profile (anchor pattern). One will see specifications with profile stated, for example 75 – 100 microns profile. This is getting close now to a good result, but we are missing one thing; Inspection. It is common to leave this to the paint manufacturer, and the contractor with a supervisor from the engineering company responsible. This is often good, but all involved have an interest to be finished with the painting, not necessarily the absolute best result. OK the asset owner could put in an inspector. However, this may act against the end result, too much extra time used, thus resulting in a technically negative result for other areas. Better perhaps for very clear guidelines of acceptability and responsibility and not least proper documentation that the preparation is correct, and or repaired to standard.

When it comes to maintenance cleanliness is priority, without cleanliness there will be premature failure. Lower forms of surface preparation can be done but will shorten the life of the coating, but may be the only practical choice.  Of course the life depends upon the coating being suitable for the preparations standard. Epoxy mastics will provide quite a reasonable lifetime even on an Sa2 prepared surface. Though life will be extended with better preparation, even with this type of coating. Still good documentation of what should be done and what was done will assist in ensuring a longer life out of the system.

OK, so we have a good preparation and most of the investment is spent, and the most important part of the work is in fact done. However it is logical that a small additional investment in the coating system is justifiable. Earlier we labored the idea of ‘in line with good practice’. This is also dangerous with regards to paint system choice. There are many traditionally used systems that are in fact wrong. For example using zinc silicates under insulation, the Zinc Silicate may very well prematurely fail due to moisture in the insulated area, that another system would have survived.

Another issue is building in lifetime modifications. Ambient condition steel on plant will be specified as up to 120 degrees centigrade operation. This may very well be the case the first years and the paint system function accordingly. However in order to get the most out of a specific plant operation, it may be beneficial to increase the temperature for a short or extended period beyond this temperature. The normal coating will fail, but for very little extra investment this failure can be avoided. In this case by a phenolic epoxy as an example.

So if we look at Life Cycle Costing as a scientific approach we take into account the cost of; preparation and cleaning; access costs including staging; application costs including any rental and diesel involved; Cost of coating system and other useable materials and any QC work hired in. Divide all this by the expected lifetime.

We are provided by guidelines for lifetime expectations from standards like ISO 12944 and they help significantly – although they do assume that all epoxies and Polyurethanes are more or less equivalent in performance. There is testing recommended – this can help. But surface preparation is assumed to be excellent. There is also no accounting for joints, welds and other damages occurring during the process, subsequent to the painting. So all this is just a guideline. But still this is probably reasonable since we can assume that the damage is the same regardless of surface preparation or the paint specification.

This article was written by Miles Buckhurst, Global Concept Director – Hydrocarbon Processing Industry

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