How many times have we cracked open a ballast tank or other area that receives minimal maintenance and discovered what could only kindly be called “coating failure?” Sometimes there is anecdotal evidence of poor conditions during the last recoating or some other factor – such as being adjacent to a heated fuel/cargo tank – but, in the end, the situation must be rectified.
The International Maritime Organization (IMO) recognized the issues (and dangers) involved with coating failures in these areas, providing guidance years ago. Some shipping companies have jumped on this, issuing instructions and implementing inspection schedules to prevent a “surprise.” On my current vessel, we have the “Planned Inspection and Maintenance System (PIMS).” At first glance, the inspections required are overwhelming, but with use, become routine.
While we aren’t coating inspectors on a full time basis, every time we walk around the deck, climb through a cargo hold or inspect a tank, that is exactly what we have to be. The article below, reprinted from the latest issue of CoatingsPro Magazine, is a prime example of information that would be useful to us as deck officers.
Never Again – The IMO PSPC : Lessons Learned and Put into Action
By D. Terry Greenfield
“Never Again”… the message behind those two words is that we have screwed up, but hopefully have “learned our lesson” from a premature coating failure and we’re never going to let it happen again.
With this issue’s focus on the Marine Industry, we’ll examine some typical failures associated with seawater ballast tanks. These essentially “Never Again” lessons learned by the marine industry that resulted in the development and implementation of the IMP International Maritime Organization (IMO) Performance Standard for Protective Coatings (PSPC). We’ll look only at the PSPC requirements that generally relate to the prevention of premature coatings failures from lessons learned in this article.
The standard is incorporated as an amendment to Safety of Life at Sea (SOLAS) regulations ANNEX 1; AMENDMENTS TO THE INTERNATIONAL CONVENTION FOR THE SAFETY OF LIFE AT SEA, 1974, AS AMENDED, CHAPTER II-1, CONSTRUCTION − STRUCTURE, SUBDIVISION AND STABILITY, MACHINERY AND ELECTRICAL INSTALLATIONS. PART A-1, STRUCTURE OF SHIPS, Regulation 3-2 – Corrosion prevention of seawater ballast tanks in oil tankers and bulk carriers.
The PSPC provides specific technical requirements for protective coatings application in dedicated seawater ballast tanks in all types of ships, 500 gross tonnage (and greater) and double-side skin spaces arranged in bulk carriers of 150 meters in length and (and greater) for most projects since July 1, 2008.
The driving force behind the development of the PSPC was to incorporate “lessons learned” into a set of processes and standards that could facilitate maximum service-life for coatings/linings projects. Success, of course depends on the type of coating system selected, as well as steel preparation, application and coating inspection, and on-going maintenance. All these aspects contribute to the ultimate performance of the coating/lining system.
In fact, most typical failures can be classified within the following categories:
• Material Selection and Performance Deficiencies
• Surface Preparation Deficiencies
• Coatings Application Deficiencies
• Maintenance Deficiencies
Materials Selection and Performance Deficiencies
Arguably the most important first step of success is to make sure that the selected coating/lining material selected is suitable for the intended service as a tank lining in seawater service. The wrong coating can be properly installed but it will not provide the intended service-life. Typically, it will fail prematurely and often catastrophically.
To address this issue, the PSPC requires that the selection of the coating system is given consideration by the parties involved with respect to the service conditions and planned maintenance. The following minimum aspects should be considered during coatings selection:
• Location of space relative to any heated surfaces. For example, coatings/linings underneath sun-heated decks or bulkheads that may form boundaries of heated spaces will have to withstand repeated heating and/or cooling without becoming brittle
• Frequency of ballasting and deballasting operations (wet-dry cycles)
• Required surface conditions
• Required surface cleanliness
• Supplementary cathodic protections, if any (When the coating is supplemented by cathodic protection, the coating shall be compatible with the cathodic protection system)
The PSPC specifies two measures for success: one in the field and one in the lab. In the field, a targeted 15-year service-life coating/lining should have a documented performance history (actual field exposure) in seawater ballast tanks for five (5) years with an observed coating condition rating at that time of not less than “GOOD.”(1) This rating represents a coatings/lining breakdown or rusted areas of less than 3% with no hard rust scale and less than 20% of observed local coatings/lining breakdown or rusting on edges or weld lines.
Qualification of the coating/lining can also be accomplished with laboratory testing. The lab methods are described in the PSPC with acceptable results detailed in that document. Although the PSPC focuses on epoxy coatings/linings, the development of alternate systems and novel technologies is encouraged.
These measures of success are designed to ensure that the system installed is suitable for use. This is a lesson learned through years of premature failures. Use a qualified coating/lining. Once an appropriate coating/lining has been selected, the focus moves to inspection, surface preparation, and the application of the coating/lining.
One of the lessons we as an industry, should have learned by now is that in-service coatings inspection works and, thus provides a significant contribution to the service-life success of coating/lining installations. This in turn provides long-term value to the owner. The PSPC recognizes this contribution and, consequently, places significant responsibility on the inspectors. The IMO Standard requires that qualified coating inspectors certified to “NACE Coating Inspector Level II, FROSIO Inspector Level III, or an equivalent.”
The PSPC requires the preparation of a detailed inspection plan to address surface preparation and coating process requirements. That plan incorporates an agreement between the shipowner, the shipyard, and the coating manufacturer as to its implementation.
Specific PSPC requirements that must be implemented in the inspection plan are noted in the PSPC and evidence of these inspections and their reports are required to be documented and included in the Coating Technical File (CUFF) (2) .These in-process inspections are vital the success of the coating/lining installation and provide actual verification that the correct parameters – climatic, surface preparations, application, etc. — have been realized. Not only does this new requirement help avoid a “Never Again” scenario, but also its focus of verification provides evidence that hard “lessons” have indeed been “learned.”
It is absolutely essential that specifications, processes, and procedures required during surface preparation and coating application are strictly followed by the shipbuilder in order to prevent the premature failure of the coating/lining system and the structural assets that it protects. For many years, NACE International has stressed the value of in-process coatings inspection and its contribution to minimizing premature coatings failures. The PSPC recognizes this with the statement: “Emphasis shall be placed on initiation of each stage of surface preparation and coatings application as improper work is extremely difficult to correct later in the coating progress.”
Surface Preparation Deficiencies
Another lesson we’ve learned is that surface preparation has a significant impact on the long-term performance of a coatings/lining system. The PSPC recognizes this in the stated requirements for surface preparation. Surface preparation occurs at two different stages during shipbuilding. The first stage is when the plates are blasted and primed with an inorganic zinc shop primer prior to construction in an automated production line (this stage was detailed in “Never Again – On Full Auto,” July 09, CoatingsPro Magazine). This process is known as Primary Surface Preparation.
As an industry, we know that mill-scale, visible surface contaminates such as oil and grease, soluble salts contamination, weld treatments, and inadequate surface profile can all be contributors to premature failure. The PSPC addresses several these issues with the following requirements:
• An ISO Sa 2.5, near-white level of surface cleanliness
• An anchor profile between 30-75 microns
We also recognize from lessons learned that the environmental conditions during surface preparation can have a significant effect on the coating’s performance. The PSPC prohibits surface preparation and priming when the relative humidity is above 85% and the surface temperature of steel is less than 3°C above the dew point.
The PSPC requires that the steel surface cleanliness and roughness profile be performed at the end of the surface preparation and before the application of the primer, in accordance with the manufacturer’s recommendations. Thus, the manufacturer plays an essential role in the implementation of the PSPC, as well as the product data sheet for the product is the central document for application.
Since premature failures of installed coatings/linings systems have caused soluble-salts contamination, the PSPC requires testing with results ≤ 50 mg/m2 of sodium chloride.
The next opportunity for contamination occurs when all the “parts” are welded together. These welds and other construction joints need to be prepared for coatings application. This process is known as the Secondary Surface Preparation stage and encompasses the PSPC secondary surface preparation requirements, during which those surfaces will be further prepared for the installation of the actual lining system. We know from experience that the sharp edges of steel plates and shapes are not easily coated and failure is very common.
The PSPC addresses this with a requirement for rounding or radiusing the edges, or removing them altogether, grinding weld beads, and removing weld spatter along with any other surface contaminant. It requires that edges have a rounded radius of 2mm minimum, or be subjected to three-pass grinding or a similarly equivalent process before painting.
Damaged shop primer and welds are required to be blasted to an ISO 2.5 near white level of cleanliness as originally required in the primary surface preparation state. After erection of the blocks, there are various requirements dependant upon the damage that has occurred to the shop primer, but a significant lesson learned requirement is that the repairs will be feathered before coatings application.
Coatings Application Deficiencies
With surface prep complete, the next focus is on the actual coatings application. Earlier we discussed edges and stripe-coating. The PSPC requires a minimum of two stripe coats and two spray coats, although with some allowance f
or the second stripe coat in order to avoid unnecessary over-thickness at the welds. This requirement is to minimize failure of the installed coating/lining at the edges and welds. Testing again for soluble salts is required before the application of the coatings/lining system.
Environmental conditions during application are specifically addressed and note that coatings will be applied under controlled conditions, in accordance with the manufacturer instructions, as well as the following requirements:
• The relative humidity is above 85%; or
• The surface temperature is less than 3°C above the dew point.
The PSPC specifically addresses the fact that each main coating layer will be appropriately cured before application of the next coat — in accordance with coating manufacturer’s recommendations. It notes that adequate ventilation is necessary for the proper drying and curing of the coatings. It requires that ventilation be maintained throughout the application process and for a period after the application is complete and during the curing process to the extent recommended by the coating manufacturer. We often forget that we’re not finished until the coating/lining has fully and completely cured. Only then can it provide the intended level of service and protection to the substrate.
The installed coating/lining must comply with the dry film thickness (DFT) requirements and be a continuous coating to properly perform. The PSPC requires an extensive level of DFT measurement to ensure that this vital condition is achieved.
Every premature coatings failure provides an opportunity to learn from our mistake and not repeat it. Although that learning opportunity is often presented it’s not always put into action. The PSPC is unique in that it represents an industry compilation of lessons learned put into a significant document for the marine industry. This may lead to achieving an ideal state of the art in seawater ballast tank coatings. Only time will tell if premature failures will indeed become “Never Again” scenarios of the past.