The anticorrosive demand is a concept applicable to any system susceptible to be affected by corrosion. It is an indicator that integrates and considers all the variables of the project, which are necessary for the most appropriate selection of the anticorrosive design required by a construction system. A high anticorrosive demand is an indication of a potentially high corrosive load on the element. In other words, the anticorrosive demand provides an estimate of the corrosion resistance capacity of a construction system for a given work condition. The anticorrosive demand can be estimated by identifying and weighting the degree of criticality of each situation and modification of the same to lower the levels of vulnerability to corrosion.
The systems designed under this concept meet the requirements for extending the initial horizon free of corrosion as well as facilitates and extends the maintenance intervals. The anticorrosive demand must be assessed considering three types of analysis:
- a) General Analysis: It considers the entire construction system.
- b) Work Condition Analysis: Chemical, mechanical, physicochemical and environmental demands.
- c) Specific Analysis: Corresponds to the analysis of specific sectors of a facility, which, according to the work condition, have greater anticorrosive demand.
For a given constructive system, the level of anticorrosive demand depends on variables such as: the ambient, the operational environment, the detail design, the materials design, the protection design and the constructive design.
In this analysis, the environment is understood as the geographical sector where a specific construction system will be located. The main types of environment in the country are: highly aggressive marine, marine-industrial, marine, desert with saline soils and pronounced thermal cycles, rainy and mountain environments. Hence, a facility built in the north of the country, by the sea, will pose greater anticorrosive demand than the same building located in the hinterland, in a rather dry and salinity-free environment. Thus, the anticorrosive demand in these environments must be properly studied, since, for example, a leaching process that takes place in a desert area, dry environment, with plentiful sun and wind, evaporates water from the leaching acid solution deposited on the surface, causing a sharp increase in the acidity and the subsequent demand for anticorrosive on the structures
3. SPECIFIC ENVIRONMENT
A specific environment is a set of operational factors where the system will operate, namely, acidity, alkalinity, condensation, process humidity, salts, bacteria, abrasion, shear, efforts, submerged or buried systems, galvanic pairs, stray currents and others. The type, concentration, magnitude and synergistic factors of these agents are variables that must be established when estimating the anticorrosive demand. In short, the environment corresponds to the set of climatic-environmental and operational conditions related to a specific working condition, being specific for each situation and that cannot be modified. The anticorrosive demand, general and specific, should be met in every point and sector of the construction system.
4. DETAILS AND FINISHING DESIGN
The proper design of joints, knots, trusses, braces, angles, beams, columns, continuous or discontinuous welding, reinforced concrete, anchor bolts, access for future maintenance, etc., is vital to keep the anticorrosive demand of the constructive system as low as possible. The greater the anticorrosive demand resulting from the environment and operational environment, the completions must offer solutions that consider simple designs, free of crevices and watertight sectors, avoid sharp edges or angles, and present easy access to different areas.
5. MATERIALS DESIGN.
The nature of the materials used influences the anticorrosive demand of a construction system. If the operative and structural conditions allow it, it is necessary to study the replacement of minor carbon steel elements by other materials such as specific alloys, plastics, reinforced plastics, rubbers, etc. Any change must be analyzed in detail to avoid the formation of galvanic cells or accelerated degradation of the new material.
6. PROTECTION DESIGN
The greater the anticorrosive demand of a construction system, the greater the requirement for a protection system. The protection capacity of a coating is closely related to its chemical resistance, adherence and impermeability to an aggressive environment. The design of the protection scheme must consider all the structures, surfaces, and individual complex sectors to have a safety factor greater than one in each point of the system. In both cases, the protection design and the execution system should be planned in detail, including: the type of resin; the quality, technical characteristics and structure of the coating; the products selected to meet the requirement; the preparation of surfaces; the application methodology; the inspection plan; and the quality control system. To address these types of projects, the traditional methodology has been to ask the product suppliers regarding technical solutions at a macro level, where the commercial factor plays a key role. This new concept of anticorrosive demand establishes that each solution must be supported by a detailed analysis of the design and materials, performed by suitable professionals in each area. It is important to mention that the concept of anticorrosive demand must also be related to the estimated time framework of the project, being the service life an important factor for the design of the technical solution. The lifetime of a construction system is related to a proper management of the anticorrosive demand and the implementation of the anticorrosive management plan indicated below
7. CONSTRUCTION DESIGN
Prior to the construction of any facility, the structure should be inspected to identify those sectors where paint has been damaged during handling and transport from the workshop. The type of repair must be recorded in the work control book according to project specifications. The repairs must be carried out in a field workshop. Later, a proper construction and assembly method should be considered to reduce paint damage to the minimum. The painting repair procedure of the assembled structure should be indicated on-site according to: evaluation of the problem; location and type of damage; equipment; safe access feasibility and others. Prior to the construction, identify areas of difficult access. The damage to paint during the construction phase should be repaired immediately given that late repair may produce poor results. During the construction and assembly, the greater the number of unresolved details and unresolved non-conformities, the greater the unmet anticorrosive demand and the lower the corrosion resistance of the structure.
The main construction factors that result in the system with a greater anticorrosive demand are;
- Not performed or poorly performed repair and touch up.
- Unsealed crevices.
- Unsealed bolted joints.
- Poorly treated or unfinished welded joints.
Finally, it is recommended to develop a step-by-step construction design that includes the detail of the most complex areas, the methodology for repairs and touch up as well as the inspection procedure and quality control.
8. ANTICORROSIVE MANAGEMENT PLAN
The anticorrosive management plan establishes variables and procedures that should be considered to keep corrosion under control. It specifies the methodologies, regulations and prevention standards to keep the anticorrosive demand as low as possible. Periodical inspections, preventive maintenance, washing and cleaning, are part of the tasks that should be considered in any installation to keep corrosion under control. By incorporating the concept of anticorrosive demand into the project together with the experience gained in previous projects, the most complex sectors and accessibility for future treatments should be represented in drawings, documents and construction and assembly protocols, according to the anticorrosive management plan defined in the original project.
As the anticorrosive demand in a given construction system is dynamic and may increase over time due to factors such as the inclusion of new elements, equipment, structures, piping, remodeling, extensions, etc., the new situation must be studied in terms of the general and local impact of the new elements and establish an anticorrosive procedure that keeps the anticorrosive demand under control.
Training: To establish and implement the concept of anticorrosive demand it is necessary to train the group of engineers in every specialty, to have a common approach regarding corrosion and control methods of the same.
The projects’ decrease in anticorrosive demand is oriented to achieve robust anticorrosive designs. This implies:
- a) Targeted use of the details engineering’s resources and materials.
- b) Evaluation of the total corrosive load from the aggressive agents and their distribution depending on the components of the system.
- c) Definition of the anticorrosive scheme at a macro and micro level to avoid the formation of corrosion centers.
- d) Define the specifications for painting at the workshop and the specification for field repair and touch up.
- e) Draw up an inspection plan including products’ sampling and testing and the support of highly qualified staff.
- f) Execute the work based on a well-planned and controlled methodology.
In summary, it is possible to state that this work system, in addition to corrosion control, provides with the following benefits:
- Service life expectancy in line with the project’s objective.
- Reduction of engineering hours related to the service, problems solving and field visits.
- Almost no cost increase from contract extensions.
- Substantial increase of the negotiating power and quality demand.
- Standardization of paints’ quality and price through standards compatible with service requirements which allows for buying a range of alternative and equivalent products.
- Easy work control with established quality policies.
- Maintain excellent work planning and daily information about the project status.
- High technical knowledge and management in case of complex situations.
- Optimization of the project’s costs.
- Allows better assets preservation.
- Reduction of faults and risk factors due to poorly executed work.
- Control of deadlines compliance.
If the demand for corrosion was not quantified, it is very likely that sooner or later the demand will increase and exceed the protection level that has not been properly designed. That is, the system operates within a safety factor less than one, exposed to a premature failure. The deterioration enters a progressive and accelerated phase, requiring a work of greater complexity, with a sharp increase in direct and indirect costs.