Part 6 of the seven-part series on material selection for chemical process equipment focuses on selection/evaluation considerations, including, and in addition to, material compatibility for specific process chemistries. Overview provided a listing of surface finishing chemical process equipment and systems that typically need material selection for various levels of exposure to process chemistries. Part 1 (Metals), Part 2 (Plastics), Part 3 (Other Materials), and Part 4 (Liners & Coatings) provided overviews of the broad range of materials available for different chemical process equipment applications. Part 5 (Paint & Powder Coating) overviewed selection of paint and powder coatings for process equipment and process system/area materials. This Part 6 starts with considerations for process conditions for candidate materials for evaluation.
Identify Process Conditions and Materials for Chemical Process Equipment
In addition to identifying chemical process equipment that will meet process performance criteria (e.g., pumping rates) and mechanical/electrical and other non-chemical service requirements for a new or existing surface finishing process line/system, consider the following for the chemical process equipment materials to meet application-specific process chemistry service needs:
- Determine process chemistry and temperature ranges: For each process area, estimate/verify process chemistry and temperature ranges over the life cycle for the process solutions. This should include initial solution mixing and temperatures that may result from exothermic reactions, solution variations during production, contaminant build-up in solutions, make-up chemistry additions, cleaning solutions, and any temporary or emergency uses for alternate process chemistries. Low concentration ranges and low temperatures are important to consider – in some cases certain materials are more effected at the low temperature or low concentration ranges for a process solution.
- Exposure Conditions: Determine the type of exposure to the process chemistries that may include constant immersion, periodic wetting/immersion, intermittent splashing, or constant or periodic exposure to mists and vapors. Be sure to consider additional corrosion potential at liquid/air interfaces (e.g., open tank liquid surface level range).
- Identify candidate materials (including materials with linings and/or coatings): To identify chemical process equipment materials that might satisfy process chemistry and temperature conditions, consider relevant applications experience, recommendations from process chemistry manufacturers and equipment manufacturers, and chemical resistance charts from reputable sources. Be very cautious of any extrapolations beyond referenced data points, and only assess the material resistance to a chemical mixture (e.g., etch solutions with mixed acids) with data that is relevant for the specific chemical solution mixtures. In cases where sufficient chemical resistance data is not available for specific materials, consider accelerated materials testing for the specific chemistries at elevated temperatures.
Consider Selection/Evaluation Factors
For candidate chemical process equipment/systems and various material options, key selection/evaluation factors include:
- Design Life: A typical design life for a surface finishing process line/system is in the range of 20-25 years. Overall line/system design life can be much shorter in cases including relatively short-term pilot or demonstration lines/systems, interim duty before facility renovation or relocation, or rapid technology advancement/changeout. Key equipment and systems, such as process tanks, process piping systems, and process structural support systems, should be adequate for the overall system design life. Process equipment components, such as sensors (e.g., pH, level, conductivity, etc.), will typically have shorter equipment-specific design life with planned replacement intervals within the overall process line/system design life.
- Cost: Cost evaluations should include total installed capital cost and balance of life cycle costs. In addition to the purchase price differences for chemical process equipment with different material options, the total installed capital cost can also vary due to different shipping, handling, and installation costs between material options (e.g., metal tanks that are much heavier than thermoplastic tanks and have different support, handling, and installation requirements). Also, accessories and other equipment may vary between material options and can significantly impact total installed cost (e.g., chemical process equipment using a less robust material may require added monitoring sensors and controls, additional containment provisions, etc.). The balance of life cycle costs can vary significantly due to differences in equipment maintenance and different replacement intervals for the chemical process equipment material options. It is common to select less robust materials such as 316 stainless steel (SS) vs tantalum for equipment such as heat exchangers where the cost multiplier could be as much as 10x with a planned replacement schedule. For instance the expected life of a SS heat exchanger may be 10 years vs 30 years for tantalum, but if the cost differential is very high then selection of SS material with a planned replacement schedule could provide greater value with acceptable performance.
- Operations and Maintenance (O&M) impacts: Consider if the material has negative impacts on process chemistry (e.g., metals dissolving or solvents leaching) and if the material needs to be eliminated from consideration for more inert materials or if material treatment (e.g., metal passivation or PVC solvent leaching) and/or process chemistry purification processes are applicable and feasible. If a less robust material means more frequent equipment changeout, consider impacts not only to technician labor and equipment replacement but also potential process shutdown.
- Implementability: Evaluation of implementability for different chemical process equipment materials includes procurement lead time (OK for project schedule?) and if there are any special construction/installation requirements or start-up and commissioning requirements. Consider whether a material is a standard product of the manufacturer and whether it has a proven track record in relevant applications.
- Coordination: Consider other project and plant equipment and systems and potential benefits for coordination/standardization for chemical process equipment to simplify spare parts inventories and maintenance requirements.
- Flexibility: More robust materials may provide flexibility for future process modifications, including potential change out of process chemistry.
- Safety and Health: Consider any differences in material-specific requirements and potential risks to safety and health during construction/installation, operation, and maintenance.
- Energy and Environmental: Consider client- and project-specific energy and environmental factors and whether alternate chemical process materials provide different impacts.
Follow-up After Material Selection
Follow-up after material selection for surface finishing process equipment and areas is important for project success. Follow-up considerations include:
- Verify that the material selections are still valid after any project changes to process chemistry, temperature, material exposure, service duty, or other process condition that could impact selection.
- Assure that the appropriately selected materials are shipped by the manufacturers and are installed correctly with all necessary repairs or replacements completed for damaged or stressed materials.
- Assure that all necessary field linings, coatings, and paint are correctly applied for all chemical process equipment and associated plant areas.
- Plan and verify that the processes are operated within the process design basis criteria/assumption ranges used for chemical process equipment and system material selections.
- Plan and verify that the surface finishing systems are maintained according to design O&M requirements (including scheduled cleaning, lubrication, component changeout, etc.)
Good documentation throughout the entire process of identifying, evaluating, and selecting materials, and also throughout implementation and use for chemical process equipment and process areas, is important for assuring that the surface finishing systems are properly designed and successfully procured, installed, operated, maintained, and managed after completion of use.
Next week, watch for the final part in this series, Part 7: Material Selection for Chemical Process Equipment – Benefits. Part 7 provides perspective on the economic, operational, and other benefits of well-designed, implemented, maintained, and documented chemical process equipment with application appropriate materials.
Integrated Technologies, Inc. is an industry-leading engineering, design, and consulting solutions firm based in Burlington, VT. We offer project planning and development, full-service engineering and design, project and construction management, and services during construction to the surfacing finishing and industrial manufacturing industries.
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