Application of the 5 WHYs Problem-Solving Tool for Replacing PVDF with CPVC Material

Problem Statement:

Can we replace PVDF pipes and valves with CPVC if PVDF spare materials are unavailable, or must we wait 6 weeks for delivery?

First Why:

Why do we need to replace the PVDF pipes and valves?

• Because the current PVDF pipes and valves are either damaged, worn out, or need to be modified/extended.

Second Why:

Why are we considering using CPVC as a replacement for PVDF?

• Because we have CPVC materials readily available, and waiting for PVDF spares would take 6 weeks, which could cause delays.

Third Why:

Why would using CPVC be problematic or a concern?

• Because PVDF and CPVC have different chemical resistances, mechanical properties, and operational temperature ranges, which could impact the system's performance and safety.

Fourth Why:

Why are the differences in chemical resistance, mechanical properties, and temperature ranges between PVDF and CPVC important?

• Because the system is designed for phosphoric acid, and using materials not suitable for this chemical could lead to leaks, equipment failure, or hazardous situations.

Fifth Why:

Why is it critical to use materials (PVDF) that are specifically chosen for this system?

• Because PVDF is chosen for its high resistance to chemical corrosion, excellent mechanical properties, and ability to handle the operational conditions of the phosphoric acid system. Using an unsuitable material like CPVC could compromise the integrity and safety of the system.

Conclusion:

Based on the Five Whys analysis, the root cause of the problem is the critical need for materials that can safely and effectively handle phosphoric acid. PVDF is selected for a reason, primarily due to its superior properties for this application.

Recommendation:

It is not advisable to replace PVDF with CPVC due to the potential risks and incompatibility with the chemical and operational conditions. Therefore, it would be safer and more prudent to wait for the 6-week delivery of the correct PVDF materials to ensure the integrity and safety of the system.

Additional Steps:

• Mitigation Plan: Develop a contingency plan to minimize the impact of the 6-week wait. This could include temporary operational adjustments, finding alternative suppliers with faster delivery times, or increasing stock of PVDF materials to avoid future delays.
• Preventive Measure: Review inventory management and supplier lead times to prevent similar issues in the future by maintaining an adequate stock of critical spare materials.

Supporting Literature:

Chemical Compatibility and Material Properties

PVDF (Polyvinylidene Fluoride):

Chemical Resistance: PVDF is highly resistant to a wide range of chemicals, including acids, bases, and solvents. It is particularly suitable for handling phosphoric acid due to its excellent resistance to chemical corrosion.

Mechanical Properties: PVDF has superior mechanical strength and durability, making it ideal for applications involving high pressure and mechanical stress.

Temperature Range: PVDF can operate effectively in a wide temperature range, typically from -40°C to 150°C, maintaining its properties even at elevated temperatures.

CPVC (Chlorinated Polyvinyl Chloride):

Chemical Resistance: CPVC is resistant to many acids and bases but may not offer the same level of resistance to phosphoric acid as PVDF. Its chemical compatibility must be carefully evaluated for specific applications.

Mechanical Properties: CPVC has good mechanical strength but may not be as robust as PVDF, especially under high-pressure conditions.

Temperature Range: CPVC can typically handle temperatures up to 90°C, which may limit its use in applications requiring higher operational temperatures.

References: Chemical Resistance of PVDF and CPVC: "Chemical Resistance of Thermoplastics" by Plastics Design Library provides comprehensive data on the chemical compatibility of various thermoplastics, including PVDF and CPVC.

Mechanical Properties and Applications: "Polyvinylidene Fluoride (PVDF) Properties and Applications" by Arkema offers detailed information on the mechanical properties and suitable applications of PVDF. "Chlorinated Polyvinyl Chloride (CPVC) Technical Manual" by Lubrizol provides insights into the mechanical properties and uses of CPVC.

Temperature Performance: "Engineering Plastics Handbook" by James Margolis includes detailed sections on the temperature performance and durability of PVDF and CPVC. These references and analysis underline the importance of using the correct material (PVDF) for handling phosphoric acid in a chemical skid system, emphasizing safety, compatibility, and operational efficiency.