Stainless Steel 316? Carbon? Ceramic? Selecting the right material of construction for your pump or valve is a tough call, especially if you're considering total cost of ownership (TCO). It's a known fact that maintenance costs account for more than 50% of process equipment's TCO. All too often we see operators select materials of construction purely based on cost, an expensive choice considering not every material holds up in all applications.
In this post, we'll talk about the pitfalls of choosing the wrong materials of construction for pumps and valves and what factors you should consider when selecting suitable materials.
Using the wrong materials of construction can (and will) lead to premature degradation, corrosion, fluid contamination, excessive wear, and leaks. Selecting a casing for a pump that cannot withstand abrasive fluid will wear faster and increase clearances, drastically reducing the performance of the pump. In a previous post, we talked about the importance of proper material selection for mechanical seals. If the wrong materials are chosen, an operator risks mechanical seal failure. The same goes with pumps, even valves.
UNDERSTAND THE FLUID'S NATURE AND COMPOSITION
Assess the fluid's pH levels, aeration impurities, chemical additions, suspended solids, etc. Understanding the fluid, and investing in the right materials initially is the right move to ensure the pump or valve will function properly throughout its lifetime.
FLUID TEMPERATURE AND PRESSURE
Make sure to take note of the fluid's temperature and pressure ranges (minimum and maximum), and if any thermal shocks are present in the fluid.
FACTOR IN FLOW AND VELOCITY
Is flow continuous, intermittent, or standby? What is the velocity of the fluid?
Think about the equipment's reliability expectations. What is the minimum life expectancy? Is this a piece of equipment that can easily and affordably be maintained or repaired if need be? If it's a critical component, the need for the highest quality materials may outweigh the need to save money on the purchase price.
EXAMPLE: CAST IRON VS. STAINLESS STEEL
Cast iron is generally the least expensive option when it comes to material selection for rotating elements and casings. But, buyer beware. While cast iron is abrasion resistant, it does not have strong corrosion resistant properties. Stainless steel, however, is a common choice for its corrosion resistance properties and has become a universally popular material choice for pumps and valves. Please note: There are different grades of stainless steel available today, so careful consideration should be taken to ensure longevity and cost effectiveness.
Material selection for process equipment isn't an exact science, but understanding the fluid's characteristics can help you make an educated decision about what materials are right for the application to avoid unnecessary maintenance costs and downtime. Selecting the right materials of construction is just one step towards increasing pump reliability and minimizing total cost of ownership.