Although aluminum and ductile iron have long been the materials of choice for hydraulic manifolds, stainless steel is often the best choice, especially for applications exposed to the corrosive effects of salt water. Known for its high strength, durability, and excellent corrosion resistance, stainless steel is the best choice for a wide range of hydraulic manifolds.
Stainless steel is manufactured by adding chromium to low-carbon steel, forming an invisible chromium oxide film on the surface. The film serves as a protective barrier that allows steel to “heal” itself simply by exposing it to oxygen. Stainless steel’s corrosion-resistant properties can be enhanced even further by adding other elements—such as nickel, nitrogen, and molybdenum—during manufacturing. The results are stain and corrosion resistance to both mechanical and chemical damage.
Project managers often overlook the numerous advantages of stainless steel because of its initial higher cost as compared to other materials. However, if you are looking for a material that can be used in a wide variety of applications and that will increase the life of your manifold, stainless steel is the best value in the long run.
Its strength, durability, and excellent corrosion resistance make stainless steel well-suited to such applications as defense, aerospace, subsea, marine, off-shore, work boats, food processing, oil and gas, and corrosive mining. These applications generally bring refer to the interaction of stainless steel with the ambient environment. However, some applications also benefit from the advantages of stainless steel interacting with the internal circuits. This is especially relevant with hydraulic systems that use water-based and other low-viscosity fluids.
Stainless steel manifolds and all valves prevent corrosive breakdown of the internal properties of the manifold and critical valve functions. For instance, water-hydraulic presses have experienced component failures after just one month of service. Using stainless-steel for these components exponentially increases the service life.
Stainless steel also carries a significant strength-to-weight advantage over other materials. Duplex grades of stainless steel possess higher strength, which translates to reduced thickness in the material. Depending on the application, this can result in lighter, more compact manifolds overall.
Common Varieties of Stainless Steel
Although stainless steel itself is known for its resilience in extreme applications, designers can choose between several grades—each with varying degrees of strength, durability, and corrosion resistance properties. The three most common types of stainless steel grades used in manufacturing are 316 (UNS S31600), 304 (UNS S0400), and 17-4 H1150 (UNS S17400).
With type 316, molybdenum is added to prevent pitting in extremely corrosive environments. It is non-magnetic and cannot be heat-treated to add strength. Manifolds constructed with 316 can only be machined with the material in its annealed state.
304 is the most common stainless steel in use today. It is similar to 316 except no molybdenum is added. 304 has good corrosion resistance, better toughness, and higher abrasion resistance. Like 316, it’s non-magnetic, cannot be heat treated to add strength, and can only be machined in its annealed state.
17-4h1150 has similar corrosion resistance as 304, but unlike 316 and 304, it is magnetic and can be heat-treated to add strength. This stainless steel won’t lose its strength at high temperatures, and it accommodates higher hydraulic pressures—with ratings up to 5,000 psi. This type of stainless is much stronger than its more popular 304 and 316 types, with a Rockwlell hardness of 28 on the C scale and yield strength of 105 ksi. Due to its exceptional strength, it is commonly found in the aerospace, chemical, and petroleum industries, as well as in food processing.
Surface Coatings for Even Higher Performance
When made from aluminum or ductile iron, manifolds can be subjected to a any of several surface treatments, such as anodizing and electroless nickel plating to that improve cosmetic appearance, corrosion resistance, paint adherence, or surface hardness. Because stainless steel is inherently strong and corrosion-resistant, the need for and breadth of surface treatments is relatively small.
Although stainless steel manifolds generally do not need of surface treatments, they can be passivated to maximize their corrosion resistance. This process removes surface contamination that could otherwise form rust or initiate corrosion.
Stainless Steel Manifold Assemblies
Progressive manufacturers of manifolds provide stainless steel manifold and valve assemblies to reduce supply chain delays. Having access to valves from several manufacturers, Daman Products can provide custom integrated solutions for various industry applications demanding stainless steel.
Before choosing a material, consider the industry application of the hydraulic manifold, its working pressure, and the environment where it will be used. If stainless steel is an option, you will increase the life of your manifold assembly in even the harshest and most extreme environments.
Material for this article was submitted by Daman Products Co. Inc., Mishawaka, Ind. For more information, call (800) 959-7841 or visit the company's website.