Posted on January 14,
Strength, corrosion resistance, and low cost of maintenance are all reasons that mechanical building services projects may call for the use of stainless steel pipe. But how should stainless steel pipe be joined together? And do I need to worry about dissimilar metal corrosion if I choose a grooved ductile iron coupling? No. In this blog post, we will explain how dissimilar metal corrosion occurs and why choosing a grooved mechanical pipe joining solution is ideal for joining stainless steel and copper piping systems.
Dissimilar Metal Corrosion is the electrochemical process that damages metal by reducing its strength and thickness. Dissimilar metal corrosion is also known as &#;Galvanic Corrosion&#; or &#;Bimetallic Corrosion.&#;
To understand dissimilar metals, you need to understand the Galvanic Series, which determines the nobility, or resistance to chemical reactions, of metals.
The Galvanic Series Chart lists metals in the order of their nobility. The metal that is more noble, and higher on the Galvanic Series chart, is called the cathode. The metal that is less noble, and lower on the Galvanic Series chart, is called the anode. Cathodic metals have a higher relative potential, or volts, than the anodic metals.
In dissimilar metal corrosion, the most severe attacks occur between metals that have greater differences in relative potentials. For example, titanium and aluminum would have a far greater or severe attack, in a dissimilar metal situation, than copper and brass would. This is due to the fact that titanium and aluminum have a greater difference in relative potentials when compare to copper and brass. (Which is illustrated by their distance from one another on the Galvanic Series chart.)
To understand how and why the &#;attacks&#; occur between dissimilar metals, we will look at the flow of ions from one metal to another.
All metals have specific relative electrical potentials. When metals of different electrical potentials are in contact in the presence of an electrolyte, a low energy electrical current flows from the anodic metal to the cathodic metal. As previously mentioned, more noble metals are cathodic; metals that are less noble are anodic and are more likely to corrode relative to the cathodic metal that it is in contact with.
When two dissimilar metals come into contact in a corrosive setting, the anodic metal undergoes galvanic corrosion while the cathodic metal maintains galvanic protection. This corrosion is created because the electrolyte provides a conduit for ion migration, moving metal ions from the anode to the cathode. The anode metal, as a result, corrodes more quickly than it otherwise would, while the cathode metal corrodes more slowly and, in some cases, may not corrode at all.
The image below is a representation of two metallic pipes made of dissimilar metals that are not joined properly, and have water flowing through them.
In this instance, the anodic metal is on the left. This metal is less noble, and the electrons are traveling from this metal to the cathodic metal through the pathway provided by the water. In other words, the water is the electrolyte transporting the metal ions from the anodic metal to the cathodic metal. Depending on the metal and the environment, the anodic metal will eventually corrode away in time. The dissimilar metal corrosion occurs because the two pipes were not electrically insulated from one another properly.
There are many instances where dissimilar metals are in contact with one another, and no corrosion occurs. An everyday example would be when you carry a copper penny and a nickel in your pocket. Using the Galvanic Series chart we see that copper is more anodic, or active, than nickel. We have two dissimilar metals that are in contact with one another; however, neither of the coins experience corrosion. That is because we are missing an electrolyte and a path.
The same concept of the nickel and penny your pocket applies to Victaulic products installed in a building services project. Some applications on these projects call for the use of stainless steel pipes. Stainless steel piping is most often utilized for its strength, corrosion resistance, and low cost of maintenance. Despite being dissimilar metals, couplings with ductile iron housings can be the best overall choice for joining stainless steel pipes.
The use of Victaulic couplings with ductile iron housings on stainless steel pipe is common practice when pipe material selection is based on compatibility with the fluid media and where the risk of external corrosion is low. Due to the design of the coupling housings and elastomer gasket, the housings will never contact the internal fluid media. The pressure-responsive gasket inside the joint provides a leak tight seal, completely isolating the fluid media within the interior of the pipe and gasket, and preventing contact with the coupling housings.
Victaulic has many years of jobsite experience with couplings with galvanized ductile iron housings installed on stainless steel piping systems without the report of galvanic corrosion between the pipe and couplings.
What happens when a corrosive setting is introduced?
Thinking back to the nickel and penny in your pocket, if by chance you jump into a swimming pool with the coins still in your pocket, then dissimilar metal corrosion will occur. This is because the three requirements, as previously discussed, are present in this situation:
Can I use stainless steel couplings on stainless steel pipe?
Yes, you can use stainless steel couplings on stainless steel pipe; however, it can be costly and may not be necessary on some applications. Some projects will specify stainless steel piping because of the external environment surrounding the piping system. While the fluid media is isolated from contact with the coupling housings by the gasket, the pipe joint must be protected from exterior water.
Situations where exterior moisture can build-up and where the dissimilar metals are in contact include:
In these situations, dissimilar metal corrosion will occur causing the galvanized ductile iron housings to show signs of surface corrosion similar to any ferrous metal when subjected to moist environments. If stainless steel piping has been chosen because of aggressive external environmental conditions surrounding the piping system, then the system engineer of record must evaluate the suitability of painted or galvanized couplings vs stainless steel couplings. For extremely corrosive external exposure, the system engineer may wish to use couplings with stainless steel housings and nuts & bolts.
Yes. Victaulic has a long history (since ) of providing couplings with ductile iron housings for use on copper tube.
The Victaulic copper connection system provides a fast, easy, clean, reliable method for joining roll grooved copper tubing with no weld/solder flame, cutting oils or metal chips. Victaulic copper connection products are permitted for use on aboveground or underground potable water systems by national organizations such as International Association of Plumbers and Mechanical Officials (IAPMO) and International Plumbing Code (IPC).
Copper connection products have been successfully used in buried service applications for many years. Soil conditions in buried pipeline services must be examined to determine what corrosive effect they will have on the system components, including the coupling housings. The system designer has a responsibility to incorporate the appropriate protective coatings on the couplings and flange adapters to protect from galvanic corrosion and aggressive soil conditions such as ground water and soil acidity/alkalinity.
Victaulic couplings&#; benefits address the problems of multiple negative environments and can provide noise and vibration control for HVAC systems. Click here to learn more.
Piping can be connected by both rigid and flexible couplings. But how are these couplings different? Click here to learn more about the history, differences, and applications of Victaulic flexible and rigid couplings.
If you want to learn more, please visit our website Solid.
Selecting a suitable class of ductile iron pipe can be challenging for professional engineers. There are many different options available that are widely used in water supplies, wastewater management processes, and industrial applications. It&#;s significantly crucial to choose the most appropriate class depending on your project needs and budget.
Generally speaking, there are two classes of ductile iron pipes, each divided into more detailed groups. C and K classes are these two practical families mainly classified by working pressure and wall thickness in order.
The most popular classes in these two groups are K7, K8, K9, C25, C30, and C40, and each offers unique properties, prices, applications, and benefits. Experts and engineers should choose one based on project demands and budget. Today&#;s Yasmin Trading blog discusses these ductile iron pipe classes in more detail. It provides you with all the information you require to make the best decision.
In the first place, you need to understand the significant differences between the C class and the K class. It helps you select the suitable ductile iron pipe class. According to McWane Ductile, Here are some general differences explained between C and K classes before dicing in more detail.
Considering all these features and differences, it is important to make the final decision wisely. Each class offers unique applications and properties used in projects with different purposes.
As explained below, the K and C class ductile iron pipes are widely used in different industries. Due to their high durability and resistance, their primary focus and application is water distribution systems. Different types of ductile iron pipe are classified into these two groups.
As mentioned, class K is divided into different groups by numbers. The number 7 in this type of ductile iron pipe indicates the internal pressure withstanding capacity. The following table discusses some technical properties of the K7 ductile iron pipe.
Pressure Rating 7 bar Tensile Strength Min. 420 MPa Elongation at Break Min. 10% Modulus of Elasticity 1.7 x 10^10 Kg/M^2 Hardness Max. 230 BHN Standard Sizes DN 80 mm to DN mm External Coating Options Red/Blue Epoxy, Black Bitumen, Zn & Zn-AI Coatings Internal Coating Options Cement Lining, Sulphate Resisting Cement Joint Methods T type, Mechanical joint, Self-anchorExperts prefer to use the K class in water distribution systems. In fact, this type of ductile iron pipe is the best for municipal water supply, industrial applications, or infrastructure projects. It is considerably corrosion-resistant, which makes it a proper choice for such challenging environments.
The K8 class of ductile iron pipes is widely used in various infrastructure projects. Their long lifespan, high durability, and minimal maintenance requirements are only some of their unique features.
Tensile Strength Min. 414 MPa Yield Strength 42,000 psi Elongation at Break Min. 10% Pressure Class 100 psiThese pipes are also lined with an internal coating to extend their lifespan and improve their corrosion resistance.
There are many different applications for the K8 class of ductile iron pipes. Engineers use them in water distribution systems, sewage conveyance, fire hydrant systems, buried pipelines, irrigation systems, and other industrial applications.
These K9 ductile iron pipes are also easy to bend, making the installation process more manageable than usual. They provide experts with a high level of fire-resistant properties and good seismic resistance, ensuring long-term reliability.
Like the K8 class in ductile iron pipes, the K9 class is also used in water management systems and is the most prevalent application. These types of pipes are similar to the K8 class but with slightly different characteristics.
The last popular selection of K-class ductile iron pipes is K12. Due to their toughness, ductility, and corrosion resistance, they are used in specific and somewhat complex projects.
Wall Thickness 7 mm Nominal Diameter 80mm to mm Rubber SBR, NBR, EPDM Zinc Coating Min. 130gsm Bitumen Coating Min. 70μm Pressure Rating -10°C to 80°C Effective Length 6m / 5.7mMoreover, polyethylene encasement is used in K12 class ductile iron pipes to enhance its resistance in corrosive environments.
Besides applying K12 pipes in water distribution systems, they are used in long-distance water transmission. Generally speaking, these pipes are used in various industries, such as chemical, oil, and gas.
Class C ductile iron pipes are designed to handle higher working pressure. Different industrial applications are determined for the C20 class of pipes. A summary of technical parameters regarding this class of ductile iron pipes is provided.
Pressure Rating 100 psi Tensile Strength 20,000 psi External Coating Options Zinc Primer Plus Bitumen, Epoxy Painting Rubber SBR, NBR Bitumen Coating Min. 70 μm Zinc Coating Min. 130 g/m²These pipes also have an internal coating to prevent rust formation and increase longevity.
The C20 class ductile iron pipes are utilized in water supply projects, drainage, sewage, irrigation, and water pipelines. They also benefit agricultural networks due to their high-pressure endurance level.
These pipes have many properties in common with other C classes but with minor distinctions.
Pressure Rating 100 psi Tensile Strength 25,000 psiThese pipes always provide experts with the best water distribution, irrigation, or industrial use solutions.
They offer many different industrial advantages, such as cooling water, process fluids, and chemical transport. The C25 class also plays a vital role in water management systems, just like other classes. Whether the project concerns fire hydrants or irrigation systems, these pipes guarantee a long-lasting performance.
Tensile strength is the most significant difference between this selection and other C classes. The table below provides more technical data.
Pressure Rating 100 psi Tensile Strength 30,000 psiThese pips, as can other available selections, can withstand pressure and load effectively.
They have the same applications and usage as other C classes. However, their mechanical properties make them suitable for use as industrial pipelines.
As explained, these pipes are manufactured with the same pressure rating in the C class but with different tensile strengths.
Pressure Rating 100 psi Tensile Strength 40,000 psiThey have similar applications to other C-class ductile iron pipes. However, experts prefer to use C40 pipes when higher tensile strength is needed in a specific project.