Through the years, across the country, contractors, engineers, authorities, and customers routinely ask questions that seem basic yet truly speak to the fundamental versatility of Ductile iron pipe (DI pipe). Among the most popular questions are:
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While visually "bumpy," the exterior of Ductile iron pipe, if you slide your hand along the surface, feels relatively smooth - like a golf ball – texture vs. feel. That's because the texture applied is entirely purposeful and proprietary to each DI pipe manufacturer.
Commonly referred to as the peen, this precise pattern of circular dimples is machined into the forged-steel mold in which the pipe is made and serves as the mechanism for the initial build of the iron pipe wall during the centrifugal casting process. Without this peen pattern in place, the molten liquid iron would mostly slosh about inside the spinning mold in a non-productive irregular fashion.
The metal known as copper readily oxidizes when exposed to moist ambient air forming an egg-shell-thin yet highly protective green patina on its surface. The best example of this over time is the Statue of Liberty, located in the New York Harbor for nearly 200 years. Her ⅛-inch thin original skin has not diminished over her significant time in the harsh marine conditions, mainly due to the naturally occurring patina.
The simple fact is - oxidation is not rust. Rust is a destructive form of metal disintegration over time. Oxidation happens and then remains stagnant and protective of the substrate to which it is attached unless ambient conditions become more corrosive than oxidation can resist.
While the green patina of copper offers a highly desired visual appeal, the same oxidation process upon the surface of a Ductile iron pipe results in varied shades-of-cinnamon splotchy appearance upon its entire surface. This annealing oxide layer on DI pipe and fittings, much like the patina on copper, is so thin it’s barely measurable yet serves to prevent deeper pitting or degradation of the metal in standard ambient conditions.
The problem is, unlike copper, it's not attractive to the eye, and therefore, all Ductile iron pipes are coated with an NSF-61 certified asphaltic-based paint known as sealcoat. Water-based sealcoats are common today and are much friendlier to the environments of the foundry and the external world.
The term "sealcoat" comes from the function of this specialized thin film of paint once served: to maintain enough residual moisture in the initial set of the thin concrete mortar lining of the pipe ensuring the lining to hydrate properly and strongly. Modern foundry techniques and processes now make this "sealing paint" optional on the pipe's interior – customers' choice – as high-speed set modern linings do not require a sealcoat to hydrate correctly. To say it most simply, asphaltic sealcoat on DI pipes and fittings is mainly cosmetic, inside and out.
Yes, ferrous oxide deposition can occur on a bare iron surface transporting potable water. At one time, this deposition did appear on some, but not all, older iron pipes without a barrier lining. However, the primary purpose of cement mortar linings in cast iron and Ductile iron pipes and fittings is to PREVENT tuberculation, which it reliably does.
The cement is a physical barrier between the absorbed mineral content of potable water streams, particularly those with softer water chemistry, and the metal substrate below the lining. The water travels upon the cement lining and has no idea of or connection to the metal below. The thickness of the cement lining is irrelevant in this prevention process.
In fact, minor displacements or isolated exceptions in the lining still typically leave a superficial haze of cement fines or product attached to the metal, which is enough to preclude any considerable tuberculation from occurring. It is a super simple and proven truth that has demonstrated itself for many decades in modern iron pipes. Anyone still pushing the "tuberculation happens in cement-lined iron pipes” narrative is pedaling nonsense.
Conversely, this same standard Portland cement mortar lining serves no intended purpose in a sanitary sewer pipeline. Tuberculation is not a concern in such sewer flows. And if a sewer stream goes septic (pH < 4.5, cyclic or otherwise), the cement mortar lining will be sacrificed in relatively short order. It essentially turns into gypsum wallboard in the rain, a weak mush that gets washed away with the septic flows and/or is dissolved by the dilute sulfuric acid excrements of the bacterial activity common to sewers with a lower pH value.
There is no true functional difference between a Ductile iron pipe spigot having one stripe or two upon its circumference. Whether one stripe or two is involved their primary purposes are:
The number of stripes otherwise is merely an indication of who manufactured the pipe and what the gasket configuration is within the companion bell of that pipe joint. There currently are three separate domestic manufacturers of Ductile iron pipe in America. The single stripe is associated to a manufacturer that employs a Fastite™ gasket, while two stripes indicate the involvement of a Tyton™ gasket.
The primary difference between these named configurations is the shape of the as-cast gasket retainer bead within the bell, be it triangular in one case and semi-circular in the other two. It is also important to note that Tyton pipe hit the marketplace several years before the Fastite design, and the use of a single stripe in the latter simply avoids any copyright or patent concerns.
Industry literature has guided users to gauge or stop post-assembly joint deflection upon exposing the full 2nd (inner) stripe of the Tyton spigot. Yet, in practical truth, the best way to determine that you've reached the maximum recommended deflection limit for any size pipe of either configuration is to stop offsetting the pipe being deflected when its spigot begins to move the bell into which it's being inserted.
That is a reliable indicator of metal-on-metal contact within the joint. Given the innate strength and flexibility of Ductile iron, no damage will occur to the spigot, barrel, or bell unless intentional excessive force (such as from a hydraulic excavator) is used to take this deflection far past the initial inner-contact point.
The greatest enemy of a Mechanical Joint’s enduring watertight status is friction. Compression of the gasket within an MJ joint (such as on a fitting or other appurtenance connection) is created by torquing the nut and bolt fasteners to draw the gland into the joint, packing the gasket consistently around the inner circumference of the joint.
A dry or insufficiently lubricated MJ gasket will create significant friction between the metal surfaces of the pipe and the rubber gasket itself. This friction makes things "feel tight during wrenching," but the friction will dissipate in short order once wrenches cease, accounting for a loss of adequate torque in the joint and, most certainly, a leak when the pipe is later filled with water. "Loose" or “weeping” mechanical joints are the number one complaint that DI product support specialists deal with, and it’s typically found that the gaskets were assembled dry.
Here's a way to tell - fully lubricated MJ gaskets will NOT pick up any sealcoat when compressed. Dry gaskets get "specked" with sealcoat. That's not an opinion. Every DI joint holds its own visible truth. So, lubricate all surfaces of every mechanical joint gasket with the manufacturers' approved lubricant, torque properly, and you'll never again have to say, "the first thing I did was dig up and check all my mechanical joints."
The proper use and assembly of Ductile iron pipe and fittings are by no means rocket science or brain surgery. It is simple, so long as you pay attention to the proven simple axioms presented in this article. If you disagree with any statements or feel we have left something out, we would love to hear from you via or .
You have the questions; we have the answers. Reach out to your local McWane Ductile Representative, check us out on LinkedIn / Facebook / Twitter, or check out the Ditch Doctor section of Iron Strong Insights for more intriguing Q & A!
As a manufacturer of Ductile iron pipe (DI pipe), we often field questions from water professionals regarding DI pipe, its uses, and how to install it properly. We even receive numerous questions about alternate materials, their differences, their uses, and the best choice for the application. And of course, when you ask, we answer…honestly, even when the answer doesn’t include Ductile iron. In this Iron Strong Blog, we’ll cover a few of our frequently asked questions (FAQ) and provide some solutions. We will continue with this FAQ series in the upcoming months.
When Ductile iron pipe was introduced to the market in , replacing cast or gray iron, pipe manufacturers agreed that there should be a standardized protocol for determining wall thickness. This standard included considerations to the inherent strength advantage of DI over its cast-iron predecessor. With assistance from the Ductile Iron Pipe Research Association (DIPRA), the pipe manufacturers began working towards an agreeable set of standards.
Are you interested in learning more about di pipe fittings? Contact us today to secure an expert consultation!
While both Pressure Class and Thickness Class refer to a specific metal wall thickness of the barrel of the pipe, the primary difference is a change in terminology in how Ductile iron is classified under the specifications. Pressure Class designations refer to the pipe's ability to hold pressure, whereas Thickness Class refers only to wall thickness. These designations allow the end-user to specify a pipe that meets the design requirements of a given pipeline.
Need more explanation on this topic? Check out this Iron Strong Blog with a video, What’s the Difference Between Pressure Class and Thickness Class, where Jeremy Gwin helps clear the confusion between the two terms and shows which iron pipe Class you should install on your next DI project.
During the manufacturing process at McWane Ductile, all pipes are inspected to ensure the spigot end, bell, and socket comply with the requirements of AWWA C151/A21.51. Gauged pipe is pipe that has been checked physically to ensure the entire length, to within two feet of the bell, falls below the maximum Outside Diameter (OD). This allows for easier installation of fittings on this pipe.
Gauged pipe is indicated with a green paint mark on the bell of the pipe to visually show that our quality assurance inspectors have determined these pipes are best suited for field cuts based on both the OD measurements of the pipe as well as pipe ovality. These marks are typically indicated on sizes 14-inch pipe and above.
Whenever possible, use a 14-inch diameter or larger pipe marked as gauged full length (GFL). We typically send 10 percent of an order with large diameter pipe as GFL. Sort this pipe after unloading and reserve for field cutting when needed. We recommended that all pipe be checked in the field with an OD tape prior to cutting.
Want some more Pro tricks and handy tip sheets? See these helpful Iron Strong Blogs:
Perhaps a better way to address this question would be to ask what brand or manufacturer of pipe are you using? This answer will determine the joint type that has been supplied.
There are two domestically manufactured push-on joint types; 1.) The Tyton Joint® as manufactured by McWane Ductile and US Pipe and 2.) the Fastite® joint as manufactured by American Cast Iron Pipe Company (American). Therefore, push-on pipe that McWane Ductile or US Pipe manufactures are interchangeable, but neither is interchangeable with pipe manufactured by American.
Bottom Line: You should use gaskets provided by the manufacturer.
Watch a video about the differences in Tyton and Fastite gaskets and read more details in this Iron Strong Blog by Jeremy Gwin: Three Common Questions About Ductile Iron Pipe Gaskets.
Here are a few more blogs with helpful hints and handy tip sheets regarding DI pipe gaskets:
Yes. These cracks (sometimes resembling a spider web) are caused by iron and cement having different thermal expansion coefficients. As the temperature changes prior to installation, these cracks can occur. These cracks are normal and are of little concern due to a process called autogenous healing.
Simply stated, autogenous healing is the ability of the cement to heal itself. In the presence of moisture, cement extrudes calcium hydroxide, which, upon exposure to the atmosphere, is converted to calcium carbonate, sealing the crack. These calcium carbonate crystals are formed when the carbon dioxide in the air and water carbonates the free calcium oxide in the cement and the calcium hydroxide liberated by the hydration of the tricalcium silicate of the cement.
See this Iron Strong Blog where Gary Gula details the process of autogenous healing and explains why tiny cracks are not a concern in DI pipe: What is Autogenous Healing of Ductile Iron Pipe? Are Small Cracks and Cobwebbing Acceptable?
Since cement-mortar lining’s introduction in , today's modern DI pipe still utilizes cement lining for a safe and reliable means of providing clean drinking water to millions of people every day.
The cement lining, although very durable, does not have the same resistance to bending stress or impact as the pipe itself. On occasion, the cement lining may incur some damage in the field. You can repair cement-mortar lining by following the instructions in ANSI/AWWA C104/A21.4 Cement-Mortar Lining for Ductile-Iron Pipe and Fittings for Water.
There are a few steps to follow to repair, such as preparing your tools and materials, removing the damaged lining, applying a repair patch to create a new smooth surface, and finishing the procedure successfully.
But rather than try to explain here, let’s take you to a more detailed Iron Strong Blog by Jeff Houser with an instructional video and helpful downloadable tip sheet: What to do When the Cement Lining in Ductile Iron Pipe is Damaged.
Ductile iron pipe is one of the most widely used pipe materials in North America. The Design Life is second to no other pipe material due to its robust design. In most soils, DI needs no additional corrosion protection. However, polyethylene encasement should be used when the soils on the project are determined to be corrosive to DI pipe.
So how do you know when the soils are corrosive? When do you incorporate the polywrap? The answer lies in the Design Decision Model (DDM®). Developed by DIPRA and Corrpro Companies in , this tool is a two-dimension risk-based model for corrosion control for DI pipelines.
In addition, McWane Ductile has NACE-certified corrosion control experts on hand to answer your DI pipe protection questions. Just contact us. We’ll even come to your job site to assist with pre-installation training.
Want more detail on polyethylene encasement and its application? Check out these Iron Strong Blogs:
So, in this blog, we’ve covered just a few of our frequently asked questions in hopes that you, as a water professional, can benefit from the answers your peers have requested. Do you have a question for us? Drop us a quick note at , and we’d be happy to provide a solution. Your question may even end up as the next major topic for our Iron Strong Blog and video series.
Contact us to discuss your requirements of Ductile Iron Pipe Fitting. Our experienced sales team can help you identify the options that best suit your needs.