In addition to the established wall thickness design, there were also additional considerations given to the wall thickness which included a 0.05&#; &#; 0.09&#; (depending on diameter) casting tolerance and a 0.08&#; service allowance. The casting tolerance would account for any minor deviations in wall thickness during the manufacture.
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The service allowance was included to help mitigate any minor corrosion that may take place in cast iron pipe. With the introduction of polyethylene encasement, this &#;corrosion allowance&#; is no longer needed, but it is still included in the overall design (as an added factor of safety).
Industry experts knew that the design of the stronger ductile iron pipe was extremely conservative and believed that the pipe could be consistently manufactured with a thinner wall.
So, in , the design criteria were revisited, and testing determined the addition of &#;CL 0&#; to the original thickness class designation was needed. However, many of the folks involved in this decision questioned whether a class 0 pipe would be accepted by end users.
Therefore, the number &#;5&#; was added to the front of the class designation and the CL50 &#; CL56 designations which still exist today were born.
You are probably thinking, that&#;s great and all, but why is there now another class consideration utilizing a pressure class rating system?
In , DIPRA member companies decided to include a pressure class rating system for the following two reasons:
Now that we&#;ve had a little history lesson, you probably want to get to the meat of the discussion and learn how to determine the correct wall thickness to specify for a given scenario.
To understand what class of pipe you should specify, you must understand that ductile iron pipe is a flexible conduit (unlike its cast iron predecessors). Because it is a flexible conduit, as is PVC, HDPE and steel conduits, the pipe can deform and re-form to its original shape as forces are applied to, and removed from, the pipe wall.
Two factors to consider when deciding what wall thickness, and therefore correlating pressure or thickness class, for your specific need:
Ductile iron pipe is the only material that considers external loading when determining the wall thickness needed for a specific pipe diameter. All others simply rely on the internal pressure of the fluid.
While there are many formulas that will help you determine the pipe wall needed for your project, McWane Ductile has developed a tool to help minimize the effort and alleviate the frustration - the &#;Thickness Design Calculator&#; as part of thePocket Engineer. If you are not familiar with the McWane Pocket Engineer, you can download here at MD Pocket Engineer. This tool has many other useful design calculators as well as access to technical information.
By utilizing the PE, you can easily input design criteria such as pipe diameter, maximum internal pressure, depth of cover, wheel load and the weight of the soil.
Once you input this information, it will yield results that tell you exactly what thickness of pipe and the correlating class of pipe that your application requires. The results are broken down by the five DIPRA / AWWA recognized trench types. It will also let you know if the internal pressure or external loading (bending stress) govern the design.
What is k7 ductile iron pipes ?
The number 7 in K7 indicates the pressure class of the DI pipe and it also represents the capacity of the pipe to withstand internal pressure. There are different pressure ratings of the K7 ductile iron pipes which depend on nominal diameter and nominal wall thickness of the pipe. The weight of the Di class k7 pipes would vary depending on the pipe size and the specifications also vary due to the dimensions.
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Class k7 vs k9 di pipes
Both Class k7 and k9 di pipes are capable of dealing with higher pressure. The weight of the K7 pipe and K9 pipe depends on the size and thickness of the pipe. Both the pipe specification depends on nominal wall thickness and nominal diameter of the pipe.
For what reason are all di k7 pipe &#;Painted black&#;?
The Di k7 pipe usually do not have a surface coating like zinc or any other paint. Thus, a dark color surface forms on the pipe which is iron oxide, and it forms during the manufacturing process.
Why are class k7 ductile iron pipes lined with cement?
The Class k7 ductile iron pipes are lined with cement so as to reduce the process of tuberculation inside the piping network.
Why does some ductile iron pipe class k7 have two spigot stripes while others only have one?
Some Ductile iron pipe k7 have stripes applied to the spigot or plain end of the pipe so as to provide an alignment guide and reference point to determine if the pipe is fully homed into the receiving bell.
How can I tell when the built di class k7 pipes joint has deflected to its maximum limit?
The actual internal pressure that K7 pipes can withstand will depend on the pipe size and its wall thickness. The internal pressure for each pipe specification should be calculated and then it can be easily identified when the built di class k7 pipes joint has deflected to its maximum limit.
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