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kr1114 (Civil/Environmental) (OP)
13 Feb 09 10:24
Hi, I am doing a conceptual design for a pipeline using three different pipe materials (PVC, HDPE, and ductile iron) - and I am not a materials guy and I apologize for my basic question.  My question is in regards to what the definition of Special Class is for ductile iron piping.  I have attached a file where I have highlighted in red the various special classes and in blue I have highlighted where there no special classes.  I have looked without success on why there are different pipe classes for the same pressure class of pipe (if they have the same pressure rating, why does the wall thickness increase for each special class? - my assumption is it is related to depth of bury and the higher the special class, the deeper the pipe can be buried).  And my other question is why is there a "-" in the special pipe section with an associated nominal wall thickness?  If there is a "-" does this mean that I should ignore the associated nominal wall thickness and use one of the special classes or what??

thanks for your help.
Helpful Member!  rconner (Civil/Environmental)
13 Feb 09 11:07
Your attached catalog reference appear to be an outgrowth of terminology used in ANSI and AWWA ductile iron pipe standards (for inch-sized) for pipe over the years.  Since 1965, many sizes of pipes have been available in six different nominal wall thicknesses originally referred to as thickness class(es) 1 through 6.  In 1975, these class designations were changed to 51 through 56 (a "5" was simply added in the front), and a new class "50" was added to most sizes (that had a slightly lesser "working pressure" rating (i.e. 200 psi) in the largest pipes, meaning classes 50-56 were available in most sizes after 1975.  
In a 1992 standard revision, while the basic ductile iron pipe design/calculation procedures were not changed, 60"-64" (1500mm-1600mm) ductile iron pipe sizes and new "Pressure Class" designations 150, 200, 250, 300, and 350 for various appropriate nominal thickness ductile iron pipes were added to the standard (internal pressure classes are of course the way many other AWWA pipe materials had been identified).  The old classes of pipes were still retained in the standards for the sizes up to 54", in effect resulting in expanded availability of nominal wall thicknesses of pipes in most sizes.  
The 1965-1975 pipe thicknesses were (and are today) referred to as "Special Thickness Classes" 50-56 etc. in the more current standards.     
 
kr1114 (Civil/Environmental) (OP)
13 Feb 09 11:28
there are a couple of things I still don't understand:

1. regarding the pipes with special classes "-" would I just ignore this and only use the special classes 50, 52, 54, etc.?

and

2. what is the reason for having different classes for a pipe rated at a specific pressure rating.  For example, a 10" pipe has a pressure rating of 250 psi but there are three special classes (50, 52, and 54) what is the purpose of this?
rconner (Civil/Environmental)
13 Feb 09 11:50
Your might want to contact the manufacturer(s) or search for arguably at least a little clearer presentation of the information (e.g. by clicking on the links at the right side of the portal http://www.acipco.com/adip/pipe/pressures-weights/).  
The most ready availablity might be of overall most commonly purchased minimum "Pressure Classes" of pipe (that as you will see from the information rate 350 psi working (or steady operating) pressure in e.g. 4"-12" common pipe sizes).   
kr1114 (Civil/Environmental) (OP)
13 Feb 09 12:31
rconner,

after I read your post I found more information from a different source.  here is the explanation:

At the turn of the century, ductile iron pipe was created in different types (type 1 to 6) - just like you described initially and then the types 1 to 6 were converted to classes 51 to 56 with a new class, class 50, added to the mix - again, just like you described.  then in the 1990's this old system of labelling was dropped and the "pressure class" system was implemented.  On the sheet I originally attached to my first post there are "-" in the special class column and immeditaly to the left is the pressure class system (the new labelling method).  All this means that there is no historical sizing for that pressure class.  For example: for a 4" pipe there is a pressure class rating of 350 and a nominal wall thickness of 0.25" but there is no special class for a 0.25" wall thickness because historically a 0.25" thick wall pipe was never produced hence the "-" in the special class column.  So if someone has an old system (i.e. prior to the change in labelling from the special class to pressure class) and they want to order a pipe to match the pipe in the ground, then they will order the corresponding "special class" pipe - so if there is a Type 1 pipe in the ground (which was changed to special class 51) and they want to replace a broken section, then they will order special class 51 which equals Type 1.

It all makes sense now - thanks again for your help rconner!
alexcmmi (Civil/Environmental)
13 Feb 09 13:32
FYI - DIPRA is your friend!  You will find your regional DIRPA engineer very helpful on these kinds of questions!  They also have A TON of great info on thier site.
swall (Materials)
13 Feb 09 14:53
Not sure how the "at the turn of the century" comment comes into play. Perhaps the phrase was directed at centrifugally cast iron pipe in general. Ductile iron did not come into existence until around 1950.

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