Ductile Iron vs Cast Iron 1

[martin888888]

I recently had a submittal come through where the contractor changed out 4" DIP to cast Iron. Was is the difference between the 2? Doesnt a cast iron pipe need to be coated due to a quicker corrosion period?

Thanks

 

[bimr]

Cast iron pipe was historically used as a pressure pipe for transmission of water, gas and sewage, and as a water drainage pipe during the 19th and 20th centuries. It comprises predominantly a gray cast iron tube and was frequently used uncoated, although later coatings and linings reduced corrosion and improve hydraulics. Cast iron pipe was superseded by ductile iron pipe, which is a direct development, with most existing manufacturing plants transitioning to the new material during the 1970s and 1980s.

Cast iron pipe is still used in some DWV applications, not in pressure applications.

What is your application?

 

[bridgebuster]

Wait a minute. If the contractor bid on DI then tell him you want DI. If he put CI in the ground too bad, he can rip it out and put in what was bid.

 

[rconner]

You do not note the specific application for the pipe involved. While gray cast iron pipe has a formidable performance record in many areas and for many applications, gray cast iron pipe has not been manufactured for water pipe applications in the USA since the late 1970's. This was due to the advent of ductile iron, that has approximately twice the strength and many times the toughness and ductility of the gray cast iron. Due to very similar chemical analysis and pipe manufacturing methods manufacture ductile iron has comparable corrosion resistance to the former gray cast iron, and when furnished with modern and correctly applied corrosion protection systems such as loose polyethylene encasement ductile iron can generally be expected to perform even better. Gray cast iron is not an equal to modern ductile iron pipe.

 

[DTOREC]

I'd be wary that the contractor is trying to save some coin at the expense of performance. DI way outperforms CI, but it's also more expensive. A good "tell" will be when you tell him no, stick with CI. If he starts gyrating in all sorts of conniptions and starts pleading, that means he either wanted to save some money, or they ordered CI instead of DI, or they bid CI instead of DI.

 

[cvg]

materials cost difference is not great, most of the cost is labor and equipment to install. I would not see any benefit to using cast iron for underground piping (assume it is underground). for interior drain and waste pipe, I see no problem with using cast iron.

 

[martin888888]

The application here is just 4" storm laterals from large proccess vaults. Very little water will ever even reach them. I dont think its a big issue as far as cost and installation. The pipe will be coated inside and out. I am not that familiar with cast iron so any info is helpful

 

[rconner]

I wonder if what the contractor is trying to substitute is "cast iron soil pipe" (CISP)? If so, in addition to lesser beam etc. strength CISP may not be furnished also with cement mortar lining, like what typically comes inside often stocked ductile iron piping. Cement lining is generally also more durable than bituminous linings,and does not typically result in internal tuberculation/build-ups in even some aggressive water exposures.

 

[martin888888]

Anyone know why Cast Iron pipe is made hub-less instead of a bell and spigot type installation? I dont really see the benefit of a hubless pipe and coupling constrcution.

 

[bimr]

The cast iron pipe that you are asking is normally installed for sewers and building DWV. Bell and spigot pipe has to be installed with pipe restraints such as thrust blocks. It is not possible to install bell and spigot piping on pipe hangers.

 

[BenJohnson]

Ductile Iron can be welded; Cast Iron cannot. Unplanned or future changes are much easier to make if you can weld on a fitting, patch, etc.

I would sit down with the contractor and discuss thoroughly why he wants to change the specs. You are using pipe in a strange situation - so he may have a good argument to use CI pipe. I am guessing money or ease of installation probably fits into the equation. (or he has a bunch of CI sitting in his storage yard he wants to get rid of). In this case, your client deserves a cut price.

99% of the time DI is superior material to use, and Cast Iron will probably not be manufactured .

 

[martin888888]

But the hubless cast iron pipe just uses couplings for pipe connctions instead of a bell and spigot. I know the difference just curious why cast iron comes hubless and the benefits of it? I really don't see any.

Do you really think future changes are easier with a weld then a simple bell and spigot connection?

 

[rconner]

I suspect in general hubless pipe, most often employing something like plain end pipes and a low-profile rubber boot and hose clamps, is probably considered a notable advance compared to e.g. formerly employed caulked (oakum etc.) bell and spigot cast iron soil pipes. I think now pipe systems are available in both sockets with compression gasket as well as hubless joining. I think hubless is used mostly for exposed, aboveground pipe systems and is also a less bulky system within wall confinements etc. While it seems straying from the original inquiry, I guess you could get more information if you are interested from the Cast Iron Soil Pipe Institute or a manufacturer like Charlotte Pipe.

 

[bimr]

Cast iron soil pipe and fittings are also used for storm drainage from roofs, yards, and courtyards in building construction. At present, cast iron soil pipe and fittings are the preferred material in high-rise structures for drain, waste and vent and sewer – without concern for building height.

http://www.charlottepipe.com/Default.aspx?Page=CastIron&type=CastIron#Types

Talk to a plumber about cast iron DWV systems if you want to know about hubless. Decades ago, DWV was joined with caulk and molten lead. Hubless fittings are a real time saver for plumbing of DWV systems.

http://www.henryplumbing.com/v5/faq/DWVsystems-CastIron.html

Welding ductile iron pipe is problematic. I have never witnessed this welding and I don't believe that it is a common practice.

http://www.ductile.org/magazine/2007_2/ductilewelding.htm

 

[bimr]

Regarding "I know the difference just curious why cast iron comes hubless and the benefits of it? I really don't see any."

If you had a 10-Foot length of pipe and used only 4-Foot of it, what would you do with the other 6-Foot if there was no hubless joining method.

http://www.charlottepipe.com/Products/Assets/02A-Cast_Iron_List_Price/SV-113.pdf

http://www.charlottepipe.com/Documents/CISPI_Tech_Man/CISPI_Tech_Man.pdf