What is the most common method of joining cast iron pipe and fittings?

Cast Iron Soil Pipe & Fittings Handbook

Chapter 2 - Installation of Cast Iron Soil Pipe and Fittings

Joining Methods for Cast Iron Soil Pipe

Compression Gaskets

            There are generally three methods used for joining cast iron soil pipe. Hub and spigot cast iron soil pipe may be joined by the compression gasket or a caulked joint. Hubless cast iron soil pipe are joined by using a hubless coupling. 

            The compression gasket is a precision molded one-piece gasket that is made of an elastomer that meets the requirements of ASTM C-564. The physical characteristics of this elastomer ensures that the gasket will not decay or deteriorate from contact with the materials flowing in the pipe or chemicals in the soil or air around the pipe. The compression joint is made as follows: 

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1. Clean the hub and spigot so they are reasonably free from dirt, mud, sand, gravel or other foreign materials. When installing pipe that has been cut, make sure the sharp edge is removed. The sharp edge may jam against the gasket's seals making joining very difficult. The sharp edge may be removed by filing or tapping the edge with a ball-peen hammer.
2. Fold and insert the gasket into the hub. The gasket must be inserted into the hub completely. Only the flange which contains the identification information remains exposed on the outside of the hub.
3. Lubricate the joint following the manufacturer's recommendations. Sizes 2" through 15" may be lubricated using a manufacturer's recommended lubricant. Some manufacturers recommend using an adhesive lubricant on large diameter pipe and fittings (5"-15"). It should be noted that use of the adhesive lubricant does not take the place of proper join restraint when required. 


4. Align the pipe so that it is straight. Using the tool of your choice, push or pull the spigot through all of the sealing rings of the gasket. You will feel the spigot end of the pipe bottom out in the hub. Fittings may be installed by using the tool of your choice or by driving the fitting home by using a lead maul. To do this, strike the fitting on the driving lug or across the full hub. Hit it as hard as necessary, the lead will deform without harming the fitting. Using the lead maul is the fastest and easiest way to install fittings on hub and spigot cast iron soil pipe. Proper safety procedures should be observed in making the joint. 

Hubless Joints

            Hubless cast iron soil pipe is joined by using the hubless coupling. Several different types of hubless couplings are available. The following will outline the installation procedures of hubless couplings that meet the requirements of CISPI 310. It must be noted that these installation procedures are not intended to be applicable for couplings other than those manufactured in accordance with CISPI 310. These couplings are manufactured using a stainless steel shield and clamp assembly and an elastomeric sealing sleeve conforming to the requirements of ASTM C-564. The following steps should be taken to ensure a proper joint. 

1. Place the gasket on the end of one pipe or fitting and the stainless steel clamp and shield assembly on the end of the other pipe or fitting.
2. Firmly seat the pipe or fitting ends against the integrally molded center stop inside the elastomeric sealing sleeve.
3. Slide the stainless steel shield and clamp assembly into position over the gasket and tighten the bands. The bands should be tightened using a calibrated torque wrench set at 60 in./lbs. For larger diameter couplings that have four bands, the inner bands should be tightened first and then the outer bands tightened. In all cases, when tightening bands they should be tightened alternately to ensure that the coupling shield is drawn up uniformly.

Caulked Joints

            Prior to the late 1950's, the caulked joint was the only method of joining hub and spigot cast iron soil pipe. To make a caulked joint the following steps are used: 

1. The spigot end of a pipe or fitting is placed inside the hub of another pipe or fitting making sure that both are clean and dry.
2. Oakum is placed in the joint using a yarning iron and then packed to the proper depth by using the packing iron. For specifying depth of lead for each size and class see table below.
3. Molten lead is then poured into the joint. The molten lead is brought up to the top of the hub.
4. After the lead has solidified and cooled somewhat, the joint is ready to be caulked. Caulking is performed with inside and outside caulking irons. Caulking the joint sets the lead and makes a leak-free joint.

             Any time caulked joints are used, safety procedures should be observed and protective equipment and clothing should be employed. Use customary precautions in using or handling molten lead. If a horizontal joint is to be made, a pouring rope must be used to retain the molten lead in the hub. 

Lead and Oakum Required to Caulk Cast Iron Soil Pipe Joints

            Oakum is made from a vegetable fiber and used for packing hub and spigot joints. Cotton and hemp can also be used. These materials are usually twisted loosely into strands or braided and formed into a circular or rectangular cross section. A rough rule-of-thumb method for estimating oakum requirements is to take 10 percent of the weight of the lead required for caulking. Table 5 provides a more accurate method for estimating oakum requirements. 

            Lead quantities can be roughly estimated by rule-of-thumb as 12 ounces per inch of diameter as a minimum. Thus a 4 inch diameter pipe would require 3 pounds of lead as a minimum. An 8 inch diameter pipe would require 6 pounds of lead. This allows for skimming-off and for a reasonable loss due to spillage in pouring. Table 6 lists suggested lead quantities for various pipe and fitting diameters. The amounts shown apply only to cast iron soil pipe and fittings made according to ASTM Standard A-74. 

            The standards of the Lead Industries Association contain the specification for lead quality. Lead for caulking purposes should contain not less than 99.73 percent of lead and no more than the following maximum allowable impurities: .08 percent copper, .002 percent zinc, .002 percent iron, .25 per cent bismuth, .02 percent silver, and a total of not more than 0.15 percent arsenic, antimony and tin. The melting point for caulking lead is 621 degrees F, and the proper pouring temperature is 790 - 830 degrees F. The lead is ready for pouring when it becomes a cherry red. After cooling, there is a shrinkage of approximately 5.8 percent from the liquid state. 

NOTE: The caulked joint is a very time consuming method of joining cast iron soil pipe. The vast majority of all hub and spigot cast iron soil pipe installed today is joined by using the compression gasket.

Handbook Table of Contents

 

Joining pipes is one of the most vital aspects of completing any plumbing job, whether it's new or a rehabilitation. The pipe joints must withstand the pressure from each line going through the joint. To employ the best pipe joining method, workers must understand the different options and which is the best choice for a given job. (One major project is replacing the old lead pipes in your home. Learn more in How to Tell If Your Home Has Lead Pipes and How to Replace Them.)

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Threaded

If you have a low-pressure system, using a simple threaded joining method is best. The threaded joint is exactly what it sounds like: One component has internal threads while the connecting piece has external threads. All manner of piping is available with threads: PVC, copper, cast iron, and GI pipes. They have a diameter range of 6 mm to 300 mm.

This joining method works only with low-pressure and low-temperature flows. Higher temperatures and pressures could cause the joints to expand and leak.

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Stab-Type Fittings

These coupling methods are used for pipe diameters with a 2-inch or smaller diameter. While there are several styles of stab fittings, they all have a similar design that includes an elastomer seal, a gripping device for effective pressure sealing and a self-contained stiffener.

With a stab-type fitting, the union between pipe ends is stronger than the pipe itself, making it ideal for polyethylene pipes, especially heating, ventilation and air conditioning applications. Stab-type fittings must be ASTM International D2513 Category I rated to ensure a complete seal and full pullout restraint.

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Soldered

One of the more common types of pipe joining methods is the heat fusion method. There are several ways to fuse by heat, with soldering being one of the first choices for many plumbers. Solder melts using temperatures below 840 degrees C.

When soldering, the skilled technician should use a paste which keeps the fittings from oxidizing. This pipe joining method is used for copper and copper alloy pipes. It is best for pipes used at a lower temperature such as home water lines.

Brazed

Brazing is the second type of heat fusion. This heating method differs from soldering by using temperatures above 840 degrees C to melt the filler material. Like soldering, workers typically use brazing methods on copper or copper alloy pipes.

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The filler material used to seal the connection between the two pipes often consists mainly of tin. However, since tin is a weaker metal, it is combined with copper, bismuth, silver or nickel to strengthen the filler and help it maintain structural integrity. Brazed joints work well for pipes transporting material of moderate temperatures.

Welded

There are two main types of welds used to connect pipes: the butt weld joint and the socket weld joint. Both methods require a skilled worker to install the fittings.

Butt Weld

A butt weld is the most common type of pipe joining welding method. Workers use this method to join two pipes of the same diameter. Generally, these joints are most prevalent in commercial or industrial pipe systems.

Joints sealed with a butt weld are not accessible for maintenance as they are a fixed joint. However, these welds provide additional strength in the joint and allow the seal to resist high pressure if sealed with filler only. Welds using an internal backing ring to reduce the amount of filler and lower the overall cost of the project may not tolerate the same pressure and may crack under heavy stress.

While welding is used for copper pipes, butt fusion is used for connecting polyethylene and high-density polyethylene pipes. Instead of using a filler to combine the two pieces, workers heat the pipe pieces by holding them against a heated plate until there is a proper melt. Once the melt is achieved, they remove the plate, push the two pieces together and hold them in place until they cool, forming one solid pipe piece. (For more on butt fusion, see Butt Fusion & Polyethylene Pipe: How to Effectively Use This Trenchless Method.)

Socket Weld

Plumbing experts tend to use a socket weld when they determine there is a higher chance of leaking from the welded joints. Instead of butting the two pieces together, one portion is inserted into the other and then welded together. This weld works best with pipes of two different diameters. Pipelines with the same diameter can also use a socket weld with fittings employed.

As with butt welding, socket welds are used with copper or other metal pipes. This method can also be used with high-density polyethylene pipe, which is called a socket fusion. As with butt fusion, the process heats the outer surface of the tube and then the interior of the fitting. Once achieving the proper melt on the two surfaces, workers join the parts by inserting the line into the joint. The two pieces solidify together as the surfaces cool.

Saddle Fusion

While the saddle fusion technique is not technically a weld, it is like the socket and butt fusions performed on high-density polyethylene pipes. Workers use this method to install a saddle fitting into the line seamlessly. As with other fusion methods, both the base of the fitting and the surface of the pipeline are melted with a heating plate. Once the appropriate melt occurs, they join the two pieces and allow them to cool while applying force to solidify the parts as one.

When appropriately performed, each of these pipe joining methods should connect the lines without any leaks. Testing should occur once the joints are connected to ensure a correct seal before project completion.

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