Making Successful Wet Taps
The wet tapping process is often the most convenient way of connecting new pipe to existing pipe without interruption of service. The procedure usually involves a tapping sleeve that is installed around the pipe to be tapped. A tapping valve is connected to the tapping sleeve and the tapping machine is connected to the tapping valve (Figure 1).
The tapping machine uses an extendible shaft to advance through the tapping valve and sleeve. A cutter and drill bit attached to the end of the shaft makes a cut through the wall of the pipe. The drill bit contains some means of retaining the section of cut pipe or coupon when retracting the shaft back through the tapping sleeve and valve. The tapping valve is then closed and the machine disconnected. That is if everything goes right. And a lot could go wrong.
Unsuccessful wet tapping procedures can be the result of (1) inexperienced personnel;(2) piping materials that are difficult to tap or not recommended for tapping; (3) or most commonly, incompatible materials and equipment. To eliminate this most common problem, it is important to use tapping materials, equipment and services from the same manufacturer, especially in larger diameter sizes.
When designing a tie-in that involves a wet tap procedure, there are three basic standards that should be considered. They are the standards that have been developed by the Manufacturers Standardization Society of the Valve and Fittings Industry, Inc. Two of these three standards have only been in existence five years or less and the third standard only covers outlet ranges two inches through twelve inches in diameter. This is why special attention should be given to larger wet taps.
The MSS Standards
MSS-Standard Practice III was first published in October 1992. This standard covers the performance and design requirements of tapping sleeves. There is no AWWA standard for the manufacture, design and testing of tapping sleeves. Dimensions included in this standard cover pipe sizes four inches through forty-eight inches and outlet sizes two inches through forty-two inches. It should be noted that fabricated steel sleeves are not included in this standard.
There are two critical dimensions included in this standard. The first dimension is the inside diameter of the branch outlet of the tapping sleeve. The inside diameter of the outlet is to be at least .25 inches larger than the nominal pipe size of the branch connection. This is to insure proper shell cutter clearance. Also, the port of the branch outlet is be perpendicular to and centered on the axis of the main. This insures straight travel of the tapping machine shaft, therefor achieving a well centered cut.
The second dimension is the distance from the centerline of the main to the flange on the outlet of the tapping sleeve. Maximum distances are listed in the standard for corresponding sizes. These values are not to be exceeded. This is to insure the tapping machine will have enough travel for the shaft to advance far enough into the pipe wall to cut out a complete section of pipe and securely retract the coupon.
MSS-Standard Practice 60 is the oldest of the three standards, being approved in 1960. This standard practice covers the dimensions of the positioning recess of the tapping sleeve and the mating raised face of the tapping valve. The proper positioning of these two flanges must be in complete alignment to insure a successful tap. The use of a non-tapping valve introduces unnecessary liability to an other-wise routine procedure.
MSS- SP-60 only covers outlet sizes two inches through twelve inches in diameter (See Figure3). This means that for tapping sleeve to valve connections fourteen inches and above, there is no approved standard. The only assurance of proper alignment at this connecting joint is to use a tapping sleeve and tapping valve from the same manufacturer.
The newest standard, accepted in 1994, is MSS- Standard Practice 113. This standard covers the connecting joint between the tapping valve and tapping machine. The introduction of this standard was aimed at preventing interfacing and interference problems between various makes and models of tapping machines and tapping valves. For the same reasons, the positioning recess of the tapping sleeve and the mating raised face of the tapping valve must be in proper alignment. The connecting joint of the opposite side of the tapping valve must mate up properly to the adapter on the tapping machine in order to assure a successful tap. >
MSS-SP-113 covers nominal pipe sizes two inches through sixty inches. The dimensions listed in this standard are taken from the only two major tapping machine manufacturers including U.S. Pipe. These dimensions are critical for proper shell cutter and drill clearance (See Figure 4). Also, pertinent information concerning various adapter configurations are listed. The flange of the tapping machine adapter which forms the connecting joint with the end flange of the tapping valve are to be both parallel and concentric with the flanges that form the connecting joint on the opposite side of the tapping valve in order to provide proper alignment of the tapping machine. In the larger sizes, the use of U.S. Pipe material and tapping equipment is the only assurance that the connecting joint between the tapping valve and machine adapter will be adequate.
Some incompatibility problems are obvious and can be identified before the tapping procedure begins. The most dangerous problems are the ones that can't be seen and become evident after the procedure has started. Remember, MSS - SP-60 only covers tap sizes two inches through twelve inches in diameter. That means different makes of material provided on projects greater than twelve inches may and many times have resulted in serious complications. In addition, MSS - SP-111 and MSS - SP -113 are relatively news standards and may e unfamiliar to some in the industry.
Careful planning and consideration must be given especially to larger sizes which standards do not cover. Most obstacles can be eliminated by using compatible materials that conform to all of the Manufacturers Standardization Society Standards. >
Whenever possible, the tapping sleeve, tapping valve and tapping equipment/services should all be secured from the same manufacturer. The U.S. Pipe as a manufacturer of these materials and equipment has the most complete line as well as the most expert experience. U.S. Pipe manufactures tapping valves through 60 inches, tapping sleeves through 36 inches X 24 inches and tapping equipment for taps through 60 inches in diameter. >TAPPING TIPS
1) Use tapping sleeve, tapping valve, tapping machine of same manufacturer.
2) Use experienced tapping/supervisory service.
3) Test tapping sleeve and valve assembly hydrostatically before tapping (Do not use air test.)
4) Block properly under the tapping sleeve and valve to support the tapping assembly.
5) Take measurements for adequate travel and clearance.
6) Do not tap material that is unsuitable for tapping.
7) Think safety first.
About the Author: Ken Southerland is the senior sales representative for <%=company%> in Nashville, Tennessee.