Making Successful Wet Taps

The wet tapping process is often the most favorable yet extremely difficult way of connecting new pipe to existing live pipe without interruption of service. The procedure normally involves a tapping sleeve that is installed on the pipe to be tapped. A tapping valve is connected to the tapping sleeve and a tapping equipment is coupled to the tapping valve.

The tapping equipment makes use of an extendible shaft that makes headway through the tapping valve and sleeve. A drill bit and cutter fastened to the end of the shaft cuts through the pipe wall. The drill bit incorporates some way of maintaining the cut pipe section when pulling back the shaft back through the tapping sleeve and valve. During the last step, the tapping valve is closed, and the equipment disconnected.

Failure in wet tapping procedures is usually attributed to:

  • Inexperienced Crews
  • Piping Materials That Are Not Easy to Tap or Not Recommended Used for Tapping
  • Inappropriate Materials and Equipment.

The most common problem is inappropriate materials and equipment. To remove this most common problem, it is crucial to utilize tapping materials, equipment and services approved from the same manufacturer, exclusively in larger diameter dimmensions.

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The MSS Standards

MSS-Standard Practice III was first circulated in October 1992. This standard contains the attainment and design demands for tapping sleeves. There is no AWWA standard for the manufacture, design and testing of tapping sleeves. Sizes comprised in this standard cover pipe diameters four inches through forty-eight inches and outlet sizes two inches through forty-two inches. It should be distinguished that manufactured steel sleeves are not contained in this standard.

There are two crucial dimensions included in this standard:

  • Inside Diameter of the Tapping Sleeve Branch Outlet. The minimum inside diameter of the outlet is 0.25 inches larger than the nominal pipe size of the branch connection. This is to ensure appropriate 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.
  • Distance From The Centerline of The Main to the Flange 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, it was published 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. 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.

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 be unfamiliar to some in the industry.

Careful planning and consideration must be given especially to larger sizes which standards do not cover. Whenever possible, the tapping sleeve, tapping valve and tapping equipment/services should all be secured from the same manufacturer. When you need a professional Wet Tapping Contractor Service, Casey Brothers Construction is the expert in this field. Contact us today for your next project.