National Grid Up-Rates Low-Pressure System With Internal Seals

By Jeff Griffin, Senior Editor | July 2011, Vol. 66 No. 7

Right method
Because the existing 24-inch cast iron and 36-inch steel mains were mechanically joined, a reinforcement method had to be determined to allow the mains to safely operate at 22 psig. Internal joint seals are typically installed on larger diameter cast iron mains in metropolitan areas that can be taken out of service, Wencis said.

“Surface conditions are typically paved roadways or concrete sidewalks,” he explained. “Subsurface conditions typically include heavy infrastructure including sewer, water, drainage, steam, electric, communications and others. The cost for internally sealing cast iron joints, for these applications, is significantly less than conventionally installing joint seals externally. For an external joint seal, an excavation must be made over the joint, the joint cleaned and prepared, an external seal installed, excavation then backfilled and compacted and final restoration applied. In addition, traffic management must be employed.”

Wencis described the Commonwealth Avenue project as a perfect application for the internal joint sealing method. He said the Weko-Seal method was chosen because of its performance track record and competitive cost.

The project was under a stringent timeline driven by the university's school year. “We could work only during summer break, and the university needed natural gas by early September.” Wencis said. “The Weko-Seal method was a significant contributor to meeting the aggressive time schedule.”

Weko-Seals are manufactured from a nitrile rubber for natural gas applications and EDM rubber for most other applications and are designed to internally and economically stop joint leakage through mitigation of infiltration and exfiltration. Flexible internal rubber leak clamps ensure a noncorrodible, bottle-tight seal around the full inside circumference of the pipe joint area.

Weko-Seal components include the internal joint seal, retaining bands and band shims, an assortment of band wedges, retaining band clips, pipe lubricant, hydraulic expander and air test assembly.

The Miller Pipeline Corp. installed the seals. Work came under a three-year contract to provide approximately 1,000 Weko-Seals annually in 20-, 24-, 30- 36- and 42-inch gas mains.

Installation process
Installation is a man-entry process, said Terry Bell, Weko-Seal product manager. After isolating pipe sections where seals will be installed and making sure the pipe was safe for entry, the steps for installing each seal were: