SEALING LARGE-DIAMETER CAST-IRON PIPE JOINTS UNDER LIVE CONDITIONS

Abstract

Utilities in the U.S. operate over 75,000 km (47,000 miles) of old cast-iron pipes for gas distribution. The bell-and-spigot joints tend to leak as these pipes age. Current repair practices are costly and highly disruptive. The objective of this program is to design, test and commercialize a robotic system capable of sealing multiple cast-iron bell and spigot joints from a single pipe entry point. The proposed system will perform repairs while the pipe remains in service by traveling through the pipe, cleaning each joint surface, and attaching a stainless-steel sleeve lined with an epoxy-impregnated felt across the joint. This approach will save considerable time and labor, avoid traffic disruption, and eliminate any requirement to interrupt service (which results in enormous expense to utilities). Technical challenges include: (1) repair sleeves must compensate for diametric variation and eccentricity of cast-iron pipes; (2) the assembly must travel long distances through pipes containing debris; (3) the pipe wall must be effectively cleaned in the immediate area of the joint to assure good bonding of the sleeve; and (4) an innovative bolt-on entry fitting is required to conduct repair operations on live mains. The development effort is divided into eleven tasks. Task 1-Program Management was previously completed. Two reports, one describing the program management plan and the other consisting of the technology assessment, were submitted to the DOE COR in the first quarter. Task 2-Establishment of Detailed Design Specifications and Task 3-Design and Fabricate Ratcheting Stainless-Steel Repair Sleeves are now well underway. First-quarter activities included conducting detailed analyses to determine the capabilities of coiled-tubing locomotion for entering and repairing gas mains and the first design iteration of the joint-sealing sleeve. The maximum horizontal reach of coiled tubing inside a pipeline before buckling prevents further access was calculated for a wide range of coiled-tubing string designs and pipe environments. Work conducted in the second quarter consisted of: (1) selecting a preferred pan/zoom/tilt camera; (2) initiating design of the digital control electronics and switching power supply for the control and operation of the in-pipe robotic modules; (3) continuing design of the repair sleeve and (4) initial testing of the wall-cleaning device. Activities in the third quarter included: (1) development of the system's pan/zoom/tilt camera control electronics and operating software, and implementing these in the surface and downhole modules and (2) further testing of the wall-cleaning elements used to clean the inside of the bell and spigot joints. Most recently, fourth quarter developments were centered on designing and testing the pipe-wall cleaning device including the selection of the drive motor and its control electronics. In addition, efforts were also focused on the design of the repair sleeve. Details of these activities are described in the body of the report along with a summary of events scheduled for the next quarter.