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

Kothari, Kiran M. ; Pittard, Gerard T.

Gas Technology Institute

关键词: Repair;    36 Materials Science;    Computers;    Specifications;    Cast Iron;   

DOI  :  10.2172/839451
RP-ID  :  NONE
RP-ID  :  FC26-02NT41316
RP-ID  :  839451

美国|英语

来源: UNT Digital Library

【 摘 要 】

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 that connect pipe sections together 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 installing 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 to customers (which would result in enormous expense to utilities). Technical challenges include: (1) repair sleeves must compensate for diametric variation and eccentricity of old 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) and Task 2 (Establishment of Detailed Design Specifications) were completed previously. Task 3 (Design and Fabricate Ratcheting Stainless-Steel Repair Sleeves) has progressed to installing prototype sleeves in test cast-iron pipe segments. Efforts in the current quarter continued to be focused on Tasks 4-8. Highly valuable lessons were learned from field tests of the 4-inch gas pipe repair robot in cast-iron pipe at Public Service Electric & Gas. (These field tests were conducted and reported previously.) Several design issues were identified which need to be implemented in both the small- and large-diameter repair robots for cast-iron pipe to assure their commercial success. For Task 4 (Design, Fabricate and Test Patch Setting Robotic Train), previous problems with bladder design and elastomeric material expansion in the large mains were addressed. A new bladder based on a commercially available design was obtained and tested with success. Minor improvements were highlighted during patch-setting tests and are now being pursued. For Task 5 (Design and Fabricate Pipe-Wall Cleaning Robot Train with Pan/Zoom/Tilt Camera), the previous field tests showed clearly that, in mains with low gas velocities, it will be necessary to improve the system's capacity to remove debris from the immediate vicinity of the bell and spigot joints. Otherwise, material removed by the cleaning flails (the flails were found to be very effective in cleaning bell and spigot joints) falls directly to the low side of the pipe and accumulates in a pile. This accumulation can prevent the sleeve from achieving a leak-free repair. Similarly, it is also deemed necessary to design an assembly to capture existing servicetap coupons and allow their removal from the inside of the pipe. Task 6 (Design and Build Surface Control and Monitoring System) was previously completed with the control and computer display functions being operated through LabVIEW. However, this must now be revisited to add control routines for the coupon catcher that will be added. This will most likely include a lift-off/place-on magnet translation function. Task 7 (Design and Fabricate Large Diameter Live Access System) progressed to completing the detailed design for a bolt-on entry fitting for 12-inch diameter cast-iron pipe in the current quarter. The drilling assembly for cutting an access hole through the wall of the gas main was also designed, along with a plug assembly to allow removing all tools from the live main and setting a blind flange on the entry fitting prior to burial. These designs are described in detail in the report. Task 8 (System Integration and Laboratory Validation) continued with the development of the robot module inter-connects and of a master LabVIEW-based system display and control software.