Development of an Internal (Trenchless) Repair Technology for Gas Transmission Pipelines

Project Number

DE-FC26-02NT41633

Goal

The goal is to develop, evaluate and validate internal repair methods for pipelines, perform a laboratory demonstration of internal repair, and develop a functional specification for a prototype system to perform combined internal inspection and repair of pipelines.

Performer(s)

Edison Welding Institute (EWI) – project management and research product
Pacific Gas and Electric (PG&E) – access to abandoned pipeline for testing
Pipeline Research Council International, Inc. (PRCI) – operator experience and needs survey

Location:
Columbus, OH 43221-3585

Background

Pressure bandage carbon fiber-reinforced patch configuration

The most common target for repair of gas transmission pipelines is external corrosion-related loss of wall thickness. To prevent corrosion damage, which can often times lead to rupture, the area exhibiting the corrosion damage must be reinforced. Other defects that commonly require repair include internal corrosion, original construction flaws, service-induced cracking, and mechanical damage. Defects oriented in the longitudinal direction that have a tendency to fail from hoop stress must be reinforced in the circumferential direction, while defects oriented in the circumferential direction that have a tendency to fail from axial stresses must be reinforced in the longitudinal direction. The most commonly used method for repair of gas transmission pipelines is the installation of welded, full-encirclement steel repair sleeves that resist hoop stress and, if the ends are welded to the pipeline, resist axial stress.

Current external repair methods for natural gas pipelines are typically applied while the pipeline remains in service. While this is would be desirable for internal repairs as well, many of the internal repair methods require that the pipeline be taken out of service. Most of the internal repair methods applied in other types of pipelines (non-natural gas lines, which typically operate at lower pressures), are performed simply to restore tightness from leaks. Such repair methods require further development to enable their application in gas transmission pipelines.

Impact

Successful development of an internal repair technology which could restore the pressure carrying capability of a damaged natural gas pipeline offers the potential for substantial impact for both the gas industry and the gas consumer. The ability to perform an internal repair in a damaged section of pipeline could minimize the significant costs associated with the excavation and external repair or replacement of a suspect area. This is particularly true in lines where access by external means is difficult (e.g., water, railroad and road crossings). Such technology potentially offers an opportunity to better maintain natural gas infrastructure and enhances reliability and safety of gas delivery by reducing the likelihood of a product loss event by providing an alternative to traditional repair methods.

Results:
Four technologies (fiber-reinforced composite liner repair, deposited weld metal repair, adhesively bonded steel patch repair, and adhesively bonded/helically wound steel strip repair) were reviewed, evaluated, and further developed for their potential application as internal repair methods for gas transmission pipelines.

A survey of natural gas transmission industry pipeline operators determined that several key factors should be considered in the selection of appropriate technologies.

This capability would be most attractive for river crossings/other bodies of water, in difficult soil conditions, under highways/congested intersections, and under railway crossings.
There is a strong potential advantage for such a technology to compete favorably with the high cost of horizontal direct drilling.
Typical travel distances to the zone needing repair can be divided into three distinct groups: up to 305 m (1,000 ft.); between 305 m and 610 m (1,000 ft. and 2,000 ft.); and beyond 914 m (3,000 ft.). All three groups will require pig-based deployment systems.
The most common pipe size diameter requiring repair (95% of those surveyed) is 558.8 mm (22 in.), across a typical range of 508 mm (20 in.) to 762 mm (30 in.).

Hydrostatic pressure testing was conducted on pipe sections with simulated corrosion damage repaired with glass fiber (GF) reinforced composite liners, carbon fiber (CF) reinforced composite liners, weld deposition, an adhesively bonded steel patch, and an adhesively bonded/helically wound steel strip. To benchmark pipeline material performance, additional pipe sections were evaluated under both virgin and corrosion damaged/un-repaired conditions. Burst pressures for GF liner repair were only slightly greater than that of pipe sections without liners, indicating that this type of liner is only marginally effective at restoring the pressure containing capabilities of pipelines. Burst pressures for CF liner repair were also marginally greater than that of a pipe section with simulated damage left unrepaired. Pipe repaired with weld deposition failed at pressures lower than that of un-repaired pipe in both virgin and damaged conditions, indicating that this repair technology is less effective at restoring the pressure containing capability of pipe than both GF and CF liner repairs. Pipe repaired with an adhesively bonded steel patch failed at pressures slightly lower than that of un-repaired pipe, indicating that this repair technology is also less than effective. Pipe repaired with an adhesively bonded/helically wound steel strip exhibited preliminary results where burst pressure exceeded the burst pressure of un-repaired pipe, indicating that this repair process could be effective at restoring the pressure-containing capability of a damaged pipe section.

Adhesively bonded/helically wound steel strip repair is clearly the most promising technology evaluated to-date, not only because of its apparent ability to restore a damaged pipe section’s burst pressure to beyond that corresponding to 100% of the specified minimum yield strength (SMYS), but also because it lends itself well to field deployment and the material itself is inexpensive. Coils can be sized to accommodate any length of corrosion damage, cinched down to allow deployment through pipe bends, and compressed down to a single strip width. Future investigation into this repair technology should be conducted to confirm preliminary results, optimize its application and to develop prototype repair systems for deploying this repair technology.