Even though casings protect the carrier pipe from mechanical damage and external loads, they may create problems and require excavation for inspection and repair. There are several instances where accurate details on casing location is not available. Identifying the unknown locations of the casings to replace, remove or perform maintenance is a major cost for pipeline operators.
These challenges could be a concern for pipeline integrity for pipelines that cannot be pressure tested or prohibit the use of In-Line Inspection (ILI) tools, because completing direct examination or performing Direct Assessment (DA) at an unknown casing location would be challenging.
This paper will show how an indirect inspection technology can be used to find buried casings without any direct contact to the pipeline or ground disturbance. In addition, the paper will share how to find these casings based on the change in the magnetic field on the pipe. This paper will present results from previous inspections and share visuals of final processed data.
Casings have historically been used at road and railroad crossings to accommodate higher loads on the buried pipeline from traffic and additional overburden associated with deeper burial depths. They also help prevent third-party damage, although at the greater depths of the crossings, this may have minimal benefit. Casings were also once considered an option to provide the capability to remove or replace carrier pipeline without disturbing the road or rail-crossing, although this is rarely necessary. Despite these benefits, the weaknesses of using casings may outweigh the benefits1. The casing may adversely affect the integrity of the carrier pipe by shielding cathodic protection (CP) current to the pipe and reducing the CP effectiveness in the vicinity of the casing. This is possible even when the casing is coated and electrolytic contact exists between the casing and the carrier pipe2.
Despite the issues with casings and availability of alternatives that can eliminate their use, they are still used today, and hundreds of casings have been installed on pipeline infrastructure built over the past 50 years. Modern directional drilling construction techniques can eliminate the use of casings by increasing burial depth to provide adequate protection at road and railway crossings. In addition, use of stronger pipeline material and/ or with greater wall thickness, concrete coatings and other methods can provide protection to the pipeline from mechanical damage and external loads. This can eliminate the use of casings.