Significance of in-line inspection
Various data sources are building the foundation of sound integrity engineering and management as key to safe pipeline operation. These are, for instance, direct assessment, above-ground measurement methods, and arguably the most conclusive, in-line inspection (ILI). Alternatives such as hydrostatic testing, where a pipeline is filled with water and pressured up to a pre-defined limit above the maximum operating pressure (MOP), often are less conclusive and/or cost-prohibitive.
Conventional in-line inspection technologies have been developed over decades, starting in the late 1960s/early 1970s, with what can be referred to as low-resolution tools for the detection and coarse classification of metal loss anomalies. With conventional or free-swimming, the industry refers to tools propelled by the pipeline product. The transported fluid, either gas or liquid, creates a differential pressure across the inspection tool’s sealing plane(s), resulting in its forward motion. Conventional ILI requires certain boundary conditions. These are, broadly speaking, the presence of launcher and receiver traps, suitable mechanical pipeline design, and operating conditions. Today, these ILI tools cannot only detect and accurately size defects such as deformations, metal loss corrosion, and cracks in the base material and weld areas but also characterize pipeline mechanical and material properties – all crucial information for integrity management programs.
Industry need for robotic ILI
Industry research estimates that approximately 40% of the world’s pipelines are unpiggable and cannot be inspected with conventional ILI tools. In the early 2000s, this led to the development of robotic (self-propelled) solutions. In the following years and decades, failures led to a further increase in demand for robotic pipeline inspections. In particular, failures caused by missing information and records to make the right integrity decisions prompted the Pipeline and Hazardous Materials Safety Administration (PHMSA) to revise the code and require pipeline information to be traceable, verifiable, and complete (TVC). Naturally, the information gap is more significant for older pipelines designed and constructed when documentation requirements were much lower and without conventional ILI in mind.
Advantages and path forward
Robotic tools exhibit various advantages over conventional ones, such as flexibility in insertion and extraction, maneuverability in challenging mechanical configurations, and independence of pipeline products as a means of propulsion. This makes them more versatile and applicable to many unpiggable pipelines.
Additional advantages that piggable pipelines could contribute from are the controlled speed and the ability to start, stop, and to move in any direction. The controlled speed generally contributes to higher data quality. At the same time, the other aspects allow for the collection of various perspectives and deeper insights, for example on complex features such as girth welds. Moreover, pipelines operated at high flow rates could be inspected without reducing product flow during inspection, maximizing pipeline operator profits.
After more than 20 years of development, the technology is still in its early stages, though today, we see a wide range of applications. Limitations in inspection range and pipeline inspection preparation are imminent challenges to overcome.
Inspection range: Today, a robotic tool is powered either via cable (tether) or batteries. Both solutions are somewhat limited in terms of the inspection range. A cable causes friction forces that, particularly in pipelines with a higher number of bends, accumulate. As power is needed for the sensors, tool electronics, and propulsion unit, battery capacity is only sufficient for shorter inspection ranges. Therefore, alternatives are required. Basic concepts for inspection range extension do exist but it will still take some time until they become a reality.
Pipeline preparation: Adequate pipeline cleanliness is a pre-condition for collecting high-quality data. Particularly unpiggable pipelines are often difficult to clean. While some basic measures are in place today, there are certainly improvement opportunities.