Pigging is an old method of cleaning out pipelines, but with the improvement in remote technology, these plain pigs can now be equipped with sensors to serve the dual purpose of inspecting and cleaning. (Read How Pigging Works in Trenchless Repair and Rehabilitation.)
Robotic pipe inspection on the other hand is only used for inspecting pipes and has nothing to do with cleaning the pipe. In fact to run a robotic crawler, the pipeline has to be first cleaned of all debris in order to enable the camera to undertake minute inspection.
Pigs and Intelligent Pigs
Pigging was originally performed using leather or straw bales wrapped in barbed wire. The pigs’ primary purpose was cleaning out a pipeline, but now pigs can be equipped with a computerized inspection probe to make it an intelligent pig which can also carry testing devices.
The pigs flow along with the flow of liquid or gas that the pipe carries and can pick up information such as corrosion and pipe irregularities. The small computer in the pigs collect, store and transmit information as it passes along.
Pigs have now become a common method of non-destructive testing, and can perform magnetic flux leakage (MFL) testing and ultrasonic testing to determine problems such as corrosion, metal loss, pitting, and hydrogen stress cracking.
Pigging allows for cleaning and testing of pipeline at the same time without affecting the flow of product in the pipeline, thus reducing the overall cost of pipe inspection.
Some types of pigs are:
Polly foam can navigate short bends and tees and port valves and come in different densities depending on their application and requirement. Polly foam can be used to lightly remove abrasion and for sealing.
These pigs have a multi-disc configuration and can be used for different purposes such as removing liquids, controlling build up, and in pipeline commissioning.
Robotic Pipe Inspection
All pipelines are not piggable, and all pipelines do not need pigs. However, all pipelines can be use robotic inspection. Unlike pigging, robotic pipe inspection only inspects, and has nothing to do with cleaning.
In fact to carry out a through robotic inspection, the pipeline to be inspected has to be cleaned of all build up and debris. Robotic pipe inspection is carried out using cameras mounted on crawlers that are self-propelled. The modern robotic crawler can carry sensors and tools through wastewater and industrial pipes even when submerged and can travel up to 2.9 km from the access point.
The robotic crawler is designed to easily transport sensors and tools through dewatered pipe, or while submerged in potable, raw water, or wastewater. The instrument can inspect pipelines at a speed of 6 meters per minute for pipes 200 mm or less in diameter, and 12 meters per minute for larger pipes.
Modern innovations in video inspection of pipes allow for tilt and pan for closer inspection, fish eye lenses that enable 180° view at any point, laser systems to measure the pipes profile, rotation capability, lighting options to illuminate its surroundings, and sonars for flooded pipe sections or inverts.
There are different kinds of cameras that can be used for robotic inspection.
Lateral launch cameras
Lateral launch cameras are capable of inspecting mainline and laterals simultaneously and can inspect mainlines to a distance up to 1000 feet from the entry point and laterals up to 150 feet from the mainline.
Push cameras are water-resistant and are inserted into the drain or sewer line by pushing the camera into the system. The inspection apparatus consists of a push rod with an attached camera. The push rod can be up to 200 meters in length making it useful for inspecting long pipelines.
Axial cameras are generally made of stainless steel and fabric tubing that helps the camera to slide easily around bends. It has an automatic self-leveling feature that always provides an upright picture.
Self-leveling cameras are a crucial part of a trenchless inspection process. Due to the circular cross section of the pipes, it is not possible to keep the robot in a horizontal position. The self-leveling feature of these cameras are mounted on a swivel arrangement that helps hold the lens upright and provide upright images at all times even when the camera is tilted.
What We've Learned
Pigging and robotic inspection have become an important part of trenchless operations. These methods have made it easier to inspect new pipelines for commissioning, and for inspecting old pipelines for damage before selecting a trenchless rehabilitation method.
This eliminates the need for digging up entire pipe sections for repair and instead can be used to focus on problem areas that need immediate attention.
Robotic inspection is more expensive than pigging and is more appropriate for detailed inspection of shorter runs of a pipeline where damages are expected or known to exist.
Pigging is the method of choice for inspections covering great distances. Lines more than 1,000 miles long have been inspected by the single pass of a pig.
Before deciding on a method, it is advisable for the contractor to make a cost estimate of both methods in order to determine the most appropriate, cost effective and time saving method for the particular project at hand.