How Pigging Works in Trenchless Repair and Rehabilitation
There are 5 basic PIG models. With the right PIG, workers can inspect and clean large portions of utility lines without having to take them out of service.
Pigging is a pipeline cleaning and inspection technique utilized by many municipalities. These advanced tools can enter the line, clear it of debris, and take essential measurements without workers having to go into the line themselves. A more in-depth look at this technique can help new users understand the benefits of this trenchless procedure.
What is Pigging?
A Pipeline Inspection Gauge, or PIG, is a tool that goes into the line to clean and measure the wall thickness. By using ultrasonic and magnetic flux testing, the machine can determine if the walls are wearing thin or if there is corrosion building up along the interior. While the name does come from the acronym of PIG, it also derives from the high-pitched squealing sound of the ultrasonic testing, which resembles that of a pig.
How Does Pigging Work?
Workers insert the PIG into the pipeline through a pig trap or launcher. The PIG propels through the pipe driven by gas, liquid introduced for the sole purpose of moving the PIG or through the natural flow if the line is still in service.
Often, workers use pipe penetrating radar to locate areas in need of pigging, reporting findings back to the operator on Closed Circuit TV (CCTV), like Closed Circuit TV Inspection (CCTVI). Measurements taken from the PIG are analyzed and used to determine if rehabilitation is necessary.
Things to Consider
Pigging is an efficient way to monitor and clean pipelines without taking the line out of service. There are a few considerations workers need to make before beginning the PIG process and when choosing the right PIG to send into the pipe.
Before pigging a pipeline, workers first need to determine the pipe design and fittings. The overall design will affect the type of PIG used in the procedure. Additionally, using the data from the pipe penetrating radar, workers must consider what obstructions may block the PIG from completing its task. Finally, the project goals are essential to determine which PIG is necessary.
Choosing the Right PIG
When selecting a PIG, job goals are only a small part of the consideration when choosing the proper tool. Each of the following plays a role in selecting the optimal PIG to be used to inspect or clean the pipeline.
- PIG Length: the PIG length needs to be 1.5 to two times the length of the pipe section in which it travels.
- Driving Cups: PIG driving cups should be a minimum of 102% of the internal diameter.
- Guiding Cups: PIG guiding cups should be at least 99% of the internal diameter.
- Sealing Discs: PIG sealing discs should measure between 103 and 108% of the internal pipeline diameter.
- Gauge Plates: PIG gauge plates must measure a minimum of 95% of the internal pipeline diameter.
- Brushes: Attached brushes should be at least 103% of the internal diameter.
Types of PIGs
There are several different types of PIGs to perform tasks within the pipeline. While there is some overlap in task performance ability, each class has a specialty which makes it best suited for specific jobs.
Inspection PIGs are designed to gather information from within the pipe. The tool collects data using two methods, magnetic flux and ultra-sonic. Magnetic flux detects leaks, cracks, corrosion and flaws in the pipeline. Ultra-sonic testing measures the thickness of the pipe walls looking for overall wear and weakness.
Data collected and sent back to the operator includes line diameter and curvature, bends, temperature and pressure. Workers analyze the information to determine if and what rehabilitation projects are necessary.
A utility PIG goes into a pipeline for the specific purpose of cleaning the line. These PIGs are equipped with attachments to scrape and remove debris from the pipe as well as seal the pipeline and remove any liquids that are not supposed to be there.
There are three basic types of utility PIGs, each with a specific job design. Mandrel PIGs consist of a metal body with replaceable discs and brushes. They are designed to clean corrosion pitting and remove black powder and liquids.
Foam PIGs are used for to remove liquids and other debris from the pipeline. Of all utility PIGs, the foam PIG is the most common type used due to its extreme flexibility. Attached brushes remove stubborn material and hydro test water.
Solid cast PIGs offer both flexibility and ruggedness to clean corrosion and stubborn materials. These PIGs are considered a general-purpose option as users can combine different brushes and cups and discs to complete the job.
Specialty PIGs are used to isolate specific sections of a pipeline which needs to be cleaned, inspected or repaired. This tool keeps the pipe pressurized while workers complete their project.
Gel PIGs are used in conjunction with a conventional pick to help remove debris, hydro testing, condensation and dewater the line. In the case of a jammed PIG, this is the tool sent in to unstick the equipment.
Smart PIGs, also known as intelligent PIGs, are used for advanced inspection activities. They are sent into pipelines to gather data on corrosion presence and location and any wall irregularities. This tool tests for pitting, welding anomalies, hydrogen induced cracking and metal loss.
Intelligent PIGs provide cleaning and inspection simultaneously. The tool also gives readings on pipeline diameter, curvature, temperature and some bends using non-destructive inspection techniques such as ultrasonic testing.
With the right PIG, workers can inspect and clean large portions of utility lines without having to take them out of service.
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