Pipeline maintenance is vital to managing risks and the flow of product in oil and gas pipelines. Consequently, there are various reasons for pigging a line. According to extensive research conducted by T.D. Williamson, these reasons fall into two main applications, as outlined below.
- Maintain continuous and optimum operations:
- Cleaning the pipeline -- to remove wax, debris, scale, other unwanted products and hence prevent corrosion or buildup reducing flow.
- Batching products in liquid pipelines – to separate diesel fuel from aero jet fuel.
- Displacing product from the pipeline – to remove hydrocarbons before decommissioning.
- Treatment of the internal surface – deployment of a corrosion inhibitor.
- Gauging the internal bore of a pipeline – to assess if there are any restrictions
inflow or bore passage issues often before a more complex tool is used.
- To stop
flowor isolate a section of pipeline– to replace a valve or section of pipe.
- Ensure the integrity of the pipeline:
- Inspection of the pipeline (using an inline inspection [ILI] tool) to assess its integrity – assessing the pipeline for damage, such as dents or corrosion.
Types of pigs
When thinking about pigs, consider them to be similar to cars. There are many manufacturers that produce different versions and even different
The simplest of
A Selection of Pig Types
Often to get a very dirty pipeline clean, it is necessary to use a sequence of pigs called a “pig train” or progressive pigging. The selection of the pigs, the sequence and the number of pigs is often determined from experience, but this can change in the field, as the debris comes in from each run. Also, there is a class of pigging that does not use mechanical pigs but such things as gels, liquid batches and even ice.
When it comes to intelligent pigs, again there are different types, depending on what the operator wants to detect. Here is a list of ILI tools and their primary purpose:
- Caliper - this is a
low resolutiontool mainly used to detect diameter changes.
- Deformation - a much higher resolution tool used to detect and accurately size geometric anomalies.
- Magnetic Flux Leakage (MFL) - detects volumetric metal loss, mill anomalies, and extra metal.
- Low field axial Magnetic Flux Leakage (LFM) - identifies changes in the steel microstructure
inthe pipe material.
- Circumferential Magnetic Flux Leakage (CMFL) - provides inspection of longitudinal pipe axis.
- Spiral Magnetic Flux Leakage (SMFL) - provides inspection of longitudinal pipe axis.
- Ultrasonic Wall Measurement (USWM) - detects volumetric metal loss and mill anomalies.
- Ultrasonic Crack Detection (USCD) - locates anomalies of zero width (cracks) in liquid lines.
- Electro-Magnetic Acoustic Transducer (EMAT) - locates anomalies of zero width (cracks) in liquid and gas lines.
- XYZ mapping - enables high-resolution mapping of the pipeline centerline to sub-meter accuracy when tied to above-ground coordinates.
- Combination tools - multiple sensors on one inspection platform providing enhanced characterization and alignment of anomalies.
Combination (Multiple-dataset) Tool
Another class of pigs are those used for isolation. These generally comprise of:
- High-friction pigs for temporary flow stopping of lower pressure pipelines.
- Activated sealing pigs which are again used for isolation of lower-pressure pipelines.
- Double block isolation pigs, which are used where safety is paramount and leakage cannot be tolerated.
Double Block Inline Isolation Tool
When to pig and how often
In maintaining your pipeline, the next question related to pigging is “when should you pig and how often?” There are a variety of circumstances that determine when and how often you should pig. Read this valuable information for details on maintaining and keeping your pipeline safe, throughout its life cycle.
Author: T.D. Williamson
Read the article online at: https://www.worldpipelines.com/special-reports/20122017/integrated-pigging-solutions/