In-line inspection (ILI) methods and pipeline integrity gauges

What Is In-Line Inspection?

An asset integrity management program aims to determine the condition of a pipeline and the maintenance required to avoid a critical failure of the asset using nondestructive testing (NDT) methods. In-line inspection (ILI) tools, referred to as intelligent pipeline integrity gauges (PIGs) or smart PIGs, carry a variety of sensors to inspect pipelines for internal and external corrosion, geometric deformation, lamination, cracks, and other defects.

Dexon has been involved with in-line inspection services since 1976 and has performed successful inspections on every continent for many of the world’s largest multinational oil and gas companies.

Selecting the Correct ILI Tool and Inspection Method

Selecting an appropriate ILI method is based on the product the pipe carries, perceived asset threats, and the physical and operational characteristics of a pipeline. Dexon’s pre-inspection process identifies potential pipeline threats such as:

• Metal loss (internal and external corrosion, slotting, pitting, pinholes and grooving)

• Geometric deformations (dents, buckling, rippling/wrinkling, gouges, ovality and peaking)

• Cracking and crack-like anomalies (weld cracks, stress corrosion cracks, fatigue cracks, hook cracks, laminations, and crack colonies)

In-Line Inspection Methods

Caliper and Geometric In-Line Inspection PIGs

Caliper PIGs carry electro-mechanical sensors to determine the geometric properties of a pipeline, measuring dents, bulging, buckling, and other geometric deformations. Caliper pigging is also used for location mapping and the geographical positioning of pipeline features.

Magnetic Flux Leakage (MFL) In-Line Inspection PIGs

Magnetic flux leakage (MFL) PIGs use powerful magnets to magnetize the pipe wall to saturation. Triaxial hall sensors measure magnetic flux leaking from defect sites.

Ultrasonic (UT) In-Line Inspection PIGs

Ultrasonic (UT) ILI PIGs measure metal loss, corrosion, cracking, and gouges in a pipeline by direct measurement of ultrasonic pressure waves inside the pipe wall. These waves provide information that can be used to measure remaining wall thickness or detect and size cracking. Ultrasonic ILI PIG Configurations include:

• UT Rotary (UT-R)

• UT Multi-Channel Ring (UT-MC Ring)

• UT Multi-Channel Octopus (UT-MC Octopus)

• UT-CS Hawk Crack Detection, Sizing, and Monitoring (UT-CS Hawk) 

Inspection Methods and Advantages

Magnetic flux leakage (MFL) and ultrasonic testing (UT) are the two primary methods used for the in-line inspection of pipelines. Dexon provides an extensive fleet of ILI PIGs covering both inspection methods suitable for all pipeline diameters.

Magnetic flux leakage (MFL) and ultrasonic testing (UT) are the two primary methods used for the in-line inspection of pipelines. Dexon provides an extensive fleet of ILI PIGs covering both inspection methods suitable for all pipeline diameters.

Ultrasonic In-Line Inspection Advantages

• Direct wall thickness measurement

• Collection of raw C-scan data

• High-resolution sampling

• Inspection of ferrous and no ferrous materials such as HDPE

• Magnetic flux leakage in-line inspection advantages

• Inspection of gas product lines

• High inspection speeds

• Ability to inspect finned tubing

• High sensitivity to pitting in carbon steel

Intelligent pigging inspection data quality is heavily affected by pipeline cleanliness, and pipeline cleaning programs should be carried out before each inline inspection run. Dexon’s Pipeline cleaning program combines cleaning PIGs and gauging PIGs to ensure there is no debris or obstructions in a pipeline that could lead to unreliable inspection data or a stalled or stuck PIG.

Considerations for In-Line Inspection

Several factors need to be considered prior to any pipeline inspection. Dexon will conduct a thorough examination of the physical and operational characteristics of a pipeline to assess its piggability and recommend inspection solutions.

PIG Launchers and Receivers

PIG launchers and receivers are devices that allow for the insertion and retrieval of PIGs without interrupting product flow. Launchers and receivers are required for all pipeline pigging operations. Temporary launchers and receivers can be built and installed as needed. Dexon offers PIGs equipped with a flotation device alleviating the need for a receiver for subsea HDPE mine tailing line inspections.

Bends

Typically, most in-line inspection tools and hard-body utility PIGs are designed to negotiate bends with a radius of 3D or greater. Most Dexon intelligent PIGs are capable of passing 1.5D bends with customization available for 1D bend return bends.

Internal Coating

Internal coatings can potentially interfere with data collection by some in-line inspection tools and a correct understanding of the coating material and bonding method needs to be established.

Wall Thickness

Piping thickness is a critical factor when selecting an inspection technology. Ultrasonic tools can inspect extra heavy wall piping while MFL technology has limitations.

Internal Diameter (ID Bore)

Dual diameter pipelines create additional considerations for in-line inspection due to the risk of the PIG stalling at the diameter change. Dexon has successfully pigged dual-diameter pipelines with a 15% change in pipe ID, although each case requires individual assessment.

In-Line Valves

All in-line valves should be opened fully (full bore) to facilitate pigging operations. Dexon physically checks all mainline valves to ensure full bore for every pigging inspection. Flapper check valves may require removal or locking in the open position during the inspection. If removal or locking is not practical PIGs may be fitted with custom engineered nose cones for automatic valve opening.

Tees

Branch connections to the pipeline may require barring to prevent the ILI tool from becoming lodged. Customized PIG design is available to overcome unbarred tees and each case is assessed by mechanical engineers.

Wyes

Wyes can be a major obstacle for PIGs and inspection tools to navigate. Dexon has successfully designed, built, and tested ILI tools that can negotiate Wyes.

Flexible Risers

Flexible risers consist of several layers of metallic and elastomeric materials. Whilst no tools currently exist that can inspect all layers of a flexible riser, Dexon’s tools have passed successfully through flexible risers and into the FPSO turret where conventional inspection takes place.

PIG Speed

Flow rates must be monitored and controlled to allow for optimum pipeline inspection results. Typically, UT intelligent PIGs require lower flow rates whereas MFL PIGs can accommodate much higher flow rates. Dexon offers flexible customized solutions to address client inspection requirements.

Temperature

Intelligent PIGs have a specific temperature range within which they function properly due to onboard electronic equipment. The upper limit of this temperature range is generally less than 40°C, although Dexon’s UT fleet can operate in temperatures as high as 65 °C, with customized tool design that offers much higher operating temperatures.

Pressure Limitations

Intelligent PIGs typically have maximum pressure limitations between 90 to 150 bar. Dexon offers customized tool development for high-pressure pipelines with customization of up to 300 bar with special mechanical considerations.