Caliper Tool & Caliper Pigging
After constructing a new pipeline system, there are various steps you must follow to ensure it operates smoothly. One step involves the pipeline pre-commissioning process.
The pipeline pre-commissioning process is necessary to ensure that your pipeline can safely transport products when in operation. This process examines several factors of your pipeline, including integrity and cleanliness.
When inspecting the integrity of your pipeline, American Pipeline Solutions uses a unique process—caliper pigging. This process is integral in determining the overall integrity of your pipeline system.
At APS, we help pipeline operators stay ahead of issues through high-accuracy caliper pigging inspections. Our caliper tools are designed to detect changes in a pipeline's internal diameter, such as dents, ovality, and bulges—conditions that may compromise the flow or integrity of the asset. Whether used during commissioning or as part of a lifetime asset integrity plan, caliper pigging plays a critical role in maintaining safe, efficient operations.
Keep reading to learn about American Pipeline Solutions’ caliper pigging process, when APS uses our caliper tool, and more.
What Is Caliper Pigging?
Caliper pigging uses a specially designed pigging device, known as a caliper tool or caliper pig, equipped with mechanical arms or fingers. As the pig travels through the pipeline, these arms detect and record variations in the internal diameter, enabling engineers to pinpoint dents, bulges, buckling, ovality, and other deformations.
This information is critical during the pipeline pre-inspection and qualification process. The data collected helps assess whether the pipeline is suitable for product transportation and informs further steps such as integrity testing and commissioning. Caliper pigs are often used alongside intelligent pigging tools like ultrasonic and magnetic flux leakage (MFL) tools for comprehensive inspection.
Why Use Caliper Pigging?
Pipeline geometry changes often go unnoticed—until they cause pressure drops, flow disruptions, or even ruptures. Caliper pigging helps address issues before they escalate.
Common Anomalies Detected
Dents – Caused by third-party damage, ground movement, or handling during installation.
Ovality – A circular pipe becomes slightly flattened, often from soil pressure or temperature cycling.
Bulges and Pipe Expansion – May signal overstress or yield from internal pressure changes.
Buckling – A sign of axial stress, typically due to temperature, ground shifts, or improper installation.
American Pipeline Solutions’ Caliper Pigging Process
Caliper pigging is part of one of American Pipeline Solutions' pipeline pre-commissioning process.
Before a caliper tool can be used, the pipeline must be cleaned of any debris. American Pipeline Solutions clears a pipeline of debris by pigging the pipeline.
Once the pipeline has been cleared of debris, it is ready for the caliper pigging process. The caliper pigging process uses a special type of pigging equipment, known as a caliper tool or caliper pig. What makes the caliper tool unique is its design.
The body of a caliper tool is designed with mechanical sensors or arms. These mechanical fingers or arms are crucial to the data gathering process while the pig is in the pipeline. As the caliper tool runs through the pipeline, these sensors record the pipeline’s internal structure.
After the caliper pigging process is complete, American Pipeline Solutions confirms that the data was gathered correctly. This step is necessary for determining whether or not the caliper pig must run through the pipeline a second time.
Once the data is confirmed, the pipeline is ready for various pipeline tests, such as pipeline integrity testing.
Caliper Pig Tool Components and Capabilities
Modern caliper pigs are highly advanced and feature several components that enhance their accuracy and utility:
1. Mechanical Arms
These measure the distance from the center of the pig to the pipe wall to assess ovality, dents, bulges, pipe expansion, and buckling.
2. Odometer Wheels
Track the distance traveled and aid in identifying the location of any deformations.
3. Inertial Measurement Units (IMUs)
Record XYZ movement to create a precise 3D map of the pipeline's internal route and shape.
4. Driving Cups
Provide a tight seal and propulsion within the pipeline while adjusting to minor changes in diameter.
These tools can be designed for a wide range of pipeline diameters, typically from 4" to 52", and custom tool development is also available.
What Data is Gathered With Caliper Pigging?
American Pipeline Solutions uses a caliper tool to measure the internal structure of your pipeline. Specifically, APS will use a caliper tool to record your pipeline’s internal diameter, wall thickness, pipe fitting, and any anomalies in the pipe.
Gathering this data allows APS to detect any issues in your pipeline before it is put into commission.
One example of how APS uses this data can be seen when recording the pipeline’s internal diameter. Once the pipeline’s internal diameter is recorded, APS will compare this data to the piping and instrumentation diagram. As a result, APS can confirm that your pipeline’s measurements align with what is specified in its piping and instrumentation diagram.
Benefits of Caliper Pigging
Caliper pigging serves a wide range of purposes throughout a pipeline’s lifecycle—from construction and pre-commissioning to general inspection, maintenance, and even decommissioning. It plays a vital role in:
1. Identifying Deformations
Such as ovality, dents, bulges, and buckling that may compromise performance or lead to failure.
2. Mapping Pipeline Geometry
Producing a precise, location-based 3D map of the pipeline is essential if the pipeline has shifted due to environmental or mechanical forces.
3. Supporting Regulatory Compliance
Ensuring that a pipeline meets safety and quality standards before commissioning.
4. Minimizing Risk and Downtime
By detecting and addressing problems early, operators can avoid major repairs and extend the system’s lifespan.
Why Is Caliper Pigging Important?
Pipelines can suffer from internal deformation, debris buildup, or poor installation. Left undetected, these conditions may reduce flow, create pressure inconsistencies, and ultimately lead to pipeline failure. Caliper pigging provides early identification of structural issues, enabling timely repairs and ongoing maintenance.
More than just a geometric analysis tool, caliper pigging contributes to a comprehensive pipeline integrity assessment. It also supports regulatory compliance and ensures a safer handover of new pipelines.
3D Mapping and Pipeline Positioning
Ground shifts, thermal expansion, and construction activity can move a pipeline from its intended position. Our caliper pigs—equipped with an IMU system—generate high-accuracy location-based data that helps pipeline engineers:
Reconstruct pipeline routes
Identify the bending strain from misalignment
Detect sag or elevation shifts
This positional data is essential for high-consequence areas or environments affected by land movement, flood zones, or seismic activity.
Caliper Pig vs. MFL or UT Inspection Tools
Caliper pigging does not detect corrosion or wall thickness loss. Those issues require magnetic flux leakage (MFL) or ultrasonic testing (UT) pigs. However, caliper pigs are often run first to ensure the pipeline can safely accommodate those more advanced tools.
Caliper Pig = Detects dents, ovality, buckling, bulges (geometry)
MFL Tool = Detects corrosion and wall thinning (metal loss)
UT Tool = Measures precise wall thickness via ultrasound (high accuracy metal loss)
These tools are complementary and often used together as part of a comprehensive inline inspection program.
When Does American Pipeline Solutions Use Caliper Pigging?
American Pipeline Solutions utilizes its caliper pigging tool during the pipeline pre-commissioning process. This process is typically used when a utility provider has constructed a new pipeline. The pipeline pre-commissioning process is required when a utility provider takes over ownership of the pipeline from a contractor.
American Pipeline Solutions can provide pipeline pre-commissioning and caliper pigging services to numerous types of pipeline systems, including:
Newly built or constructed pipelines
New water and wastewater pipeline systems
New natural and other types of gas pipeline systems
Newly constructed and installed pipelines on academic campuses
This is by no means an exhaustive list of the types of pipelines that can utilize APS’ caliper pigging services. Customers are encouraged to contact the APS team to determine the best process for their newly constructed pipeline.
FAQs:
What is a caliper pig and how does it work?
A caliper pig is a specialized inspection tool fitted with mechanical arms or fingers that measure changes in a pipeline’s internal diameter. As it travels through the line, those arms deflect when they encounter dents, ovality, bulges, or buckling. The tool records this data so engineers can locate and quantify deformations along the pipeline.
What kinds of anomalies can caliper pigging detect?
Caliper pigging identifies geometry-related issues such as dents, ovality, bulges, pipe expansion, and buckling. These conditions may be caused by third-party damage, soil movement, temperature cycling, or construction errors. Detecting them early helps prevent pressure inconsistencies, flow restrictions, and potential failures once the pipeline is placed into service.
Why is caliper pigging important before commissioning a pipeline?
Before a new line is commissioned, operators need to confirm that it matches the design geometry and can safely carry product. Caliper pigging verifies internal diameter, checks for construction-induced damage, and confirms that no significant deformations are present. This step supports integrity testing, reduces start-up risk, and provides a documented baseline for future inspections.
What data does a caliper tool collect during a run?
A caliper tool measures internal diameter changes, records the position of dents, bulges, and ovality, and can capture XYZ movement through an inertial measurement unit. Combined with odometer readings, this data produces a location-based picture of the pipeline’s internal geometry and route. APS compares these results to design drawings or P&IDs to confirm that the as-built line matches the specifications.
Does caliper pigging replace MFL or UT inspection tools?
Caliper pigging does not replace MFL or UT inline inspection tools. A caliper pig focuses on geometry—dents, ovality, buckling, and expansion—while MFL and UT tools are designed to detect corrosion and wall thickness loss. In practice, caliper pigs are often run first to confirm tool passage and geometry, followed by MFL or UT for a full metal loss assessment.
Why must the pipeline be cleaned before running a caliper pig?
Debris left inside a pipeline can interfere with the mechanical arms on a caliper pig and distort the measurements. APS cleans the line with appropriate pigs before caliper pigging so the tool can move freely and contact the true pipe wall. This step improves data quality, reduces the chance of hang-ups, and minimizes the need for repeat runs.
What pipeline sizes can caliper pigs be used in?
Caliper pigs can be designed for a wide range of diameters, typically from 4 inches up to 52 inches. Tool configuration and arm design are adjusted to match the line’s size, wall thickness, and geometry. APS scopes each project to ensure the selected caliper tool is compatible with the pipeline’s diameter, features, and operational constraints.
How does caliper pigging contribute to regulatory compliance and handover?
Caliper pigging provides documented evidence that a new or modified pipeline has acceptable geometry before it is placed into service. The data supports pre-commissioning and integrity testing requirements, and helps owners demonstrate that the line meets internal and regulatory standards. For asset handover, caliper reports form part of the integrity record delivered from contractor to operator.
Are you looking for pipeline pre-commissioning and caliper pigging services?
Contact American Pipeline Solutions to learn more about our effective caliper pigging and pipeline pre-commissioning services today.
