What is the Difference Between Pull-Through & Push-Through Testing for In-line Inpsecion (ILI) Tools?

What is the Difference Between Pull-Through & Push-Through Testing for In-line Inpsecion (ILI) Tools? 

Before an in-line inspection (ILI) tool is deployed, engineers must answer two questions: 
1. Will the tool pass the pipeline? 
2. Will it accurately assess defects? 

The most advanced inspection technology in the world means nothing if it gets stuck 10 kilometers into a run—or delivers terrible data while running through a pipe. 

That is where pull-through and push-through testing come in. 

While similar, the two methods serve different roles in validating ILI tool performance.  

Push-Through Testing 

Push-through testing focuses on mechanical passage and operational performance. 

In this setup, engineers propel the tool through a test string using hydraulic or pneumatic force. This allows them to evaluate:
• Passage through restrictions and tight tolerances 
• Tool flexibility in bends and diameter changes 
• Compression behavior under forward load 
• Mechanical wear over long distances 

Because the tool is driven dynamically through the line, push-through testing helps determine whether it can both navigate the pipeline geometry and operate reliably under realistic movement conditions. 

However, these tests are resource-intensive, typically requiring pumps, large water volumes, and larger execution teams. 

Pull-Through Testing 

Pull-through testing focuses primarily on defect detection performance under controlled conditions. 

Here, the tool is pulled through the pipeline using a winch or similar system, allowing engineers to evaluate: 
• Ability to detect and size defects 
• Signal quality and sensor response 
• Magnetization effectiveness in thick-wall pipelines (for MFL tools) 

Pull-through testing is ideal for validating inspection capability without the added complexity of setting-up a massive pump & bringing a large team to the test yard. 

However, pull-through testing does not fully replicate real operating conditions or flow-driven tool behavior. It is also not possible for technologies that rely on liquid coupling, such as ultrasonic testing. 

Push-Through vs. Pull-Through Wrap Up  

• Push-through = navigation and operational validation 
• Pull-through = controlled defect detection validation 

In practice, both methods are often used together to prepare a tool prior to deployment.