Testing Methodology to Improve Pig Designs for Unpiggable Pipelines
Fiberbuilt UPSF 2019 Paper: Use of Dry-Pull Testing to Predict In-Pipeline Performance Through Various Pipeline Anomalies
To reduce uncertainty and risk of pigging through difficult-to-pig pipelines, a best practice is to establish pig passage through any unpiggable features and pipeline geometries in a series of controlled above ground experiments.
Controlled flow loop testing using either pumped liquids or compressed gases as a driving medium can be used to prove pig passage through replicated pipeline defects or difficult-to-pig features. In this method, a partial pig or full pig train assembly can be inserted into an accessible above ground closed loop pipeline test system. The pig is driven through the loop using the energized drive fluids (liquids or compressed gases). Flow loop testing may closely simulate the actual pipeline conditions and passage of the pig through the features being tested due to the presence of compressed pipeline fluids around the pig body. Flow loop testing is complex and potentially dangerous due to the presence of energized fluids in an above ground pipeline test system. This type of testing can also be expensive due to the complex pumping/compression equipment required and handling of the fluids at surface.
An alternative method for testing pig passage is the use of a winch pulling test apparatus to pull the pig assemblies through the pipeline features being evaluated. In this method, a partial pig or full pig train assembly is inserted into an above ground pipeline test section. The pig assembly is simply pulled through the test section of pipe using the mechanical winch apparatus. The complexity and potential danger of using energized drive fluids can be eliminated as the test section can be operated open to the atmosphere with no elevated differential pressures.
Through past and ongoing product development and research efforts, Fiberbuilt has had the opportunity to test many different seal, brush and pig assembly combinations through both pumped flow-loop tests and dry-pull tests.
This paper outlines the dry-pull and closed-loop testing methods and limitations and compares the drag/passage data of various pig features through different pipeline anomalies. Several different pig features are isolated and evaluated separately: seals, radial cleaning brushes and complex corrosion pit cleaning brushes. Flow loop (differential pressure) and dry pull load test data for several complete pig assemblies are also presented and the results compared.
To illustrate a typical design-test-verify cycle used in the development of unique pigging tools for difficult to pig applications, the flow loop data proving passage of a new 3-inch to 6-inch multi-diameter cleaning pig is compared to the dry-pull test data through the same test section.
In summary, dry-pull testing pipeline pigs and pig components through difficult to pig features in a controlled environment can be a useful tool for rapidly proving and assessing pig passage. In conjunction with targeted design efforts, these dry-pull tests can be used to iteratively assess and improve pig designs to maximize performance.