Using Differential-Pressure Data to Effectively Remove Black Dust

Black powder in pipeline as a threat to in-line inspections

A 204-km, 16” gas-transportation pipeline suffered from a black-dust problem ever since it had been commissioned. Despite regular cleaning and maintenance, large amounts of black powder continued to accumulate, posing a major threat to the success of pending in-line inspections.

The challenge

A preliminary pigging study had concluded that potentially hundreds of tons of black powder were currently present in the pipeline. Therefore, the preferred removal option would be a progressive mechanical cleaning approach using various types of pigs. Not only was the sheer amount of debris a concern to the pigging experts, the known wear on cleaning tools in black-dust pipelines also raised concerns about the associated risk of pigs becoming lodged in the pipeline, possibly impacting progress in the line.

During a 3-year pigging campaign, the operator performed 88 pig runs, 16 of which took place in a 3-week period in an attempt to prepare the pipeline for the upcoming scheduled ILI program. Throughout the campaign, the cleaning runs continued to bring 40 to 80 kg of sludgy debris into the receiver trap, which was only a fraction of the total amount present in the pipe. This was not acceptable for a successful ILI run, as the presence of large amounts of debris would significantly affect the tool's sensors and thus compromise the quality of the inspection data.

Our solution

ROSEN's approach to this case began by clarifying the objectives and framework of the cleaning project. The pipeline was to be cleansed of black-powder deposits to a level that would meet the criteria necessary to ensure the success of an ILI. The key geometrical parameters and operating conditions were as follows:

  • 204-km length
  • 16-inch diameter
  • High abrasion due to missing internal coating
  • Full-bore valves
  • No tight bends
  • Relatively constant wall thickness
  • 70-bar operating pressure
  • Average velocity of 3 m/s

After understanding all of the operational parameters, assessing the solutions available and reviewing the well-documented pigging records of the runs previously performed by the pipeline operator, ROSEN's experts proposed an aggressive mechanical cleaning campaign.

Accordingly, ROSEN Ultimate Clean tools were prepared to run alternately in the high-wear environment. They featured two main configurations:

  • Aggressive scrapers with descaling cups to loosen debris from the pipe wall
  • Bulldozer tools with high-density pencil brushes to mobilize the loosened debris downstream to the receiver trap at the end of the pipeline

Additional features for both pigs included:

  • Spider-nose bypass arrangements
  • Magnets to attract magnetic dust
  • Spring-loaded brushes with a near-constant pre-load to the pipe wall
  • Electromagnetic transmitters (ITX) for pig tracking and locating purposes
  • Pipeline data logger (PDL) for recording pipeline and pig parameters during the cleaning runs

The PDL instrument provides an insight into the process of cleaning. Among the parameters recorded, the differential pressure (DP) represents the propulsion force acting on the pig itself. The force comprises both the actual friction between the seals and the pipe wall and possible friction due to debris being pushed by the cleaning tool.

Once the pipeline cleaning tools were in place, it was ensured that the approach complied with applicable industry standards, regulatory requirements and the pipeline operator's HSE guidelines. The effectiveness of the solution became quickly apparent. The analysis of the recorded PDL data showed how the loose dust was transported downstream and accumulated in the last section of the pipeline before finally being removed. After the first 24 runs of the cleaning campaign, the debris removed changed in its consistency: it became visibly drier.

After 46 cleaning runs, conducted over a period of 4 months, the quantity of dust recovered per run was down to only 14 kg. This was significant, considering that peaks previously had been up to 625 kg. Thus, the pipeline was considered sufficiently cleaned for a successful inspection. The final RoCombo MFL-A/XYZ in-line inspection service successfully collected data over the complete 204-km pipeline length in a single run.

Your benefit

The custom definition of a cleaning program and dedicated collaboration enabled a successful cleaning of the pipeline. The result met the standards required to undertake an ILI that produced high-quality data. In addition, the measurement instruments installed for pig tracking and the recording of various parameters during the cleaning runs provided additional insights, which increased the efficiency of the pipeline cleaning program while reducing the risks. The PDL data made it possible to detect that dust was accumulating near the end of the pipeline during the cleaning process and allowed for the removal of the accumulated dust prior to the start of the inspection pig runs.

The high quality of the data continues to benefit subsequent analyses and thus decision making in the integrity management program, which contributes to the safe and incident-free operation of the pipeline.