Pipeline Wear: The Hidden Cost in Dredging Estimates

Pipeline wear can have a direct effect on the cost and duration of a dredging campaign. Reaching the allowable pipeline wear limit can bring dredging to a halt while the pipeline is inspected, rotated or replaced. Project estimates therefore need to account for spare pipe, maintenance labour, vessel and plant standby, and resulting lost production. Reliable pipeline wear estimates help turn this operational risk into planned allowances for cost and downtime.

To support these estimates, in2Dredging (i2D) is further developing an in-house empirical pipeline wear model for predicting wear in straight slurry pipelines. The model improves slurry pipeline wear predictions by relating measured wear to site conditions, operating parameters and equipment characteristics that influence wear.

Why Wear Rates Belong in Project Estimates

A production estimate describes how quickly a dredger can excavate and transport material. It does not indicate when the pipeline may require maintenance or replacement. Two dredging options with similar hydraulic performance can therefore have different maintenance costs and exposure to downtime.

Despite this, slurry pipeline wear is often omitted from project estimates. This can leave no specific allowance for rotating pipelines or replacing pipeline sections, and the associated interruption to dredging.

The practical question is how much slurry can pass through a pipeline section before its allowable wall loss is reached. Relating this wall loss to the volume transported provides a pipeline wear rate. This rate provides an indication of when the pipeline may need to be inspected, rotated or replaced. It can also inform the required quantity of spare pipe, the expected number of interventions and the associated downtime.

These pipeline wear estimates can then be progressively refined as actual wall-thickness measurements, slurry volumes and operating data become available during the works.

Developing the Pipeline Wear Model

Pipeline wear results from the interaction between abrasive particles, the pipeline-wall material and the slurry flow. Our research initially considered a broad range of operating, sediment and material properties that could potentially influence wear.

The empirical correlation used in the pipeline wear model was subsequently reduced to a small set of variables. These variables were selected based on what could be consistently supported by the measured wear data available for calibration. Regression analysis was then used to fit the correlation. Its response was also checked against expected physical behaviour to avoid selecting coefficients based on statistical fit alone.

Particle characteristics and pipeline-wall material properties remain important influences on slurry pipeline wear. However, available datasets rarely vary these parameters sufficiently to isolate and quantify their individual effects. Loewen’s 2013 research thesis highlighted this data gap. Similar limitations were also encountered during a pipeline wear research program overseen by Simon Burgmans in the early 2010s.

More recent studies have added useful measurements, but comprehensive datasets remain scarce. Slurry pipelines are routinely monitored to protect their integrity. However, the resulting wear records are seldom accompanied by complete supporting data. This includes the slurry, particle, pipe material and operating data required to develop and validate a broadly applicable wear model.

From Wear Prediction to Maintenance Planning

For each relevant pipeline section, the predicted pipeline wear rate can be related to cumulative slurry throughput. A planning calculation compares the available wear allowance with the predicted wall loss per unit in-situ volume of slurry transported. The available wear allowance is calculated from the initial wall thickness, less the minimum acceptable thickness and an appropriate margin. This provides an indicative slurry throughput before intervention may be required.

Combining this result with the expected throughput and operating hours provides an indicative inspection, rotation or replacement window. This allows pipeline wear estimates and required maintenance to be incorporated directly into the dredging program and cost estimate.

The result is generally more useful when considered as a range rather than as a single predicted replacement date. Higher and lower wear scenarios can be carried through the program and cost estimate. This allows their effect on spare pipe requirements, maintenance time and production to be assessed.

Once dredging commences, measured pipeline wall thickness, actual slurry volumes and operating conditions can be used to revise the pipeline wear estimates. This allows maintenance to be scheduled before a failure results in an unplanned stoppage.

Where the Pipeline Wear Model Applies

The pipeline wear model has been developed for straight pipeline sections. Bends, fittings, pumps and other components experience different particle trajectories and local wear mechanisms and therefore require separate assessment.

Wear can also be uneven around the circumference of a straight pipe, particularly where coarse solids concentrate near the invert. An average predicted pipeline wear rate should therefore not be interpreted as confirmation that the most exposed part of the pipeline wall has sufficient remaining thickness.

i2D tests the model against measured wear data and assesses how its predictions respond to the principal input parameters. Additional field measurements covering different sediments, pipe materials and operating regimes will further support this assessment. They will also help establish where the correlation can be applied reliably and where project-specific allowances or calibration are required.

The pipeline wear model is intended as an engineering and estimating aid. It does not replace pipeline inspection and monitoring, nor should its predictions be interpreted as a guarantee of service life.

Integrating Pipeline Wear into Dredging Estimates

Developing our own tools allows i2D to integrate slurry hydraulics, dredging production and pipeline maintenance planning into a single estimating workflow. The value of the pipeline wear model lies in making engineering assumptions visible. It also translates these assumptions into practical decisions about pipe selection, spare requirements, planned maintenance, downtime and project cost. As more measured wear data becomes available, the model can be further refined using both controlled data and measurements collected during dredging campaigns.