Pipeline Integrity Management of Unpiggable Pipelines by Corrosion Modelling and Prediction Based on Topside Piping Inspection Data in the Mature Field Offshore North West Java
Authors: Iskandar Dedy , Hartawan Iman B. , Soelistiyono Dony , Soetjipto Hermanto , Irfan Fahmi 
Published: November 2020

Pertamina Hulu Energi - Offshore North West Java, also known as PHE-ONWJ, owns 426 subsea pipelines from which only 185 are active operating to support PHE-ONWJ's production activity and the rest, 241 pipelines, are inactive which status is either remain idle or being preserved. Need to be noted that 67% or 284 pipelines aged more than 30 years, which is more than its design life. From which, 120 pipelines are still actively operating distributing fluids such as Oil, Gas and 3-phase. Multiple events of leak have occurred which implicates PHE-ONWJ's production activity.

Based on observation, more than 90% of leak events occurred, were caused by internal corrosion. The specific cause is that PHE-ONWJ pipelines transports such fluids that contains corrosive agents such high CO2 content, sands or solid particles, SRB and water.

The existing integrity management plan such as in-line inspection, fluid sampling, chemical injection and others have been performed onto several pipelines. However, since the size of PHE-ONWJ's pipeline network facility is complex and massive, to perform in-line inspection to all pipelines is not economically beneficial. Moreover, performing in-line inspection induced high risk and not all of the pipelines are piggable either because of its design or operating condition. Therefore, by considering such conditions mentioned previously, an effective and efficient pipeline integrity management developed based on corrosion rate prediction from topside piping within corrosion circuit with pipeline.

It is clear unwanted event such leak shall interrupt PHE-ONWJ production activity, moreover the age of most pipeline facility are old which means it has probability to fail, even though not all leak event associated with the age of the pipeline. To maintain and predict failure event such as leak or even rupture, a corrosion model has been developed. This model is constructed from combining several parameters which are; fluid sampling, In-Line Inspection of several pipelines with different services, Topside piping inspection data, Operating history and pipeline design data. The model generated in the form of an equation that associates topside piping corrosion rate and pipeline corrosion rate which both were obtained from inspection data and the boundary is operating and design history of the pipeline itself.

The developed model or equation is continuously validated as In-Line Inspection (ILI) performed onto several pipelines that previously has been assessed by using the internal corrosion model. Since the model developed, an accuracy ranging from 80-99% has been achieved in predicting maximum internal corrosion rate of PHE-ONWJ's pipeline. Which later on, this corrosion model become as a basis in determining pipeline's integrity status, remaining life and assisted in assessing the pipeline risk which outcome are mitigation / action plan. All of these were obtained by only using topside inspection data.

Even though the corrosion model developed is able to represent PHE-ONWJ's pipeline internal corrosion rate, further study should be done to be applicable onto other facility or even company pipelines. Therefore, a joint study may be made to create such corrosion model for pipelines. The goal is to have an in-depth approach in managing matured and unpigable pipeline integrity that operates across the world with such effectiveness and ensure all stakeholders that the pipeline is safe to operate.