Decommissioned Pipeline Mercury Assessment

Benefits

Atteris delivered value to the client by: • Defining possible mercury decontamination methods for the pipeline. • Providing a cost estimate for the decontamination operation, which was prepared considering a stand-alone mobilisation/demobilisation of intervention vessels, as well as a sensitivity case using intervention vessels of opportunity.

Background

Sections of a decommissioned carbon steel pipeline routes under areas of indigenous cultural significance. At the time of the assessment, the pipeline was filled with Nitrogen and pressurised. Because of this, the Client wanted to understand whether there is a risk of mercury contamination of the pipeline.

Mercury is a commonly found in gas-condensate pipeline systems, as iron is one of the few metals that cannot form an amalgam with mercury. Inside a carbon steel pipeline, the potential contamination can be due to the presence of free mercury droplets and mercury compounds trapped within mill scale and corrosion products. Standard pigging and cleaning operations can only remove larger droplets of liquid mercury which are not bound to the surface of the pipeline.

Work Performed by Atteris

Atteris estimated the extent of mercury contamination in a pipeline to determine whether it was environmentally acceptable. The assessment considered data from X‐ray fluorescence (XRF) analysis, book values for contamination and inferred Hg contamination based on historical onshore Hg removal bed change‐out data.

As the estimated mercury concentration did not meet acceptance criteria, Atteris assessed decontamination methods including the use of lixiviants such as iodine/iodide and nitric acid and chelating agents such as citric acid and ethylenediaminetetraacetic acid (EDTA). Other decontamination methods were also assessed, including conversion to environmentally benign compounds and amalgams.

A high-level methodology for decontamination was recommended and a cost-estimate for performing the operation was provided.