This paper considers some of the challenges and learnings associated with the application of chemicals for preservation of coated pipe/flow line for a major LNG project in Australia. This includes a comparison of the effectiveness of biocide and oxygen scavenger chemistries for treating seawater. It also discusses monitoring philosophies and the unique approach taken in designing and optimizing the chemical injection system to address the environmental and technical challenges of this project.
The gauge testing of flowlines and pipelines in large-scale LNG projects of Australasia is an important compliance stage required prior to commissioning. Due to the extended timeline necessary to complete downstream infrastructure, pipelines and flowlines are usually deployed well before the treatment facilities are constructed, and may be shut-in awaiting connection for relatively long durations, following the hydrotesting procedures. If left unprotected, the pipeline becomes susceptible to corrosion predominately due to the presence of bacteria, but also due to the presence of dissolved oxygen and the saline nature of the hydrotest fluid which is typically seawater. Chemical treatment strategies for preserving these lines can consist of a bacteria control agent (biocide), and an oxygen scavenger, and occasionally a corrosion inhibitor which is added to mitigate corrosion in case all the oxygen has not been removed. Treatment strategies are often dependent on the required shut-in duration, local environmental regulations, and the asset integrity management specifications defined by the operator.
For the project presented in this paper, the integration of data obtained from the various stages of testing and computational modeling supported the design of an effective treatment program for this application. This was achieved despite of a number of unique challenges arising from stringent environmental constraints and the tight operating specifications required in this project.
A case history is provided describing the novel approach adopted in selection of pipeline preservation treatment chemicals through the assessment of various parameters, including laboratory studies (conducted to verify product performance under different operating conditions), as well as Computational Fluid Dynamics (CFD) modeling studies aimed at optimizing the chemical injection location, residence time, and flow regime. It is anticipated that such a systematic approach in design and optimization of treatment programs can provide a multitude of benefits in similar projects operating in environmentally-sensitive locations.