Chemical Treatment Strategies for Pipeline Mothballing

Chemical treatment is a part of overall Conventional Natural Gas X pipeline mothballing program. Its effective implementation is the key for the success of preservation scheme. The biocide treatment involves pre-clean, biocide injection, corrosion inhibition for preservation and associated monitoring. There are basically two treatment options available. However, the chemicals selection and application in these two options are different. This must be considered in planning stage. An optimum treatment cannot be achieved by strategy switchover during the process. From the pipeline operational history and samples, the types of volume of residue are to be determined. For unpiggable sections, the possibility of foam brush, batching pigs and gel solution injection should be investigated.

For dry layup strategy, biocide/corrosion inhibitor solution will be pumped down to the line either by pumping pressure (non-piggable segments) or pigging heads (piggable sections). The pipeline will be drained and dried after the fly-by treatment and preserved under positive pressure nitrogen atmosphere.

To achieve premium result, the biocides of the selection have to be:

• Fast action(killing speed)
• Premium biofilm penetration
• Biodegradability
• No free formaldehyde existence in solution or formaldehyde vapour release allowed
• Easy for deactivation and disposal
• Compatibility to propellant
• Compatibility to oxygen scavengers

For wet layup option, biocide/corrosion inhibitior solution will be pumped into the pipeline. The solution will be left in the pipeline sections during the mothballing period. To achieve premium result, the biocide of the selection needs to be:

• High efficacy
• Long length of bacterial control
• Compatibility to corrosion inhibitors
• Compatibility to oxygen scavengers
• Easy field testability