Prevention of Corrosion in Carbon Steel Pipelines Containing Hydrotest Water – An Overview

A critical step in proving a pipeline is fit for operational use is the hydrostatic test, in which it is filled with water and pressurized to 125% of its Maximum Allowable Operating Pressure (MAOP). The water that is used in this testing can cause corrosion of the pipe, potentially leading to its failure early in operating life. Failures have occasionally been reported even before a pipeline enters service.

The most common mechanisms by which carbon steel pipelines may undergo corrosion on exposure to hydrotest water are Microbially Induced Corrosion (MIC), oxygen-related corrosion, galvanic corrosion and under-deposit corrosion. An overview of these mechanisms is presented, along with a discussion of the influence of different environmental factors on them. Factors considered include water source, degree of filtration, exposure period and temperature, air pockets, presence of internal pipe coatings and pipeline future service conditions.

Maintaining the risk of pipe corrosion from hydrotest water to within acceptable limits is discussed. Factors considered are:

• How long the untreated water may be allowed to be present in the pipeline.
• Should water treatment be required, what must be used?
• Disposal requirements for the treated water, including chemical treatments.

Key Words: Hydrostatic, Hydrotest, MIC, Microbially Induced Corrosion, Pipeline, Oxygen-Related Corrosion, Under Deposit Corrosion, Internal Coating, Biocide, Corrosion Inhibitor, Oxygen Scavenger