Characterizing Pressure Fluctuations on Buried Pipelines in Terms Relevant to Stress Corrosion Cracking

Pressure records for high pressure hydrocarbon pipelines that have previously shown to have occurrences of trans-granular stress corrosion cracking (tSCC) were supplied by ten Canadian Energy Pipeline Association (CEPA) member companies. These pressure records were analyzed by performing six methods of pressure cycle counting described in the ASTM standard E1049-85. A comparison was made of the magnitude and frequency of these counted pressure cycles at compressor/pump discharge and suction locations as well as intermediate locations along the pipeline. An attempt to relate the derived pressure cycles to tSCC growth was made by applying previously published “superposition” type cumulative damage models in calculating tSCC growth rates. Information about the relative importance of fatigue growth in the total tSCC lifecycle as well as the ability to distinguish tSCC susceptible areas on a pipeline based on differences in pressure cycles was gained. Characteristic pressure cycle spectra were developed from the supplied pressure data which describes the different modes of pipeline operation including liquid or gas hydrocarbon transportation as well as mainline or lateral operation which may be of use in further research efforts in this area.