Materials Performance

JUN 2019

Materials Performance is the world's most widely circulated magazine dedicated to corrosion prevention and control. MP provides information about the latest corrosion control technologies and practical applications for every industry and environment.

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Page 49 of 80

47 MATERIALS PERFORMANCE: VOL. 58, NO. 6 JUNE 2019 operating conditions of the pipeline. The minimum data requirements for preassess- ment are those data elements that are criti- cal to the success of DG-ICDA and that impact D G-ICDA region definition and identification. The following categories of historical and current data have been iden- tified as critical and necessary for perfor- mance of DG-ICDA on this pipeline. • Pipe materials • Construction practices • Topographical data • Operational practices • Internal corrosion monitoring activities • Pipe inspection and repair The pipeline was constructed from API 5L grade X60 material 3 with a wall thickness of 11 mm (0.438 in), using an electric-resis- tance welding process with no internal coatings. The pipeline was operating at a pressure of 4.44 MPa (644 psi) at 20 °C (68 °F), 44.11% of specified minimum yield strength, and a flow rate of 237 kNm 3 /h (212 MMSCFD). The operating pressure varied from 4.41 to 4.82 MPa (640 to 699 psig), but there was no history of aggressive pressure cycling. There were no valves, or any other choking devices, installed in the section of the line that was assessed and the compres- sor station was >80 km (50 mi) away from the segment being assessed. Gas quality data indicated the water vapor content to be <7.8 kNm 3 /h (7 lb/ MMSCFD). The pipeline segment was a continuous length and did not contain new input (gas feed) locations that could intro- duce water or corrosive contaminants. The evaluation of preassessment information indicated that DG-ICDA is feasible for this segment. It was determined that the pipe- line could be defined to be one DG-ICDA region because operating conditions, pipe attributes, and gas flow characteristics have been, and were expected to continue to be, essentially identical for the pipeline. Step 2—Indirect Inspection This step involves performing detailed flow modeling to identify the most probable locations of water accumulation and select- ing dig sites for direct examination. Since pipeline elevation data were not readily available, a pip elin e current mapping aboveground sur vey was performed to determine the ground elevation and the depth of cover of the pipe. The data col- lected during the survey were used to calcu- late the pipe inclination angle using the equation: u = arcsin d(elevation) d(distance) ⎛ ⎝ ⎜ ⎜ ⎜ ⎜ ⎞ ⎠ ⎟ ⎟ ⎟ ⎟ (1) Figure 1 shows the pipe elevation and the calculated inclination angle plots. Details of the f low modeling calculations are presented in the section titled Flow Modeling Calculations (p. 48). Step 3—Direct Examination The objective of the direct examination step of the DG-ICDA process is to excavate and inspect the pipe at a site or sites identi- fied by the pre-assessment step and the indirect inspection step and then deter- mine if internal corrosion has occurred. Step 4—Post-Assessment Post-assessment involves determining the remaining life and the reassessment FIGURE 1 Pipeline elevation profile and inclination. FIGURE 2 Liquid holdup in pipelines.

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