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Fig. 2. Operating pressure for 72% SMYS.

At 80% reduced wall thickness, a margin of about 0.6 mm exists for the operation pressure. The calculated minimum wall thickness of 1.9 mm (0.075 in.) corresponds to the 80% reduction of the wall thickness. Therefore, not withstanding references
(ABS, 2000; ASME, 1991), the pipeline can be operated with 10.3 barg (150 psi) of operation pressure even after 80% reduction of wall thickness.
3.3. Limitation imposed by ASME B31G (ASME, 1991)
3.3.1. Corrosion pit depth exceeding 80% of the wall thickness
This criterion was developed to consider ruptures of a section of corroded pipe and does not account for the possibility that a defect may leak. If any pit depth in an area of corrosion exceeds 80% of the wall thickness, then the section must be
repaired or replaced.
3.3.2. Corrosion pit depth less than 12.5% of the wall thickness
There is no limit on the length of corrosion when all of the measured pit depths are less than 12.5% of the wall thickness. The reason for this is that such cases would be expected to have the same remaining strength as a pipe that just meets
the minimum wall thickness requirement for the same grade of API line pipe.
3.3.3. Contiguous corroded area
A contiguous corroded area having a maximum depth of more than 10% but less than 80% of the nominal wall thickness of the pipe should not extend along the longitudinal axis of the pipe for a distance greater than that calculated from  ASME (1991):
(4)
where L is the maximum allowable longitudinal extent of corroded area and d is the measured maximum depth of the corroded area. If the corrosion depth is between 10 and 17.5%, use B = 4.0 in Eq. (4). Maximum allowable longitudinal lengths are  presented in Fig. 3. The maximum allowable lengths depend on the maximum corrosion pit depths.
3.4. Corrosion analysis with rstreng
rstreng is a computer program to calculate the safety factor for a corroded pipe using the inspected data. The program utilizes three methods developed by Pipeline Research Council International, Inc. (PRCI) report. The three methods are ‘effective
area method’, ‘modified B31G criterion—0.85dL area’, and ‘B31G criterion’. The B31G criterion results in the most  conservative safety factors against the burst pressures. The following results are obtained from the rstreng analysis: the calculated burst pressures are about 10 times higher than the operating pressure within the limits of the corroded lengths and pit depths imposed by ASME B31G. Fig. 3 presents the limits on allowable corrosion lengths based on ASME B31G.