10139 Using Effective Area Method with ILI Data for Calculating Failure Pressure Can Reduce the ILI Measurement Uncertainty in the Resulting Calculated Failure Pressure

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Product Number: 51300-10139-SG

ISBN: 10139 2010 CP

Author: Harvey Haines and Dennis Johnston

Publication Date: 2010

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ILI data typically has an uncertainty associated with the reported anomaly size. Typically this is reported as ±10 percent of the wall thickness for 80% of the data. This uncertainty is also present in the failure pressure calculated from the ILI data. Pressure calculations are often applied using a two parameter assessment method such as modB31G or an effective area calculation such as KAPA or RSTRENG. Effective area calculations are often preferred because there is less conservativeness in the failure calculation. Recently the authors studied the effect of tool uncertainty on the uncertainty of the calculated failure pressure through modeling. While modB31G calculations have a fair amount of uncertainty in the calculated failure pressure, caused by the uncertainty of the tool sizing the flaw, effective area calculations have less uncertainty. This paper shows an example of this reduced uncertainty from theoretical calculations. As a result of this work we believe there are two reasons to use effective area calculations with ILI measurements, one because the calculated failure pressures are less conservative and two because there is less statistical uncertainty in the calculated failure pressures.

Keywords: effective area method, RSTRENG, modified B31G, in-line inspection, measurement uncertainty