With alternative MAOP pipelines operating at up to 80% SMYS
, PHMSA wanted to eliminate any potential low-strength pipe in these pipelines.
Cycle counting results in a dataset that reports all of the cycles counted from the input data along with the magnitude of the cycle (in terms of %SMYS
--a line operating at 50% of SMYS
that cycled from slack to M(A)OP would have 1 cycle through 50% SMYS
This is why the reassessment interval is considerably longer for the axial stress level of 60%, compared to 75% SMYS
PHMSA has already given a number of major pipelines approval to operate at 80 percent of SMYS
under special permits.
Currently, the MAOP for sparsely populated Class 1 locations is a maximum of 72 percent of SMYS
of the steel.
8 Code that pipelines could operate safely at stress levels up to 80 percent of SMYS
Based on that assumption, many pipelines were calculated to operate at over 20% specified minimum yield strength (SMYS
) when they were actually operating below 20% SMYS
Under the proposed rule, companies would have to do a full integrity management (IM) program on lines operating at or below 20 percent SMYS
, located in or within a quarter-mile of a USA.
PHMSA's approach uses a less than 20% SMYS
exclusion for certain MCA Class 1 and 2 locations, while INGAA's approach uses a less than 30% SMYS
exclusion for all MCA locations.
But 20 percent of SMYS
or below exemption would cover 18 percent of those utility lines.
Delving a little deeper into the identified ruptures, analysis showed there were seven pipeline ruptures that occurred in service while operating at a pressure below 20% SMYS
For lines operating above 40 SMYS
, the operator must either install a full encirclement split sleeve or replace the pipe.