Procedure for Understanding RSTRENG Assessment – 49 CFR § 192.714 and § 192.933

Based on U.S. federal regulations and industry guidance, a RSTRENG assessment for corrosion defects on onshore gas transmission pipelines under 49 CFR § 192.714 and § 192.9.33 must follow a series of steps to determine the pipe’s remaining strength and required repair action. RSTRENG is a Level 2 assessment method that uses the “effective area” approach to evaluate complex corrosion profiles.   ASME B31.G Original and ASME B31.G Modified are a Level 1 assessment and use maximum depth and length to evaluate a single pitting area.

The core of the RSTRENG procedure is to compare the pipeline’s maximum allowable operating pressure (MAOP) to a calculated predicted failure pressure (P_f ) multiplied by a safety factor (which is the reciprocal of the design factor) for the pipeline’s specific class location. 

Step 1: Compare predicted failure pressure to regulatory criteria:

For Class 1 and 2 pipelines: 

• If (P_f ) is less than 1.39 times the Maximum Allowable Operating Pressure (MAOP), remediation is required within two years of discovery.
• If (P_f ) is less than 1.1 times the MAOP, immediate repair is required upon discovery.
• If (P_f ) is greater than or equal to 1.39 times the MAOP, the condition can be monitored during subsequent assessments.  An evaluation of corrosion growth is required per B31.8S-2018 and defects must be repaired prior to response time per Figure 7.2.1-1 (reference 49 CFR 192.714(c)).  Features that require repair prior to the next scheduled assessments are called “scheduled”.

For Class 3 and 4 pipelines: 

• If (P_f ) is less than 1.50 times the MAOP, remediation is required within two years.
• If (P_f ) is less than 1.1 times the MAOP, immediate repair is required upon discovery.
• If (P_f ) is greater than or equal to 1.50 times the MAOP, the condition can be monitored during subsequent assessments. An evaluation of corrosion growth is required per B31.8S-2018 and defects must be repaired prior to response time per Figure 7.2.1-1 reference 49 CFR 192.714(c)).  Features that require repair prior to the next scheduled assessments are called “scheduled”.

Step 2: Determine required remediation 

Based on the comparison in Step 1, classify the required action: 

• Immediate repair conditions: Remediate upon discovery. The operator must also reduce the operating pressure of the affected pipeline until the condition is fixed.
• Two-year conditions: Repair within two years of discovery.
• Monitored conditions: Record and track the anomaly during future integrity assessments based on metal loss growth rates.