PACIFIC GAS & ELECTRIC CO — Integrity Assurance Notification

MAOP RECONFIRMATION METHOD 6Pacific Gas and Electric Company (PG&E) has performed a comprehensive evaluation of all station features at its Vacaville Regulator Station (“Vacaville Station”) to reconfirm the Maximum Allowable Operating Pressure (MAOP).1 This station is located outside of Travis Airforce Base east of Fairfield, California and provides regulated gas to the Vacaville Valve Lot and to the Travis Airforce Base Meter Set district regulator. PG&E’s initial phase of this project identified all traceable, verifiable, and complete (TVC) records to reconfirm MAOP based on design and pressure test records. Thirty-two (32) joints at Vacaville Station were identified as having non-TVC records of a pressure test2 in this review. There are three joints considered in this evaluation that are located in a high consequence area (HCA). The remaining joints are not located in a HCA or a moderate consequence area (MCA). There are 11 joints located in a Class 3 location and 21 joints located in a Class 1 location. PG&E proposes to establish a TVC MAOP record via 49 Code of Federal Regulations (CFR) §192.624(c)(3), Method 3.3. At Vacaville Station, records were non-TVC for materials properties of the 32 joints. PG&E utilized nondestructive examination (NDE), satisfying the requirements of §192.607, to verify the materials properties of these joints. A combination of NDE to establish material strength, chemical composition, hardness, microstructure, wall thickness, and long seam was deployed. These joints’ grade and nominal wall thickness were determined using a combination of materials verification-NDE data and engineering analysis. Joint Charpy V-notch toughness and subsequently material fracture toughness were calculated based on vintage and operating temperature. PG&E utilized NDE-based ECA methodologies for reconfirming MAOP at Vacaville Station, satisfying the requirements of §§192.624(c)(3) and 192.632. Flaw detection-NDE was performed on these joints to detect external (outer diameter), internal (inner diameter), and mid wall indications. The Predicted Failure Pressure (PFP) was calculated for all discovered flaws and theoretical maximum remaining flaw sizes based on NDE detection and sizing thresholds. PFP calculations used the API 579 level 2 model. Computations established that the PFP of these joints, for all flaws, is above 1.5 times the corresponding MAOP (1.5 x 650 psig = 975 psig and 1.5 x 400 psig = 600 psig). Fatigue analysis was performed using relevant operational pressure history data. Fatigue life (remaining life) simulations produced a remaining life of over 500 years. PG&E proposes, and is seeking the PHMSA’s approval, to reconfirm MAOP of four joints at Vacaville Station via §192.624(c)(3) ECA of the 10/01/2019 PHMSA rule, Pipeline Safety: Safety of Gas Transmission Pipelines: MAOP Reconfirmation, Expansion of Assessment Requirements, and Other Related Amendments (ID: PHMSA-2011-0023-0464).#