2015 CCJ Best Practices Awards: Best of the Best

Gas-line safety programs at combined-cycle plants typically include cathodic protection monitoring, cursory inspection, and reactive maintenance—and little more. Not true at PG&E’s Gateway Generating Station, which recently developed and implemented a far more robust program to protect against gas leaks. The 2 × 1 7FA-powered facility in Antioch, Calif, is managed by Ben Stanley.

Plant O&M personnel teamed with PG&E’s Applied Technology Services (ATS) to develop a comprehensive program that included the inspections and preventive maintenance necessary to keep Gateway’s gas system safe and reliable. Goals were the following:

• Assure gas supply equipment is properly inspected and maintained.

• Confirm that all regulations applicable to gas systems are included in plant procedures.

• Assure that current and suggested maintenance tasks align with industry standards and best practices.

ATS reviewed guidelines from government agencies and others to understand how new, improved inspection methods could be applied inside the plant, so long as there were no conflicts with standards that did apply inside the plant boundary. The scope of this inspection effort covers the gas yard, gas-turbine (GT) supply piping and performance heaters, and HRSG duct burner and all of the associated equipment—including piping, valves, regulators, gauges, instrumentation, etc. 

The following preventive maintenance action items were identified during this collaborative effort and entered into the plant’s work management systems:

• Engage a qualified NACE Level II inspector to check coated and uncoated metal surfaces on a regular basis to (1) assess coating condition and film thickness, with adhesion testing where necessary; (2) determine the extent and severity of any corrosion and surface chalking, (3) measure the depths of any pits found in pipe surfaces, flanges, and valves—especially at soil-to-air interfaces, pipe supports, and deck penetrations; and (4) check for corrosion under thermal insulation.

• Inspect below-grade piping to assess the effectiveness of the installed cathodic protection (CP) system. Testing of the CP system and a review of findings are part of this effort.

• Conduct regular mechanical inspections to ensure pipe supports are not distorted and/or overloaded, components are labeled properly, drains and vents are properly capped so there are no open pipes or lines, and all valves are operating as designed.

• Regularly check for gas leaks at all connections, components, and devices within the gas yard and turbine supply areas—monthly by the plant O&M staff, annually by ATS. Tag and enter into the work management system for quick resolution any gas leaks above 10 ppm.

• Test the plant’s emergency stop valve annually (at a minimum) and confirm proper operation of all of hard-wired inputs—such as emergency test button, high pressure trip switches, etc.

In addition to the work performed in coordination with ATS, plant staff contributed to the following additional safety-program enhancements:

1. Installation of remote gas-sensor calibration capability. Gas sensors in turbine enclosures are impossible to calibrate while the unit is operating, because of the high temperature. The plant I&E staff installed a remote calibration system so sensors can be safely calibrated from outside the enclosure. This ensures that the sensors stay in calibration year-round without having to shut down the turbine to perform this task.

2. Training in the use of remote methane leak detectors and handheld gas detectors. With the support of PG&E’s Leak Survey & Damage Prevention Dept, Gateway obtained a Remote Methane Leak Detector (RMLD, Fig 2).

The plant O&M staff was trained on the proper procedures and operation of the RMLD, which provides a safe and reliable method for identifying gas leaks up to 100 ft from the source. This is especially useful when checking for leaks on an operating GT, because leak detection can only be done safely from the door of the turbine enclosure.

In addition to the RMLD, the plant has other reliable methods of gas detection (Fig 3) and personnel were trained in the safe operation, calibration, and use of these devices (Fig 4).

Results. The collaborative efforts of the PG&E team led to a comprehensive program that ensures gas-system components remain safe and reliable. Any issues found are addressed quickly and all of the history is properly documented in the work management system. Having a combination of support from subject-matter experts and plant employees ensures that everyone is involved in the process and key activities are performed in a timely manner.