At the Asia Turbomachinery & Pump Symposium 2018, Vasanth Bhat and Thangavel Suthan from Singapore Refining Company (SRC) presented a compelling case study on the failure of a steam turbine governor valve in their Wet Gas Compressor (WGC) unit. This critical asset, driven by a four-stage back pressure turbine, experienced two major failures in the main valve stem of the steam inlet valve, leading to significant operational challenges.

𝗡𝗢𝗧𝗘: 𝘚𝘢𝘮𝘦 𝘪𝘴𝘴𝘶𝘦 𝘩𝘢𝘱𝘱𝘦𝘯 𝘢𝘵 𝘰𝘶𝘳 𝘴𝘵𝘦𝘢𝘮 𝘵𝘶𝘳𝘣𝘪𝘯𝘦 𝘥𝘳𝘪𝘷𝘪𝘯𝘨 𝘉𝘍𝘞 𝘱𝘶𝘮𝘱. 𝘛𝘩𝘦 𝘪𝘴𝘴𝘶𝘦 𝘸𝘢𝘴 𝘳𝘦𝘴𝘰𝘭𝘷𝘦𝘥 𝘣𝘺 𝘛𝘩𝘪𝘤𝘬𝘦𝘯𝘪𝘯𝘨 𝘵𝘩𝘦 𝘤𝘦𝘯𝘵𝘦𝘳 𝘴𝘵𝘦𝘮 𝘢𝘯𝘥 𝘴𝘱𝘦𝘤𝘪𝘢𝘭 𝘤𝘰𝘢𝘵𝘪𝘯𝘨. 𝘛𝘩𝘦 𝘪𝘴𝘴𝘶𝘦 𝘵𝘳𝘢𝘯𝘴𝘧𝘦𝘳𝘦𝘥 𝘵𝘰 𝘎𝘰𝘷𝘦𝘳𝘯𝘦𝘳 𝘴𝘵𝘦𝘮 𝘵𝘩𝘢𝘵 𝘸𝘢𝘴 𝘵𝘩𝘦𝘯 𝘳𝘦𝘪𝘯𝘧𝘰𝘳𝘤𝘦𝘥 𝘢𝘯𝘥 𝘵𝘩𝘦 𝘱𝘳𝘰𝘣𝘭𝘦𝘮 𝘳𝘦𝘴𝘰𝘭𝘷𝘦𝘥.

𝗞𝗲𝘆 𝗛𝗶𝗴𝗵𝗹𝗶𝗴𝗵𝘁𝘀 𝗳𝗿𝗼𝗺 𝘁𝗵𝗲 𝗖𝗮𝘀𝗲 𝗦𝘁𝘂𝗱𝘆:
1️⃣ 𝙁𝙞𝙧𝙨𝙩 𝙁𝙖𝙞𝙡𝙪𝙧𝙚 (𝙊𝙘𝙩’12):
– The valve stem broke at the threaded section due to fatigue (𝘤𝘰𝘯𝘧𝘪𝘳𝘮𝘦𝘥 𝘣𝘺 𝘮𝘦𝘵𝘢𝘭𝘭𝘶𝘳𝘨𝘪𝘤𝘢𝘭 𝘢𝘯𝘢𝘭𝘺𝘴𝘪𝘴).
– Vibration levels were 25-30 mm/sec pk, with a dominant frequency of 200 Hz.
– Corrective actions included replacing the stem and bush, but vibrations remained high.

2️⃣ 𝙎𝙚𝙘𝙤𝙣𝙙 𝙁𝙖𝙞𝙡𝙪𝙧𝙚 (𝙅𝙪𝙣𝙚’14):
– The valve stem broke internally, and the rear bush was excessively worn out.
– Vibration amplitude spiked to over 1000 mm/sec pk, indicating resonance.
– The turbine had to be shut down, and further analysis revealed the need for design modifications.

3️⃣ 𝗥𝗼𝗼𝘁 𝗖𝗮𝘂𝘀𝗲 & 𝗦𝗼𝗹𝘂𝘁𝗶𝗼𝗻:
– The failures were attributed to flow-induced vibrations (𝙺̲𝚊̲𝚛̲𝚖̲𝚊̲𝚗̲ ̲𝚟̲𝚘̲𝚛̲𝚝̲𝚎̲𝚡̲ ̲𝚘̲𝚜̲𝚌̲𝚒̲𝚕̲𝚕̲𝚊̲𝚝̲𝚒̲𝚘̲𝚗̲) and resonance at 200 Hz.
– The OEM proposed modifications to the valve stem and bush design, which were implemented during a 2015 overhaul.
– Post-modification, while overall vibrations remained high, the dominant 200 Hz peak was eliminated, and the unit has been operating without abnormalities since.

𝗟𝗲𝘀𝘀𝗼𝗻𝘀 𝗟𝗲𝗮𝗿𝗻𝗲𝗱:
🔹 𝘙𝘦𝘳𝘢𝘵𝘦 𝘙𝘦𝘷𝘪𝘦𝘸𝘴: Closer scrutiny is needed during turbine rerates to address potential flow-related vibrations.
🔹 𝘍𝘢𝘪𝘭𝘶𝘳𝘦 𝘈𝘯𝘢𝘭𝘺𝘴𝘪𝘴: Even rare or first-time failures in critical machinery require detailed investigation to prevent recurrence.

This case underscores the importance of collaboration between end-users and OEMs in diagnosing and resolving complex machinery issues. Kudos to the SRC team for their thorough analysis and successful resolution!