Greene, Tweed recently developed, and successfully tested, a fugitive-emissions stem seal per API 622 requirements.
At the conclusion of the API 622 test, Greene, Tweed’s stem seal achieved an average leakage rate of 5 parts per million (ppm), far exceeding the allowable leakage limit of 500ppm, and did not require adjustment. The test requires five thermal cycles from ambient temperature to 500°F (260°C) with 1,510 mechanical cycles, using methane as the test gas. Each set of ambient and thermal cycles is divided into 300 cycles per day and a final 10 cycles where the final leakage measurement is taken. Additionally, Greene, Tweed’s 5ppm average is substantially less than the 100ppm allowed by API 624.
The fugitive emissions qualified design incorporates three v-ring sealing elements and two thermoplastic end adapters. The v-ring stack is composed of one elastomeric v-ring, Chemraz ® 555 (FFKM), two thermoplastic v-rings, Avalon ® 56 (PTFE), and two end adapter rings made of Greene, Tweed’s patented enhanced PEEK material, Arlon ® 3000XT.
As a valve-sealing solutions provider for more than 25 years in the oil & gas and petrochemical & power industries, Greene, Tweed’s new fugitive emissions qualified stem seal is only one of the innovative products that will support valve manufacturers and end-users in meeting fugitive emissions regulations.
Chemraz555, with an upper temperature limit of 600°F (316°C), Chemraz555 is suitable for use in a wide variety of media including acids, caustics, aldehydes, esters, esthers, aromatics, hot water, steam, methanol, ketones, TBA, MTBE, and mixed process streams.
Avalon 56 is a modified PTFE material with a higher elongation and creep resistance, making it an excellent seal for longer-term applications. It also has a history of success in low pressure dynamic gas sealing applications. Avalon 56 has an upper temperature limit of 600°F (316°C), and acts both as a backing seal for the rubber material at low temperatures as well as a soft seal at higher temperature.
Arlon ® 3000 XT is an engineered thermoplastic developed to withstand extreme conditions and is the only material of its kind. With improved creep and extrusion resistance at temperatures above 350°F (177°C), it enhances performance over existing PAEK polymers. In Dynamic Mechanical Analysis (DMA), Arlon 3000 XT had a Tg 35°F (20°C) high than PEEK, and provided superior mechanical property retention from 350°F (177°C) to 600°F (316°C). In extrusion testing at 35ksi and 550°F (288°C), it outperformed both virgin and filled grades of PEEK and PEKEKK. In addition, Arlon ® 3000 XT exhibits chemical resistance comparable to PEEK.