Mechanical Characterization of Valve Compression Packing at High Temperature

Packed stuffing boxes are sealing devices used in valves, compressors and pumps. The compression packing is the most critical element of this assembly. Packing rings are compressed axially to produce lateral contact pressures large enough to confine the processed fluid within the pressurized valve and avoids leakage to the outer boundary. Although popular, this old method of sealing has seen very limited analytical and numerical development. There is no standard design procedure for engineers to follow, and the existing standard test procedures are limited to qualification and quality control tests such as API622, 624, ISO-15848 1 and 2. As a result, structural integrity and leak tightness are rarely verified, and consequently 60 % of pressurized equipment requiring fugitive emissions compliance are valves that use this type of sealing device. The mechanical properties of compression packing materials are the main factors affecting fluid tightness at room and high temperatures and yet there is little or no data available either in manufacturer’s catalogues or in the literature. Packed stuffing box research is scant and focuses mostly on the distribution of the contact pressure between the stem and packing at room temperature without considering packing mechanical properties such as rigidity, thermal expansion, creep and aging. It is proposed, in this project, to measure the mechanical properties such as pressure transmission ratio, short-term creep deformation and thermal expansion coefficient of two packing materials at high temperature. This initiative will serve as a basis to launch a North American testing program to develop ASTM-like testing procedures for compression packing at high temperature.