Friction and Wear of Bronze Filled PTFE and Graphite Filled PTFE in 40 MPA Hydrogen Gas

Abstract

Several kinds of Polytetrafluoroethylene (PTFE) composites are currently being used in reciprocating hydrogen gas compressors as seal material which should articulate against metal counterfaces in pressurized hydrogen gas. Although their friction and wear behavior has large impact on the efficiency and reliability of gas compressors, available information about tribological characteristics of PTFE composites in high pressure hydrogen gas is quite limited. In this study, friction and wear of graphite filled PTFE and bronze filled PTFE were evaluated in the 40 MPa hydrogen gas environment by using a pin-on-disk type apparatus enclosed in a high pressure vessel to supply experimental data for the design of gas compressors in hydrogen fuelling stations. AISI316L austenitic stainless steel disk was used as a sliding counterface. All experiments were conducted under dry condition with the average contact pressure of 1.8 MPa, the sliding speed of 100 mm/s and the gas temperature of 327 K. The friction force exerted between PTFE composites and stainless steel was evaluated by a load cell during the experiment and the wear rate of composites was evaluated from the weight loss of pin specimens. In addition, chemical analysis of the polymer transfer film formed on the disk surface were conducted by using X-ray photoelectron spectrometer. Friction and wear tests were also conducted in 40 MPa helium gas for comparison. Results indicated that bronze filled PTFE was more sensitive to the gas pressure and gas species; it showed good friction and wear behavior in high pressure hydrogen, although friction in high pressure helium became very high. On the other hand, the effects of high pressure gas environment were relatively small for the friction and wear of graphite filled PTFE.

Friction and wear of PTFE composites with different filler in high purity hydrogen gas

“…The authors investigated the friction and wear of PTFE and PTFE composites in gaseous hydrogen under normal pressure [37][46] and high pressure [47] [48] to understand the intrinsic effect of hydrogen. The main motivation of our polymer tribology studies in hydrogen is to improve the durability and reliability of piston rings used in the oil-free reciprocating hydrogen gas compressor for refuelling FCVs from the tribological aspect.…”

<em>In Situ</em> High Pressure Hydrogen Tribological Testing of Common Polymer Materials Used in the Hydrogen Delivery Infrastructure

“…Current ex situ techniques for tribological testing of polymer materials require samples to be exposed to high pressure hydrogen which are then depressurized before being tested using a commercial tribometer. 15,24,25 The test methodology in this protocol was designed to permit testing of the tribological properties of polymer samples in a high pressure environment in situ. By testing polymer materials such as the EPDM samples presented above while they are pressurized, this protocol allows for a more realistic measurement of the dense pressure-compressed polymer sample found in components of the hydrogen delivery infrastructure.…”

“…9,10,11,12 While these examples of damage due to hydrogen exposure have been previously studied, the compatibility of polymer components within hydrogen environments has only recently become of interest. 13,14,15,16 This is largely a result of metallic components providing structural integrity in nuclear and oil and gas applications whereas the polymer components usually act as barriers or seals. 17,18,19,20 As a result, the friction and wear properties of polymer materials within components such as polytetrafluoroethylene (PTFE) valve seats and nitrile butadiene rubber (NBR) O-rings become important factors in their ability to function.…”

A Review on Applicability, Limitations, and Improvements of Polymeric Materials in High-Pressure Hydrogen Gas Atmospheres

“…[123] Sawae et al [124] developed a pin-on-disk method tribometer to place inside an autoclave to conduct in-situ tests in high-pressure hydrogen conditions identifying sliding friction and wear properties. They tested PTFE disk specimens (graphite filled [124,125] and bronze filled [126] ) and exposed these to 40 MPa of high-pressure hydrogen at 100 C. The coefficient of friction (COF) results did not seem significantly changed for tests at different hydrogen pressures as well as in reference test conditions with high-pressure helium or atmospheric conditions. However, a lower wear behavior was experienced in every PTFE grade when they were exposed to high-pressure hydrogen compared with other conditions.…”