PTFE expansion joint
The PTFE expansion joints are unreinforced PTFE that come standard with iron 150# drill flanges.  Stainless flanges are available.  They are avaialable in 2, 3, or 5 convolutions of varing movements.  The 2-convolution joint is sometimes referred to as a "coupling".
Molded flexible couplings and expansion joints of PTFE designed to help protect pumps, compressors and other expensive equipment.
Bellows-type flexible couplings and expansion joints are contour molded of black PTFE by a patented process. They are corrosion resistant, non-aging, with extraordinary flex life and unmatched reliability. These superior units cost no more than those made of lesser materials. The flexible element is formed over the full sealing face of the end flanges eliminating troublesome separate gaskets.

Note the change in pressure rating with