U.S. Bellows, Inc. recently fabricated four rectangular primary flexible seal joints for sliding flanged connections. Designed at 2 PSIG for 1350°F, the seal joints provide for one inch of axial movement to prevent damage to flange connections. EJMA Standards and B31.3 code were used in the design and fabrication of these joints. The purpose of the rectangular seal expansion joint is to prevent leakage to outside of the burney windbox. The corners are double mitered to reduce stress. Inconel 625LCF material was used in fabricating the bellows while A240 tp 310 material was used for the frame. An air test at 5 PSIG was implemented as well as dye penetrant test to ensure product quality.