[en] Containment piping penetration bellows are an integral part of the pressure boundary in steel containments in the United States (U.S.). Their purpose is to minimize loading on the containment shell caused by differential movement between the piping and the containment. This differential movement is typically caused by thermal gradients generated during startup and shutdown of the reactor, but can be caused by earthquake, a loss-of-coolant accident (LOCA), or 'severe' accidents. In the event of a severe accident, the bellows would be subjected to pressure, temperature, and deflection well beyond the design basis. Most bellows are installed such that they would be subjected to elevated internal pressure, elevated temperature, axial compression, and lateral deflection during a severe accident. A few bellows would be subjected to external pressure and axial elongation, as well as elevated temperature and lateral deflection. The purpose of this experimental program is to examine the potential for leakage of containment bellows during a severe accident. The test series subjects bellows to various levels and combinations of internal pressure, elevated temperature, axial compression or elongation, and lateral deformation. The experiments are being conducted in two parts. For Part I, all bellows specimens are tested in 'like-new' condition, without regard for the possible degrading effect of corrosion that has been observed in some containment piping bellows in the U.S. Part 1 testing, which included 13 bellows tests, has been completed. The second part of the experimental program, in which bellows are subjected to simulated corrosive environments prior to testing, has just just begun. The Part 1 experiments have shown that bellows in 'like-new' condition can withstand elevated temperatures and pressures along with large deformations before leaking. In most cases, the like new bellows were fully compressed without developing any leakage. At the time of writing, the corroded bellows test program has just begun. If available, results from these tests will be presented at the conference. (author)