Relationship between internal pressure strength of flexible metal tubes and bellows shapes

BACKGROUND: This study is concerned with the development of the hydrogen gas dispenser used in hydrogen stations for fuel cell vehicles (FCV). Most of the current flexible hoses suppling the high-pressure hydrogen gas to FCV are made of rubber and resin-based materials. They are required to have the characteristics of resistance to permeation of the gas and to inhibit the internal fractures known as blisters. If the materials can be replaced with metal materials, those difficulties may be resolved. OBJECTIVE: The relationship between the internal pressure strength of flexible metal tubes and their convolution shapes is investigated by experiments and computer-aided engineering (CAE) analyses. METHODS: Two kinds of stainless steels with high Ni equivalent are used for flexible tubing. The U-shaped bellows and the compressed bellows made by compressing them in the axial direction are fabricated, and then CAE analyses of their internal pressure strength are performed Internal pressure rupture tests are also carried out on both bellows. RESULTS: The internal pressure strength of the compressed bellows with a pitch of 1.6 mm was more than twice that of the U-shaped bellows with a pitch of 4.3 mm. CONCLUSION: It was found that the smaller the pitch of the bellows, the larger the internal pressure strength.