With regard to an endurance of 2500 operation cycle, with normal operating frequency, the first service can be provided just after 20 year. Because of the normal erosion of the corrosion protection of 5 - 10 Micro millimeter (depends on the stress) we recommend, however, to check the equipment in intervals of 5 years. The usually expected freedom from maintenance of 20 years is partly based on operational experience and partly an technical improvement with the corresponding findings. Because of this we attach great importance on our equipments. Maintenance should be least according to section 6.1, 6.2 and 6.4 to 6.7