The lifetime of pressurized parts under temperature load is limited due to degradation mechanisms such as creep, fatigue and corrosion. The increase of boiler outlet temperatures in conventionally fired power plants and increasing process temperatures in other industries requires the use of creep-resistant steels. Suitable materials are expensive and difficult to manufacture. An alternative approach to increase the lifetime of pressurized components under temperature load is the use of composite pipes. A highly creep resistant jacket made of fiber reinforced ceramic matrix composite (CMC) is applied to new or existing pipes. In laboratory tests the CMC jackets increased the lifetime of hollow cylinder specimens by a factor of about six.

In an already scheduled on-site test a CMC jacketed pipe bend will be installed in the Large Scale Power Plant (GKM) in Mannheim, Germany. To monitor the condition of the steel pipe and the CMC jacket, different techniques are applied. The creep strain is measured at different positions of the steel pipe with high temperature resistant strain gauges. The strain of the compound of pipe and jacket is monitored using resistance wires. Additionally, a monitoring of acoustic emissions (AE) in the CMC jacket will be installed. Failure processes like matrix cracking or fiber breakage excite acoustic signals that can be recorded by high temperature resistant acoustic emission sensors applied to the surface of the CMC. An increase in acoustic activity and intensity is an indicator for ongoing damage processes. Under certain conditions even a localization of the acoustic sources is possible. This paper shows results from a previous project and the preliminary investigations for the scheduled on-site test.

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