**1. Introduction**

In the European conventional power generation, a small number of newly constructed units have been recorded in at least several recent years, which is caused by, but not limited to, a lot of factors related mainly to environmental protection. Therefore, the electricity producers direct their main efforts at maintaining the availability of existing power units while ensuring their safe service. The inspections of and repairs to the energy installations that are in use and whose design service life was in most cases significantly exceeded while at the same time providing the reliable efficient diagnostics seem to be the proper way for the achievement of these objectives.

However, the performance of periodic inspections and repairs is not sufficient to maintain the current level of electricity and heat production in Poland. The modernisation of the units being operated is required as well. To maintain the current level of production, it is estimated that each year the modernisation of units with a total capacity of at least 2000 MW is necessary. Therefore, the important issue to be resolved has become not only the condition assessment of the pressure section of boiler and forecast about its further safe service but also the design modernisation with selection and use of new materials allowing for construction and installation of new components [1–10]. The required increase in efficiency and extension of service time of the operating high-power units, i.e. 200, 360 and 500 MW, far beyond the design time up to the expected min. 350,000 h involves the need to replace certain components because of the end of their life and to modernise them. Certain critical components being replaced are often made of new-generation steel for the power

generation industry [11–20]. At the same time, these units are expected to be operated in the control system and to comply with standards of the European directive on limitation of harmful emissions into the atmosphere.

As part of the diagnostics, it is necessary to perform the condition assessment not only for the basic material of the components working under creep conditions but also for the material of welded joints. The condition assessment of the welded joint material is necessary to determine the ability of the components to transfer the required service loads during their further service [21–34].

If there is a need to repair or replace a part or entire component with a new one, the capability of the basic material of the operated component to make such a repair or replacement should be determined. When condition of this material after service allows a repair, it is necessary to develop the repair technology from time to time.

The subject matter of the testing, including non-destructive and destructive tests, related to the long-time operated and repair welded joints of materials after long-term service with materials after service or with new materials is a separate issue dealt with by the Institute for Ferrous Metallurgy for many years.

The developed and applied research methods and the adopted procedure allow for the correct condition assessment of the basic material and welded joint material (HAZ and weld). The test results for long-time operated as well as repair and modernisation welded joints obtained so far allowed expanding the material database with such data and proposing the procedure for making such welded joints when necessary.

#### **Figure 1.**

*The class of microstructure and exhaustion degree of the material of straight connection pipes (before the weld at the inlet side and after the weld at the agent outlet side) of the section of 200 MW primary steam pipeline unit boiler after 220 h service under creep conditions.*

**35**

**Figure 2.**

*Creep Characteristics of Engineering Materials DOI: http://dx.doi.org/10.5772/intechopen.86078*

**2. Condition assessment of the material of welded joints in components operated beyond the design time by non-destructive methods**

The criterial element deciding about the suitability for further service of butt-welded joints of components operating under creep conditions is the exhaustion degree of basic materials determined based on the revealed state of microstructure and its determined class as well as the degree of internal damages and the class of damages of the heat-affected zone (HAZ) and weld material. The example of the results of non-destructive tests on microstructure of the primary

*Assessment of the material condition with regard to changes in the structure and occurred internal damages caused by creep of parent material and circumferential welded joints in the vertical section of the primary steam pipeline made of 14MoV6-3 steel after approximately 220,000 h service (matrix replicas, SEM).*

*Creep Characteristics of Engineering Materials*

limitation of harmful emissions into the atmosphere.

required service loads during their further service [21–34].

issue dealt with by the Institute for Ferrous Metallurgy for many years.

and proposing the procedure for making such welded joints when necessary.

generation industry [11–20]. At the same time, these units are expected to be operated in the control system and to comply with standards of the European directive on

As part of the diagnostics, it is necessary to perform the condition assessment not only for the basic material of the components working under creep conditions but also for the material of welded joints. The condition assessment of the welded joint material is necessary to determine the ability of the components to transfer the

If there is a need to repair or replace a part or entire component with a new one, the capability of the basic material of the operated component to make such a repair or replacement should be determined. When condition of this material after service allows a repair, it is necessary to develop the repair technology from time to time. The subject matter of the testing, including non-destructive and destructive tests, related to the long-time operated and repair welded joints of materials after long-term service with materials after service or with new materials is a separate

The developed and applied research methods and the adopted procedure allow for the correct condition assessment of the basic material and welded joint material (HAZ and weld). The test results for long-time operated as well as repair and modernisation welded joints obtained so far allowed expanding the material database with such data

*The class of microstructure and exhaustion degree of the material of straight connection pipes (before the weld at the inlet side and after the weld at the agent outlet side) of the section of 200 MW primary steam pipeline* 

**34**

**Figure 1.**

*unit boiler after 220 h service under creep conditions.*
