# The Assessment of the Technical Condition of Complex Fatigued Load-Carrying Structures
## 1 Introduction  
The issue of assessing the technical condition of industrial facilities is a problem that has been discussed in the academic community for years, where numerous approaches developed by scientists are implemented in industry [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18]. There are many reasons for the need to assess the technical condition of machines. The two main reasons are operational safety and operational economic considerations. The first is often related to legal acts aimed at ensuring the safety of employees at workstations, and the second is an individual issue for each user entity.  
Because of the ongoing global transformation, the economic aspect is more often connected with the ecological aspect. Increasing ecological demands require companies to modernize their production processes or completely change their business profile. Some branches of the extractive industries, which are characterized by a high initial investment cost and a long amortization time, are an example. New ecological trends and the related uncertainties regarding the prospects for further operation of some enterprises make the analysis of the profitability of replacing fatigued technical objects with new ones, for possibly a short service life, of extraordinary importance. A gradual economic transformation takes time. During this period, the plants must continue to function regularly, but the purchase of new facilities may be economically unprofitable. For these reasons, the aim is to use existing facilities for as long and as safely as possible. This requires periodic assessment of the technical condition based on which steps are taken to ensure the safety of their operation [19, 20].  
The assessment of technical condition is a complicated and time-consuming process; in the case of fatigued and old (often more than 20 years) load-carrying structures, it is additionally difficult. The reasons for complications include: the need to verify the current geometry of the object, considering numerous damages and structural changes that occurred during the operation period, and dealing with missing elements of technical documentation. The objects of investigation often operate in difficult conditions (dynamic loads, heat loads, and aggressive corrosion environments), making it challenging to carry out the verification [21, 22, 23].  
Based on the assessment of the technical condition, a renovation policy is established, which extends the service life of the facilities. Such activities may lead to modernization; anexample is the bucket wheel [12]. The methods of extending the service of technical objects include efficiency improvements [24], reduction in the dynamic loads' impact [25; 26], and work safety improvements [27; 28; 29].  
The following sections present the necessary steps to verify the technical condition of fatigued load-carrying structures. Each of the stages is described based on two different objects operating in a mineral processing plant. Such a plant is characterized by difficult operating conditions (destructive weather, chemical environment accelerating corrosion, and additional heat loads).