The right to safety of purchased goods is one of the most important consumer rights. Therefore, an accurate analysis of safety of machinery and equipment purchased on the secondary market is an extremely important issue. One of its elements should be the assessment of the degree of service live usage. In the case of cranes, the subject of such an assessment covers both the supporting structure of the device and its mechanisms and installations. Information on evaluation of the service life expiration of the secondhand cranes may be necessary and support the decision-making process associated with the purchase of the device. The paper deals with the problem of evaluating the expiration of the service life of the supporting structure of cranes coming from the secondhand market. The result of such evaluation makes it possible to determine whether the production capacity of a device has been exhausted. This forms the basis for the decisions on any possible further operation of the crane. The work presents an approach based on the provisions of standard ISO 12482: 2014. This document is the basis for service life evaluation for cranes. The approach presented in it makes the way of analysis dependent on the method used to collect operational data. In this paper the evaluation of service life expiration was prepared on the example of a ship to shore gantry cranes. These devices are characterized by particularly large dimensions and weight. Damage of their supporting structure can lead to the significant losses. Some of these devices change the location during operation. Therefore, it is important to know the current level of their service life usage. A case, in which the operational history of a device is not known, was considered. In the paper the special attention was paid to the methodology of estimating the load distribution coefficient. In order to describe the hypothetical load spectrum, triangular distribution was proposed. The results of the calculations for the structure of port cranes are presented and discussed.