The following paper presents temperature and pressure transients in selected thick-walled elements of pipelines, such as T-pipes and main steam gate valve. Temperature will be measured at selected points within the element's wall thickness. Measured temperature and pressure transients will be used to determine temperature and stress distribution within the whole element. Calculations will be carried out by means of finite element method. Calculated temperature and stress transients can be used to determine element life. More accurate estimation of transient temperature and stress distribution will contribute to a reduction in maximum stresses, which especially arise during transient start-up and shut-down boiler operations.