This case study explores the static stress assessment of a continuous steam generation system (SGS) using finite element method analysis. The focus is on a small-diameter plant that utilizes molten salt to generate steam in a heat exchanger at a solar plant facility. The plant includes four sequential components: an economizer, an evaporator, a superheater, and a feedwater heater. These heat exchangers operate continuously under high pressure and temperature conditions.
Given the system’s continuous operation and lack of thermal cycling, a fatigue assessment is not deemed necessary. The static stress assessment is conducted in compliance with ASME Section VIII, Division 1 and Division 2 standards.
Assessment
The static stress assessment involved a detailed examination of critical areas within the heat exchanger units. Each unit was subdivided into several component models for individual assessment of primary stresses. The primary goal was to ensure that the heat exchangers would not experience plastic collapse or rupture in the shell body during operation.
High-stress areas identified in the finite element model were analyzed by linearizing the membrane and bending stress components. These stresses were then compared against the allowable limits set by ASME Section VIII, Division 1. Key components under scrutiny included isolation enclosures, tube-side and shell-side nozzles, fixed tubesheets, and various forged connections. The internal pressure and sustained nozzle loads were evaluated for their impact on the primary stress distribution.
Results
The results of the analysis indicated that all calculated stresses were within the allowable limits established by the ASME codes. Consequently, no design changes or additional calculations were deemed necessary. The heat exchanger components were found to be compliant with the appropriate design codes (ASME Section VIII, Division 1 or 2). It was concluded that a fatigue assessment was not required, as the continuous operation of the system precludes significant thermal cycling effects.
This assessment confirms that the current design is robust and capable of withstanding the operational stresses without necessitating modifications or additional procedural changes during start-up.
