Abstract: When it is necessary to perform post-weld stress relief heat treatment for the on-site assembly and welding of supersized towers, the overall heat treatment method with better effect is recommended preferentially in the codes and standards. The on-site vertical overall heat treatment method was adopted to release post-weld stress for the 76.5-meter-high propylene tower described in this paper. However, the structural strength of the tower decreases with high temperature, which poses risks of failure. A 78-meter-high scaffold was erected on site for the vertical assembly welding and heat treatment of the tower. The thermal expansion of the tower during heat treatment which may result in an increase in height and diameter should be taken into consideration for the scaffold. Therefore, the scaffold could not be held against the tower wall and it needed to maintain a certain distance from the tower wall. How to set up this kind of standalone scaffold to ensure safety? The use of internal combustion method for overall heat treatment is economical, practical and efficient., but how to set up the burner to prevent the tower internals from being burned and deformed? This series of problems were the difficulties in implementing this scheme. In this paper, finite element analysis software ANSYS was used to analyze the structural stress during the overall heat treatment process of the propylene tower. The results showed that the strength, rigidity and stability of the tower during the heat treatment process could meet the requirements. Aiming at the above series of difficulties, corresponding countermeasures have been taken to ensure the safe and smooth completion of the overall heat treatment of the tower. The treatment method in the paper can provide reference for the construction of vertical overall heat treatment of large towers.

Key words: tower, overall heat treatment, strength, stability, finite element, scaffold