Cold Bending of A۳۳۵ Gr.P۹ Tubes of Heaters of Catalytic Reforming Unit of Lavan Oil Refining Company

The platformer heaters of catalytic reforming unit of Lavan oil refining company include the Three heaters of the Box Heater type with Arbor coil. The tubes used in these heaters are made of ASTM A۳۳۵ Gr.P۹ with a diameter of ۳ inches and a thickness of ۵.۴۹ mm. Generally the hot bending method along with a preheat up to a temperature of about ۹۰۰-۱۰۲۰ °C and subsequently normalizingtempering heat treatment after bending is the conventional method which is used in the world as well as by the main heaters’ manufacturer for the bending of these tubes. However in order to replace the tubes of the heaters of Lavan oil refining company with a bending radius of ۱۵۲۴ mm and a bend opening of ۱۸۰ ° and a length of ۲۹۵۹ mm and because of operational force for backing the heaters in service the by preparation of a procedure by Lavan Oil Refining Company experts, cold bending method with a preheat temperature of about ۱۸۰ °C followed by a stress relief heat treatment at ۶۹۰ °C for ۲۰ min was used. Since this bending method was not common in the past and was performed in Iran for the ۱ st time, in order to ensure the validity of the above method, destructive tests includingcold tensile test, hot tensile test at the design temperature of the heaters (۶۰۹ °C), Brinell hardness test,macroscopic and microscopic examinations were used and compared with the results of similar tests on straight tubes in both pre- and post-Stress relief conditions.In addition non-destructive tests of magnetic particle test and portable hardness test as well as dimensional examinations were performed on all bends. According to the comparisons between the results of the destructive tests, the leastchanges in the microstructural and mechanical properties at room temperature and design temperature were observed between the bending part and the straight part of the tubes and the correctness of this bending method was confirmed. Finally, the bended tubes were installed and put into service in the heaters of Lavan Oil refining Company on March ۲۰۱۸ and now they are in service with no problem and properly after about four years continuously.