Fatigue Behaviour of Coke Drum Materials and Its Application to Extend the Service Lives of Coke Drums

• Author / Creator

  Chen, Jie

• Coke drums are vertical pressure vessels used in the delayed coking process in petroleum refineries. They are normally constructed of carbon or low carbon alloy steels internally clad with stainless steel to protect the coke drums from corrosion during operations. Significant temperature variation during the delayed coking process causes damage in coke drums in the form of bulging and cracking. Hundred thousands of dollars are spent to repair the units and the loss from the disruption of the production could be even much higher. There are studies on the fatigue life estimation for coke drums, but these are based on uniaxial strain-fatigue life curves at various constant temperatures, which do not consider cyclic temperature conditions. There are relatively few investigations involving experiments to simulate and predict the damage and fatigue life of coke drums. To more accurately analyze the fatigue damage mechanism of coke drums, a systemic-experimental investigation on fatigue behaviours of coke drum materials has been carried out in this study. A thermal-mechanical fatigue (TMF) testing system has been successfully designed and developed to perform the complex TMF tests. The developed system can successfully simulate cyclic thermal-mechanical loading conditions experienced by coke drums. In addition, an alternative strain control and measurement technique is developed for strain-controlled fatigue tests at elevated temperature. The fatigue lives of the candidate materials are first investigated under isothermal condition. More complex TMF tests are then performed on these candidate materials. Two coke drum base materials (C-½Mo and 2¼Cr-1Mo) are investigated and compared under isothermal and thermal-mechanical cyclic loadings. Based on the current experimental study and, in combination with the API survey data, it is concluded that C-½Mo is a better base material than 2¼Cr-Mo from the standpoints of fatigue resistance. Since the coke drums are constructed by welding a number of shell plates, the fatigue behaviours of weld and heat affected zone (HAZ) material are also studied. A modified four-point correlation (FPC) method has been developed to predict the fatigue lives of weld and HAZ material based on their tensile properties. Finally, based on the TMF data of the coke drum materials obtained through this study, along with a new statistical fatigue life prediction method developed in our group, the fatigue lives of coke drums can be more reasonably predicted. This study leads to better understanding of damage mechanisms occurring in coke drums. The comprehensive coke drum material data obtained through this study are valuable for designers and operators of coke drums. More important, a number of useful guidelines including optimal selection of materials, more accurate analysis method and reliable life prediction method for coke drums are summarized. Application of these guidelines will be beneficial for designing and manufacturing of more robust new coke drums, as well as for extending service lives of the existing coke drums from the operational and maintenance point of view.

• Subjects / Keywords

  • Coke Drums
  • Fatigue life prediction
  • Thermal mechanical fatigue
  • Fatigue testing

• Graduation date

  Fall 2014

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/R37659N45

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.