Review Wax formation in oil pipelines: A critical review Ararimeh Aiyejina a , Dhurjati Prasad Chakrabarti a,⇑ , Angelus Pilgrim a , M.K.S. Sastry b a Department of Chemical Engineering, The University of the West Indies, Trinidad and Tobago b Department of Electrical and Computer Engineering, The University of the West Indies, Trinidad and Tobago article info Article history: Received 23 December 2010 Received in revised form 9 February 2011 Accepted 20 February 2011 Available online 27 February 2011 Keywords: Waxy crude oil Oil-pipe Solid–solid transition Solid–liquid equilibrium Wax precipitation wax removal abstract The gelling of waxy crudes and the deposition of wax on the inner walls of subsea crude oil pipelines present a costly problem in the production and transportation of oil. The timely removal of deposited wax is required to address the reduction in flow rate that it causes, as well as to avoid the eventual loss of a pipeline in the event that it becomes completely clogged. In order to understand this problem and address it, significant research has been done on the mechanisms governing wax deposition in pipelines in order to model the process. Furthermore, methods of inhibiting the formation of wax on pipeline walls and of removing accumulated wax have been studied to find the most efficient and cost-effective means of maintaining pipelines prone to wax deposition. This paper seeks to review the current state of research into these areas, highlighting what is so far understood about the mechanisms guiding this wax deposition, and how this knowledge can be applied to modelling and providing solutions to this problem. Ó 2011 Elsevier Ltd. All rights reserved. Contents 1. Introduction ......................................................................................................... 672 2. Detection of deposited wax ............................................................................................. 672 2.1. Detecting blockages.............................................................................................. 672 2.2. Detecting wax deposits ........................................................................................... 672 3. Wax deposition mechanisms ............................................................................................ 673 3.1. Molecular diffusion mechanism .................................................................................... 673 3.2. Soret diffusion .................................................................................................. 673 3.3. Brownian diffusion mechanism .................................................................................... 673 3.4. Gravity settling mechanism ....................................................................................... 673 3.5. Shear dispersion mechanism ...................................................................................... 673 3.6. Shear stripping mechanism ....................................................................................... 674 3.7. Nucleation and gelation kinetics ................................................................................... 674 3.8. Deposition in two-phase flow ..................................................................................... 674 4. Effect of emulsified water on gelation .................................................................................... 675 5. Cloud point, pour point and gel point correlations .......................................................................... 675 6. Review of some existing wax deposition models ............................................................................ 675 6.1. Thermodynamic models .......................................................................................... 676 6.2. Hydrodynamic model ............................................................................................ 677 7. Wax aging models .................................................................................................... 679 7.1. Counter diffusion................................................................................................ 679 7.2. Ostwald ripening ................................................................................................ 680 8. Correct analogies for correlated heat and mass transfer in turbulent flow ....................................................... 680 9. Inhibition of wax deposition ............................................................................................ 681 0301-9322/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.ijmultiphaseflow.2011.02.007 ⇑ Corresponding author. Address: Dept. of Chemical Engineering, The University of The West Indies, St. Augustine, Trinidad and Tobago. Tel.: +1 868 6622002x4001; fax: +1 868 6624414. E-mail address: dhurjatiprasad@yahoo.co.in (D.P. Chakrabarti). International Journal of Multiphase Flow 37 (2011) 671–694 Contents lists available at ScienceDirect International Journal of Multiphase Flow journal homepage: www.elsevier.com/locate/ijmulflow