Smart subsea maintenance: An integrated approach to wax and flange management

Abstract

ABSTRACT Wax crystallization in crude oil transportation channel occurs when wax temperature falls below the Wax Appearance Temperature (WAT). This poses a critical flow assurance risk in the oil and gas industry with common consequences including restriction to effective pipe diameter, increase pumping costs, and threats to structural integrity through pressure spikes, or in worst scenario, complete pipeline clogging. this study develops an integrated mathematical model to simulate wax accumulation in a 40 km pipeline using Bonny Light crude data. The framework couples thermodynamic solubility theory (Van’t Hoffs), precipitation kinetics, nucleation dynamics, and Fick’s mass transfer with a modified Darcy-weishbach pressure drop analysis and a Von mises criterion flange integrity assessment consistent with ASME B16.5 class 900 standards. A three-tier automated alert system (GREEN, AMBER, RED) was developed to continuously map computed Von mises utilization ratio to operational risk level with an escalated rate map for early warning. The model was validated against Shell Nigeria Bonny Light field data and demonstrates strong predictive accuracy (R 2 = 0.905, r = 0.988). Simulation results show that WAT (318 K) was reached at 11.43 km, leaving 71.5% of the pipeline susceptible to deposition. After 30 days, peak deposition reached 10.99 mm (20.5 kg/m 3 ) between 25 and 27 km from the inlet. This accumulation caused a 6.6% increase in total pressure drop (0.9745 MPa to 1.0382 MPa). Von mises flange stress peaked at 66 MPa at the inlet, corresponding to a utilization ratio of 0.40, confirming that all spatial nodes remained within the GREEN safety classification throughout the 30-day simulation. To maintain pipeline health, pigging intervals should be shortened from the initial 28 days to 14-21 days, with mechanical pigging concentrated on the 20-32 km segment. Future work should incorporate transient flow effects, laboratory flow loop validation using Bonny Light sample to refine the wax kinetic constants drawn from literature, and multi-segment geometry.