Effects of Solid Precipitation and Surface Corrosion on the Adhesion Strengths of Sintered Hydrate Deposits on Pipe Walls

Abstract

A hydrate directly growing and sintering on a pipe wall is an important hydrate deposition case that has been relatively unexplored. In the present study, the adhesion strengths of a sintered cyclopentane (CyC5) hydrate deposit under different solid precipitation and surface corrosion conditions were measured and discussed. It was found that the hydrate adhesion strengths increased by 1.2–1.5× when the soaking time of the carbon steel substrate in a 5 wt % NaCl solution increased from 24 to 72 h, which reduced the water wetting angle from 112 ± 3.5° to 94 ± 3.3°. The wax coating reduced the strength of CyC5 hydrate adhesion by up to nearly 20-fold by reversing the substrate wettability and affecting the hydrate morphology. The measurements performed on scales indicate that calcium carbonate scales strengthen the adhesion strength because of the decrease in the water wetting angle. In addition, honeycomb holes on the surface reduce amplification. Furthermore, settling quartz sand on the wall reduced the adhesion strengths by decreasing the effective sintering area of the hydrate on the underlying base. Finer sand and higher concentrations led to lower strengths. On the basis of the verified linear correlation between the hydrate adhesion strength and the adhesion work of droplets on different substrates and the influence of water conversion during deposition, both an equation and a key constant parameter were obtained to predict the sintered hydrate deposit adhesion strengths on substrates.

Unraveling Adhesion Strength between Gas Hydrate and Solid Surfaces

“…Taking the adhesion strength (Figure (B)) into account, it should be mentioned that the densely packed interface structure of the hexagonal ice leads to a significantly higher adhesion strength than that of others. As such, the areal water density adjacent to solid surface is another crucial factor to hydrate adhesion besides the known surface hydrophobicity identified by previous experiments. − The results thus deepened the understanding of hydrate adhesion at the nanoscale. Moreover, with the adsorption of guest molecules, the water molecules at the interface are gradually replaced by guest molecules, and the water–solid interface is replaced by the water–gas interface, which further weakens the adhesion of hydrates (in actual situations, the interface caused by the local large bubbles can also be classified as this case).…”

“…Experimental studies have shown that the hydrate-deposition process initiated by the water layer is a key mechanism causing hydrate-plugs. , In addition, there are many experimental results for the adhesion of hydrates on solid surfaces. − Although these studies have provided valuable information on hydrate adhesion, due to the limitation of the current experimental resolution, rigorous physical insights into intrinsic adhesion per se are not yet available. The fundamental, open questions regarding the adhesion of hydrates on solid surface can be summarized as follows: (1) How does hydrate establish a connection with solid surface?…”

Anti-gas hydrate surfaces: perspectives, progress and prospects

“…Recently, Liu et al found that wax coatings can significantly reduce the strength of cyclopentane hydrate adhesion by 95%. 193 By setting quartz sand on the wall, the hydrate-adhesion strength was found to reduce, owing to the decreasing contact area between sintered hydrate and the wall surface. The anti-hydrate performances of superhydrophobic surfaces were also systematically investigated by Fan et al most recently.…”

Effect of the Ethylene Vinyl Acetate Copolymer on the Induction of Cyclopentane Hydrate in a Water-in-Waxy Oil Emulsion System

“…Gas hydrate, a type of cage-like crystal structure constructed by water and gas molecules, is generally formed in a low-temperature and high-pressure environment. − The gas molecules, such as methane, ethane, carbon dioxide, and so forth, − are able to be enveloped by the cages of water molecules, forming structure I, II, and H hydrate. − The formation of hydrate becomes a challenge in the development of deep-water fields, where the oil or gas is exposed to the environment of high pressure, low temperature, and water cuts. , Therefore, hydrate forms more easily in the deep water environment and increases the risk of plugging pipelines. − Webb et al studied the effect of water fraction in a water-in-dodecane emulsion on the rheological behavior of a hydrate slurry via a high-pressure rheology apparatus. The results show that the viscosity of the hydrate slurry increases apparently with the increase of water fraction from 5 to 30%.…”