Effect of Some Material, Manufacturing, and Operating Variables on the Friction Coefficient in OCTG Connections

Abstract

Results are presented from an experimental study conducted to determine friction coefficient behavior in OCTG connections. The study was conducted using the OCTG friction and galling tester at Texas Tech University. The tester employs tubular pin and box specimen pairs fabricated from 73-mm (2 7/8 in.) diameter OCTG tubing. Friction coefficient was determined for test specimens made of material grades L80 and J55 at loads of up to 620 kN (140,000 lb) acting on a surface area of up to 645 mm2 (1 in.2) with sliding velocities of 0.53 and 1.78 cm/s (1 and 3.5 ft/min), and nominal surface roughnesses of 0.37, 1.2, and 1.5 micron (15, 47, and 60 μin.) Ra. An API Modified thread compound was used for all tests. When plotted versus the applied load, the friction coefficient behavior is seen to be highly nonlinear. In addition to load, the variables of sliding velocity, material, and surface roughness are shown to have an effect. Preliminary experiments show that the test surface geometry also has a significant effect on the friction coefficient.

Tribological Behavior of Thread Compound for Applications in Oil and Gas Industry

“…On the whole, the friction coefficient values from the block-on-ring tests present similar patterns for all compounds evaluated. This is consistent with a study already developed by Carper et al [9] with pin-on-box tests where little difference in friction performance between API Modified thread compound and a nonmetal-containing compound is shown. In Figure 8 (left) a typical set of results for a charge stroke of a block-on-ring test is presented.…”

“…This behavior is typical of boundary lubrication regime. Although the friction evolution is similar to that obtained by Carper et al [14] in rotating pin-on-box tests lubricated with API Modified thread compound, the friction coefficient results obtained in this study are slightly higher than those reported by [15] for the range of contact pressure evaluated in the current tests. Also, from the graph in Figure 8 (left) it can be seen that a marked decrease in the COF value with the completion of the ring revolutions is noted after 5.2 s and 10.4 s. This is in line with the running-in phenomenon where the friction decreases when the surface asperities become burnished.…”

“…This dope evidenced a wear reduction of about 15 to 20% in comparison with the others lubricants. The "A" dope had an excellent wear performance because the lead and zinc additives of this dope were compacted between the contact surfaces, preventing metal-metal contact [14]. Figure 7 shows a SEM image and an energy-dispersive Xray (EDS) spectroscopy demonstrating the presence of lead and zinc on the wear scar.…”

“…The most common of them, based on API RP 5A3 standard, contain heavy metals such as copper, lead and zinc in their composition thus restricting their application in some regions, due to environmental hazards. Therefore, the need for replacing them by other dopes containing graphite, PTFE and other non-metallic solids is becoming increasingly important [7][8][9][10]. The main purpose of this work was to evaluate the tribological behavior of different thread compounds used in the oil and gas industry.…”

Numerical and experimental distribution of temperature and stress fields in API round threaded connection

“…The axial displacements of all nodes are zero on the middle symmetry plane of the coupling, and their radial displacements are free. The friction coefficient of the thread interface is commonly in the range 0.016-0.026 [10] when the interface makes use of thread grease. The FEA mesh is shown in Fig.…”