Experimental Investigation of Galling Resistance in OCTG Connections

Abstract

The results of galling experiments are strongly dependent on the method used and vary from test machine to test machine. However, by a well-developed test method and testing machine, one can obtain reliable and repeatable results. The primary objective of this research is to develop a new test method and machine for evaluating galling resistance in OCTG (oil country tubular goods) connections. Through the application of basic principles of statistical design of experiments, the galling resistance in OCTG threaded connections has been investigated. For estimating the nominal failure stress, two statistical methods, namely, up-and-down and frequency distribution, have been applied and compared. Galling resistance, one of the most important design factors of OCTG connections, has been studied and discussed.

Running-in of metal-to-metal seals and its influence on sealing ability with application to the design of biodegradable thread compounds

“…Thread compounds are made according to API specifications [4] and are different from normal greases [42] because of their high solids content of up to 60%. They need to give repeatable friction for the torque based assembly [43], avoid galling during assembly [44][45][46][47] and help in sealing ability once the casing connection is assembled [18,[48][49][50]. In addition, the thread compound needs to perform under the conditions present in the well.…”

“…Several explanations for its success in protecting the surface during assembly and sealing ability are given. Ertas [47] attributes it mainly to the lead particles that form a protective film. While zinc and copper are said to be added to control the friction coefficient.…”

“…In addition, the copper particles are the largest and probably aid in thread sealing [17,18]. Finally the graphite is not of lubrication grade and therefore acts mainly as filler [47]. This, together with the broad particle size distributions of the metallic additives [17], should help in the sealing ability [47].…”

“…Finally the graphite is not of lubrication grade and therefore acts mainly as filler [47]. This, together with the broad particle size distributions of the metallic additives [17], should help in the sealing ability [47]. Carper et al [46] found that this protection is limited to the rather low contact stress of 303 MPa in typical oil industry steel grades (Section 1.2).…”

“…In addition, the work of [43,45,47] indirectly assesses the influence of phosphate conversion coatings on the galling behaviour of connections during make-up. The coating was applied on the specimens to be able obtain sensible results in their screening tests.…”