Experimental Studies on Galling Onset in OCTG Connections: A Review

With today's high prices for natural gas and oil, the demand for oil and country tubular goods (OCTG), with superior performance properties, is very high. Failures in OCTG can be attributed to numerous sources, for example, makeup torque, corrosion, and galling. Thread galling is the most common mode of failure. This failure often leads to leakage, corrosion of the material, and loss of mechanical integrity. The failure of OCTG eventually amounts to excessive operational costs for the gas and oil industry. The have been numerous approaches taken to improve the galling resistance of OCTG connections. The advocacy of these approaches is often achieved through experimental studies using galling testers. In this paper, it is proposed to classify the galling testers in seven distinct groups. There is a need to design and use effective galling testers to understand and improve the performance of OCTG connections. Thus, the objective of this paper was to present a concise review of literature related to the galling testers that may have applications to OCTG.

Contact Mechanics of a Hard Cylinder on a Viscoelastic Layer

The rolling/sliding contact of a hard cylinder on a viscoelastic layer is re-examined. The one-dimensional Maxwell model, with the addition of a parallel spring, is used to model the normal stiffness of the viscoelastic layer A solution for the pressure distribution is presented. It is shown that the maximum tractive force that the cylinder can sustain before complete sliding is a function of the sense and magnitude of the rolling velocity. Two regimes of loading are considered - constant cylinder normal force and constant cylinder indentation.

Pressure Distribution Within EHD Point Contacts Based on Measured Film Thickness

Surface topography significantly influences the behavior of lubricated contacts between highly loaded machine elements. Most oil- or grease- lubricated machine elements such as gears, rolling bearings, cams and traction drives operate in mixed lubrication conditions and the lubricant film thickness is directly related to the main practical performance parameters such as function, wear, contact fatigue and scuffing. For determination wear and especially contact fatigue, the values and distribution of the pressure in rolling contact are required. The theoretical studies usually involve the numerical solution of pressure and film thickness in the contact, using some physical mathematical model built around the Reynolds equation to describe the flow and the theory of elastic deformation of semi-infinite bodies. Such calculations can be extremely time consuming, especially when lubricant films are very thin and/or contact load very high. This study is aimed at obtaining pressure distribution within lubricated contact from measured film thickness. Lubricant film thickness distribution within the whole concentrated contact is evaluated from chromatic interferograms by thin film colorimetric interferometry. Consequently, an elastic deformation is separated from the film thickness, geometry and mutual approach of the surfaces. Calculation of the pressure distribution is based on inverse elasticity theory. EHD lubricated contact with smooth surfaces of solids was first investigated. Calculated pressure, distributions were compared with data obtained from full numerical solution to check the accuracy. The approach was also applied to surfaces with dents and their influence on distribution of pressure in lubricant film.

Numerical Simulation and Analysis for 3D Elastic-Plastic Rough Contacts

A 3D elastic-plastic rough contact (EPC) solution and code is developed using a modified semi-analytical method. The total surface deflection is induced by the contact pressure and plastic strain. A purely elastic contact field and a residual field arising from the plastic deformation are simulated iteratively to gain the final approximate solution for the elastic-plastic rough contact. Frictionless normal contact between a rigid ball and an elastic-plastic half space with polished, turned, and honed rough surfaces was numerically simulated using the developed EPC code. The distributions of surface pressures, real contact area, total stresses, residual stresses, residual displacements, and plastic strains are obtained through simulation. The effects of surface roughness, wavelength, and plastic hardening behavior upon the calculated results are analyzed.

Abrasion Under Humide Condition for Tool Steels H-13 and AISI D-2

In the present work, is developed the tribologic characterization of steels AISI H-13 and D-2, submitted to nitruration ionic process to determine wear resistance in aqueous conditions. Wear test are realized with an abrasion wear tool in an aqueous environment, designed and constructed by SEPI, ESIME, IPN, according to the norm ASTM G105-89. The aim of this investigation is to use a new material at lower prize which has an excellent wear resistance properties for high abrasion in aqueous environments, as occurs in several cases as mining industry equipments.

Seal Lubrication of an Automotive Water Pump

A noisy mechanical seal is a grave problem, especially in water pumps designed for the automotive industry. The noisiness is often caused by dynamic instability (stick-slip behavior), which occurs when the seal lubrication changes from hydrodynamic to mixed. Starting from this hypothesis, the paper shows a theoretical model that describes the interaction between the seal disks. Therefore this model correlates the acoustic emission to the working conditions of the water pump.

Hybrid Air Foil Bearings With External Pressurization

Foil bearings are widely used for oil-free microturbomachinery. One of the critical technical issues related to reliability of the foil bearings is a coating wear on the top foil and rotor during start/stops. Especially for heavily loaded foil bearings, large start torque requires a large drive motor. Bearing cooling is also mandatory for certain applications because the foil bearings can generate significant amount of heat depending on operating conditions. Usually axial flow is used through the space between the top foil and bearing sleeve. In this paper, a hybrid air foil bearing with external pressurization is introduced. A flexible steel tube is attached to the backside of the top foil with orifice holes, and externally pressurized air is directly supplied to the bearing clearance to lift off the rotor before rotor spins. The hybrid operation eliminates the coating wear during start/stop cycles, reduces drag torque during starts, and eliminates axial flow cooling. The hybrid foil gas bearing was constructed using a multiple compression springs to demonstrate a feasibility of the concept. A simple analytical model to calculate top foil deflection under hydrostatic pressurization has been developed. Predictions via orbit simulations indicate the hybrid air foil bearings can have much higher critical speed and onset speed of instability than hydrodynamic counter part. Measured load capacity was slightly higher than hydrodynamic bearing even under smaller amount of air flow. In addition, the hybrid operation was very effective for bearing cooling even if the cooling flow rate was lower than hydrodynamic counterpart. The measured very small drag torque during the start/stop demonstrates the hybrid foil bearing can have near-infinite life time without wear of the bearing and rotor surface. The experimental studies show high potential of the hybrid air foil bearings for various oil-free turbomachinery, especially for heavily loaded high temperature applications.

Mechanical Properties of CrN Films Deposited by Magnetron Sputtering Method

The mechanical properties of CrN films coated by radio frequency (rf) magnetron sputtering method were investigated. CrN films were coated on stainless steel, silicon wafer and glass substrates using sputtering of a Cr target in nitrogen ambient. The films were coated by varying the deposition temperature, nitrogen partial pressure and rf power density. The films coated were characterized by nanoindentation method, microhardness, optical, and corrosion tests. In order to use CrN as mechanical coating material, the surface roughness, hardness and adhesion properties have to be determined. The film properties were measured using atomic force microscopy and nanoindentation method and analyzed as a function of deposition conditions. It was found that these properties can be varied by changing the deposition conditions.

Modeling Leakage With Mica-Based Compressive Seals for Solid Oxide Fuel Cells

Fuel cells represent a promising energy alternative to the traditional combustion of fossil fuels. In particular, solid oxide fuel cells (SOFCs) have been of interest due to their high energy densities and potential for stationary power applications. One of the key obstacles precluding the maturation and commercialization of planar SOFCs has been the lack of a robust sealant. This paper presents a computational model of leakage with the utilization of mica-based compressive seals. A finite element model is developed to ascertain the macroscopic stresses and deformations in the interface. In conjunction with the finite element model is a microscale contact mechanics model that accounts for the role of surface roughness in determining the mean interfacial gap at the interface. An averaged Reynolds equation derived from mixed lubrication theory is applied to model the leakage flow across the rough, annular interface. The composite model is applied as a predictive tool for assessing how certain physical parameters (i.e., seal material composition, compressive applied stress, surface finish, and interfacial conformity) affect seal leakage rates.

Nondimensional Analysis on the Mitigation of Hard Surface Roughness Induced Torque on Hard Cylinders by Introduction of a Soft Interfacial Layer for Precision Positioning Applications

It is widely known that surface roughness and other geometric imperfections can impose a limit on the positioning precision of actuators. The case of a hard cylinder rolling on a hard layer is investigated here, as it is applicable to friction drives. It is proposed that a soft interfacial layer between the drive roller and drive rail can mitigate the effects of geometric imperfections on positioning accuracy. Positioning accuracy is characterized by way of a 'roughness torque', which is the maximum torque that the roller sustains due to roughness of the rail. It is assumed that lower roughness torque values lead to greater positioning accuracy. Finite element analysis and an analytic approach are employed to investigate the situation.