Authors: I.C.Popescu, IBS, Bucharest, Romania R. M. Negriu, ECONET PROD, Bucharest, Romania S.G. Badea, ECONET PROD, Bucharest, Romania C. Besleaga, ECONET PROD, Bucharest, Romania

SC ECONET PROD SRL, BUCURESTI, ROMANIA

Case Study Regarding the Behaviour of the Structural Gradient from Various Composite

Materials (WC-Co/WC-Ni), Used to Manufacture Ball Valves for the Oil Extraction Industry

econetprod@mail.com; isarlea@yahoo.com; ic.popescu@yahoo.com; cristibesleaga@yahoo.com

1. INTRODUCTION Piston pumps used for the extraction of oil contain

closing/ opening valves to allow bringing the oil to the surface. Basically a pump has two valves, each comprising of a locking ball and valve seat respectively (Fig.1.). These elements are mainly stressed by wear, corrosion caused by abrasives powder content and the substances contained in oil (eg. hydrogen sulfide) at the temperature from the oil layer, layer pressure and the column of oil to the surface, the thermo-mechanical stresses induced by the pumping conditions, the shocks produced by opening and closing valves etc. there are two main types of deterioration: internal manufacturing defects that lead to breakage / separation of smaller or larger pieces and accelerated wear of the balls and seats resulting in the loss of sealing of the pumping chamber, thus resulting the inefficiency of the pump.

2. Experimental tests First tests have demonstrated the

need to develop a process to ensure concentricity of the two layers (core and outer) and to prepare proper pressing and sintering of the second layer.

Abstract: Valves (ball and seat) equip pumps for extracting petroleum. The balls have to withstand complex erosive-abrasive wear in corrosive environments, combined with micro cutting and micro fatigue. The effect of high temperatures will also occur in the extraction through underground combustion. Experimental batches of balls with structural gradient were made using virgin and recovered materials and PM technologies. The experiments followed the recovery of material from worn-out balls, by removing the worn-out layer and completion with virgin material, and also making balls with structural gradient from dust with various qualities. We analyzed using the finite element the tension states and the life span of the balls was estimated. We present an analysis of the ways of deterioration, the used technologies, the control technologies, the experimental results, the behavior of these balls and new research paths, to optimize the process of producing balls with gradient.

Keywords: petroleum pumps, balls, wear, recovered materials, PM technologies, C.A.D

Figure 1: Piston pumps used for the extraction of oil

Fig. 2. The uneven thickness of the outer layer

Fig. 3. The pores occurring in large numbers at the interface of the two layers

We proposed a new technology, in course of patenting, which is based on a special technological procedure.

Fig. 4. Device for filling matrix from isoprene rubberDevices the making of the mold filling in which is placed the ball forming the base material with powder (virgin or

recovered): 1- ball; 2- pad; 3- vibrating plate; 4- filler (CW powder, virgin or recovered); 5- rubber sleeve; 6- stopper for filling hole; 7- shoulder for fastening of coating rubber; 8- conic shape; 9- separation surfaces prepared for bonding;

10- mounting ring; 11- pad; 12- rubber sleeve; 13- stopper; 14- filler (CW powder, virgin or recovered).

Fig. 5. Coating of rubber sleeve with a ball of recovered material

(disassembled and ready for isostatic pressing)

Fig. 6. The hardness measured on the section of a reconditioned ball

Reconditioning is done on our own developed technology, the basis ball being recovered from balls made of a single layer of WC-Co and that were discarded due to advanced wear which no longer allowed the maintaining of the working pressure. The balls were grinded to a size where all visible traces of damage were removed and this was determined by visual inspection and by penetrant liquid inspections.

The technological process imposed choice of WC-Co compositions and WC-Ni which satisfy the following conditions: a) the inner layer must ensure good mechanical resistance; b) the outer layer must provide good resistance to abrasion and corrosive environment; c) physical- mechanical properties of both materials must be similar so the tension produced in termobaric stresses due to differences of mechanical properties be minimal.

3. The simulation of stresses on the ball made with gradient of properties of material

The ball from the valve was modeled with the valve seat. The ball is modeled as consisting of two layers of material, the base material being WC-Co with 12% Co and the outer layer material consists of WC-Ni with 12% Ni. Because it is assumed that during sintering and then during hot isostatic pressing all internal tensions are eliminated, they are not taken into account. It is also assumed that the manufacturing process is perfect and no defects of any kind arise. In order to simulate the material properties of the contact area between the two types of carbide is considered that these properties are uniform and are the average of the mechanical properties of the carbides used. We made a complex simulation in which we took into consideration both the solicitations due of pressure and those produced by the temperature from deposit.

Fig. 7: Meshing of the model in finite elements 4. Conclusion Experiments and simulations have shown that the lifetime of the valve components is determined mainly by internal defects produced by a non-optimized technology, the wear caused by the pumped

oil and the stress to fatigue of the ball and valve seat. The state of tensions produced by thermo- mechanical stresses for balls made of two layers may have a degree of hazard imposed by the different physical and mechanical characteristics of the layer’s materials and by the uneven thickness of the outer layer.

The strains state produced by the thermo- mechanic stresses for the balls made from two layers can present a degree of danger imposed, on the one hand by the different physic and mechanic parameters of the materials of the layer and uneven thickness of the outer layer and on the other hand by the structural defects from contact zones between layers.

Congress Centre Basel, Switzerland

16th - 19th September 2012

european powder metallurgy association

Fig. 8: The stresses state and the main maximum stresses in the assembly