Wear 250 (2001) 107–113 A contribution to the surface analysis and characterisation of HVOF coatings for petrochemical application A. Scrivani a,∗ , S. Ianelli a , A. Rossi a , R. Groppetti a , F. Casadei b , G. Rizzi c a Department of Industrial Engineering, University of Parma, Viale delle Scienze, 43100 Parma, Italy b Centro Sviluppo Materiali SpA, Via di Castel Romano 100, 00128 Rome, Italy c Flametal SpA, Via di Vittorio 53, 43045 Fornovo Taro (PR), Italy Abstract The appropriate selection of bulk materials and coatings of valve components is an important factor for the economic success of oil and gas production activities in the petrochemical field. Materials and coatings are important because particle erosion and surface wear are associated to corrosion by hydrogen sulphide during oil and gas flow. The wear of high pressure valves of gas system will lead to pollution, safety problems and cost increases. The most common solution of these problems is the deposition of hard materials as tungsten carbide or chromium carbide by thermal spray. These coatings are deposited by high velocity oxygen fuel (HVOF) thermal spray process to obtain a very high hardness with excellent cohesion and adhesion. Tungsten carbide cobalt–chromium based coating, chromium carbide nickel–chromium coating as well as Inconel 625 have been adopted in the specifications of petrochemical companies and their behaviour and wear, erosion and corrosion properties are reported in the literature. This paper addresses the experimental study, surface analysis and functional characterisation of HVOF coatings innovative for the specific application such as NiAl and composite material WC/intermetallic compounds containing Ni, Cr, Co and Mo. These coatings have been systematically submitted to corrosion and functional tests based on the determination of the behaviour of the coatings in H 2 S and CO 2 atmosphere and to wear and erosion according to standard ASTM G75-95 (slurry test); material loss and surface damage have been determined; the coatings have been completely characterised from the point of view of the structure (morphology, porosity, hardness, wear) and of the surface properties by means of a prototype 3-dimensional (3-D) stylus micro-geometrical surface analysis system; their corrosion and functional behaviour have been compared with the behaviour of the above mentioned coatings. The slurry test allows a clear discrimination among the performances of analysed coatings. Namely, WC/Mo compound, because of its carbide content, shows fairly good behaviour in an erosive environment and higher erosion resistance than Inconel 625 and NiAl; all the tested coatings show similar behaviour in a corrosive environment. © 2001 Elsevier Science B.V. All rights reserved. Keywords: NiAl; WC/Mo; HVOF; Wear; Corrosion 1. Introduction One of the most important problems in the petrochemical industry is the behaviour of materials in an aggressive en- vironment with the presence of hydrogen sulphide, carbon dioxide and sand, which contribute to corrosion, erosion and wear of the surface. The wear of high pressure valves of gas system will lead to pollution, safety problems and costs. The use of hard material coatings reduces this prob- lem from the point of view of erosion and wear. Generally, these coatings are produced by high velocity oxygen fuel (HVOF) thermal spray process to obtain very hard coat- ings with excellent cohesion and adhesion. Research is in progress to propose new materials, which could im- prove corrosion, erosion and wear resistance and decrease ∗ Corresponding author. E-mail address: andreascrivani@turbocoating.it (A. Scrivani). costs. Tungsten carbide cobalt–chromium based coating, chromium carbide nickel–chromium coating and Inconel 625 have been adopted in the specifications of the main industrial petrochemical companies. Their behaviour and wear, erosion and corrosion properties have been studied and reported in the literature [1]. This paper addresses the experimental study, surface analysis and functional characterisation of HVOF coatings innovative for the specific application such as NiAl and composite material WC/intermetallic compounds contain- ing mainly Ni, Cr, Co and Mo. All the examined coatings have been deposited by HVOF to improve microhardness, cohesion and adhesion. Due to the high impact velocity of particles the coatings show an high density and cohe- sive strength of the individual splats. These characteristics contribute to high hardness and abrasion resistance of coat- ings; high density and low porosity also improve corrosion resistance. 0043-1648/01/$ – see front matter © 2001 Elsevier Science B.V. All rights reserved. PII:S0043-1648(01)00621-4