Erosion & Erosion-corrosion Assessment of Materials for use in the Oil Sands Industry
Figure 1: Examples of Slurry Erosion and Erosion Corrosion Damage in Oil Sands Applications
Figure 2: A) Slurry Jet Erosion Rig; B) Coriolis Rig; and C) Slurry Pot Erosion Corrosion Tester
The recirculating slurry piping loop propels a premixed slurry towards the test surface with a jet velocity of ~16m/s. This is higher than the speeds typically found in many applications; however, this is necessary in order to produce accelerated wear conditions. The standard test parameters involve the use of a 1:10 AFS 50–70 silica sand:water slurry with a test duration of two hours. This erosive was chosen as its particle size is comparable to the mean size of the predominant quartz solid constituent of the oil sand slurries and is commonly used in the industry for comparison purposes. The choice of erosive is key to determining the wear mechanisms that occur during testing and hence in service.
A wide range of materials have been examined using the slurry jet system, at angles of 20, 45 and 90°. Figure 3 presents results for several classes of materials and highlights the superior behaviour of the plasma transfer are welding (PTAW WC) overlay and cemented tungsten carbide (WC) under such conditions.
Another area of recent interest has been elastomeric materials, which are finding increasing utilisation in many slurry environments. Their high resistance to slurry attack has necessitated the implementation of a more severe slurry jet erosion test environment. This involves using a more angular erosive, silicon carbide (SiC), which is harder and possesses a larger particle size, to promote greater material removal via cutting mechanisms. With the semi-rounded silica erosive, elastomers typically exhibit plastic deformation through a fatigue-based mechanism, which produces limited material removal. Given the low hardness of the elastomers, the use of the SiC erosive results in greater material loss and hence a more discriminatory test procedure. Results from slurry jet testing have produced reliable information on the behaviour of various materials and have been shown to be a good guide for service performance. For example, the excellent erosion resistance of neoprene and natural rubbers compared to polyethylene linings, which have been used in a variety of oil sands locations over the past 15–20 years, has been identified.
Coriolis Scouring Erosion
An associated technique for examining erosion applications where the impact angle is typically
tester utilises centrifugal and Coriolis accelerations to rapidly pass an erosive slurry across a sample surface and has been shown to provide a convenient and reproducible technique for scouring erosion evaluation. Data obtained have correlated well with service performance,7,8
a particularly important requirement when using laboratory-based tests for critical material selection decisions.
The importance of assessing materials under these conditions is that the low-angle impacts of hard particles in a slurry do not always posses the
EXPLORATION & PRODUCTION – VOLUME 8 ISSUE 2 This
Figure 3: Slurry Jet Erosion Results for Various Material Classes
100 120 140 160
20 40 60 80
0 Low C steel pipe
450 AR steel
Cr white iron castings
20°
Crc overlays PTAW WC overlay
Impingement angle 45°
90°
critical velocity necessary for producing the plastic deformation of a material. Hence, using the Coriolis technique materials are examined for their resistance to both elastic and plastic deformation. Properties such as toughness and elasticity therefore play major roles in determining the extent of damage.9
This is in contrast to the slurry jet rig, where the majority of damage is caused by high-energy normal particle impacts.
One class of materials found in a multitude of erosive applications that have exhibited good slurry jet erosion resistance are chrome white irons. These alloys rely mainly on the dispersion of hard metallic carbides,
which is
generally M7C3, for their superior wear resistance. The carbides are distributed throughout various ferrous matrices, which provide additional properties and characteristics, such as corrosion resistance. It is generally understood that the performance of these alloys is influenced strongly by the carbide volume fraction (CVF),10,11
with erosion resistance increasing
with CVF to the disadvantage of fracture toughness and corrosion resistance. Carbide size also has a pronounced influence on intrinsic brittleness, with coarse primary carbides in particular having a propensity to pre- and in-service cracking.
85
Cemented WC
Volume loss (mm3
)
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