- Email: [email protected]
The friction and wear of various hard-face claddings for deep-hole drilling
Wear 263 (2007) 234–239
Short communication
The friction and wear of various hard-face claddings for deep-hole drilling John Truhan a,∗ , Ravi Menon b , Frank LeClaire b , Jack Wallin b , Jun Qu c , Peter Blau c a
University of Tennessee, Knoxville, TN, USA Stoody Company, Bowling Green, KY, USA c Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN, USA b
Received 22 August 2006; received in revised form 29 January 2007; accepted 30 January 2007 Available online 19 March 2007
Abstract Hard-face claddings are used for banding drill shafts that rotate against well casings while lubricated by drilling mud. This tribosystem should have the lowest friction possible in order to minimize drilling power requirements, and the lowest total system wear to maximize component life. Blocks representing a variety of hard-face claddings were slid against rotating rings of AISI 4140 casing material and lubricated by simulated drilling mud that consisted of a slurry of silica sand, clay, and water. The cladding specimens included currently used alloys and several candidate compositions. There was an excellent correlation between the friction coefficient and the wear, by weight loss, of both the cladding and the casing alloys. There was also a good direct correlation between the wear of the cladding and the wear of the casing. Claddings with finer grain sizes and finer, more uniformly distributed hard carbides had higher hardness and produced lower wear on both the cladding and the casing counter-face. The complex mechanisms involved with three-body wear and friction in interfaces lubricated by slurries present a challenge for further study. © 2007 Elsevier B.V. All rights reserved. Keywords: Deep-hole drilling; Slurry; Abrasion; Hard-face cladding
1. Introduction Deep-hole drilling for mining applications presents a challenge in the choice of drilling materials due to the extremely harsh operating environment in which they must perform. Low wear is obviously desirable to increase shaft and casing life and reduce maintenance while low friction is desirable to reduce the energy needed for drilling. Extensive development efforts have been undertaken on hard-faced claddings for drill shafts to reduce wear and friction. However, any evaluation of the cladding alloys must also include an evaluation of the response of the counter-face, i.e., the well casing. The optimum choice of materials would be the combination producing the least wear and friction for the tribosystem. There are several industry-recognized tests for the evaluation of cladding and casing materials lubricated by a drilling “mud” slurry, but each has advantages and disadvantages. The DEA-42 Maurer Test is a proprietary test for casing wear and requires the use of large specimens. This test is difficult to perform,
∗
Corresponding author. E-mail address: Truhan John [email protected] (J. Truhan).
0043-1648/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.wear.2007.01.046
and consequently, is relatively expensive. The ASTM G65 drysand/rubber wheel test [1] and the ASTM G105 wet sand/rubber wheel test [2] for abrasion resistance are less expensive and easier to carry out, but they do not allow for the influence of a metal counter-face. In previous work [3], a pin-on-disk test was used to measure the friction between various cladding alloys and AISI 4140 counter-face representative of casing material under slurry-lubricated conditions. Although a relatively simple test to conduct, the degree of wear could not be measured accurately due to the production of a shallow, diffuse wear scar. This was primarily due to the relatively small area of contact and the relatively large particles of silica in the slurry creating rapidly varying interfacial conditions. While, there have been numerous publications on slurry erosion and the effects of drilling mud (e.g., [4–6]), little has been published concerning the effects of abrasive slurries on friction. The current study expands on the previous work [3] by reporting a new block-on-ring procedure that enables both friction and wear measurements. Conditions were selected so that the tests could be run in a short time but produce enough wear to use weight loss as an unambiguous measure. The objectives of this study were: (1) to develop a rapid, inexpensive bench test which correlates with field experience and other
J. Truhan et al. / Wear 263 (2007) 234–239
235
Table 1 Summary of experimental conditions Rotational speed Tangential speed Ring alloy and hardness Test time Sliding distance Applied load
300 rpm 94 cm/sec AISI 4140, 217 BHN 2.00 min 112.8 m 90.5 N
Table 2 Composition of slurry (mud) Bentonite (Quik GelTM ) Silica sand (Clemtex #5) Water
Fig. 1. (a) Overall view of the block-on-ring test configuration showing the static load in place. (b) Close-up view of the block (cladding), ring (casing), and the slurry reservoir below the ring.
industry-recognized tests, (2) to evaluate drill shaft cladding materials for optimum friction and wear behavior against well casing materials lubricated by a drilling mud slurry, and (3) to compare the wear resistance of current commercial claddings with that of advanced candidate claddings. 2. Experimental procedure and materials The block-on-ring tests were carried out using commercially available equipment shown in Fig. 1(a and b) (Plint Model TE53, Phoenix Tribology Ltd., UK). Fig. 1(a) shows an overall
31.8 g 144.2 g 500 ml
view of the apparatus with the dead-weight loading visible on the right. Fig. 1(b) shows the mounted test coupons. The 12.7 mmwide slider block with the hard-face cladding is mounted on the upper holder and the rotating ring, representing the casing alloy, is mounted below it. A reservoir contains the slurry. The lower part of the ring picks up the slurry as it rotates and carries it to the interface. A metal shield, not shown, prevents the slurry from splashing out. Friction force is measured with a load cell and the data are collected using a computer data acquisition system. The test parameters are summarized in Table 1. The load and test duration were selected to produce enough wear on both the block and ring to use weight loss as the wear metric. Since the availability of sample materials was limited, only two replicate tests were allowed for each cladding. The slurry was a simulated drilling mud, whose composition is given in Table 2. In order to get the most uniform distribution, the clay was first mixed in the water until thoroughly dispersed and then the silica was slowly added with continued stirring. Since settling was inevitable between tests, the slurry was agitated just prior to filling the reservoir. The 60 mm-diameter rings were used to represent the casing material and were AISI 4140 alloy steel tempered to a hardness of 217 BHN. The block claddings represent both currently used alloys and several developmental ones. A block of 4140 steel similar to the ring was also tested as a reference couple. Since
Table 3 Composition and hardness of hard-facing claddings Block material
Generic description
Hardness
Block HRC relative to ring
Nominal composition (wt%)
TJ4140 1P 12P
Tool joint material Martensitic tool steel Martensitic titanium/niobium carbide
285 BHN (30 HRCa ) 51 HRC 40 HRC
1.0 1.7 1.3
13P
Martensitic niobium, molybdenum carbide Martensitic niobium, molybdenum, tungsten carbide Martensitic tool steel Semi-austenitic stainless steel Martensitic niobium, boron tool steel Martensitic titanium carbide
64 HRC
2.1
0.4 C, 1.0 Cr, 0.2 Mo 0.5 C, 5 Cr, 0.2 Mo 0.8 C, 7.5 Cr, 0.6 Mo, 2.5 Nb, 0.9 Ti 1.0 C, 8 Cr, 0.7 Mo, 3 Nb
66 HRC
2.2
41 HRC 53 HRC 58 HRC 55 HRC
1.4 1.8 1.9 1.8
14P 15P 17P 18P 19P a
Conversion of BHN to HRC based on ASTM E140.
1.0 C, 3.5 Cr, 4 Mo, 3.5 W, 2 Nb 0.4 C, 5 Cr, 0.5 Mo, 0.3 V 0.1 C, 20 Cr, 3 Nb, 3 B 0.6 C, 1 Ni, 3 B, 3 Nb 1.0 C, 5 Cr, 3 Ti
236
J. Truhan et al. / Wear 263 (2007) 234–239
Fig. 2. Cladding microstructures representative of the two broad categories of uniformity: (a) Alloy 1P, (b) Alloy 19P, (c) Alloy 12P, (d) Alloy 14P, and (e) Alloy 17P.
there is directionality to the microstructure of the cladding due to the deposition process, care was taken to orient the block so the deposition direction matched that for service conditions. The nominal compositions of the various claddings tested are summarized in Table 3. Alloys identified as 1P, 15P, 17P, 18P, and 19P are current cladding materials. The remaining cladding
alloys were developed by the Stoody Company for wear performance as well as ease of application. The majority of the cladding alloys, except Alloy 17P, have in a martensitic matrix with or without dispersed secondary carbides and borides. Alloy 17P is the only stainless steel in the test program and consists of a dispersion of chromium borides in a semi-austenitic matrix.
J. Truhan et al. / Wear 263 (2007) 234–239
Representative microstructures of the test alloys are shown in Fig. 2(a–e). Alloy 1P (Fig. 2(a)) is a martensitic tool steel hardfacing deposit. In addition to martensite there is some retained austenite. Alloy 19P (Fig. 2(b)) has a similar matrix along with dispersed TiC. Alloy 12P (Fig. 2(c)) is similar to Alloy 19P but some of the Ti has been replaced with Nb and Mo to produce better wear performance. In the developmental Alloy 14P (Fig. 2(d)), the Ti has been completely replaced with Nb, Mo, and W. Although this replacement results in a small increase in the total system wear, the applicability of the hard-facing is significantly improved due to the reduction of Ti in the wire consumable used to deposit it. Alloy 17P (Fig. 2(e)) was the only stainless steel hard-facing tested. Its microstructure shows acicular chromium borides in a semi-austenitic matrix. In contrast to the alloys shown in Fig. 2(b–d), there is no finely dispersed secondary micro-constituent.
237
Fig. 4. Block (cladding) and ring (casing) wear results stacked to show total system wear.
3. Results and discussion Friction and wear results from this investigation are summarized in Fig. 3. The highest friction and wear, not surprisingly, occur for the reference couple: self-mated 4140. As expected, the amount of wear for the clad blocks was reduced by almost an order of magnitude compared to the self-mated couple. Wear reductions for the rings were not as dramatic, with reductions on the order of 20–40%. The friction coefficient for all cladding combinations exhibited little variation and is only slightly lower than that for the self-mated couple. Frictional behavior was likely to be controlled mainly by the properties of the slurry with its substantial amount of entrained silica dust. Harder materials probably allowed less silica particulate indentation and therefore, slightly reduced the frictional drag in the interface. As stated previously, it is important that the wear-resistant hard-face cladding should not accelerate the wear of the casing. Fig. 4 shows the sum of the wear on both specimens as the total system wear for the various cladding combinations. Most of the variation in total system wear is due to the ring wear contribution, demonstrating the importance of not focusing on the cladding wear exclusively. Certain combinations perform substantially better than others. The lowest total tribosystem wear was achieved by couples using the 12P and 19P claddings.
Fig. 3. Summary of friction and wear results for the various claddings.
Fig. 5. Relationship between the friction coefficient and wear for both the block (cladding) and ring (casing).
As indicated in Fig. 5, there was a distinct relationship between friction and wear, and that was irrespective of composition or microstructure, implying that the hard-face claddings sliding against the slurry-lubricated casing material behaved in a mechanistically similar manner. The more energy available to do frictional work, the more material was abrasively removed. Fig. 6 data indicate an approximate trend between block wear and the ring wear. Lower block wear tended to accompany lower ring wear. A possible explanation may be found in the highly abrasive nature of the slurry. The silica dust in the slurry is much
Fig. 6. Relationship between block (cladding) wear and ring (casing) wear.
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J. Truhan et al. / Wear 263 (2007) 234–239
Fig. 7. Wear scars for the (a) block and (b) ring for self-mated 4140 steel.
harder than either surface and therefore, can cause wear in both, but the relative amount may differ. When a harder material rubs against a softer one, there is always the question as to what degree the harder material causes wear in the softer. From a quasi-static point of view, the degree to which a hard particle trapped between two softer surfaces will penetrate either of those surfaces should correspond directly to their relative hardness (the ratios of the HRC of the block relative to the ring are given in Table 3). However, that quasi-static argument does not take into account the fact that in slurry wear, the hard particles are passing through the interface entrained within a viscous fluid, tumbling, and cutting. Plowing or cutting occurs only when sufficient load can be transferred to a particle or agglomerate that happens to be aligned advantageously to produce a nick or scratch. If one of the surfaces is so ductile that hard particles become momentarily embedded, there could be two-body abrasion as well as threebody abrasion occurring. Post-test optical examination did not reveal any apparent silica embedded into the 4140 rings, but oxidation of the test specimens during the time between testing and observation obscured the finer wear scar features. Additional studies by electron microscopy would have been desirable, but the scope of the project did not allow them. There were no evident correlations between the cladding hardness and either the friction coefficient, block weight loss, or the ring weight loss. This result is somewhat surprising since the cladding hardness for the various materials ranges from about
40–66 HRC, a wide variation. Although the fundamental reasons for these results remain unclear, it is evident that cladding hardness alone was not a good predictor of wear or friction behavior in this particular tribosystem. It is interesting to note that the friction coefficients measured in this study are roughly a factor of two higher than previously measured using a pin-on-disk test [3]. It is likely that the higher surface area and converging linear contact of the block-on-ring tests allows for a more representative slurry composition to be confined within the interface. The small surface area of the rounded pin tip would not be expected to trap much silica dust, especially the larger particles. Support for the lack of particle entrainment in the pin-on-disk tests can be found in their friction coefficients. Friction coefficients for slurry-lubricated pin-ondisk tests were comparable to those run with water lubrication alone (0.33 compared to 0.35). There appears to be a connection between the cladding microstructure and tribological performance. In general, claddings with a finer, more uniform grain size, and a uniform dispersion of carbides had better friction and wear performance than claddings with more heterogeneous microstructures. This can be seen by comparing the microstructures in Fig. 2. Fig. 2(b–d) represents the claddings that had better overall performance. These include both developmental claddings and one commercial one. Their microstructures are similar despite their differences in hardness due to different carbide types. In con-
Fig. 8. Wear scars for the 14P cladding on the (a) block and (b) 4140 steel ring.
J. Truhan et al. / Wear 263 (2007) 234–239
trast, cladding alloys represented in Fig. 2(a and e) display coarser, more heterogeneous microstructures, with correspondingly poorer friction and wear performance. Although these results are not unexpected, they are in contrast with previous results [3] and that demonstrates the difficulty with using the pin-on-disk test with slurry-lubrication. Figs. 7 and 8 show the appearance of the typical wear scars on both the block and ring for high and low wear couples. The selfmated 4140 steel couple in Fig. 7 displays severe abrasive wear, consistent with the high wear measured for that combination. By contrast, the morphology of the wear scar for a clad block showing low friction and wear (14P in this case) shows abrasive wear as well, but with much finer parallel scoring and a smaller scar area, particularly on the block side. Understanding the scope of the complex interaction between fluid dynamics, instantaneous mechanical contact, and fluid chemistry goes well beyond the scope of this communication. However, the results of this work suggest that while the slurry characteristics have a major influence on sliding friction between cladding and casing materials, the selection of materials can influence it as well, and that the total tribosystem wear can be reduced by judicious selection of material compositions. It is hoped that these results will provide experimental support for further systematic studies on the interactions of materials and slurries in drilling environments. 4. Conclusions • The block-on-ring test configuration, which is relatively simple to use, can be helpful in evaluating both the friction and the wear of drill shaft cladding alloys against a casing alloy in slurry-lubricated conditions. • Block-on-ring results produced more quantitative wear measurements than were possible using pin-on-disk tests on similar materials. • There was a very good correlation between friction and wear of both the cladding (block) and the casing (ring) materials in slurry-lubricated conditions.
239
• There was a good correlation between the cladding wear and casing wear. • There was no apparent correlation of the cladding hardness alone with either cladding friction or wear, although harder claddings produced less casing material wear. • A fine, uniform cladding microstructure produced lower friction and wear than coarser microstructures. • The newer developmental cladding alloys generally performed better than most of the current commercially available claddings. Acknowledgements This research was sponsored by the Assistant Secretary for Energy Efficiency and Renewable Energy, Office of FreedomCAR and Vehicle Technologies, as part of the High Temperature Materials Laboratory User Program, Oak Ridge National Laboratory, managed by UT-Battelle, LLC, for the U.S. Department of Energy under contract number DE-AC0500OR22725. References [1] ASTM G 65-04, Standard Test Method for Measuring Abrasion Using the Dry Sand/Rubber Wheel Apparatus, Annual Book of Standards, vol. 03.02, ASTM International, West Conshohocken, Pennsylvania. [2] ASTM G 105-02, Standard Test Method for Conducting Wet Sand/Rubber Wheel Abrasion Tests, Annual Book of Standards, vol. 03.02, ASTM International, West Conshohocken, Pennsylvania. [3] J.J. Truhan, R. Menon, P.J. Blau, The evaluation of various cladding materials for down-hole drilling applications using the pin-on-disk test, Wear 259 (2005) 1308–1313. [4] M.R. Duignan, S.Y. Lee, RPP-WTP Slurry wear evaluation: literature review, Westinghouse Savannah River Company Report WSRC-TR-2001-00156, 2001. [5] Y. Peysson, Solid/liquid dispersions in drilling and production, Oil Gas Sci. Technol. Rev. IFP 59 (1) (2004) 11–21. [6] P. Skalle, K.R. Backe, S.K. Lyomov, L. Kilaas, A.D. Dyrli, J. Sveen, Microbeads as lubricant in drilling muds using a modified lubricity tester, Society of Petroleum Engineers, Paper SPE 56562, 1999.
Short communication
The friction and wear of various hard-face claddings for deep-hole drilling John Truhan a,∗ , Ravi Menon b , Frank LeClaire b , Jack Wallin b , Jun Qu c , Peter Blau c a
University of Tennessee, Knoxville, TN, USA Stoody Company, Bowling Green, KY, USA c Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN, USA b
Received 22 August 2006; received in revised form 29 January 2007; accepted 30 January 2007 Available online 19 March 2007
Abstract Hard-face claddings are used for banding drill shafts that rotate against well casings while lubricated by drilling mud. This tribosystem should have the lowest friction possible in order to minimize drilling power requirements, and the lowest total system wear to maximize component life. Blocks representing a variety of hard-face claddings were slid against rotating rings of AISI 4140 casing material and lubricated by simulated drilling mud that consisted of a slurry of silica sand, clay, and water. The cladding specimens included currently used alloys and several candidate compositions. There was an excellent correlation between the friction coefficient and the wear, by weight loss, of both the cladding and the casing alloys. There was also a good direct correlation between the wear of the cladding and the wear of the casing. Claddings with finer grain sizes and finer, more uniformly distributed hard carbides had higher hardness and produced lower wear on both the cladding and the casing counter-face. The complex mechanisms involved with three-body wear and friction in interfaces lubricated by slurries present a challenge for further study. © 2007 Elsevier B.V. All rights reserved. Keywords: Deep-hole drilling; Slurry; Abrasion; Hard-face cladding
1. Introduction Deep-hole drilling for mining applications presents a challenge in the choice of drilling materials due to the extremely harsh operating environment in which they must perform. Low wear is obviously desirable to increase shaft and casing life and reduce maintenance while low friction is desirable to reduce the energy needed for drilling. Extensive development efforts have been undertaken on hard-faced claddings for drill shafts to reduce wear and friction. However, any evaluation of the cladding alloys must also include an evaluation of the response of the counter-face, i.e., the well casing. The optimum choice of materials would be the combination producing the least wear and friction for the tribosystem. There are several industry-recognized tests for the evaluation of cladding and casing materials lubricated by a drilling “mud” slurry, but each has advantages and disadvantages. The DEA-42 Maurer Test is a proprietary test for casing wear and requires the use of large specimens. This test is difficult to perform,
∗
Corresponding author. E-mail address: Truhan John [email protected] (J. Truhan).
0043-1648/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.wear.2007.01.046
and consequently, is relatively expensive. The ASTM G65 drysand/rubber wheel test [1] and the ASTM G105 wet sand/rubber wheel test [2] for abrasion resistance are less expensive and easier to carry out, but they do not allow for the influence of a metal counter-face. In previous work [3], a pin-on-disk test was used to measure the friction between various cladding alloys and AISI 4140 counter-face representative of casing material under slurry-lubricated conditions. Although a relatively simple test to conduct, the degree of wear could not be measured accurately due to the production of a shallow, diffuse wear scar. This was primarily due to the relatively small area of contact and the relatively large particles of silica in the slurry creating rapidly varying interfacial conditions. While, there have been numerous publications on slurry erosion and the effects of drilling mud (e.g., [4–6]), little has been published concerning the effects of abrasive slurries on friction. The current study expands on the previous work [3] by reporting a new block-on-ring procedure that enables both friction and wear measurements. Conditions were selected so that the tests could be run in a short time but produce enough wear to use weight loss as an unambiguous measure. The objectives of this study were: (1) to develop a rapid, inexpensive bench test which correlates with field experience and other
J. Truhan et al. / Wear 263 (2007) 234–239
235
Table 1 Summary of experimental conditions Rotational speed Tangential speed Ring alloy and hardness Test time Sliding distance Applied load
300 rpm 94 cm/sec AISI 4140, 217 BHN 2.00 min 112.8 m 90.5 N
Table 2 Composition of slurry (mud) Bentonite (Quik GelTM ) Silica sand (Clemtex #5) Water
Fig. 1. (a) Overall view of the block-on-ring test configuration showing the static load in place. (b) Close-up view of the block (cladding), ring (casing), and the slurry reservoir below the ring.
industry-recognized tests, (2) to evaluate drill shaft cladding materials for optimum friction and wear behavior against well casing materials lubricated by a drilling mud slurry, and (3) to compare the wear resistance of current commercial claddings with that of advanced candidate claddings. 2. Experimental procedure and materials The block-on-ring tests were carried out using commercially available equipment shown in Fig. 1(a and b) (Plint Model TE53, Phoenix Tribology Ltd., UK). Fig. 1(a) shows an overall
31.8 g 144.2 g 500 ml
view of the apparatus with the dead-weight loading visible on the right. Fig. 1(b) shows the mounted test coupons. The 12.7 mmwide slider block with the hard-face cladding is mounted on the upper holder and the rotating ring, representing the casing alloy, is mounted below it. A reservoir contains the slurry. The lower part of the ring picks up the slurry as it rotates and carries it to the interface. A metal shield, not shown, prevents the slurry from splashing out. Friction force is measured with a load cell and the data are collected using a computer data acquisition system. The test parameters are summarized in Table 1. The load and test duration were selected to produce enough wear on both the block and ring to use weight loss as the wear metric. Since the availability of sample materials was limited, only two replicate tests were allowed for each cladding. The slurry was a simulated drilling mud, whose composition is given in Table 2. In order to get the most uniform distribution, the clay was first mixed in the water until thoroughly dispersed and then the silica was slowly added with continued stirring. Since settling was inevitable between tests, the slurry was agitated just prior to filling the reservoir. The 60 mm-diameter rings were used to represent the casing material and were AISI 4140 alloy steel tempered to a hardness of 217 BHN. The block claddings represent both currently used alloys and several developmental ones. A block of 4140 steel similar to the ring was also tested as a reference couple. Since
Table 3 Composition and hardness of hard-facing claddings Block material
Generic description
Hardness
Block HRC relative to ring
Nominal composition (wt%)
TJ4140 1P 12P
Tool joint material Martensitic tool steel Martensitic titanium/niobium carbide
285 BHN (30 HRCa ) 51 HRC 40 HRC
1.0 1.7 1.3
13P
Martensitic niobium, molybdenum carbide Martensitic niobium, molybdenum, tungsten carbide Martensitic tool steel Semi-austenitic stainless steel Martensitic niobium, boron tool steel Martensitic titanium carbide
64 HRC
2.1
0.4 C, 1.0 Cr, 0.2 Mo 0.5 C, 5 Cr, 0.2 Mo 0.8 C, 7.5 Cr, 0.6 Mo, 2.5 Nb, 0.9 Ti 1.0 C, 8 Cr, 0.7 Mo, 3 Nb
66 HRC
2.2
41 HRC 53 HRC 58 HRC 55 HRC
1.4 1.8 1.9 1.8
14P 15P 17P 18P 19P a
Conversion of BHN to HRC based on ASTM E140.
1.0 C, 3.5 Cr, 4 Mo, 3.5 W, 2 Nb 0.4 C, 5 Cr, 0.5 Mo, 0.3 V 0.1 C, 20 Cr, 3 Nb, 3 B 0.6 C, 1 Ni, 3 B, 3 Nb 1.0 C, 5 Cr, 3 Ti
236
J. Truhan et al. / Wear 263 (2007) 234–239
Fig. 2. Cladding microstructures representative of the two broad categories of uniformity: (a) Alloy 1P, (b) Alloy 19P, (c) Alloy 12P, (d) Alloy 14P, and (e) Alloy 17P.
there is directionality to the microstructure of the cladding due to the deposition process, care was taken to orient the block so the deposition direction matched that for service conditions. The nominal compositions of the various claddings tested are summarized in Table 3. Alloys identified as 1P, 15P, 17P, 18P, and 19P are current cladding materials. The remaining cladding
alloys were developed by the Stoody Company for wear performance as well as ease of application. The majority of the cladding alloys, except Alloy 17P, have in a martensitic matrix with or without dispersed secondary carbides and borides. Alloy 17P is the only stainless steel in the test program and consists of a dispersion of chromium borides in a semi-austenitic matrix.
J. Truhan et al. / Wear 263 (2007) 234–239
Representative microstructures of the test alloys are shown in Fig. 2(a–e). Alloy 1P (Fig. 2(a)) is a martensitic tool steel hardfacing deposit. In addition to martensite there is some retained austenite. Alloy 19P (Fig. 2(b)) has a similar matrix along with dispersed TiC. Alloy 12P (Fig. 2(c)) is similar to Alloy 19P but some of the Ti has been replaced with Nb and Mo to produce better wear performance. In the developmental Alloy 14P (Fig. 2(d)), the Ti has been completely replaced with Nb, Mo, and W. Although this replacement results in a small increase in the total system wear, the applicability of the hard-facing is significantly improved due to the reduction of Ti in the wire consumable used to deposit it. Alloy 17P (Fig. 2(e)) was the only stainless steel hard-facing tested. Its microstructure shows acicular chromium borides in a semi-austenitic matrix. In contrast to the alloys shown in Fig. 2(b–d), there is no finely dispersed secondary micro-constituent.
237
Fig. 4. Block (cladding) and ring (casing) wear results stacked to show total system wear.
3. Results and discussion Friction and wear results from this investigation are summarized in Fig. 3. The highest friction and wear, not surprisingly, occur for the reference couple: self-mated 4140. As expected, the amount of wear for the clad blocks was reduced by almost an order of magnitude compared to the self-mated couple. Wear reductions for the rings were not as dramatic, with reductions on the order of 20–40%. The friction coefficient for all cladding combinations exhibited little variation and is only slightly lower than that for the self-mated couple. Frictional behavior was likely to be controlled mainly by the properties of the slurry with its substantial amount of entrained silica dust. Harder materials probably allowed less silica particulate indentation and therefore, slightly reduced the frictional drag in the interface. As stated previously, it is important that the wear-resistant hard-face cladding should not accelerate the wear of the casing. Fig. 4 shows the sum of the wear on both specimens as the total system wear for the various cladding combinations. Most of the variation in total system wear is due to the ring wear contribution, demonstrating the importance of not focusing on the cladding wear exclusively. Certain combinations perform substantially better than others. The lowest total tribosystem wear was achieved by couples using the 12P and 19P claddings.
Fig. 3. Summary of friction and wear results for the various claddings.
Fig. 5. Relationship between the friction coefficient and wear for both the block (cladding) and ring (casing).
As indicated in Fig. 5, there was a distinct relationship between friction and wear, and that was irrespective of composition or microstructure, implying that the hard-face claddings sliding against the slurry-lubricated casing material behaved in a mechanistically similar manner. The more energy available to do frictional work, the more material was abrasively removed. Fig. 6 data indicate an approximate trend between block wear and the ring wear. Lower block wear tended to accompany lower ring wear. A possible explanation may be found in the highly abrasive nature of the slurry. The silica dust in the slurry is much
Fig. 6. Relationship between block (cladding) wear and ring (casing) wear.
238
J. Truhan et al. / Wear 263 (2007) 234–239
Fig. 7. Wear scars for the (a) block and (b) ring for self-mated 4140 steel.
harder than either surface and therefore, can cause wear in both, but the relative amount may differ. When a harder material rubs against a softer one, there is always the question as to what degree the harder material causes wear in the softer. From a quasi-static point of view, the degree to which a hard particle trapped between two softer surfaces will penetrate either of those surfaces should correspond directly to their relative hardness (the ratios of the HRC of the block relative to the ring are given in Table 3). However, that quasi-static argument does not take into account the fact that in slurry wear, the hard particles are passing through the interface entrained within a viscous fluid, tumbling, and cutting. Plowing or cutting occurs only when sufficient load can be transferred to a particle or agglomerate that happens to be aligned advantageously to produce a nick or scratch. If one of the surfaces is so ductile that hard particles become momentarily embedded, there could be two-body abrasion as well as threebody abrasion occurring. Post-test optical examination did not reveal any apparent silica embedded into the 4140 rings, but oxidation of the test specimens during the time between testing and observation obscured the finer wear scar features. Additional studies by electron microscopy would have been desirable, but the scope of the project did not allow them. There were no evident correlations between the cladding hardness and either the friction coefficient, block weight loss, or the ring weight loss. This result is somewhat surprising since the cladding hardness for the various materials ranges from about
40–66 HRC, a wide variation. Although the fundamental reasons for these results remain unclear, it is evident that cladding hardness alone was not a good predictor of wear or friction behavior in this particular tribosystem. It is interesting to note that the friction coefficients measured in this study are roughly a factor of two higher than previously measured using a pin-on-disk test [3]. It is likely that the higher surface area and converging linear contact of the block-on-ring tests allows for a more representative slurry composition to be confined within the interface. The small surface area of the rounded pin tip would not be expected to trap much silica dust, especially the larger particles. Support for the lack of particle entrainment in the pin-on-disk tests can be found in their friction coefficients. Friction coefficients for slurry-lubricated pin-ondisk tests were comparable to those run with water lubrication alone (0.33 compared to 0.35). There appears to be a connection between the cladding microstructure and tribological performance. In general, claddings with a finer, more uniform grain size, and a uniform dispersion of carbides had better friction and wear performance than claddings with more heterogeneous microstructures. This can be seen by comparing the microstructures in Fig. 2. Fig. 2(b–d) represents the claddings that had better overall performance. These include both developmental claddings and one commercial one. Their microstructures are similar despite their differences in hardness due to different carbide types. In con-
Fig. 8. Wear scars for the 14P cladding on the (a) block and (b) 4140 steel ring.
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trast, cladding alloys represented in Fig. 2(a and e) display coarser, more heterogeneous microstructures, with correspondingly poorer friction and wear performance. Although these results are not unexpected, they are in contrast with previous results [3] and that demonstrates the difficulty with using the pin-on-disk test with slurry-lubrication. Figs. 7 and 8 show the appearance of the typical wear scars on both the block and ring for high and low wear couples. The selfmated 4140 steel couple in Fig. 7 displays severe abrasive wear, consistent with the high wear measured for that combination. By contrast, the morphology of the wear scar for a clad block showing low friction and wear (14P in this case) shows abrasive wear as well, but with much finer parallel scoring and a smaller scar area, particularly on the block side. Understanding the scope of the complex interaction between fluid dynamics, instantaneous mechanical contact, and fluid chemistry goes well beyond the scope of this communication. However, the results of this work suggest that while the slurry characteristics have a major influence on sliding friction between cladding and casing materials, the selection of materials can influence it as well, and that the total tribosystem wear can be reduced by judicious selection of material compositions. It is hoped that these results will provide experimental support for further systematic studies on the interactions of materials and slurries in drilling environments. 4. Conclusions • The block-on-ring test configuration, which is relatively simple to use, can be helpful in evaluating both the friction and the wear of drill shaft cladding alloys against a casing alloy in slurry-lubricated conditions. • Block-on-ring results produced more quantitative wear measurements than were possible using pin-on-disk tests on similar materials. • There was a very good correlation between friction and wear of both the cladding (block) and the casing (ring) materials in slurry-lubricated conditions.
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• There was a good correlation between the cladding wear and casing wear. • There was no apparent correlation of the cladding hardness alone with either cladding friction or wear, although harder claddings produced less casing material wear. • A fine, uniform cladding microstructure produced lower friction and wear than coarser microstructures. • The newer developmental cladding alloys generally performed better than most of the current commercially available claddings. Acknowledgements This research was sponsored by the Assistant Secretary for Energy Efficiency and Renewable Energy, Office of FreedomCAR and Vehicle Technologies, as part of the High Temperature Materials Laboratory User Program, Oak Ridge National Laboratory, managed by UT-Battelle, LLC, for the U.S. Department of Energy under contract number DE-AC0500OR22725. References [1] ASTM G 65-04, Standard Test Method for Measuring Abrasion Using the Dry Sand/Rubber Wheel Apparatus, Annual Book of Standards, vol. 03.02, ASTM International, West Conshohocken, Pennsylvania. [2] ASTM G 105-02, Standard Test Method for Conducting Wet Sand/Rubber Wheel Abrasion Tests, Annual Book of Standards, vol. 03.02, ASTM International, West Conshohocken, Pennsylvania. [3] J.J. Truhan, R. Menon, P.J. Blau, The evaluation of various cladding materials for down-hole drilling applications using the pin-on-disk test, Wear 259 (2005) 1308–1313. [4] M.R. Duignan, S.Y. Lee, RPP-WTP Slurry wear evaluation: literature review, Westinghouse Savannah River Company Report WSRC-TR-2001-00156, 2001. [5] Y. Peysson, Solid/liquid dispersions in drilling and production, Oil Gas Sci. Technol. Rev. IFP 59 (1) (2004) 11–21. [6] P. Skalle, K.R. Backe, S.K. Lyomov, L. Kilaas, A.D. Dyrli, J. Sveen, Microbeads as lubricant in drilling muds using a modified lubricity tester, Society of Petroleum Engineers, Paper SPE 56562, 1999.