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Short communication
Hardbanding failure in a heavy weight drill pipe
G.V.S. Murthy
⇑
, Goutam Das, Swapan Kumar Das, Nikhat Parveen, S.R. Singh
Materials Science and Technology Division, National Metallurgical Laboratory (CSIR), Jamshedpur 831 007, India
article info
Article history:
Received 11 August 2010
Received in revised form 15 March 2011
Accepted 23 March 2011
Available online 31 March 2011
Keywords:
Drill pipe
Hardbanding
Charpy energy
Pearlite
Pro-eutectoid grain boundary ferrite
Ó2011 Published by Elsevier Ltd.
1. Introduction
A heavy weight drill pipe (HWDP) is a type of drill pipe whose walls are thicker and collars are longer than conventional
drill pipe. HWDP should be stronger and should have higher tensile strength than conventional drill pipe, as it is placed near
the top of a long drill string. Drill pipes are subjected to various types of loads and are operated under different environmen-
tal conditions. The heavy weight drill pipes are the most expensive elements of the drill pipe string and their durability is
essential for the economical drill work efficiency. In the exploration work, abrasive wear occurs and the durability of the
heavy weight drill pipe is decreased. The abrasive wear is the result of the friction between the heavy weight drill pipe with
the inner surface of the casing or the open hole wall. In order to improve the wear resistance of heavy weight drill pipes the
hardbanding technology is worldwide applied.
Hardbandng of drill pipe tool joints and other drilling equipment has been around since the late 1930 [1–3]. Originally
hardbanding was applied primarily to protect the drill pipe and other tools from premature abrasive wear. Since, that time
there have been numerous changes in hardbanding and its application, but only within the last few years has new technol-
ogy been introduced that allows hardbanding to protect the casing and the drill pipe at the same time. Several types of wear
resistant alloys are now available for hardbanding. Most of them are designed to protect the casing, the marine riser or the
drill pipe, but only one or two can sufficiently protect all at the same time, from premature abrasive wear. The proper hard-
banding with the right application can substantially increase the tool joint wear life; reduce casing wear caused by drill
string, downhole drag and torque, and rig fuel consumption and allow operators to run lighter weight and grade casing.
The essential features and advantages of all of these hardbanding alloys are: (i) It has a very low coefficient of friction,
which minimizes rapid casing wear caused by drill string contacting the casing wall; (ii) It has excellent resistance to the
high stress abrasion experienced in open hole; (iii) It can be applied raised to give maximum casing and tool joint wear
reduction and (iv) It can be applied over existing deposits with some limitations like the existing hardbanding must be in
1350-6307/$ - see front matter Ó2011 Published by Elsevier Ltd.
doi:10.1016/j.engfailanal.2011.03.014
⇑
Corresponding author.
E-mail address: gvs@nmlindia.org (G.V.S. Murthy).
Engineering Failure Analysis 18 (2011) 1395–1402
Contents lists available at ScienceDirect
Engineering Failure Analysis
journal homepage: www.elsevier.com/locate/engfailanal
Author's personal copy
serviceable condition before the application. Also the applicators must strictly adhere to the recommended procedures man-
ual for proper application.
In the present investigation the root cause for the failure of a heavy weight drill pipe has been carried out. The drill pipe
has been in operation for a very short duration of time and the material specification is AISI 1340 grade.
After a through visual examination of the as received two pieces of the failed pipe, it was felt the following tests were
essential in order to arrive at the cause for the observed failure; (i) Visual examination of the both the pieces of the failed
drill pipe; (ii) Elemental analysis; (iii) Hardness; (iv) Mechanical property evaluation such as tensile testing and Charpy im-
pact test; (v) Microstructural characterization using optical microscope (OM) and scanning electron microscope (SEM) and
(vi) Fractography of the failed specimens to reveal the nature of failure.
2. Experimental results and discussion
2.1. Visual observation
Two pieces of the failed heavy weight drill pipe measuring 5
1
2
inch OD, 3
1
4
inch ID, and lengths about 4 inch and 2 inch
respectively in the as received condition are shown in the Fig. 1a–d. It is clearly seen that the outer surface hardbanding has
been done at three distinct places at an angle of about 120°to each other. An internal plastic (yellow in color) coating is also
seen. The hardband portion on the outer surface measured about 1 inch in thickness. No damage is seen either on the inter-
nal plastic coating or on the outer surface except for regular equally spaced shallow grip marks. It is also observed that the
fracture surface is fully rusted.
2.2. Chemical Analysis
Chemical analysis has been carried out by atomic absorption spectrometer, using the standard procedures. The chemical
composition of the pipe material is obtained as described above and the results are given in Table 1. These results show that
the pipe conforms to the compositional standards of such materials.
Similarly, the chemical composition of the hardbanding material has been obtained using the Spark Emission Spectrom-
eter and the results are given in Table 2. The chemical composition of the hardbanding material that has been used agrees
very well with the reported data [4].
2.3. Hardness measurements
Hardness measurements were carried out on a standard hardness testing machine calibrated to the usual standards, with
a diamond cone in Rockwell scale. Rockwell hardness numbers were obtained on the cross-sectional region of the pipe. The
ab
cd
Fig. 1. (a–d): Macro photographs of the failed heavy weight drill pipes, showing (a) the rusted portion (b) the hard band regions (c) and (d) the shallow grip
marks.
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hardness data was taken starting from the hardbanding region, intermediate diffusion zone and pipe material. An average of
3 readings has been taken for each measurement and is shown in Table 3.
The hardness data also show that the hardbanding area has a high hardness ffi54 Rc, whereas the joint portion (diffusion
area) there is a decrease in the hardness (43 Rc). In case of the pipe material the hardness value is 24 Rc. All these values of
the hardness also agree very well with the reported hardness of the hardbanding material as well as with the pipe materials.
2.4. Mechanical testing
Tensile tests were performed on round specimens machined from the supplied pipe (as per the ASTM standard E-8M-04)
of the failed tube. Three specimens were tested and the average tensile properties are reported here. All tests were carried
out in an electromechanical dynamic testing system fitted with a 100 kN capacity load cell. The machine was equipped with
Table 1
Elemental compositional analysis of the pipe material (wt.%).
Element C Mn P S Si Fe
Pipe 0.44 1.38 0.009 0.006 0.28 Balance
Standard 0.38–0.43 1.60–1.90 0.035 (max) 0.04 (max) 0.15–30 Balance
Table 2
Elemental compositional analysis of the hardband material (wt.%).
Si C Cr Mn P S Fe
0.48 0.56 15.71 2.0 0.005 0.001 Balance
Table 3
Hardness data across the cross-section of the pipe sample.
Specimen area Hardness in R
c
(Load 150 Kg)
Hardbanding region 54
Difussion zone 43
Pipe material 24
Table 4
Mechanical properties of the sample (pipe material).
Property YS (MPa) UTS (MPa) % Elongation Charpy impact energy (J) Hardness (Hv)
Pipe 485 823 8.5% 10 254
Standard 436 703 25% 70 245
Fig. 2. Fractographs of the impact tested sample (taken from the pipe material), showing cleavage type of cracks indicating the brittle nature of fracture of
the pipe material.
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a digital controller interfaced to a computer through IEEE 488/GPIB protocols. The tests were conducted using Flaps 5; a Win-
dows based software. The software has provision for controlling the test conditions like displacement rate, and data acqui-
sition on load, displacement and strain in different channels. The strain was measured through an extensometer of 25 mm
gauge length, attached to the middle of the specimen gauge. The tests were conducted at a displacement rate of 0.5 mm/min
at ambient temperature.
Charpy V-notch Impact tests were conducted with specimens extracted from the pipe material. Tests were conducted as
per ASTM standard E-23-07 on a full size specimen. All tests were carried out in a pendulum type impact test machine. The
average impact toughness value is reported here.
The nominal values for such steels (AISI 1340) are YS: 436 MPa; UTS: 703 MPa; % elongation: 25%; Impact toughness: 70 J;
hardness: 245 HV.
It may be noticed that the pipe has YS, UTS and Hardness values close to the nominal values of AISI 1340. However, %
elongation, a measure of ductility of material, and impact energy is significantly lower than the specified values. This
may be an important contributing factor for failure to occur.
Thus the pipe material AISI 1340 steel shows a very low toughness although the hardness is within the prescribed limits.
This implies that the material might have achieved the hardness requirement but does not meet the standard toughness re-
quired for such steel. It may be due to improper heat treatment.
Further the impact tested sample was examined for any features indicating the nature of the fracture. This was done
because the impact toughness value obtained in the present case was very low, as shown in Table 4 (10 J) compared to
Fig. 3. Macrophotograph of the polished and etched transverse section sample showing three different regions.
Fig. 4. Optical micrographs of the (a) hard band material (b) joint region (c) heat affected region and (d) pipe material.
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the reported value of ffi70 Joules for AISI 1340 steels. The fractograph is shown in Fig. 2. It clearly shows the cleavage type of
cracks indicating the brittle nature of fracture of the pipe material also and hence the low impact energy.
2.5. Micro structural characterization
Microstructural characterization was carried out using optical microscopy and scanning electron microscopy. Standard
metallographic technique was employed for grinding and polishing the samples. All samples were etched with 2% Nital solu-
tion to reveal the microstructure under the microscope.
Fig. 5. Optical micrograph montage to cover the entire cross-section of the specimen; showing the origin of the micro crack is in the hard band region.
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As a first step towards understanding the microstructures, a macro photo of the polished and etched sample is shown in
the Fig. 3. It clearly shows the three different regions i.e., the hardband area, the diffusion zone and the pipe material.
The optical micrographs taken in the different regions are also presented in the Fig. 4. The hard band region shows a cast
dendritic structure. (Fig. 4a). Fig. 4b shows the joint region, while Figs. 4 c and d show the heat affected zone and the pipe
material respectively.
Fig. 6. SEM micrograph in the pipe material showing the formation of coarse grain structure.
Fig. 7. SEM micrograph of the pipe material (at a higher magnification) showing the formation of pearlite alongwith pro-euctectoid grain boundary ferrite.
Fig. 8. SEM micrograph of the joint region, showing the formation of the microcracks.
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It was observed that the hardband region had a large number of microcracks extending up to the diffusion zone. In Fig. 5,
a montage of the optical micrographs covering the entire cross-section starting from the hardband region up to the pipe is
shown where one such crack is seen.
Similarly the scanning electron micrographs are shown in Figs. 6–9. The first micrograph (Fig. 6) shows the microstruc-
ture of the pipe material with a coarse grain structure. Fig. 7 is the microstructure of the pipe material (at a higher magni-
fication) showing the pearlite structure with pro-eutectoid grain boundary ferrite. The pro-eutectoid grain boundary ferrite
is a deleterious microstructural constituent and may result in low impact energy. Therefore its occurrence should be avoided
by careful heat treatment.
It is apt to point out that the low energy Charpy energies of the pipe material might have also compounded the failure.
This is due to the fact that the material was pearlitic (Fig. 7) and a high carbon pearlite has a high ductile to brittle transition
temperature (DBTT). This may be the reason for the observed low Charpy energies of the pipe material. A similar observation
was reported earlier [5]. Moreover as was pointed out the pipe might have achieved the desired hardness but the low Charpy
Fig. 9. SEM micrograph of the hard band material showing dendritic microstructure consists of primary carbides network (dark phase) and cracks along the
grain boundary & dendrite arms.
a
bc
Fig. 10. Fractographs showing the nature of the failure: (a) a low magnification SEM micrograph covering the entire fracture surface (b) high magnification
of the hardband region marked as X1 in (a) showing the dendritic structure (c) high magnification of the diffusion region marked as X2 in (a).
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values show the improper heat treatment which should avoid pro-eutectoid grain boundary ferrite which is a deleterious
microstructural constituent and may result in low impact energy .
Fig. 8 shows the microstructure of the joint region, showing the formation of microcracks in the region of the hardband
material only. Also note that the boundary between the band material and the heat affected zone is quite distinct.
Fig. 9 shows the SEM microstructure of the hardband material. The microstructure shows the presence of primary Cr car-
bides in the form of dendrities. Also from the EDS analysis it is seen that the dendrite arm is rich in chromium and carbon.
2.6. Fractography
Fractography of the failed samples was carried out after a thorough cleaning of the surface from the accumulated rust
with a solution which would dissolve only the rust and leave the fracture surface intact. Low magnification fractograph
(Fig. 10a) showing the entire fracture surface consisting of hardband region and base pipe is shown. The mode of fracture
was brittle and crack propagated through dendrite arms in the hardband region as shown in SEM fractograph Fig. 10b.
The interface region also shows a brittle fracture in cleavage mode as shown in Fig. 10c.
From the above experimental observations it is seen that the material specifications of the pipe material is in agreement
with the reported values. The hardness and the chemical composition agree very well with that for the specified steels i.e.,
AISI 1340 grade. The observed microstructure of the pipe material is also in agreement.
However, there are some inherent problems encountered with the particular alloy being used for hardbanding, and is un-
like other wear resistant alloy used for such purposes. It is a type of alloy, rich in chromium and carbon and is brittle in nat-
ure. This material is prone to fracture and several incidences of spalling have been reported earlier [6,7] and the company no
longer recommends the use of this alloy. In fact it has been discontinued for sale since December 2006. It is expected that the
excess of chromium forms chromium carbides, which is wear resistant, but prone to brittle fracture. This was observed in the
present case also as is shown from the microstructure and EDAX.
Thus, it is a well established fact that high resistances against wear by abrasion are best achieved with Fe-based alloys,
and more particularly with those alloys of this group wherein a precipitation of pro-eutectic primary hard phases occurs.
This is the case that has been observed in the present study (Fig. 7) which is typical. It is also an inescapable fact that the
primary phase (chromium carbide in the present case Fig. 9) is more or less crack sensitive, as a function of the density
of the primary phases, as well as density of the secondary hardening phases. In totality, and from the metallurgical approach
Fe–Cr–C alloys such as the one used here for hardbanding, are wear resistant but cracking is generally extensive, which af-
fects the through wall thickness of the hardband.
So from the experimental findings as above both the hardbanding material used as well as the steel used for the pipe are
really not meeting the requirements of such applications and are prone to failure sooner or later. Hence the failure occurred
in this case which was but natural.
3. Conclusions
Based on the above findings, it can be concluded that the heavy weight drill pipe meets all the desired specifications ex-
cept for % elongation and impact energy which are significantly lower than the specified values. However due to the inherent
nature of the alloy used for hardbanding, the cracking has been observed. Also the initiation of the cracks is mostly in the
hardband material and is due to the formation of chromium carbides, which although wear resistant is also, crack sensitive.
Similarly the heat treatment given to the pipe is not enough to meet the toughness requirement. This is evident from the
very low impact toughness as well the features of the fractured impact specimen.
Acknowledgements
The authors would like to thank Director, National Metallurgical Laboratory – CSIR, Jamshedpur for his kind permission to
carry out and publish this work.
References
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[2] Barrios J. In: Proceedings of the IADC/SPE Asia pacific drilling technology conference, APDT, hardbanding for drilling unconsolidated sand reserviours.
[3] Bouzakis K, editor. Proceedings of the 3rd International conference on manufacturing engineering (ICMEN), October 2008. EEAM and PCCM 2009; p. 341
[and references therein].
[4] Technical Information Arnco technology trust Ltd. 357 Briarpark, Houston, Texas, USA Website: http:/arcotech.com.
[5] Putatunda SK, Yang J, Gundlach RB. Development of an austenitic structural steel. Mater Des 2005;26:534–44.
[6] John G. The facts and myths of hardbanding. Mobley Arnco Technol. Ltd. Dt. October, 2000 and the actual case histories presented therein.
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