Paper No.

74CORROSIOK)LThe NACE International Annual Conference and Exposition

DRILL PIPES FOR SOUR SERVICE

C.P. LINNE, F. BLANCHARD, G.C. GUNTZVallourec Research Center

P.O. Box 1759620 Aulnoye-Aymenes, FRANCE

B.J. ORLANS-JOLIETVallourec Oil & Gas

P.O. Box 159620 Aulnoye-Aymeries , FRANCE

ABSTRACT

Deep wells containing H2S necessitates drill strings that combine high strength and SulfideStress Cracking (SSC) resistance. Conventional API 5D drill pipe and API Spec7 tool joints do notmeet these requirements. This paper is aimed at evaluating the performances of new 95 ksi grade andnew 105 ksi grade drill pipes for sour service. Mechanical properties and SSC resistance have beeninvestigated on both pipes, tools and weld areas. Optimized chemical composition, manufacturingprocess and heat treatment are pointed out.

JQvF wrds : SSC, sour service, drill pipe, high strength, HX3, pipe body, tube upset, tool joints.

INTRODUCTION

Commercial reserves have been discovered in the Mobile Bay area [1,2] with productionintervals ranging from 6000 m to 7500 m. The drilling of such ultra deep and deviated wells genemteshigh torque and drag forces necessitating the use of drill strings with high torsional and tensile

strength [3]. In addition well tests have shown HX3 concentration up to 8.8 mole percent with 1.0mole percent average value.

Copyright@l$l$lGby tWcE International. Requests for permission to publish this manuscript in any form, in part or in whole must be made in writing to NACEInternational, Conferences Division, P.O. BOX 218340, Houston, Texas 77218-8340. The material presented and the views expressed in thispaper are solely those of the author(s) and are not necessarily endorsed by the Association. Printed in the U.S.A.

With the development of this kind of deep sour wells it is no more possible to useconventional X95 or G 105 API 5D[4] drill pipes with conventional API Spec 7 tool joints unlesssevere precautions are taken to control the drilling ellviromnent (use of oil based muds with pH 10 orgreater and use of sulfide scavengers).

Supported by the successful development of a sour service DP80 proprietary grade offeringhigh resistance to SSC and supported also by a long experience in sour gas drilling equipment in suchareas as Guatemala, West Africa, South-West France and the Middle East, our design of new DP95

and new DP 105 for drill pipe and tool joints offers to operators the opportunity to use SSC resistantdrill strings in ultra deep sour wells.

Comparatively to OCTG which benefits of from extensive data, the SSC behavior of drillpipes is much less known. This study brings a new point of view on drill pipes for sour serviceespecially because the heterogeneity of the product itself _ a tool joint welded on upsetted end oftubes_ is taken into account.

EXPERIMENTAL PROCEDURES

Materials

The 95 ksi grade (DP95) and 105 ksi gracle (DP105) drill pipes were formulated alongtraditional high quality OCTG pipe manufacturing principles to meet SSC resistance, weldability,hardness control and toughness. The nominal dimensions (Table 1) for the mother pipes, upsettedends and tool joints are important factors in selecting chemistry suitable for subsequent heat treatmentprocesses. Element analysis of the steels were determined using the glow discharge spectrometertechnique. Reported chemical compositions are shown in Table 2 for both pipes and tool joints.

The alloys for mother pipes are all modifications to the AISI 4130 (UNS G41300) type steelsin the chromium-molybdenum family of steels. These are evolutions of our sour service proprietary

grades with combination of Nb and B microalloying, lower carbon and low residual elementssteelmaking practice [5,6]. Mo was increased as we know that this element is very efficient to raisethe HX3 corrosion resistance [7].

The tool joints are usual NC50 forgings in accordance with AISI 4137H [8] and adapted heattreatment regarding the grades 95 and 105 ksi.

The tool joint is spin friction welded to the quench and tempered upsetted pipe. Afterwelding, the heat affected zone (HAZ) is again quench and temper heat treated to restore ductility.The heat treatment parameters are given in Table 3.

A complementary stress relieving as suggested in previous studies [9] was then added to theheat treatment processing focused in the HAZ-upset area.

Testing methods

Mechanical tests. The actual yield strength values were measured by tensile tests on roundspecimens taken longitudinally at midwall thickness of tubes and tool joints. According to the APIspecification , the yield strength is the tensile stress requested to produce a total elongation of the gagelength : 0.5% for DP95 and 0.6% for DP105 [8]. In the case of weld areas, the weld line is set in thecenter of the gauge section.

As far as impact tests are concerned, Charpy V notched specimens taken in the longitudinaldirection were tested at -20”C. Considering the wall thickness, energy values were normalized perunit of area.

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Finally, transverse and longitudinal microstructure homogeneity was evaluated by Rockwell CHardness measurements respectively on rings taken ti-om pipes and tools, and on longitudinal cuts of

the welds.

SSC tests. Sulfide stress cracking tests were conducted per NACETM0177-90 Method A[10]. The test environment was the standard NACE solution (5%wt NaCl and 0.5%wt acetic acid indistilled water) saturated with pure H2S gas. Complementary SSC tests conditions were involvedspecifically on the weld areas to simulate the wells conditions : higher pH and lower HzS partialpressure (Table 4. The environment coded WI is a NACE solution which pH=5 was adjusted by HC1addition at the beginning of the test. Regarding environment coded W2, the solution is synthetic seawater [11]. W 1 and W2 were saturated with a gas mixture of 109Z0Hd3 in Nz . The same gas mixturehas been used with a NACE solution and called NACE modified conditions.

The tensile tests were performed with proof ring devices. Double walled glass vessels wereused to control and record the temperature of the solution continuously throughout the test. AfterInachiniIlg, the specimens were polished with 600 grit paper and electrolytically. The environmentwas first purged with nitrogen and then saturated with 13X3(pure or mixture) continually bubblingafter initial saturation. An oxygen trap was utilized.

The applied stress level was a percentage of the Specified Minimum Yield Strength (SMYS)of the grade (95 ksi or 105 ksi) to determine the SSC threshold stress on both pipes, tool joints andweld areas. The Figure 1 points out the location of the samples in the different parts of the drill pipe.

Stress relieving test. This stress relieving treatment consisting in a tempering at 550”C wasperformed on a sample containing the area frolm upset to tool including the HAZ. Both the upset and

the weld were tested regarding NACE TMO 177-90 Method A.

RESULTS AND DISCUSSION

Mechanical properties

The detailed mechanical properties of the new drill pipe 95 ksi and 105 ksi grades are

displayed in Table 5. The tubes and consecutively the upsets are positioned in the highest part of thegrade. The tool joints are evaluated to a moderate strength. As for toughness properties, tools and

tubes show a very high ductility with energy values even higher than 150 J/cmz. Regarding the welds,the yield strength more difficult to control, is just above the SMYS which enabIes to limit thehardness in the weld area. As illustrated in Figure 2, 30 HRC for DP95 and 32 HRC for DP105 are

the maximum values encountered in the neighboring of the weld line. Regarding tubes, upsets andtool joints, the hardness measurements are respectively consistent with the 25 HRC and 28 HRCcriteria for DP95 and DP105.

It is now well established that the microstructure through the hardness, and the strength Ievel

are two of the most important parameters that determine the SSC resistance of a steel [12,13]. In factthe homogeneity of microstructure on tubes and tools measured by the hardness range (max-min) isan additional factor representative of the SS C resistance ability of steels with hardness level between25 HRC and 32 HRC [14,15]. The low dispersion 2 HRC on DP95 and DP105 tubes are verysatisfactory results. Consecutively to the significantly different microstructure between tubes and tool

joints, no predictive assumption can be raised about the SSC behavior of welds.

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SSC results

PiDe bodv and tool : NACE environment according to TM0177 is a very severe test condition(pH around 3 and pure H2S saturation gas). The literature [16] provides threshold values that showgeneral trends on the SSC resistance of drill pipes : around or 50% of SMYS for X95, 40% of SMYSfor G 105 and less than 40% of SMYS for respective tool joints. As for mother tubes and tool jointsof new DP95 and new DP105, they show significantly improved results (~dble 6), no failure occurseven at 9090 SMYS high stress level neither on tools nor tubes. Moreover, tests performed on tools at100% of SMYS lead mainly to late failures, Regarding the pipe body of DP1 05, no failure occurs at

this ultimate level. These results underline the improvement obtained from the basic grades.

Pipe umet : First tests lead to a threshold stress of 70% SMYS, quite 20% SMYS far from thehigh resistance level of pipes. According to the thickness ratio between pipe and upset, this threshold

stress is very satisfactory and enables to achieve the global resistance level of the drill pipe.

Weld area : As written in the NACE MR0175, material requirement for drilling inenvironments containing H2S are in fact suggestions to control environment which are primarymeans to avoid SSC : maintenance of pHIO or higher to neutralize H2S in the drilled formation anduse of chemical sulfide scavengers [17]. These considerations and well conditions encountered in sourareas oriented our SSC investigations on new test conditions adapted to study the weld area. Asolution with 10YoHAi and pH around 5 is a rather satisfactory consensus between NACE conditionsand drilling conditions as recalled in T~ble 4. Regarding to the NACE environment, weld line samplessuffer from quick failures so that the threshold stress could be extrapolated to 30% SMYS.Nevertheless, tests run in W1 and W2 conditions lead to a no failure result up to 70% SMYS and even90% SMYS for W2 conditions which translates a very satisfactory behavior to the drilling corrosivefluids (Table 7).

Stress relievin g : The additional heat treatment of stress relieving applied on upset as well onweld do not drive to any benefit : failures still occur at the same level than without it, it means inNACE conditions : 80% SMYS for upset and 50% SMYS for weld. The industrial heat treatment isthen sufficient to achieve the SSC resistance of the drill pipes.

CONCLUSIONS

The development of new drill pipe grades DP95 and DP105 for sour service was large] y easymade through our know how concerning the sour service proprietary grades . Chemical compositionswith lower carbon, increased molybdenum and microalloying were designed with a tailored quenchand temper heat treatment for the mother tube , the tool and the weld. These products allow to achievean highly improved SSC resistance as highlight the threshold stresses :

- tube / tool 2 90% SMYS- upset 270% SMYSRegarding the weld area, the NACE conditions appeared too severe and not in accordance

with environment described by pH higher than 10 with H2S partial pressure lower than 1.5 psi (O.1atm). New conditions are suggested (W 1 and W2) with pH around 5 and gas mixture composed of10% H23 in N2. In these modified conditions SSC results are summed up by a threshold stress higherthan 70% SMYS (Figure3).

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[1].

[2].

[3].

[4j.

[5].

[6].

[7].

[8].

[9].

[1OJ.

[11].

[12].

[13].

[14].

[15].

[16].

[17].

REFERENCES

R.M. Shivers, J.B. Greer, J. E. Srnitll, IADC/Sl?E Dtilling Conference, Houston9O (1990)

A. Ikeda, Y. Morita, N. Matsuki, The Sumitomo Search N037 November 1988 (1988)

A. Kalivoda, Hutn. listy CSVTS p. 416-419 (1984)

API SPECIFICATION 5D, Specification for Drill pipe (1992)

B.J. Orlans-Joliet, F.A. Pellicani, G.C. Guntz, Corrosion 93, New Orleans, paper 147 (1993)

F.R. David, G.C. Guntz, MF.J. Galis, Corrosion 89, New Orleans, paper 474 (1989)

P.J. Grobner, D.L. Sponseller, D.E. Diesburg, Corrosion N035, p.240-250 (1979)

API SPECIFICATION 7, Specification for Rotary Drill Stem Elements (1994)

R.P. Badrak, Corrosion 95, Orlando, paper49(1995)

NACE TM0177-90 standard (1990)

ASTM 1084/D

C.S. Carter, M.V. Hyatt, NACE Reference Book N“ 5, p. 524-600 (1973)

E. Anelli, L. Cariboni, F. Leone, A. Mascanzoni, Int. Conf. on Steel Rolling, Tokyo,paper 26 (1985)

L.A. Lee, SPE/IADC Drilling Conference, New Orleans 85 (1985)

M. Watkins, R. Ayer, Corrosion 95, Orlando, paper 50 (1995)

M. TWkins, G.A. Vaughn, Corrosion 85, Houston, paper 220 (1985)

MR0175-94, Standard Material Requirement, section 11 (1994)

ACKNOWLEDGEMENTS

Thanks to IDPA, Vallourec Oil& Gas (VLOG) and Vdlourec Research Centre (CEV) for their

participation at this research program.

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TABLE 1: NOMINAL DRILL PIPE DIIWENS1ONS

Type Part Description I.D. O.D. Wall

thickness(mm) (mm) (mm)

DP95 Tube 5“ #1950 Ibs.ft 108.6 127 9.19Tool joint 6 3/8 3 3/4 95.3 161.9

DPI05 Tube 5“ #1 950 lbs.ft 108.6 127 9.19Tool joint 6 5/8 3 1/4 82.6 168.3

TABLE 2: CHEMICAL COMPOSITION OF THE DIFFERENT DRILL PIPES PARTS (10-3 wt %)

Type Part c Si Mn P S Cr Ni MO Ti Nb B

DP95 Tube 208 255 1030 10 5 445 121 226 52 2 2.0

Tool joint 378 225 880 9 5 962 118 260 3 1 0.1

DP105 Tube 246 195 567 9 2 829 61 513 15 25 2.2

Tool joint 365 227 876 9 5 953 117 259 3 1 0.1

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TABLE 3: WELDING AND HEAl” TREATMENT PROCESSING

Type Tube Tool joint Welding HAZ + weld

Heat Heat Axial Heattreatment treatment pressure treatment

DP95 Water Quench Tempering 67 bar Austenizing at 960”C+ Tempering at 670”C + Tempering

at 6600C at 7000C

DPI 05 Water Quench Tempering 86 bar Austenizing at 960”CTempering at 640°C + Temperingat 6900C at 700”C

4

TABLE -t : SSC TEST CONDITIONS ON WELD AREAS

NACE NACE WI VJ2

TMO177 modified Drilling conditions

Type solution IU4CE NACE NACE Sea Water

initial pH 2.7 2.7 5 8.2

H2S partial pressure 15 psi 1.5 psi 1.5 psi 1.5 psi

pH after saturation 2.8 2.9 5.3 6.5

TABLE 5: MECHANICAL PROPERTIES

Type Part YS E CVN HRC

grade at -20”C min max

(ksi) (ksi) (MPa) (ksi) (MPa) (%) (J/cm2)

(MPa)

DP95 Tube 106 730 117 806 20 177 23.2 25

Upset 110 758 121 834 19 161

95-110 Tool joint 103 710 12(3 827 25 163 2–0 2–4

654-758 Weld area 96 661 115 792 _ 38 _ _

DPI05 Tube 109 751 122 841 21 196 23.7 25

Upset 117 806 128 882 20 167

105-120 Tool joint 111 765 125 868 16 134 2–3 27.5

723-827 Weld area 107 737 127 875 _ 37 _ _

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TABLE 6: SSC RESULTS IN THE N.ACEENVIRONMENT

Type Ssc Tube Tool joint Upsettensile tests

Failure 100”/0 100% 80 O/.DP95 as “/0SMYS

No Failure 90% 90% 70%

Failure 1OOO/. 8 OO\oDP105 as 7. SMYS

No Failure 100% 9 00/0 70%

TABLE 7: SSC RESULTS ON WELD AREAS

TESTS CONDITIONS

Type NACE NACE Wfl W2

tensile tests modified

Failure 50 0/0 50% 90%

DP95 as %.SMYS

No Failure 70 % 9 o%

Failure 50 0/0 5 o% 90%

DPI05 as %SMYS

No Failure 700/0 90%

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Wdd area Upset Pipe

1

\R.“.”. ”l.. ”.”,’.

l/~/Y.~/’////~f m Ewu.z+d /

.“. ’..” “.’+

..:. :.:::. j///// f./////J P~

-

HAZ

FIGURE 1: LOCATION OF SAMPLES FOR SSC TESTS ON DRILL PIPES

DP95Weld, line

I11II

24.5 2!9.5 ,129.5 22.5

IIIII

DP105 II

1

II

26 31.5 ~ 28.5 27.5

/

I1

Upset Weld line Tool joint

FIGURE 2: HRC RESULTS IN WELD AREAS

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I ● Failure at 0/0SM’fS O No failure at 0/~SMYS I

I ● 0

N%CE

W2o

WI

u) A()~o 1(n0

G 20% [T

Drilling conditions

I +------bo0/0

o 2 4 6 8 10 12 14E

low corrosivity pH

FIGURE 3: ALLOWABLE CORROSIVE CONDITIONS FOR WELD AREAS

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