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This article was downloaded by: [Florida State University] On: 13 November 2014, At: 12:46 Publisher: Taylor & Francis Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK Materials and Manufacturing Processes Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/lmmp20 High Nitrogen Alloyed Steels for Nonmagnetic Drill Collars. Standard Steel Grades and Latest Developments G. Saller a & H. Aigner b a Böhler-Edelstahl GmbH & Co KG , Kapfenberg, Austria b Schoeller-Bleckmann Oilfield Technology GmbH & Co KG , Ternitz, Austria Published online: 16 Aug 2006. To cite this article: G. Saller & H. Aigner (2004) High Nitrogen Alloyed Steels for Nonmagnetic Drill Collars. Standard Steel Grades and Latest Developments, Materials and Manufacturing Processes, 19:1, 41-49, DOI: 10.1081/AMP-120027497 To link to this article: http://dx.doi.org/10.1081/AMP-120027497 PLEASE SCROLL DOWN FOR ARTICLE Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) contained in the publications on our platform. However, Taylor & Francis, our agents, and our licensors make no representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the Content. Any opinions and views expressed in this publication are the opinions and views of the authors, and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon and should be independently verified with primary sources of information. Taylor and Francis shall not be liable for any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use of the Content. This article may be used for research, teaching, and private study purposes. Any substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to anyone is expressly forbidden. Terms & Conditions of access and use can be found at http:// www.tandfonline.com/page/terms-and-conditions

High Nitrogen Alloyed Steels for Nonmagnetic Drill Collars. Standard Steel Grades and Latest Developments

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Page 1: High Nitrogen Alloyed Steels for Nonmagnetic Drill Collars. Standard Steel Grades and Latest Developments

This article was downloaded by: [Florida State University]On: 13 November 2014, At: 12:46Publisher: Taylor & FrancisInforma Ltd Registered in England and Wales Registered Number: 1072954 Registered office: MortimerHouse, 37-41 Mortimer Street, London W1T 3JH, UK

Materials and Manufacturing ProcessesPublication details, including instructions for authors and subscription information:http://www.tandfonline.com/loi/lmmp20

High Nitrogen Alloyed Steels for NonmagneticDrill Collars. Standard Steel Grades and LatestDevelopmentsG. Saller a & H. Aigner ba Böhler-Edelstahl GmbH & Co KG , Kapfenberg, Austriab Schoeller-Bleckmann Oilfield Technology GmbH & Co KG , Ternitz, AustriaPublished online: 16 Aug 2006.

To cite this article: G. Saller & H. Aigner (2004) High Nitrogen Alloyed Steels for Nonmagnetic Drill Collars. Standard SteelGrades and Latest Developments, Materials and Manufacturing Processes, 19:1, 41-49, DOI: 10.1081/AMP-120027497

To link to this article: http://dx.doi.org/10.1081/AMP-120027497

PLEASE SCROLL DOWN FOR ARTICLE

Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) containedin the publications on our platform. However, Taylor & Francis, our agents, and our licensors make norepresentations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose ofthe Content. Any opinions and views expressed in this publication are the opinions and views of the authors,and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be reliedupon and should be independently verified with primary sources of information. Taylor and Francis shallnot be liable for any losses, actions, claims, proceedings, demands, costs, expenses, damages, and otherliabilities whatsoever or howsoever caused arising directly or indirectly in connection with, in relation to orarising out of the use of the Content.

This article may be used for research, teaching, and private study purposes. Any substantial or systematicreproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in anyform to anyone is expressly forbidden. Terms & Conditions of access and use can be found at http://www.tandfonline.com/page/terms-and-conditions

Page 2: High Nitrogen Alloyed Steels for Nonmagnetic Drill Collars. Standard Steel Grades and Latest Developments

MATERIALS AND MANUFACTURING PROCESSES

Vol. 19, No. 1, pp. 41–49, 2004

REVIEW

High Nitrogen Alloyed Steels for Nonmagnetic

Drill Collars. Standard Steel Grades

and Latest Developments

G. Saller1,* and H. Aigner2

1Bohler-Edelstahl GmbH & Co KG, Kapfenberg, Austria2Schoeller-Bleckmann Oilfield Technology GmbH & Co KG,

Ternitz, Austria

Key Words: Nonmagnetic drill collar; Austenitic stainless steel; High nitrogen

steel; Manufacture; Bohler P560; Mechanical properties; Pitting corrosion.

1. INTRODUCTION

The use of nonmagnetic drill collars for the oilfield industry started in the

seventies and eighties of the last century with a change in drilling technology. Since

then, nonmagnetic Cr-Mn-N steels have become established on the market.Due to the continued advancements of drilling technology the materials have to

fulfill higher demands, especially on mechanical and corrosion properties. Therefore

Bohler-Edelstahl GmbH and Co KG (Bohler) and Schoeller Bleckmann Oilfield

GmbH and Co KG (SBO) have developed a new steel grade (Bohler P560, SBO-

P580), which has excellent properties for drilling applications.

*Correspondence: G. Saller, Bohler-Edelstahl GmbH & Co KG, P.O. Box 96, A-8605

Kapfenberg, Austria; E-mail: [email protected].

41

DOI: 10.1081/AMP-120027497 1042-6914 (Print); 1532-2475 (Online)

Copyright & 2004 by Marcel Dekker, Inc. www.dekker.com

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2. APPLICATIONS OF NONMAGNETIC DRILL COLLARS

Starting around 1970, a new technology for drilling wells was developed on theoilfield market. Before the change, one well was usually drilled from one rig withoutcontrolling the direction of the drill string during the drilling job.

The aim of the new technology, called Directional Drilling, was to control and tobe able to change the direction of a hole during the drilling operation. The processdeveloped allows areas to be reached where the installation of a rig directly over thetarget is very difficult. Figure 1 shows examples for this case.

An economical advantage is that Directional Drilling permits the drilling ofmultiple holes from just one oil platform.

In the beginning, Directional Drilling was based on measurements of themagnetic field of the earth to determine the exact position of the drill bit. Nowadays,many parameters of the area surrounding a drilled hole are measured while drilling.This logging of data is combined with sophisticated drilling techniques.

The development of Directional Drilling called for new types of steels for drillingapplications, because the sensitive devices for magnetic measurements must not beinfluenced by the drilling components. Strictly nonmagnetic steels are, therefore,used for the parts near the motor section of the drill string. Because of the difficultenvironment and the high mechanical requirements these materials must also possesshigh mechanical and fatigue strength and excellent stress and pitting corrosionproperties.

Nonmagnetic drill collars are about 9.5m in length, have an outside diameter of100 to 255mm, a center bore between 50 and 150mm, and threads on both ends.These collars have to guarantee a nonmagnetic zone near the motor section.

Very complicated parts with a length of about 2 to 9.5m are required for highlysophisticated measurement while drilling (MWD) systems. These housings carry allthe electronic equipment for logging data while drilling.

3. STANDARD MATERIALS

At the beginning of Directional Drilling, Cr-Ni steels were used for non-magnetic collars. These were replaced by nitrogen alloyed Cr-Mn-steels when theformer ‘‘Vereinigte Edelstahlwerke,’’ a steel company that contained both BohlerEdelstahl and Schoeller Bleckmann, put the first Cr-Mn-N steel on the market.

Nowadays, only Cr-Mn-N types are on the oilfield market as nonmagnetic steelsfor drill collars. On the other hand, nickel-base alloys are used for this application ifthere are highly corrosive drilling environments.

Table 1 shows actual values of the chemical composition of standard materialsused (Alloy A–J) and gives the guaranteed limits for the Bohler and SBO standardbrands.

The steels can roughly be classified into two groups. The first group is relativelylow alloyed and similar to SBO-P530 (Bohler P553) with about 13% to 14% Cr,18% to 20% Mn, and 0.25% to 0.35% N. The Pitting resistance equivalent number

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(PREN)-value according to PREN¼ [% Cr]þ 3.3 � [% Mo]þ 16 � [% N][2] is

between 18 and 21.The second group of steel grades has a PREN-value from 25 to 32 due to

elevated chromium and nitrogen contents and is similar to SBO-P550 (Bohler P555).

One material of this class uses molybdenum to increase the corrosion properties.The main reason for the development of the higher alloyed types of Cr-Mn steels

was the use of more and more aggressive drilling fluids, which resulted in severe

pitting and crevice corrosion problems. An additional beneficial effect was the

improvement in the mechanical properties, especially an increase of the yield

strength due to the higher amounts of nitrogen.

Table 1. Chemical composition (wt%) of Cr-Mn-N steels for drill string components.

C Mn Cr Mo Ni N PRENa

Alloy A 0.04 20.5 13.0 0.4 0.3 0.32 19

Alloy B 0.02 18.0 14.2 0.5 1.9 0.34 21

Alloy C 0.03 18.1 13.2 0.4 2.0 0.30 19

Alloy D 0.03 19.8 13.4 0.4 0.5 0.33 20

Alloy E 0.02 19.3 16.8 0.1 0.6 0.54 26

Alloy F 0.02 19.0 19.6 0.8 1.9 0.63 32

Alloy G 0.02 19.5 17.8 0.9 1.8 0.55 30

Alloy H 0.03 20.5 16.9 0.1 0.6 0.51 25

Alloy J 0.02 15.0 15.4 2.1 2.3 0.40 29

SBO-P530 max. 18.50 13.00 max. max. 0.25 appr. 20

(Bohler P553) 0.06 20.00 14.00 0.45 1.50 0.35

SBO-P550 max. 19.00 17.50 max. max. 0.50 appr. 28

(Bohler P555) 0.06 20.50 19.00 0.45 1.50 0.60

aPitting resistance equivalent number.

Figure 1. Examples of difficulties of installing a drilling rig directly over the target.[1]

Nonmagnetic Drill Collars 43

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4. MANUFACTURE OF NONMAGNETIC DRILL

COLLARS AND MWD-COLLARS

The production of nonmagnetic drill collars is carried out in close cooperationbetween Bohler-Edelstahl and Schoeller-Bleckmann Oilfield Technology. Figure 2gives an overview of the stages of fabrication.

The melting is done in a 50 t electric arc furnace and is followed by secondarymetallurgy treatment and alloying. After that, ingots with a weight of 1.6 to 7.5 tonsare cast. The whole process of melting and casting is done at atmospheric pressure.The facilities used for the hot working of the drill collar prematerial are a 5200 tforging press and a rotary forging machine.

After hot working, Bohler Edelstahl delivers the semifinished material toSchoeller Bleckmann Oilfield Technology, where the manufacture is continued bythe cold-working process. The next step is testing of the mechanical properties andthe microstructure. After the subsequent machining, ultrasonic testing and thetesting of the magnetic properties over the full length of the bar are carried out.In addition, a final machining according to customers drawings is frequentlycarried out.

5. DEVELOPMENT OF BOHLER P560 (SBO-P580)

Since the drilling fluids used were becoming more and more aggressive andcausing severe attacks of localized corrosion on standard steels, Bohler Edelstahl andSchoeller Bleckmann Oilfield started to develop a new steel for MWD-systems.

When beginning the work on the new alloy, the research and discovery (R&D)team decided to follow the concept of the standard steels and, therefore, to place thenew steel in the field of high-nitrogen Cr-Mn austenitic stainless steels.

Because the aim was a clear enhancement of the resistance against localizedcorrosion in solutions containing chloride ions, planning included increasing the

MeltingMelting

SecondarySecondaryMetallurgyMetallurgy

IngotIngotCastingCasting

HotHotForgingForging

11

22

33

44

ColdColdFormingForming

55

MachiningMachining

77

TestingTesting

88

TestingTesting

66

MeltingMelting

SecondarySecondaryMetallurgyMetallurgy

IngotIngotCastingCasting

HotHotForgingForging

11

22

33

44

ColdColdFormingForming

55

MachiningMachining

77

MachiningMachining

77

TestingTesting

88

TestingTesting

88

TestingTesting

66

TestingTesting

66

SBOSBO

Figure 2. Manufacture of nonmagnetic drill collars.

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contents of nitrogen, chromium, and molybdenum. Nitrogen was also applied to

improve the mechanical strength and, therefore, the fatigue strength.Besides the required enhancements, there are some boundary conditions that

had to be considered when designing the alloy.Steels for MWD-parts have to be strictly nonmagnetic. Therefore, they must

have a stable austenitic structure. If the chromium and molybdenum content is

increased there is a need for elements which stabilize the austenitic lattice. One way

to estimate the austenite stability is to use one of the Schaeffler diagrams modified

for high-nitrogen Cr-Mn steels as shown in Fig. 3.Furthermore it is necessary to consider, for the development of this new, high-

nitrogen alloy, that the whole process of melting and casting is carried out at

atmospheric pressure. Therefore a sufficiently high nitrogen solubility in the melt,

which can be predicted by different formulas published in the literature,[4–6] is an

important parameter.The fine tuning of the alloy was done using the software Thermo-Calc and the

database TCFe2000. Its previous version was reported to be more suitable for the

calculation of Cr-Mn-N steels than the SSOL database.[7]

The theoretical approaches were verified and complimented by the results from

several trial melts. Modifications with varied chemical composition were manu-

factured and tested for selected properties. The chemical composition of the final

optimized alloy named Bohler P560 (SBO-P580) is given in Table 2.

10 15 20 25 300

5

10

15

20

marten-site

austenite

A+M+F

M+F

A+FA+M

ferriteNi eq

=[%

Ni]+

[%C

o]+0

,1*[

%M

n]-0

,01*

[%M

n]2

+18*

[%N

]+30

*[%

C]

Creq

=[%Cr]+1,5*[%Mo]+1,5*[%W]+0,48*[%Si]+2,3*[%V]+1,75*[%Nb]+2,5*[%Al]

Böhler P553(SBO-P530)

Böhler P553Böhler P553(SBO(SBO--P530)P530)

Böhler P555(SBO-P550)

Böhler P555Böhler P555(SBO(SBO--P550)P550)

developmentdevelopment

M+FBöhler P553(SBO-P530)

Böhler P553Böhler P553(SBO(SBO--P530)P530)

Böhler P555(SBO-P550)

Böhler P555Böhler P555(SBO(SBO--P550)P550)

developmentdevelopment

Figure 3. Detail of Schaeffler diagram modified by Speidel and Uggowitzer.[3]

Table 2. Chemical composition of alloy Bohler P560 (SBO-P580).

C Mn Cr Mo Ni N

SBO-P580 max. 22.00 20.50 max. max. 0.80

(Bohler P560) 0.06 24.50 22.50 1.50 2.50 0.95

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6. SELECTED PROPERTIES OF BOHLER P560 (SBO-P580)

Bohler and SBO steels for drill collars are used in the cold formed condition.Therefore all the tests were carried out in this condition.

6.1. Microstructure

The microstructure of Bohler P560 (SBO-P580) is fully austenitic. Dislocationslip bands due to the cold working process can be seen on the microsection. Sinceneither ferrite nor strain-induced martensite can be found, a nonmagnetic behaviorcan be expected for this alloy.

In order to reach good corrosion and ductility properties, it is very important toavoid the precipitation of chromium nitrides.[8] Despite the high nitrogen content ofBohler P560 (SBO-P580), its structure is free of grain boundary precipitates in thecold forged condition.

6.2. Magnetic Properties

The drill collars made from Bohler P560 (SB-P580), and thus the steel itself, haveto be strictly nonmagnetic, because they carry very sensitive electronic devices. Avery low relative permeability, its permitted maximum value is mr¼ 1.005, has beenachieved by the new alloy even in the cold forged condition, due to its stableaustenitic structure.

6.3. Mechanical Properties

The nitrogen content of Bohler P560 (SBO-P580) has been clearly increasedcompared to the standard steel grades Bohler P553 (SBO-P530) and Bohler P555(SBO-P550) and similar steel grades on the market. Therefore this alloy has anenhanced cold work hardening behavior that leads to an increase of the yieldstrength and ultimate tensile strength shown in Fig. 4.

The specimens for the tensile tests were taken from the cold forged bars at adepth of 25mm under the surface. The values shown in Fig. 4 originated fromspecimens from many different collars with a range of the outside diameter from 100to 255mm and from various melts. That is why the scatter band is relatively wide.

The ‘‘impact toughness’’ shows a slight decrease, while the yield and tensilestrength have been clearly elevated. Nevertheless an impact energy for CharpyV-notch specimens of at least 82 Joule at room temperature is guaranteed forBohler P560 (SBO-P580). The mean value of all impact tests is about 140 Joule.

The mechanical properties for dynamic loading are also very important for drillcollar steels. Figure 5 shows the results of the rotary beam bending tests for the newalloy and the standard steel grades. As can be seen in the diagram, a ‘‘fatiguestrength’’ of approximately 450N/mm at 107 cycles can be achieved by Bohler P560(SBO-P580). That means an increase of the fatigue strength of about 12% compared

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to the alloy Bohler P555 (SBO-P550), which can be foremost explained by the higheryield strength of Bohler P560 (SBO-P580) in the cold forged condition.

6.4. Corrosion Properties

The most important aim of the development of Bohler P560 (SBO-P580) was toincrease the resistance against localized corrosion attack, especially against chloride-induced pitting corrosion and stress corrosion cracking.

In order to evaluate the resistance against ‘‘chloride-induced pitting’’ corrosion,current density-potential curves have been recorded. The tests were carried out onthe cold-forged material at a temperature of 20�C using solutions containingdifferent concentrations of chloride ions.

As shown in Fig. 6, the benefit of increasing the content of the elementschromium, nitrogen, and molybdenum is illustrated clearly by a very obviousincrease in pitting corrosion potential against the standard hydrogen electrode at acurrent density of 10�4 A/cm2. A pitting corrosion potential of 1550mV for achloride concentration of 1000 ppm and of 800mV for a chloride concentration of80,000 ppm can be achieved by the new alloy.

The characterization of the resistance against ‘‘stress corrosion cracking’’ wasdone using a constant load test in boiling magnesium chloride solution at 155�C.A specimen passes the test when being stressed by the testing load without breakingfor 720 h. Specimens made of Bohler P560 (SBO-580) passed the test at maximumloads of 400N/mm2.

7. SUMMARY

The technology of Directional Drilling for oil wells calls for strictly non-magnetic materials for drill string components near the drill bit. Further, the steels

Mechanical Strength (Cold Forged)

0

200

400

600

800

1000

1200

1400

BöhlerP553(SBO-P530)

BöhlerP555(SBO-P550)

BöhlerP560(SBO-P580)

BöhlerP553(SBO-P530)

BöhlerP555(SBO-P550)

BöhlerP560(SBO-P580)

Böhler (SBO) steel grade

stre

ng

th [

N/m

m²]

scatter bandmin. value

yield strength YS ultimate tensile strength UTS

Figure 4. Mechanical strength of standard steel grades and Bohler P560 (SBO-P580) in the

cold forged condition.

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used have to provide high strength and ductility and good corrosion resistance. That

is why the Cr-Mn-N type of steel has established itself on the oilfield market fordrilling applications.

Due to increased demands on the mechanical and corrosion properties which

cannot be fulfilled by the common standard austenitic steels, Bohler Edelstahl andSchoeller Bleckmann Oilfield developed the new alloy Bohler P560 (SBO-P580). This

high-nitrogen Cr-Mn steel is characterized by a combination of high strength, highfatigue strength, good ductility, and an excellent resistance against localized

Fatigue Strength

0

100

200

300

400

500

600

700

1,00E+05 1,00E+06 1,00E+07 1,00E+08

cycles

stre

ss a

mp

litu

de

[N/m

m²]

Böhler P553 (SBO-P530)Böhler P555 (SBO-P550)Böhler P560 (SBO-P580)

Böhler P553(SBO-P530)

Böhler P555(SBO-P550)

Böhler P560(SBO-P580)

rotary beam bending test

Figure 5. Fatigue strength evaluated by rotary beam bending test.

Corrosion Resistance in Chloride-Containing Solution

-200

0

200

400

600

800

1000

1200

1400

1600

1800

10 15 20 25 30 35 40

PREN = [%Cr] + 3.3 x [%Mo] + 16 x [%N]

pit

tin

g c

orr

osi

on

po

ten

tial

vsS

HE

[m

V] (

curr

ent

den

sity

= 1

0-4A

/cm

²)

1000 ppm80000 ppm

Böhler P560(SBO-P580)

testing solution:1000 ppm and

80000 ppm chloride ions

testing temperature:20 ˚C

Böhler P555(SBO-P550)

Böhler P553(SBO-P530)

Figure 6. Pitting corrosion potential vs. SHE of standard steel grades and Bohler P560

(SBO-P580).

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corrosion induced by chlorides. These properties make Bohler P560 (SBO-P580) verysuitable for use for highly sophisticated drill collars and in aggressive environments.

REFERENCES

1. Le Peuvedic, J.P. Introduction to directional drilling. Directional Drilling andDeviation Control Technology; Editions Technip: Paris, 1990; 8.

2. Sedriks, A.J. Pitting. Corrosion of Stainless Steels, 2nd Ed.; John Wiley & Sons,Inc.: New York, 1996; 111.

3. Uggowitzer, P.J.; Magdowski, R.; Speidel, M.O. Nickel free high nitrogenaustenitic steels. ISIJ International 1996, 36 (7), 901–908.

4. Stein, G.; Menzel, J. Herstellung, weiterverarbeitung und technische anwen-dungsmoglichkeiten massiv aufgestickter stahle. In Stickstofflegierte Stahle;Speidel, M.O., Uggowitzer, P.J., Eds.; Verlag Thubal-Kain: Zuerich,Switzerland, 1991; 33–45.

5. Satir-Kolorz, A.; Feichtinger, H.K.; Speidel, M.O. Uber die loslichkeit vonstickstoff in eisen- und stahlgusslegierungen unter erhohtem druck.Giessereiforschung 1989, 41 (4), 149–164.

6. Medovar, B.I.; Saenko, V.Ya.; Grigorenko, G.M.; Pomarin, Yu.M.; Kumysh,V.I. Special features of nitrogen alloying steels in ASR. Arc-Slag Remelting ofSteels and Alloys; Cambridge International Science Publishing: Cambridge,England, 1996; 39–48.

7. Cotton, J.A.; Knutsen, R.D.; Sundman, B. Modification of the stainless steeldatabase for high manganese, chromium and nitrogen contents. High NitrogenSteels ’98, Proceedings of the 5th International Conference on High NitrogenSteels, Espoo, Finland, May 24–26, and Stockholm, Sweden, May, 27–28, 1998;Hanninen, H., Hertzman, S., Romu, J., Eds.; Trans Tech Publications Ltd.:Zuerich, Switzerland, 1998; 89–94.

8. Gavriljuk, V.G.; Berns, H. Key properties. High Nitrogen Steels; Springer-Verlag: Berlin Heidelberg, Germany, 1999; 169–198.

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