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1. Introduction

In recent years, the number of easily-developed oil

and gas wells has decreased, while deep wells and high-

temperature and high-pressure wells have increased. On

the other hand, with the improvement of drilling technol-

ogy, wells with complex congurations, such as direc-

tional and horizontal wells, have also increased. The

trend in the horizontal well rig count in North America

is shown in Fig. 1. Therefore, the requirements placed

on connections of casings and tubings under com-bined loads such as tension and compression, internal

and external pressure, and bending, have also become

increasingly severe. JFE Steel developed a premium

joint, JFEBEAR, which was designed to use in such

environments. An outline was presented in the previous

report1).

In the past, API RP5C52), the Recommended Prachce

of the American Petroleum Institute, was widely used

as a connection evaluation procedure, but evaluation

procedures have also become stricter, as seen in the new

procedure, ISO 136793), which was issued ofcially in

2002.

In this report, the features of JFEBEAR, tests

according to ISO 13679, and the production status are

described.

2. Features of JFEBEAR

The features and design concept of JFEBEAR are

presented below.

The following performance is required in the

threaded connection.

(1) Tensile strength

(2) Sealability under combined load of tension, com-

pression, internal and external pressure, bending, etc.

(3) Galling resistance to make-up/break-out of the con-

nection

(4) Stabbing performance during running operation

(5) Resistance to thread and seal deformation due to

dope pressure during make-up(6) Tool life and accuracy in thread cutting

The design features of JFEBEAR are shown in

Fig. 2, and the design concept is presented in Fig. 3

from the viewpoint of the relationship between features

and performances requirement.

2.1 Thread Form

A hook thread, which has a negative load ank angle

of 5, is applied in JFEBEAR. In companson with the

API buttress-type thread, a hook thread is advantageous

in terms of joint tensile strength and sealability under

tension and bending. However, a hook thread gener-

ally has a negative effect on galling resistance and tool

life. In order to solve this problem, the corner radius of

the load ank was optimized in JFEBEAR, resulting in

superior galling resistance. JFEBEAR also has a larger

stabbing ank angle of 25 for better stabbing of the pin

into the coupling. The larger corner radius and stabbing

ank angle also contribute to improved tool life.

A smaller gap between the pin and coupling stabbing

ank is preferable in terms of the compression rating,

but an insufcient gap carries the risk of galling associ-

ated with lead error. The gap of the JFEBEAR stabbingank is optimized considering both of these require-

ments. JFEBEAR also has a large gap between the pin

crest and coupling root to ensure disposability of the

dope during make-up, and this prevents deformation of

the thread and seal due to dope pressure.

2.2 Seal Geometry

The major characteristic of a premium joint is a

metal-to-metal seal. Both galling resistance and sealabil-

ity are important performance factors for the seal.

The seal of JFEBEAR is composed of a contouredpin surface and cone-shaped coupling surface. Figure 4

shows an example of the Von Mises equivalent (VME)

Jan.

1995

Jan.

1996

Jan.

1997

Jan.

1998

Jan.

1999

Jan.

2000

Jan.

2001

Jan.

2002

Jan.

2003

Jan.

2004

Jan.

2005

0

Rigcount

20

40

60

80

100

120

140

160

180

200

Fig. 1 Horizontal well rig count in North America

Premium Joint, JFEBEAR for OCTG

Originally published inJFE GIHONo. 9 (Aug 2005), p. 4650

JFE TECHNICAL REPORT

No. 7 (Jan. 2006)New Products & Technologies

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stress of the seal area, and Fig. 5shows the seal contact

pressure on the seal surface. The contact pressure has

a convex distribution, in which the maximum stress

appears in the middle of the contact area. On the other

hand, in a seal with a cone shape in both the pin and the

coupling, the contact pressure shows a concave distribu-

tion4). If there is deviation in local dimensions or surface

roughness, a seal with a concave contact pressure seems

preferable for minimizing negative effects and achiev-

ing the designed sealability. In addition to the contact

pressure, the travel length of the contact surface should

be considered in order to prevent galling. If the contact

length is not too long, the contact area may change dur-

ing make-up, and the actual travel length of each contact

portion may become short. This contoured-type seal has

also been applied in JFE Steels FOX connection5)with

excellent results.

A larger shoulder angle is advantageous for seal-

ability, but a smaller angle is preferable for minimizing

deformation due to external pressure and compression.

The shoulder angle of JFEBAER is 15.

3. Performance Evaluation of JFEBEAR

3.1 Connection Testing Procedure

Formerly, API RP5C5 was widely used as a con-

nection testing procedure, but currently ISO 13679 is a

standard testing procedure which is recognized by major

oil companies, etc.

The features of ISO 13679 are outlined below.

3.1.1 Number of specimens

There are 4 connection application levels (CAL).

Requirement

(1) Stabbing

(2) Sealability

(5) Tool life

(4) Dope pressure

(3) Anti-galling

Tension

Compression

Internal pressure

External pressureBending

Feature

Thread form

Seal geometry

Stabbing flank angle: 25

Shoulder angle: 15

Contoured metal-metal seal: Optimum

Load flank corner R: Large

Load flank angle: 5

Stabbing flank clearance: Optimum

Fig. 3 JFEBEAR design concept

Seal position

Contactpressure(MPa)

0

200

400

600

800

1 000

1 200

1 400

1 600

Fig. 5 Contact pressure distribution on JFEBEAR sealsurface

Thread form

Seal geometry

Contoured metalto metal seal

5

25

15

60.3, 73.0 mm :8TPI88.9, 101.6 mm :6TPI114.3 mm and above:5TPITaper :1/16

Fig. 2 JFEBEAR design features

JFEBEAR, 127.0 6.99 mm

1 435 MPa 866 MPa 296 MPa 274 MPa

Fig. 4 Stress distribution of JFEBEAR seal

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CAL 4 is the highest level, and 8 specimens are used for

each evaluation. In case of threaded and coupled con-

nections, one specimen consists of 2 pin ends and one

coupling.

3.1.2 Thread dimensions

Each specimen must be prepared with the required

thread-seal interference, such as high-low, low-high,

high-high, low-low. As new connection testing factors,

the thread taper combinations pin fast-box slow, pin

slow-box fast, and pin nominal-box nominal have been

added to evaluate the change of the actual interference

of thread and seal.

3.1.3 Make-up

For all A ends of the pins and coupling single

make-up is required. For the other B ends, multiple

make-up/break-out is required to evaluate galling resis-tance and a nal make-up.

Photo 1 is an example of the pin and coupling sur-

face of an HP2-13CR-110 JFEBEAR joint after multiple

make-up/break-out. Blasting is performed on the pin

surface, to remove chromium alloy beads and copper

plating is applied to the coupling surface to improve

galling resistance. An API-modied thread compound

was used as a lubricant for make-up.

3.1.4 Baking

Baking of the connection is performed to eliminate

the sealing effect of the thread compound.

3.1.5 Sealability tests

Three sealability tests, series A, B, and C, are

specied.

Series A consists of sealability tests with a combined

load of tension, compression, and internal and external

pressure. Figure 6shows an example of the load path in

test series A. Oil and gas wells are designed based on thespecied minimum yield strength. In the internal pres-

sure region, testing is carried out along the 95% VME

yield stress envelope. For external pressure, the maxi-

mum load is limited to the API collapse pressure. The

compression rating can be determined based on advice

from the supplier, but 80% compression is currently the

general requirement. JFEBEAR has been tested at up

to 80% compression. Another feature of ISO combined

load testing is that the load path of quadrant 1 to 4 is

repeatedly applied. This is due to check sealability after

the load path because slight deformation of seal may

occur due to the combined load, especially compression.

Gas and liquid are used for internal and external pres-

Load (1 000 N)

Pressure(M

Pa)

External

Internal

VME and connection load envelope

100% VME

95% VME LP8

LP7

LP6LP5

LP4LP3

LP1

LP14

LP13LP12LP11

LP10

LP9

Q2: Compression Internal pressure Q1: Tension Internal pressure

Q4: Tension External pressureQ3: Compression External pressure

2250

125

100

75

50

25

0

25

50

75

100

125

2000 1750 1500 12501000 750 500 250 0 250 500 750 1000 1250 1500 1750 2000

Compression Tension

Nom Connection Load Envelope

100% API Collapse

Fig. 6 Test series A load path

Specimen #3B make and break test (HP2-13CR-110)

Photo 1 Make and break test result

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JFE TECHNICAL REPORT No. 7 (Jan. 2006) 53


sure testing, respectively.

An example of nite element analysis (FEA) for an

HP1-13CR-110 JFEBEAR joint is described below. Cur-

rent FEA has some limitations, in that 3-dimensional

distributions (thread spiral, for example) are not consid-

ered as this is an ax-symmetric model, and the setting of

boundary conditions such as the coefcient of friction is

not sufciently accurate. However, the tendency or trend

in the contact pressure distribution is considered to be

worth analyzing and evaluating. The combined load path

in this FEA is shown in Fig. 7. The trend of the contact

area pressure, which is an area shown in Fig. 4, at each

load point is given in Fig. 8. The contact area pressure

appears rst on the seal surface due to make-up, and

then decreases as a result of tension. It then increases

again under internal pressure, and continues to increase

as the axial loading mode changes to compression and

the load reaches its maximum. However, after thus,when both external pressure and tension are applied, the

contact area pressure decreases to its minimum. If the

same load path is applied again, the contact area pres-

sure under tension is lower than in the rst path, whereas

the minimum contact area pressure under external pres-

sure and tension is almost the same as in the rst path.

Series B consists of combined load tests with bend-

ing in addition to tension, compression and internal

pressure.

Series C is called thermal cycle tests, and its pur-

pose is to evaluate sealability with tension and internalpressure by applying 100 thermal cycles from 52C to

180C (Fig. 9). This cycle is adopted because the tem-

perature of the well remains high during production due

to the production uid, but drops during shut downs.

The purpose of Series C is to evaluate the effect of these

changes in temperature.

Series A is performed for specimens 1, 4, 5, and 7,

and series B for specimens 2, 3, 6, and 8. This is fol-

lowed by series C for specimens 1 to 4.

3.1.6 Limit load tests

Limit load tests are carried out to investigate the

structural and sealing limit by applying a combined

loads greater than the VME yield stress or API collapse

pressure (Fig. 10). These are performed after nishing

the sealability tests and are for information purposes.

3.2 Status of Connection Testing

JFE Steel has been carrying out JFEBEAR connec-

tion testing according to ISO 13679. Several sizes have

already passed these tests successfully.

4. Production of JFEBEAR

The basic design and development of JFEBEAR

were completed in 1999, and testing based on various

procedures was carried out. Users highly appreciate the

advantages of JFEBEAR, which include easy make-up

in running operation and has superior sealability, and

production is increasing consistently. In 2004, JFEBEAR

was used in a deep-water project in the Gulf of Mexico.

JFE Steel will continue to improve its technical ser-

vice system as well as production to enhance the status

of JFEBEAR as the companys standard premium joint.

External pressure

VME95%

Internal pressure

Make upTensionCompression

Fig. 7 Load step for FEA

Load point

Contactareapressure(MPa-mm)

10

100

200

300

400

500

600

700

800

900

1 000

2 3 4 5 6 7 8 9 101112131415 1 2 3 4 5 6 7 8 9 101112131415

Fig. 8 Contact area pressure change

Time

30 min 50 times 30 min50 times

52C

180C

9 10

Temperature

21

5

64

3 57 8 7

2

Fig. 9 Thermal cycle test condition

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5. Conclusion

(1) JFE Steel developed a premium joint, JFEBEAR,

which is applicable to severe environments such as

deep wells, high-temperature and high-pressure wells,

and directional and horizontal wells.

(2) JFEBEAR is composed of a hook thread and con-

toured metal-to-metal seal. Its unique design achieves

high sealability, galling resistance, and easy make-up

operation.

(3) Connection tests of JFEBEAR according to the

ISO 13679 CAL 4 have been carried out, and several

sizes have successfully passed these tests.

(4) JFE Steel will continue to perform connection test-

ing and enhance production and technical service for

JFEBEAR.

References

1) Takano, J.; Yamaguchi, M.; Kunishige, H. Kawasaki Steel

Giho. vol. 34, no. 1, 2002, p. 2128.

2) API Recommended Practice 5C5(RP5C5). 1st Ed. 1990-01.

3) ISO 13679. 1st ed. 2002-12.

4) Narita, A.; Maeda, J.; Nagasaku, S. Sumitomo Metals. vol. 46,

no. 1, 1994, p. 65.

5) Yamamoto, K.; Kobayashi, K.; Maguchi , T.; Ueno, K. Kawa-

saki Steel Giho. vol. 21, no. 3, 1989, p. 202207.

Load (1 000 N)Compression

2 500 2 000 1 500 1 000 500 500 1 000 1 500 2 000 2 5000

25

50

75

100

125

125

100

75

50

25

LP4

LP6

VME and connection load envelope

Q2: Compression Internal pressure

Q3: Compression External pressure

Q1: Tension Internal pressure

Q4: TensionExternal pressure

LP8 LP7

LP3

LP2

LP1

LP5

Exte

rnal

Pressure(MPa)

Internal

Tension

95% VME

100% VME

Fig. 10 Limit load test path

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