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K55 casing, API casing pipe, API 5CT pipe
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API 5CT K55 Casing Pipe

Date:2025-12-31View:16Tags:K55 casing, API casing pipe, API 5CT pipe

K55 casing pipe is a type of steel pipe primarily used in the oil and gas industry for extracting hydrocarbons. It acts as a conduit, transporting oil and gas from underground reservoirs to the surface. As a medium-strength grade, K55 strikes a good balance between cost, strength, and manufacturability, and is widely used in shallow and medium-pressure oil and gas wells. It is one of the most widely used API casing pipe steel grades globally.


API Specification Scope

API 5CT specifies the delivery conditions for steel casing pipe and tubing used in well installations, covering pup joints, fittings, fitting materials, and accessory materials, and establishes requirements for three product specification levels (PSL-1, PSL-2, and PSL-3). The requirements for PSL-1 form the basis of this standard.

PSL-1: Basic level, applicable to conventional well conditions.

PSL-2: Adds chemical, shock, and NDT requirements.

PSL-3: Highly acidic and highly corrosive environments (not applicable to K55).

K55 casing pipe is only applicable to PSL-1 and PSL-2.


API Rating Grouping

The API 5CT standard classifies casing pipe and tubing into four groups; K55 belongs to Group 1.

Group 1: All casing pipe and tubing of grades H, J, K, N, and R

Group 2: All casing pipe and tubing of grades C, L, M, and T

Group 3: All casing pipe and tubing of grade P

Group 4: All casing pipe of grade Q


API 5CT Connections

API 5CT casing pipe connections must conform to API SPEC 5B. K55 optional connections include:

SC: Short Round Thread

LC: Long Round Thread

BC: Buttress Thread

NU: Non-Upset Tubing

EU: External Upset Tubing

IJ: Integral Joint

Premium Connections (Special Threads)


K55 Casing Pipe


K55 Casing Pipe Mechanical Properties

K55 casing pipe mechanical properties are designed to ensure durability and reliability under a wide range of operating conditions. Typical mechanical properties include:

Tensile strength: 655-758 MPa (95-110 ksi)

Yield strength: Minimum 379 MPa (55 ksi)

Elongation: Minimum 19% within 2 inches


K55 Casing Pipe Chemical Composition

The chemical composition of K55 casing pipe ensures a balance of strength, toughness, and weldability. Typical chemical compositions include:

Element

Composition (%)

Carbon (C)

0.28 max

Manganese (Mn)

1.20 max

Phosphorus (P)

0.030 max

Sulfur (S)

0.030 max

Silicon (Si)

0.55 max


Manufacturing of K55 Casing Pipe

The manufacturing process of K55 casings includes the following steps to ensure their quality and performance:


1. Steelmaking

High-quality carbon steel is produced using processes such as electric arc furnace (EAF) or converter (BOF).


2. Forming

The steel is formed into a cylindrical shape using processes such as seamless rolling or welding.


3. Heat Treatment

The casing undergoes heat treatment processes such as normalizing or quenching and tempering to improve its mechanical properties.


4. Finishing

The casing is finished to achieve the required surface quality, dimensions, and tolerances.


API 5CT K55 Casing Steel Color Code

Name

J55

K55

N80-1

N80-Q

L80-1

P110

Casing

a bright green band

two bright green bands

a bright red band

a bright red band + a green band

a red band + a brown band

a bright white band

Coupling

entire green coupling + a white band

entire green coupling

entire red coupling

entire red coupling + a green band

entire red coupling + a brown band

entire white coupling


API 5CT K55 Tolerance

Item

Allowable Tolerance

Outer diameter

Pipe body

D≤101.60mm±0.79mm

D≥114.30mm+1.0%

-0.50%


API 5CT K55 Casing Pipe Dimension

DN

O. D.

Weight

W. T.

　

End Machining Form

　

Steel Grade

in

mm

lb/ft

kg/m

in

mm

H40

J55

L80

N80

C90

P110

K55

T95

4 1/2

4.500

114.3

9.5

14.14

0.205

5.21

PS

PS

–

–

–

–

10.5

15.63

0.224

5.69

–

PSB

–

–

–

–

11.6

17.26

0.250

6.35

–

PSLB

PLB

PLB

PLB

PLB

13.5

20.09

0.290

7.37

–

–

PLB

PLB

PLB

PLB

15.1

22.47

0.337

9.56

–

–

–

–

–

PLB

5

5.000

127

11.5

17.11

0.220

5.59

–

PS

–

–

–

–

13

19.35

0.253

6.43

–

PSLB

–

–

–

–

15

22.32

0.296

7.52

–

PSLB

PLB

PLB

PLBE

PLB

18

26.79

0.362

9.19

–

–

PLB

PLB

PLBE

PLB

21.4

31.85

0.437

11.1

–

–

PLB

PLB

PLB

PLB

23.2

34.53

0.478

12.14

–

–

–

–

PLB

–

24.1

35.86

0.500

12.7

–

–

–

–

PLB

–

5 1/2

5.500

139.7

14

20.83

0.244

6.2

PS

PS

–

–

–

–

15.5

23.07

0.275

6.98

–

PSLB

–

–

–

–

17

25.3

0.304

7.72

–

PSLB

PLB

PLB

PLBE

PLB

20

29.76

0.361

9.17

–

–

PLB

PLB

PLBE

PLB

23

34.23

0.415

10.54

–

–

PLB

PLB

PLBE

PLB

26.8

39.88

0.500

12.7

–

–

–

–

–

–

29.7

44.2

0.562

14.27

–

–

–

–

–

–

32.6

48.51

0.625

15.88

–

–

–

–

–

–

35.3

52.53

0.687

17.45

–

–

–

–

–

–

38

56.55

0.750

19.05

–

–

–

–

–

–

40.5

60.27

0.812

20.62

–

–

–

–

–

–

43.1

64.14

0.875

22.22

–

–

–

–

–

–

6 5/8

6.625

168.28

20

29.76

0.288

7.32

PS

PSLB

–

–

–

–

24

35.72

0.352

8.94

–

PSLB

PLB

PLB

PLBE

PLB

28

41.67

0.417

10.59

–

–

PLB

PLB

PLBE

PLB

32

47.62

0.475

12.06

–

–

PLB

PLB

PLBE

PLB

7

7.000

177.8

17

25.3

0.231

5.87

PS

–

–

–

–

–

20

29.76

0.272

6.91

PS

PS

–

–

–

–

23

34.23

0.317

8.05

–

PSLB

PLB

PLB

PLBE

–

26

38.69

0.362

9.19

–

PSLB

PLB

PLB

PLBE

PLB

29

43.16

0.408

10.36

–

–

PLB

PLB

PLBE

PLB

32

47.62

0.453

11.51

–

–

PLB

PLB

PLBE

PLB

35

52.09

0.498

12.65

–

–

PLB

PLB

PLBE

PLB

38

56.55

0.540

13.72

–

–

PLB

PLB

PLBE

PLB

42.7

63.54

0.625

15.88

–

–

–

–

–

–

46.4

69.05

0.687

17.45

–

–

–

–

–

–

50.1

74.56

0.750

19.05

–

–

–

–

–

–

53.6

79.77

0.812

20.62

–

–

–

–

–

–

57.1

84.97

0.875

22.22

–

–

–

–

–

–

7 5/8

7.625

193.68

24

35.72

0.300

7.62

PS

–

–

–

–

–

26.4

39.29

0.328

8.33

–

PSLB

PLB

PLB

PLBE

PLB

29.7

44.2

0.375

9.52

–

–

PLB

PLB

PLBE

PLB

33.7

50.15

0.430

10.92

–

–

PLB

PLB

PLBE

PLB

39

58.05

0.500

12.7

–

–

PLB

PLB

PLBE

PLB

42.8

63.69

0.562

14.27

–

–

PLB

PLB

PLB

PLB

45.3

67.41

0.595

15.11

–

–

PLB

PLB

PLB

PLB

47.1

70.09

0.625

15.88

–

–

PLB

PLB

PLB

PLB

51.2

76.19

0.687

17.45

–

–

–

–

–

–

55.3

80.3

0.750

19.05

–

–

–

–

–

–

8 5/8

8.625

219.08

24

35.72

0.264

6.71

–

PS

–

–

–

–

28

41.62

0.304

7.72

PS

–

–

–

–

–

32

47.62

0.352

8.94

PS

PSLB

–

–

–

–

36

53.57

0.400

10.16

–

PSLB

PLB

PLB

PLBE

PLB

40

59.53

0.450

11.43

–

–

PLB

PLB

PLBE

PLB

44

65.48

0.500

12.7

–

–

PLB

PLB

PLBE

PLB

49

72.92

0.557

14.15

–

–

PLB

PLB

PLBE

PLB

9 5/8

9.625

244.48

32.3

48.07

0.312

7.92

PS

–

–

–

–

–

36

53.57

0.352

8.94

PS

PSLB

–

–

–

–

40

59.53

0.395

10.03

–

PSLB

PLB

PLB

PLBE

–

43.5

64.73

0.435

11.05

–

–

PLB

PLB

PLBE

PLB

47

69.94

0.472

11.99

–

–

PLB

PLB

PLBE

PLB

53.5

79.62

0.545

13.84

–

–

PLB

PLB

PLBE

PLB

58.4

86.91

0.595

15.11

–

–

PLB

PLB

PLB

PLB

59.4

88.4

0.609

15.47

–

–

–

–

–

–

64.9

96.58

0.672

17.07

–

–

–

–

–

–

70.3

104.62

0.734

18.64

–

–

–

–

–

–

75.6

112.5

0.797

20.24

–

–

–

–

–

–

10 3/4

10.750

273.05

32.75

48.74

0.279

7.09

PS

–

–

–

–

–

40.5

60.27

0.350

8.89

PS

PSB

–

–

–

–

15.5

67.71

0.400

10.16

–

PSB

–

–

–

–

51

75.9

0.450

11.43

–

PSB

PSB

PSB

PSBE

PSB

55.5

82.59

0.495

12.57

–

–

PSB

PSB

PSBE

PSB

60.7

90.33

0.545

13.84

–

–

–

–

PSBE

PSB

65.7

97.77

0.595

15.11

–

–

–

–

PSB

PSB

73.2

108.93

0.672

17.07

–

–

–

–

–

–

79.2

117.86

0.734

18.64

–

–

–

–

–

–

85.3

126.94

0.797

20.24

–

–

–

–

–

–

11 3/4

11.750

42

62.5

0.333

8.46

PS

–

–

–

–

–

47

69.94

0.375

20.24

–

–

–

–

–

–

54

80.36

0.435

8.46

–

–

–

–

–

–

60

89.29

0.489

9.53

–

–

–

–

–

–

65

96.73

0.534

11.05

–

–

–

–

–

–

71

105.66

0.582

14.42

–

–

–

–

–

–

13 3/8

13.375

339.73

48

71.43

0.330

8.38

PS

–

–

–

–

–

54.5

81.1

0.380

9.65

–

PSB

–

–

–

–

61

90.78

0.430

10.92

–

PSB

–

–

–

–

68

101.19

0.480

12.19

–

PSB

PSB

PSB

PSB

PSB

72

107.15

0.514

13.06

–

–

PSB

PSB

PSB

PSB

16

16.000

406.4

65

96.73

0.375

9.53

PS

–

–

–

–

–

75

111.61

0.438

11.13

–

PSB

–

–

–

–

84

125.01

0.495

12.57

–

PSB

–

–

–

–

109

162.21

0.656

16.66

–

P

P

P

–

P

18 5/8

18.625

473.08

87.5

130.21

0.435

11.05

PS

PSB

–

–

–

–

20

20.000

508

94

139.89

0.438

11.13

PSL

PSLB

–

–

–

–

106.5

158.49

0.500

12.7

–

PSLB

–

–

–

–

133

197.93

0.635

16.13

–

PSLB

–

–

–

–

P——Plain；S——Short-thread；L——Long-thread；B——Buttress thread；E——Extreme thread


J55 vs. K55 Casings (PSL1 and PSL2)

J55 and K55 have similar chemical compositions and mechanical properties, but J55 has lower minimum tensile strength requirements and elongation. Other specifications are the same, such as heat treatment methods, non-destructive testing, Charpy impact testing, and hydrostatic testing.


Minimum yield strength of J55/K55: 379-552 MPa;

Minimum tensile strength of J55: 517 MPa, elongation ≥ 19%;

Minimum tensile strength of K55: 655 MPa, elongation ≥ 15%.


PSL1 vs. PSL2 Heat Treatment Requirements

PSL1: Delivered hot-rolled, without heat treatment;

PSL2: K55 casing pipes should be normalized along their entire length or normalized and tempered; if thickening is required, it should be done after normalizing or normalized and tempered.


Charpy Impact Test

Pipe Body:

Full Size ≥ 27 J

Size Specimen ≥ 20 J

Couplings:

Longitudinal Specimen

≥ 27 J (Full Size)


Non-Destructive Testing

J55/K55 PSL1: No mandatory non-destructive testing requirements.

J55/K55 PSL2: All grades of pipes shall be inspected for longitudinal defects on their internal and external surfaces using one or more of the following methods to meet L4 acceptance criteria:

1. Ultrasonic testing according to ISO 9303 or ASTM E213;

2. Magnetic flux leakage testing according to ISO 9402 or ASTM E570;

3. Eddy current concentric coil testing according to ISO 9304 or ASTM E309;

4. Magnetic particle testing of the outer surface of the pipe according to ISO 13665 or ASTM E709.


FAQ

1. What is the API 5CT K55 casing pipe price?

Prices are affected by the following factors: outer diameter & wall thickness, PSL-1 / PSL-2, thread type (BTC / LTC / STC / Premium), whether couplings are included, order quantity & lead time.

K55 is typically 3–8% more expensive than J55.


2. Is a coupling mandatory for API 5CT K55 casing pipe?

Yes.

API 5CT casing pipe typically uses an external thread + coupling connection. The coupling material must be consistent with the casing pipe steel grade and pass the same standard testing.


3. What are the main differences between K55 and P110 casing pipe?

K55: Low strength grade (approximately 55 ksi yield strength), suitable for shallow/light well conditions.

P110: High strength grade (approximately 110 ksi yield strength), suitable for deep/high-load well conditions.

  

K55 casing, API casing pipe, API 5CT pipe

Eastern Steel Manufacturing Co.,Ltd
Add: No. 229, Tongzipo West Road, Lugu International Industrial Park, Yuelu District, Changsha, China 410221
Phone:0086-0731-85591060
Whatsapp/wechat:0086 15802647516

E-mail: sales@eastern-steels.com


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