heavy wall casing in c110 grade

7/18/2019 Heavy Wall Casing in C110 Grade

http://slidepdf.com/reader/full/heavy-wall-casing-in-c110-grade 1/12

117

HEAVY WALL CASING IN Cl10 GRADE

FOR SOUR SERVICE

C.P. LINNE, F. BLANCHARD, F. PUISSOCHET

Vallourec Research Center

Corrosion & Metallurgical Department

P.O. Box 17

59620 Aulnoye Aymeries, FRANCE

B.J. ORLANS-JOLIET

R.S. HAMILTON

Vallourec & Mannesmann Tubes

Tubular Industries Scotland Ltd

Vallourec Mannesmann Oil & Gas France Imperial threading works

OCTG Division

Clydesdale heat treatment plant

23 rue de Leval

Airdrie, SCOTLAND

59620 Aulnoye Aymeries, FRANCE

_ABSTRACT

The recent developments of high pressure and sour wells in the North Sea area have increased

the need for high strength H2S resistant carbon steels. Steel chemistry and heat treatment solutions

have been available to provide products suitable for use in these environments within the constraints of

classic well design since the early 90’s but operators are now demanding higher strength and heavier

wall products for HPHT wells.

Well completion design teams are now specifying from OCTG suppliers C 110 grade products

in increasingly heavy wall and the challenge facing suppliers is to guarantee product integrity not only

of these heavy wall casing but also the associated coupling stocks.

This paper was aimed at evaluating the performances of thick walled C 110 tubulars (up to 2”)

for sour environments. Metallurgical characteristics (microstructure, structure, microhardness),

mechanical properties (hardness, tensile, toughness), Sulfide Stress Cracking resistance (smooth

tensile, DCB) have been investigated throughout the wall thickness.

The C 110 proprietary grade proved to be an excellent material for use as Oil Country Tubular

Goods (OCTG) in typical North Sea environments with improved assessment of H2S corrosion

resistance properties according to both NACE and EFC (European Federation of Corrosion)

philosophies.

I<evwordg

: Oil Country Tubular Goods, Carbon Steels, High Strength, Sulfide Stress Cracking,

Sour Environment, Hydrogen Sulfide, Heavy Wall, Casing, pH, C 110.

Copyright

019~ hv NACE International. Requests for permission to publish this manuscript in any form, in part or in whole must be made in writing to NAC

- - - -,

Internation

al, Conferences Division. P.O. Box 218340, Houston, Texas 77218-8340. The material presented and the views expressed in th



INTRODUCTION

The need for higher strength Sulfide Stress Cracking (SSC) resistant steels has become more

apparent with the increasing energy demands and the decrease of easily obtained sweet oil and gas

reserves. Oil fields now being explored in the USA and gas fields in the North Sea area require drilling

to depths beyond 5500 m with bottom hole pressures and temperatures greater than 1000 bar and

2OO”C, where hydrogen sulfide is often found in the crude oil and gas ; moreover the static well-head

pressure is expected to be around 800 bar. Such depths and pressures represent the extreme limits for

the use of C95 casing. Actually, wall thickness would be so wide and gaps so narrow that there will be

a serious probability of uncontrolled casing wear during the drilling operations. Therefore well

engineering departments have applied the pressure on the suppliers for the development of a Cl 10

casing grade, which could be used safely.

It is important, from the economic aspect as well as that of safety, that appropriate materials are used to

successfully withstand the demands made upon them [l]. The choice of material is dependent on

adequate mechanical properties whilst ensuring their integrity in the service environment.

As for the development of Central Graben area (North Sea), the conditions defined by 30-60 bar of

CO2 (i.e. a pH below 3.5) and 30-50 mbar of H2S represent a sour service environment [2], much

beyond the limits of any standard Pl 10.

The development of deep high pressure high temperature (HPHT) wells of sour gas has always raised

the problem of the incompatibility between high strength steels and a good resistance to SSC. The

Cl 10 proprietary grade for sour service proposed in the early 90’s [3] proved to be an interesting

alternative assuring both a minimum threshold stress of 85% SMYS according to NACE TM0177

standard and a potential reduction of the string weight of about 25% [4].

The new trends are to extend the application limits of Cl 10 casing in extremely high BHP deep

reservoirs inducing a high burst requirement i.e. heavy wall casing (higher than 1 “WT) associated with

the corresponding coupling stock (as thick as 2” ). This need is also highlighted by additional items

such as casing hangers and crossovers which are also thick-walled components.

Hence, the intention of the present study was to assess the feasability of heavy

wall casing and

coupling stock in Cl 10 grade without impairing the mechanical and corrosion properties so research

was conducted on the variation of both microstructure, toughness and SSC resistance as a function of

the wall position in thick-walled tubulars.

EXPERIMENTAL PROCEDURES

Materials

Three pipes, processed commercially, from 3 different heats were included in the

investigations : one casing length 10 314” OD x 1.05” WT (273 mm x 26.67 mm) and 2 coupling

stocks 289 mm OD x 37.8 mm WT, and 3 12 mm OD x 49 mm WT. The products were manufactured

via a BOS / electric arc furnace + ladle furnace + vacuum degassing + continuous casting route and

seamless rolling mill. To reach the required mechanical properties, i.e. a minimum yield strength of

110.000 psi, the heat treatment was optimized according to quench and tempering steps. The

combination of steel chemistry design (Chromium-Molybdenum and microalloying element additions)

and external/internal quenching was designed to achieve both high hardenability and, hardening and a

high tempering temperature (69O’C) to give optimum mechanical properties and SSC resistance.

Elemental analysis of the steels was determined using the glow discharge spectrometer

technique. As for C and S contents, the LECO t&ion technique was involved as a more accurate

means of determining these. Reported chemical compositions are shown in Table 1.

Testing methods

Mechanical tests. The actual yield strength values (0.2% offset) were measured longitudinally

by tensile tests according to ASTM ES standard. O1Omm and 05mm round bar specimens were taken

respectively at midwall thickness (MW) and throughout the thickness (OD-MW-ID) as described on

figure 1.



Full size (10 x 10 mm) Charpy V notched specimens taken in the longitudinal direction

throughout the wall thickness were tested from -6O’C up to 20°C to determine the influence of the m

location on the brittle/ductile transition. Tests were also performed on

coupling stocks in he transverse

direction at -40°C as shown onto figure 2.

Finally, the microstructure homogeneity was evaluated on both as quenched and quenched &

tempered products by microscope observations after Nital etching and microhardness investigations.

Tensile tests at high temneratures. The development of the Cl10 grade steel is aimed at

broadening consistently the application range for HPHT wells, especially in terms of temperature, In

order to evaluate the mechanical behavior of casing up to servrce limits, high temperature tensile tests

were performed on round specimens. These investigations were carried out at stabilized temperatures

from 1OO’Cup to 25O’C in 50°C stages.

The interest was focussed on the evolution of the 2 main parameters involved in the design of

completions : Yield Strength (YS, 0.2% offset) and Ultimate Tensile Strength (UTS).

SSC testing. A corrosion test is described by four elements : a sample, a corrosive medium, a

stress and an evaluation criterion. For a casing string, this means classical mechanics and stresses, and

smooth tensile specimens provide the most relevant results. Two philosophies are proposed to deal

with medium and stress : NACE [5] that has established for decades the use of a defined set of

parameters (NACE solution + %SMYS as applied stress) and on the other hand the European point of

view summarized hereafter [6]. The corrosive medium must meet the two leading parameters, pH and

PH2S that better replicate the environment. The stress must be the maximum stress which can be

applied in service on the steel. Indeed, this stress may reach the actual YS. However, for experimental

reasons? the stress applied must be limited to 90% of the actual YS. The present paper is also aimed at

companng the two approaches, Finally, since cracking normally occurs either quickly or never, the

exposure time is limited to one month. The acceptance criterion is no more than one failure out of three

tested samples.

s.~ooth.Ten~:l e.~~.~).testing. Sulfide stress cracking tests were conducted according to NACE

TMO177-90 method A. Specimens were machined according to a schematic provided on figure 3 in

parallel with the mechanical study to characterise the SSC performance relative to the WT position :

OD, ID and MW.

The test environment was initially the NACE solution with pH = 2.7 obtained by acetic acid

addition at the beginning of the test. Then the saturation was maintained by a pure H2S gas. The

applied stress level was 85% of the Specific Minimum Yield Strength (SMYS).

Complementary SSC testing conditions were involved specifically to simulate the Elgin and

Franklin (EEC) well conditions : higher pH, lower H2S partial pressure and lower salinity.

Moreover, the conditions defined by the European Federation of Corrosion (EFC) [7] were

also listed as an alternative standard severity to reproduce both oil environment (high pH 4.5) and gas

environment (low pH 3.5). The lower environmental severity is balanced by increasing the stress level

up to 90% of actual yield stress.

The tests were performed with proof ring devices, Double walled glass vessels were used to

control and record the temperature of the solution continuously throughout the test. The test

temperature was 23’C, since the room temperature is known to be the worst case for SSC. After

machining, the specimens were polished with 600 grit paper and electrolytically. The environment was

first purged with nitrogen and then saturated with H2S (mixture) continually bubbling after initial

saturation. An oxygen trap was utilized.

Table 2 gives an extensive overview of the key parameters involved in SSC ST testing.

Crack progression in cylindrical tensile specimens occurs normal to the pipe axis, whereas in

the Double Cantilever Beam (DCB) specimen, the crack propagates parallel to the pipe axis. A range

of different specimen configurations ensured that the cracking behaviors in both directions have been

addressed. Moreover, authors have previously established that thicker steel of the same material is

more subject to cracking than a thin one considering pre-existing notches [8]. SO, the assessment of

good resistance to H2S and crack propagation is of great interest.



DCB.Qe.sting. Sulfide stress cracking tests were conducted according to NACE TMO177-90

Method D. Precracked specimens were loaded to a predetermined stress by means of a double taper

wedge which provided a constant displacement during the test. The specimens were then placed in

NACE solution for 14 days. As the cracks extend due to SSC the load, and hence the stress intensity

factor, decreases until it reaches the KISSC value beyond which the crack will not grow. Two weeks

are enough to reach the final crack length of carbon steels [5]. Transverse orientation specimens are

known to have lower toughness than specimens of longitudinal orientation [9], so various geometry

configurations were tested as shown in figure 4.

RESULTS AND DISCUSSION

Mechanical properties

Metallurgical results : The cleanness of the steel was evaluated according to ASTM E45 method

A (Table 3). These results were excellent regarding elongated inclusions which are especially

detrimental for toughness and corrosion.

Hardenabilitv [lo]: As a result of balancing the composition to achieve a high YS level with

improved H2S cracking resistance, a high hardenability steel has resulted. The JOMINY curve shown

in figure 5 highlights the efficiency of water quenching for heavy wall casing.

After water quenching, Vickers hardness readings were performed each millimeter through the

thickness. The very flat curve shown in figure 6 illustrates the full penetration of the quench. The

hardness level of 5OOHV, corresponding to 49 HRC, is higher than the API criterion for 90% of

martensite :

HRC 2 58 %C+27=46.7 with 0,34%wt C

As shown in figure 7, the typical as-quenched structure is fully martensitic and, as a consequence, well

quenched and tempered after tempering.

Since SSC resistance is a function of the amount of martensite formed on quenching, with the

best resistance obtained for material that possessed 100% martensite, flat microhardness profile [l l]

implies homogeneous microstructure of these heavy products up to 2”WT and therefore good

corrosion properties of this Cl 10 proprietary grade are expected.

According to ASTM E112: with saturated picric acid etching, the austenitic grain size was

measured between 9 and 10 accordmg to the thickness and the cast. An illustration is shown on figure

8. The refinement of the structure is a key point in guaranteeing high performances in sour

environment [ 121.

Mechanical results : Detailed mechanical properties are displayed in table 4 for tensile tests and

on figure 9 for hardness measurements. The hardness profiles are roughly flat respectively around

285, 283 and 295HV. The 2”WT coupling stock presents a slightly harder OD with a 1OHV drop at

Mw.

On the Rockwell scale, the hardness homogeneity is satisfied along the thickness within 2 HRC

deviation and conforms with a 30HRC maximum criterion.

Prismatic tensile results are also reported and led to an interesting comparison with 010 mm

round tensile : YS are systematically greater with the latter geometry as a consequence of the skin

effect. For 05 and 010 mm round tensile machined on MW the difference is slight enough to be

attributed either to the standard deviation of the experiment hardness or to the small drop in hardness

profile.

The 26.67 and 37.8 mm thick pipes show very consistent values on round specimen between

the OD-ID locations and pipe body MW. As for the 2”WT coupling

stock, all the portions meet the

Cl 10 grade with tensile properties in accordance with the hardness trends.

Ductility : Figure 10 highlights the ductile behaviour of the steel in the longitudinal direction

downto -60°C where the criterion 54J/dO”C (average) is well satisfied whatever the thickness and

sampling location even for the 2”WT coupling stock. In relation to the previous remarks concerning

the hardness profile, its MW behaves a range lower than the skins which show an excellent ductility.

Typical values of 130J are achieved for the casing at -40°C. Finally, the transverse results obtained on



The results show that mechanical characteristics are slightly influenced by the

pipe dimensions but

nevertheless the Cl 10 specifications are completely satisfied from the point of view of microstrwtwe,

structure homogeneity, tensile, hardness and toughness properties.

Hiah temnerature mechanical results : New questions are raised through the development of

HPHT wells concerning the mechanical properties of pipes at high temperature even in a range

exceeding the actual service limits, up to 25O’C. Table 5 provides some interesting answers. At 2OO”C,

a typical limit of Central Graben area, the steel loses 12% on YS and 5% on UTS.

SSC

results

ST testing : As shown on Tables 6 and 7, tests were carried out in 5 various environment in a

view to assess extensively the SSC resistance of the steel.

Considering MW specimen, only one failure occured among the 22 tested specimens, More

precisely one out of three 2” WT coupling stock specimen did crack late after 358 hours of exposure in

the pH3.5 EFC gas environment. It is noticeable that the material did pass the EEC test characterised

by an initial pH of 4. Specifically, the PI&tress level combination is a key parameter. Moreover as

pointed out in table 2, the end pH values are respectively 4.10-4.18 for EFC gas solution and 4.20-

4.25 for EEC solution. As shown on figure 11, it clearly appeared that without HCl adjustement

during the test, it is not possible to maintain the buffer effect for 30 days. On the other hand, previous

qualification trials and published results [14] have already revealed this acceptable limit of (maintained)

pH 4.1 with 10% H2S in CO2 gas saturation (PH2S =O.l bar).

Considering OD-ID location, all 21 specimens passed the NACE test. The SSC resistance of

OD and ID samples is as good as that of classical MW samples even for high yield strength values

around 120 ksi. Additionally, the materials passed also the EFC oil conditions at pH 4.5 with 0.1 bar

H2S.

DCB testing : Data are shown in table 8. KlSSC values are situated in an average range

36 MPadm - 46 MPadm for both geometry. The results largely surpass the 33 MPadm criterion [2]

considered as an equivallent to the no-failure criterion on ST specimen. Moreover, the very high

KlSSC (46 MPadm) obtained on the 2” WT coupling stock confirms the SSC resistance of the

material [ 151 even if it exhibited slightly lower mechanical performances homogeneity.

CONCLUSIONS

Our previous works [4] established in the early 90’s a combination of steel chemistry and hea

treatment parameters that enabled Cl 10 grade casing to be supplied for sour service. New

developments in rolling and heat treatment have led to the scope of supply to be increased. Both casing

and coupling stocks can now be delivered as thick wall products (up to 2”) with the same propertres

garanteed :

- restricted yield strength range of 10 ksi : 1 lo-120 ksi

- 90% minimum martensitic quenched structure

- controlled hardness : HRC < 30

- high toughness level : CVI 2 54 J at -40°C

- SSC threshold 2 85% SMYS in NACE solution

- KlSSC > 33MPadm in NACE solution

These performances were satisfactory and consistent on the three locations throughout the thickness

on external skin (OD), on internal skin (ID) and at mid wall thickness (MW). Moreover, the materials

pass SSC tests in various EFC oil and gas conditions so extensively assessing the corrosion resistance

of our C 110 proprietary grade.

ACKNOWLEDGEMENTS

Thanks to Tubular Industry Scotland Limited (TISL), Vallourec & Mannesmann Tubes and

Vallourec Research Center (CEV) for their participation in this research program.



REFERENCES

[Il.

PI

131

[41

[51

161

[71

PI

PI.

DOI

[ill.

[121

[131

[141

[151

M.B. Kermani, D. Harrop, R.D. Mac Cuish, J.R. Vera “Sulfide stress cracking of downhole

Tubular”, Corrosion 91, Houston, paper 272, (1991)

M.B. Kermani, D. Harrop, J.L. Crolet, M.L.R. Truchon “Experimental limits of sour service

for tubular steels”, Corrosion 91, Houston, paper 21, (1991)

NACE Standard MRO175-97, NACE International, (1997)

B.J. Orlans, F.A. Pellicani, G.C.Guntz, J.J. Ser-vier “Development of Cl10 grade for sour

service I’, Corrosion 93, New Orleans, paper 147, (1993)

NACE TM01 77-90 standard (1990)

J.L. Crolet, “Materials selection policy for II% media”, Corrosion 94, Baltimore, paper 66

(1994)

EFC report n’16, ” Guidelines on materials requirements for carbon and low alloy steels for

H2S-containing environments in oil and gas production”, The Institute of Materials (1995)

J.Brison Greer “Effects of metal thickness and temperature on casing and tubing design for

deep, sour wells”, Journal of Petroleum Technology, April (1973), p.499-510

John P. Frick “Variations in environmental cracking resistance of thick-walled low alloy steel

tubulars”, Corrosion 88, St Louis, paper 53, (1988)

G.M. Waid, R.T. Ault “The development of a new high strength steel with improved hydrogen

sulfide cracking resistance for sour oil and gas well applications” , Corrosion 79, Atlanta, paper

180 (1979)

M.Watkins ‘Microstructure - The critical variable controlling the SSC resistance of low alloy

steels”, Corrosion 95, Orlando, paper 50, (1995)

H. Asahi, M. Ueno, “Effect of austenite grain size of low alloy martensitic steel on SSC

resistance”, Corrosron 90, Houston, paper 66 (1990)

APISCT, fith edition (1995)

J.L. Crolet, J. Jelinek, S. D’Agata, M. Bonis, M.F. Louge “Selection of a Cl 10 casing grade

for mildly sour service”, EUROCORR 94, Boumemouth UK, (1994)

D. L. Sponseller “Interlaboratory testing of seven alloys for SSC resistance by the DCB

(TM0177-90D) method”, Corrosion 91, Houston, paper 3, (1991)



TABLE 1 : CHEMICAL COMPOSITION OF THE DIFFERENT HEATS (1O-3 wt )

Dimensions Heat C Mn Si P S Cr MO Ni Nb Al V

(mm)

273 x 26.7 Tl

339 460 324 12 1,9 931 759 28 35 29 49

312 x 48.6 Cl 318 502 303 7 1 988 850 89 38 28 46

289 x 37.8 C2 338 422 296 8 1 947 853 79 38 32 45

TABLE 2 : SSC TESTS CONDITIONS

EFC oil 1

EFC gas

EFC oil 2 EEC

NACE

Applied stress 9O%YS 9O%YS 9O%YS

9O%YS 85%SMYS

Gas 1OO%H2S 10% H2SKO2 10% H2s/co2 10% H2s/co2 lOO%H2S

NaCl (g/l)

50

50 50 1 50

Acetate(g/l) 4

4 4 10.464

Acetique(g/l)

5

HU

yes

yes yes

yes

Start pH

4.5

3.5 4.5 4 2.7

End pH

4.5

4.10-4.18 4.5 4.20-4.25 3.50-3.60

TABLE 3 : ASTM E45A INCLUSION RATING

‘We

A

B

C

D

Code

Fine Thick Fine Thick Fine Thick Fine Thick

Tl

0.5 - - -

2 -

Cl

0.5 -

1 -

1 -

1

-

c2

1.5 -

1 -

0.5

1.5

TABLE 4 : MECHANICAL PROPERTIES

05

010

prismatic

Code Dimensions Location

YS UTS ratio

YS UTS ratio

YS UTS ratio

(mm)

(ksi) (ksi) ( )

(ksi) (ksi) ( )

(ksi) (ksi) ( )

OD 121 134 90

Tl 273 x 26.67 MW 121 134 90 117 132 89

ID 118 133 89

OD 118 133 89

Cl 312x48.65 MW 110 128 86 111 128 87 111 129 86

ID 116 131 89

OD 115 127 91

c2 289x37.8 MW 113 127 89 115 127 90 113 130 87

ID 114 128 89



TABLE 5 : EVOLUTION AT HIGH TEMPERATURES OF

YIELD STRENGTH (YS) & ULTIMATE TENSILE STRENGTH (UTS)

Code Dimensions

(mm)

Stress

at 20°C

At temperature (“C)

W)

20 100 150 200 250

YS=

117 1.00 0.95

0.91 0.88 ‘0.83

T2 273 x 26.67

u-l-s=

130 1.00 0.96

0.95 0.94 0.95

TABLE 6 : SMOOTH TENSILE SSC RESULTS AT MID WALL THICKNESS

Code

NACE

EEC

EFC oil 1

EFC gas

Gas lOO H2S lO H2S/CO2 lOO H2S lO H2S/CO2

Dimensions

Start pH

2.7

4

4.5

3.5

(mm)

Applied stress 85 SMYS

9O YS

9O YS

9O YS

Tl

212NF

212w

273x 26.67

Cl

313NF

i NF 3:3

NF

213NF

312

x

48.65

(1 failure at 356h)

c2 313

w

313

NJ

289 x

37.8

2/3 NF means 2 unbroken specimens & 1 valid crack for 3 tested specimens within 720h

TABLE 7 : SMOOTH TENSILE SSC RESULTS AT OD AND ID SKINS

Code

NACE

EFC oil 2

Gas

lOO H2S

lO H2S/C02

Dimensions Start pH

2.7 4.5

(mm)

Applied stress

85 SMYS

9O YS

OD ID

OD ID

Tl

313

NF 212NF 313NF l/lNF

273 x 26.67

Cl

212NF 212NF

l/l NF 3/3 NF

3 12x 48.65

c2

313NF

l/l NF

289 x 37.8



TABLE 8 : KlSSC (MPadm) DERIVED FROM DCB TESTS IN NACE SOLUTION

Code Dimensions

Location Test piece1 Test piece2 Average

(mm)

Tl 273 x 26.67

transverse

33.9

39.9 36.9

OD long 39.4 32.4 35.9

Cl

312 x 48.65 MW long

47.2 45.8

46.5

ID long

37.5

37.5

FIGURE 1 : LOCATION OF ROUND TENSILE SPECIMENS

THOUGHOUT WALL THICKNESS

FIGURE 2 : LOCATION OF CHARPY SPECIMENS THOUGHOUT WALL

THICKNESS (1) LONG. (2) TRANS.

FIGURE 3 : LOCATION OF NACE SMOOTH TENSILE SPECIMENS THOUGHOUT

WALL THICKNESS



FIGURE 4 : LOCATION OF DCB SPECIMENS THOUGHOUT WALL THICKNESS

273 6,67mm

FIGURE 5 : JOIMINY CURVE FOR Cl10 GRADE STEEL

60

50

40 130

20

10

~ ~

O

0

10

20

Distance (mm)

i

30

40

FIGURE 6 : HARDNESS THROUGH THE WALL THICKNESS

OF AS QUENCHEDPRODUCT

100

0 4

0 10 20 30 40

Distance from OD (mm)



FIGURE 7 : MICROSTRUCTURE (M500) (after Nital etching)

AS-QUENCHED

QUENCHED & TEMPERED

FIGURE 8 : PRIOR AUSTENITE GRAIN BOUNDARIES (M500)

ASTM SIZE X (after picric acid etching)

FIGURE 9 : HARDNESS THROUGH THE WT OF Q&T PIPES

Tl (273x26.67 mm)

Cl (312x48.65 mm)

C2 (289x37.8 mm)

320/

0 5 IO 15 20

25 30

Distance from OD (mm)

35 40

45 50



FIGURE 10 : CV NOTCH RESULTS OF LONGITUDINAL (L)

AND TRANSVERSE (T) IMPACT TESTS

150

I

50

T

X OD C2(T) j

X ID C2(T)

1 + MW C2(T)

I

i-mini 54J 1

0 :

-60

t

I

I

i

-40

-20

0

20

Temperature (“C)

FIGURE 11 : CURVE pH vs time FOR VARIOUS SSC TEST ENVIRONMENTS

4.25

350

0

100 200

300

400 500 600

700

600

Time (hour)

heavy wall casing in c110 grade

Documents