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Experience of qualification test of CRA material
Sandvik Sanicro 28 (UNS N08028) for
down hole tubular in sour gas well applications
TECHNICAL ARTICLE NO. S-TU221-TA. 12/2013 SANDVIK MATERIALS TECHNOLOGY
Kukuh Soerowidjojo, Technical Sales and Marketing Area
Manager
Sandvik Materials Technology SE-811 81 Sandviken Sweden
Abstract Introduction
High prices of world petroleum products have enabled energy
companies to extract oil and gas from more expensive and
challenging environments; i.e. deeper offshore sites, deeper wells
and more sour fields and more severe environments with greater
pressure and higher temperatures.
Material selection is therefore a very important aspect to minimize
failures caused by corrosion attacks. Selecting materials for highly
sour environments based on the guidelines from NACE MR
0175/ISO 15156:2009, paragraph 7, requires qualification tests and
further investigation to ensure that the selected material, provided
by the supplier, will perform as expected during operations.
In this investigation of SCC and SSC in sour environments were
performed under the guidelines of ISO 7539-1, ISO 7539-3 and
ISO 7539-4. This qualification process is a normal practice in order
to verify whether a material is suitable to serve in the given well
conditions as alternative to NACE TM0177.
The selected material was Sandvik Sanicro™ 28 (UNS N08028) in
cold worked and non-annealed condition, produced by a pilgering
process in two sizes: 114.3 mm OD x 6.45 mm wall thickness for
the production tube; and 126 mm OD x 14 mm wall thickness for
the coupling stock. Specimens were prepared for both tensile and
U-bend sour tests in an autoclave. These included:
• Five U-bend specimens in each size, according to ISO
7539-3:1989, for sulfide stress cracking tests.
• Two sub-size smooth tensile specimens in each size,
machined from the supplied material in accordance with
ISO 7539-4:1989, for sulfide stress cracking tests.
The duration of the test was 720 hours, stress level up to 90% of
the yield strength at test temperature to provide more extreme
conditions than in the actual application and accelerate corrosion
attacks. At the end, a microscopic investigation was performed
under 20X magnification to seek for any cracking.
The results were satisfactory, in both specimens. These findings
confirmed that Sanicro 28 (UNS N08028) – 110 ksi could be used
in the specified environment.
Cold worked high alloyed materials – like nickel based alloys,
pipe with cold pilgering or drawing process – will produce a high
tensile material with resistance to corrosion in severe
environments introduced in oil and gas wells. Apart from
mechanical properties, which are designed to bear all the stresses
that occur during operations, corrosion resistance is an important
feature – especially resistance to Stress Corrosion Cracking and
Sulfide Stress Cracking. This particularly applies whenever H2S
and CO2 gases are present in wet conditions.
Materials acquiring these properties will enable engineers to
explore and extract oil and gas in a more economical way.
However, these materials also have service limitation in
corrosive environments. It is therefore advisable that end users
request a test to ensure that the material is suitable for the
application in their respective fields. In this respect, NACE
provides test procedures to qualify the material whenever
aggressiveness of the environment gets close to the service
boundary of the material.
Offshore construction technology has also enabled Oil and Gas
companies to operate in deeper sea which demand high strength
materials in severe conditions.
Evidence of failure in materials can be found in inappropriate
applications in the field. Some examples of failures are shown
below for material Duplex 2205 – 125 ksi minimum yield strength;
size 88.90 mm OD x 6.45 mm w.t.; with coupling size 98.50 mm
OD x 12.18 mm w.t.
Cracked at the coupling part and later found in the tube
Figure 1. An example of failure at inappropriate application;
microstructure examination under 500X magnifcation
2
Further investigation has found that the material suffered
embrittlement, which may have been caused by hydrogen
introduced by H2S.
Sanicro 28 (UNS
N08028)
performance in sour
environment
Sanicro 28 (UNS N08028) chemical
composition (nominal values)
Initially, Sanicro 28 (UNS N08028) was designed for sulfuric acid and
phosphoric acid production for either pipes or heat exchangers. Further
development made Sanicro 28 (UNS N08028) useful in more
applications like in the Oil and Gas industry for both upstream and
down- stream requirements, due to its excellent corrosion resistant
properties. One application of Sanicro 28 (UNS N08028) is for
downhole production tube, produced in cold pilgered and non-annealed
condition to achieve high strength.
Figure 2. Sanicro™ 28 microstructure 500X optical magnification
through light optical microscopy (LOM)
Material selection
process - Literature
study
According to NACE MR0175-ISO 15156-3, Sanicro 28 (UNS
N08028) in solution annealed and cold worked condition is
categorized in the solid solution nickel based alloy group, 4c.
The use in down hole equipment is recommended for any
application which falls under these conditions, as described in
Table 2 which is taken from NACE MR0175-ISO15156-3 table
A.14
In H2S environments, solution annealed and cold worked Sanicro
28 (UNS N08028) showed excellent resistance to SCC/SSC
attacks. Previous research by Sandvik Materials Technology
Research & Development (R&D) to investigate its performance
was conducted under laboratory conditions created a diagram
shown in Figure 03. Any condition below the line is a ‘no-
corrosion attack region’.
The condition given by the client falls in a safe region.
Based on these literature findings, Sanicro 28 (UNS N08028)
should be sufficient for optimum performance in the client’s
required well condition.
Table 1. Sanicro™ 28 chemical composition
C Si Mn P S Cr Ni Mo Cu
max. max. max. max.
0.020 0.6 2.0 0.025 0.015 27 31 3.5 1.0
3
Table 2. Taken from NACE MR0175-ISO 15156-3 table A.14
Material type Temperature Partial pressure Chloride pH Sulfur Remarks
oC (oF)
H2S,pH2S
kPa (psi) mg/l
resistant ?
Max. Max. Max.
232 (450) 200 (30) See “Remarks” See “Remarks” No
column column
Any combination of
Cold worked
alloys of types 4c,
4d and 4e
218 (425) 700 (100) See “Remarks”
column
204 (400) 1000 (150) See “Remarks”
column
177 (350) 1400 (200) See “Remarks”
column
See “Remarks” No
column
See “Remarks” No
column
See “Remarks” No
column
chloride concentration and
in situ pH occurring in
production environment is
acceptable
Any combination of
hydrogen sulfide,
132 (270) See “Remarks”
column
See “Remarks”
column
See “Remarks”
column
Yes chloride concentration
and in situ pH production
environment is acceptable
Material selection
process - Laboratory
test
PH2S
kPa psi
10000
Gas field conditions.
1000
Corrosion
Following good code of conduct practices, the company that owns
the project and its location will not be mentioned in this paper.
However, the company has allowed us to show the well condition
where the tube will be used. It is the basis of this test, described as
follows:
1000
100
100
10
No corrosion
Client’s field conditions
Test temperature: 150o
C (302o
F)
CO2 partial pressure: 41 Bar (594.65 psi) H2S partial
pressure: 5.5 Bar (79.77 psi) Chlorides:
75,000 mg/l (as NaCl)
Bicarbonate: 0.1 (as sodium bicarbonate)
pH at temperature*: 3.75 – 4.25
Total pressure at temp: 54 Bar (783.20 psi); including
7.5 bar (108.78 psi) vapor pressure
10
1
1
0.1
100 200 300 400 500 ˚F
* pH at temperature estimated from data in EFC 16, using H2S
and CO2 partial pressure and the bicarbonate addition.
0
5% NaCl 15% NaCl
100
Failure
Pitting, no failure
No corr, attack
200 ˚C
Temperature
1000 psi CO2 and stressed to 100%
Figure 3. Sanicro™ 28 laboratory sour test result
4
Test procedure ‘U’bend
specimen
Test specimens were made of two sections of pipes representing
tube. The two sizes were: 114.3 mm OD x 6.45 mm wall
thickness produced with lot number 34672-6; and coupling stock
126 mm OD x 14 mm w/t produced with lot number 34594-2.
Five ‘U’ bend specimens were machined from each product form,
prepared in accordance with ISO 7539-3. The ‘U’ bend specimens
were identified by stamping an identification number, of C120 (A-
E) for tube material and C121 (A-E) for coupling stock material,
to keep the traceability.
The sulfide stress corrosion cracking tests were performed in
accordance with ISO 7539-1 and ISO 7539-3. The tests were
undertaken using Cortest Inc. ¼ liter autoclaves and calibrated
proof rings, and were performed at a stress level of
90% of the actual 0.2% proof stress of the material at test
temperature, equaling a stress level of 712.8 N/mm2.
Each specimen was placed in an autoclave filled with 250 ml of
de-aerated test solution to fully immerse the test specimen gauge
section. The autoclave was sealed and placed in the proof ring and
each specimen was stressed to the desired test stress. The
autoclave was de-aerated with oxygen-free nitrogen for two hours
and then pressure tested to 60 bars with nitrogen.
Following the pressure test, the nitrogen gas was vented from the
autoclave. The solution was then saturated with 3.8 bar H2S gas at
100–200 ml per minute for two hours at room temperature (the
pressure required to achieve 5.5 bar H2S partial pressure at the test
temperature). The autoclave was then over-pressured with 28.4 bar
of CO2, left for one hour to allow CO2 gas to absorb into the test
solution, and re-pressured at 28.4 bars. The autoclave was then
heated to 150°C ± 3°C and any excess pressure was bled from the
autoclave. The autoclave pressure at the test temperature was
54 bars.
The overall test duration was 720 hours. During this period, both
autoclaves were monitored for temperature and pressure.
Figure 3. Autoclave for ‘U’ bend specimen sour test with its
schematic picture
Table 3. Details of cut-piece samples sent to laboratory
Grade Pipe dimension Lot no. Certificate no. Pipe test no.
Sanicro™ 28 114.3 mm OD x 6.45 mm w/t 34672-6 A-03-008470 C121
Sanicro 28 (UNS
N08028)
126 mm OD x 14 mm w/t 34594-2 A-03-008304 C120
5
On completion of the test period, the autoclave was cooled down to
room temperature, depressurized and the ‘U’ bend specimens were
removed for examination. The ‘U’ bends were cleaned and
assessed under a low power binocular microscope at 20X
magnification.
Test procedure tensile sour
test
The sulfide stress corrosion cracking tests were undertaken in
accordance with ISO 7539-1 and ISO 7539-4. The tests were
undertaken using Cortest Inc. ¼ liter autoclaves and calibrated
proof rings, performed at a stress level of 90% of the actual 0.2%
proof stress of the material, equaling a stress level of 787.5 N/mm2.
Each specimen was placed in an autoclave filled with 250 ml
of de-aerated test solution in order to fully immerse the test
specimen gauge section.The autoclave was sealed and placed
Test specimens were made of two sections of pipes representing
tube: 114.3 mm OD x 6.45 mm w/t produced with lot number
34672-6; and coupling stock 126 mm OD x 14 mm w/t produced
with lot number 34594-2.
Two sub-sized specimens were machined for each pipe in
accordance with ISO 7539-4:1989. The tensile specimens were
identified by stamping with identification numbers, C123 and
C125 for tube material and C122 and 124 for coupling stock
material, to keep the traceability.
in the proof ring, and each specimen was stressed to the
desired test stress. The autoclave was de-aerated with
oxygen-free nitrogen for two hours and then pressure tested to
60 bar with nitrogen.
Following the pressure test, the nitrogen gas was vented from the
autoclave. The solution was then saturated with H2S gas at 100 –
200 ml per minute for two hours at room temperature, and at 3.8
bar pressure (the pressure required to achieve 5.5 bar H2S at the
test temperature). The autoclave was then over-pressured with
28.4 bar of CO2, left for 1 hour to allow the CO2 gas to absorb in
the test solution and re-pressurized at 28.4 bars. The autoclave
was then heated to 150°C ± 3°C and any excess pressure bled
from the autoclave. The total pressure at the test temperature was
54 bars.
The overall test duration was 720 hours. During this period, both
autoclaves were monitored for temperature and pressure.
Observation
Test specimens were made of two sections of pipes representing
tube: 114.3 mm OD x 6.45 mm w/t produced with lot number
34672-6; and coupling stock 126 mm OD x 14 mm w/t produced
with lot number 34594-2.
Two sub-sized specimens were machined for each pipe in
accordance with ISO 7539-4:1989 (dimension as CTS-27). The
tensile specimens were identified by stamping with identification
numbers, C123 and C125 for tube material and C122 and 124 for
coupling stock material, to keep the traceability.
On completion of the test period, both autoclaves were
cooled down to room temperature and vented to atmospheric
pressure. Test specimens were removed, cleaned and examined
under binocular microscope at 20X magnification.
Result
As we have predicted from literature studies, solution annealed
and cold worked Sanicro 28 (UNS N08028) had performed very
well under the test conditions. There were no cracks in all of the
specimens tested after 720 hours exposure.
Figure 4. Sour environment tensile test with proof ring and autoclave
and its schematic diagram
6
Specimen C122 (report TR 3030128A)
Figure 5. Tensile test specimen view after 720 hours exposure in the
test conditions.
Specimens C120 A - E (report TR 3030128C)
Figure 6. ‘U’ bend specimens after 720 hours exposure in the given
test condition
Purging the testing solution to remove oxygen is very important
considering that oxygen could increase the corrosion rate very
significantly, and this would not represent the actual operating
condition in the oil/gas well, where oxygen content could be as
low as 5 - 8 ppb. Consequently, this testing process was conducted
very carefully to achieve optimum results.
Sanicro 28 (UNS N08028) – with nickel content between 30.3 – 34
w.t.% and a Pitting Resistance Equivalent (PRE)** minimum of 38
– is suitable for medium to highly sour gas fields. Using a Sanicro
28 (UNS N08028) SSC diagram and NACE MR0175/ISO15156
guidelines as an initial stage of material selection is therefore very
useful in order to identify whether solution annealed and cold
worked Sanicro 28 (UNS N08028), can be used in the specified
environment.
For any CO2 partial pressure below 1,000 psi and/or pH higher
than 2.9, it is possible to accept higher partial pressure of H2S in
the environment. This also works for lower chloride content, so we
can accept higher H2S partial pressure. Hence, returning to the
Sanicro 28 (UNS N08028) SSC/SCC diagram at figure 3, the
border line will move upwards to accept the higher partial pressure
of H2S while considering the above pre-conditions.
However, it is advised to perform sour corrosion test according to
NACE TM 177 to qualify the material for such case(s).
Due to a lengthy testing time of 720 hours, in addition to all other
preparations, the total time required to complete the test report
could be as long as 2 months or even more. This must be
considered as part of the procurement timeframe by a project
manager. Nevertheless, this step could help the company to make a
decision on material selection and avoid premature failure of the
production string.
Hardness has an important role in the sensitivity of the corrosion
resistant alloy to SSC phenomena. In this respect, NACE MR
0175/ISO 15156 also specifies maximum hardness acceptable for
each type of material. Materials with slightly harder are still very
much affected by the way the tube is produced in cold processes.
Even though the average hardness of the material meets the
specification, the variation of hardness in different locations
within the tube wall – especially close to the skin – might be so
high as to detrimentally effects SSC resistance. Sanicro 28 (UNS
N08028) – 110 psi SMYS, which falls in ISO 13680/API 5CRA -
2010 category 27-31-4, gives different values depend on its
Product Specification Level (PSL). ISO 13680/API 5CRA - 2010
PSL 1 gives a value of maximum HRC 35 according to table A.3.
On the other hand, ISO 13680/API 5CRA - 2010 PSL 2 gives a
value of maximum HRC 33 according to table A.27 and C.27.
After gas production running for years, normally there would be
some changes in the gas composition where pH2S and pCO2 would
increase in some extent. However, considering there are so many
margins between the current well conditions and service
borderline of Sanicro 28 (UNS N08028), we can expect that
Sanicro 28 (UNS N08028) is able to cope with SSC attacks in the
longer run.
Conclusion
From the above findings and discussions, we can conclude:
1. Sanicro 28 (UNS N08028) – 110 ksi CRA material provided for
the test is sufficient to resist corrosion attack in the client’s field
environment, as described in the test condition, though there
might be changes in gas composition for long run.
2. ISO 7539-1/3/4 test procedures are viable to be part of a
project as long as there is sufficient time allocated for the test.
In fact, this test was completed in 2.5 months due to a very
busy test schedule at the laboratory.
7
S-TU221-TA-ENG
Appendix 1
LAB DATA CHART FOR MATERIAL Sanicro™ 28 (126 mm O.D. X 14 mm wt)
TESTED PER NACE STANDARD TM0177-96 (Method A, Tensile test) (1)
SPECIMEN GEOMETRY [ ] STANDARD [ √ ] SUB-SIZE TENSILE NOMINAL DIAMETER 3.08/3.81mm GAUGE LENGTH
TEST EQUIPMENT[ √ ] SUSTAINED LOAD - PROOF RING [ ] POSTTEST PROOF RING DEFLECTION MEASUREMENT CHEMISTRY
[ ] SOLUTION A [ ] SOLUTION B [ √ ] OTHER SOLUTION
[ √ ] OUTLET TRAP TO EXCLUDE OXYGEN? [ √ ] TEMPERATURE MAINTAINED 150˚C ± 3˚C
SPECIMEN PROPERTIES
TIME
(HOURS TO FAILURE
AT % YIELD)
NF = No Failure at 720 hours
Solution
pH (5)
Heat Treat
Applied
Remarks
Material
Identification
(2)
Ioc
(3)
Orn
Y.S.(4)
(N/mm²)
T.S.
(N/mm²)
EI % RA %
Hardness
HRC
70 80 90 Start Finish
C 122 792 N.F.
5.5 bar H2S
41 bar CO2
C 124 792 N.F.
5.5 bar H2S
41 bar CO2
NOTES:
(1) Test method must be fully described if not in accordance with NACE Standard TM0177.
(2) Location of specimen from test piece may be O.D., Mid-Radius (MR), Centre (C), Edge (E).
(3) Orientation may be longitudinal (L) or transverse (T).
(4) Yield strength is assumed to be 0.2% offset unless otherwise noted.
(5) Enter pH for test conducted on passing specimen at highest stress if summarizing data.
1
Appendix 2
LAB DATA CHART FOR MATERIAL Sanicro™ 28 (114 mm O.D. X 6.45 mm wt)
TESTED PER NACE STANDARD TM0177-96 (Method A, Tensile test) (1)
SPECIMEN GEOMETRY [ ] STANDARD [ √ ] SUB-SIZE TENSILE NOMINAL DIAMETER 3.79/3.80mm GAUGE LENGTH
TEST EQUIPMENT [ √ ] SUSTAINED LOAD - PROOF RING [ ] POSTTEST PROOF RING DEFLECTION MEASUREMENT
CHEMISTRY [ ] SOLUTION A [ ] SOLUTION B [ √ ] OTHER SOLUTION
[ √ ] OUTLET TRAP TO EXCLUDE OXYGEN? [ √ ] TEMPERATURE MAINTAINED 150˚C ± 3˚C
SPECIMEN PROPERTIES
TIME
(HOURS TO FAILURE
AT % YIELD)
NF = No Failure at 720 hours
Solution
pH (5)
Heat Treat
Applied
Remarks
Material
Identification
(2)
Ioc
(3)
Orn
Y.S.(4)
(N/mm²)
T.S.
(N/mm²)
EI % RA %
Hardness
HRC
70 80 90 Start Finish
C 123 875 N.F.
5.5 bar H2S
41 bar CO2
C 125 875 N.F.
5.5 bar H2S
41 bar CO2
NOTES:
(1) Test method must be fully described if not in accordance with NACE Standard TM0177-96.
(2) Location of specimen from test piece may be O.D., Mid-Radius (MR), Centre (C), Edge (E).
(3) Orientation may be longitudinal (L) or transverse (T).
(4) Yield strength is assumed to be 0.2% offset unless otherwise noted.
(5) Enter pH for test conducted on passing specimen at highest stress if summarizing data.
2
S-TU221-TA-ENG
Appendix
CHEMICAL ANALYSIS
Material Test Plan
Acceptance criteria ASTM B 668 UNS N08028
Element
required
C
%
Si
%
Mn
%
P
%
S
%
Cr
%
Ni
%
Mo
%
Cu
%
Fe
%
N
%
Test frequency
Min 26.0 30.3 3.0 0.6
Remain
der
ISO 13680 para
10.4
Max 0.020 0.6 2.5 0.025 0.020 28.0 34.0 4.0 1.4 0.10 1 test/heat
Tolerances on product analysis as per ASTM B829. Test frequency of product analysis 2 tests/lot (ISO 13680 para 10.4)
Type of test Specification
MECHANICAL TESTS
Number of tests Type of sample Acceptance criteria
Tensile test at room temperature ISO 13680 para 11.2
referring to ISO 6892 and
table 3 para 8.3.1, 10.5.2,
10.5.3.1
1 test/lot
(lot max 50 pipes,
ISO 13680 tab 13)
STRIP
LONGITUDINAL
DIRECTION
min max
Yield strength 0.2% (Rp 02)
Tensile strength (Pm)
Elongation on 2”
Mpa 760 (110 ksi) 965 (140 ksi)
Mpa 795 (115 ksi)
% 11
Hardness test
ISO 13680 PARA 8.3.1
table 3 four quadrants
1 test/lot
ISO 13680 para
11.3 figure 5,
10.5.3.3 on ring
HRC 33
Hardness variation
among values
ISO 13680 PARA 8.3.1
table 4
HRC
3 (will be
applied on
quadrants at
the same
sample lot
only)
Type of test Specification
LABORATORY TESTS
Number of tests Type of sample Acceptance criteria
Micrographic examination
ISO 13680 para 11.6.1
ASTM E 562
1 test/lot
Polished test piece
hold in bakelit. ISO
13680 para 10.5.36
Microstructure test ISO 13680 Para 8.5.3
Mass correction factor from the manufacturer: α = 1.0204 refer to ISO 13680:2010(E) para 9.1.1
** Pitting Equivalent Number = %Cr + 3.3 x %Mo + 16 x %N is a number to rank CRAs against Pitting corrosion attacks which
correspond to Stress Corrosion Cracking attacks in chloride environments.
10
References
1. Hans Eriksson and J, Michael Nicholls
Sandvik Materials Technology AB R&D Center, S81181
Sandviken Sweden Testing and selection of duplex stainless
steels for sour environments NACE Corrosion conference,
Corrosion 91, March 91, Houston, TEXAS
2. Hans Eriksson and Sven Bernhardsson
Sandvik Materials Technology AB R&D Center, S81181
Sandviken Sweden Testing and selection of duplex stainless
steels for sour environments NACE Corrosion conference,
Corrosion 91, March 91, Houston, TEXAS
3. C. Bradshaw and M.Peet.
Sheffield Testing Laboratory, Sheffield, United Kingdom
Report on Autoclave Testing of Sanicro 28 (UNS N08028) material
Report number TR 3110428 A/B/C 17 November 2003 for
Sandvik Materials Technology UK
4. Sven Bernhardsson, Jan Oredsson and Carl Carlborg
Sandvik Materials Technology AB R&D Center, S81181
Sandviken Sweden Performance of Ni-Fe-Cr-Mo alloy in sour
Oil and Gas applications Paper 225, NACE Corrosion
Conference, Corrosion 85, Boston, MA, March 25-29, 1985
5. Jean-Louis Crolet and Michel R. Bonis
Elf Exploration Production, France.
How to pressurize autoclaves for corrosion testing under CO2
and H2S pressure Paper 102 Corrosion 98, NACE Corrosion
conference, June 9-11, 1998 San Diego, CA.
6.Guocai Chai
Sandvik Materials Technology AB R&D Center, S81181
Sandviken Sweden Tensile properties, Sanicro 28 (UNS
N08028), High temperature Technical report document no.
T010690
7. NACE INTERNATIONAL, Houston Texas.
NACE MR 0175/ISO 15156-1:2001 Specification Petroleum
and natural gas industries – Materials for use in H2S-containing
Environments in oil and gas production
Part 1 : General principles for selection of cracking-resistant
materials. ISBN 1-5759-1765
8. NACE INTERNATIONAL, Houston Texas.
NACE MR 0175/ISO 15156-3:2003 Specification Petroleum
and natural gas industries – Materials for use in H2S-containing
Environments in oil and gas production
Part 3 : Cracking-resistant CRAs (corrosion-resistant alloys)
and other alloys ISBN 1-5759-1765
9. NACE INTERNATIONAL, Houston Texas
NACE TM 177-96 Standard test method: “ Laboratory
testing of metals for Resistance to Sulfide stress cracking and
Stress corrosion cracking in H2S environment”
ISBN 1-57590-036
Sandvik and Sanicro are trademarks owned by Sandvik
Intellectual Property AB.
11
SANDVIK MATERIALS TECHNOLOGY
SE-81 I 81 Sandv1 ken, Sweden, Phone +46 26 26 00 00, Fax +46 26 26 02 20
www.smt.sandv1k.eom

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S-TU221-TA-ENG

  • 1. Experience of qualification test of CRA material Sandvik Sanicro 28 (UNS N08028) for down hole tubular in sour gas well applications TECHNICAL ARTICLE NO. S-TU221-TA. 12/2013 SANDVIK MATERIALS TECHNOLOGY Kukuh Soerowidjojo, Technical Sales and Marketing Area Manager Sandvik Materials Technology SE-811 81 Sandviken Sweden
  • 2. Abstract Introduction High prices of world petroleum products have enabled energy companies to extract oil and gas from more expensive and challenging environments; i.e. deeper offshore sites, deeper wells and more sour fields and more severe environments with greater pressure and higher temperatures. Material selection is therefore a very important aspect to minimize failures caused by corrosion attacks. Selecting materials for highly sour environments based on the guidelines from NACE MR 0175/ISO 15156:2009, paragraph 7, requires qualification tests and further investigation to ensure that the selected material, provided by the supplier, will perform as expected during operations. In this investigation of SCC and SSC in sour environments were performed under the guidelines of ISO 7539-1, ISO 7539-3 and ISO 7539-4. This qualification process is a normal practice in order to verify whether a material is suitable to serve in the given well conditions as alternative to NACE TM0177. The selected material was Sandvik Sanicro™ 28 (UNS N08028) in cold worked and non-annealed condition, produced by a pilgering process in two sizes: 114.3 mm OD x 6.45 mm wall thickness for the production tube; and 126 mm OD x 14 mm wall thickness for the coupling stock. Specimens were prepared for both tensile and U-bend sour tests in an autoclave. These included: • Five U-bend specimens in each size, according to ISO 7539-3:1989, for sulfide stress cracking tests. • Two sub-size smooth tensile specimens in each size, machined from the supplied material in accordance with ISO 7539-4:1989, for sulfide stress cracking tests. The duration of the test was 720 hours, stress level up to 90% of the yield strength at test temperature to provide more extreme conditions than in the actual application and accelerate corrosion attacks. At the end, a microscopic investigation was performed under 20X magnification to seek for any cracking. The results were satisfactory, in both specimens. These findings confirmed that Sanicro 28 (UNS N08028) – 110 ksi could be used in the specified environment. Cold worked high alloyed materials – like nickel based alloys, pipe with cold pilgering or drawing process – will produce a high tensile material with resistance to corrosion in severe environments introduced in oil and gas wells. Apart from mechanical properties, which are designed to bear all the stresses that occur during operations, corrosion resistance is an important feature – especially resistance to Stress Corrosion Cracking and Sulfide Stress Cracking. This particularly applies whenever H2S and CO2 gases are present in wet conditions. Materials acquiring these properties will enable engineers to explore and extract oil and gas in a more economical way. However, these materials also have service limitation in corrosive environments. It is therefore advisable that end users request a test to ensure that the material is suitable for the application in their respective fields. In this respect, NACE provides test procedures to qualify the material whenever aggressiveness of the environment gets close to the service boundary of the material. Offshore construction technology has also enabled Oil and Gas companies to operate in deeper sea which demand high strength materials in severe conditions. Evidence of failure in materials can be found in inappropriate applications in the field. Some examples of failures are shown below for material Duplex 2205 – 125 ksi minimum yield strength; size 88.90 mm OD x 6.45 mm w.t.; with coupling size 98.50 mm OD x 12.18 mm w.t. Cracked at the coupling part and later found in the tube Figure 1. An example of failure at inappropriate application; microstructure examination under 500X magnifcation 2
  • 3. Further investigation has found that the material suffered embrittlement, which may have been caused by hydrogen introduced by H2S. Sanicro 28 (UNS N08028) performance in sour environment Sanicro 28 (UNS N08028) chemical composition (nominal values) Initially, Sanicro 28 (UNS N08028) was designed for sulfuric acid and phosphoric acid production for either pipes or heat exchangers. Further development made Sanicro 28 (UNS N08028) useful in more applications like in the Oil and Gas industry for both upstream and down- stream requirements, due to its excellent corrosion resistant properties. One application of Sanicro 28 (UNS N08028) is for downhole production tube, produced in cold pilgered and non-annealed condition to achieve high strength. Figure 2. Sanicro™ 28 microstructure 500X optical magnification through light optical microscopy (LOM) Material selection process - Literature study According to NACE MR0175-ISO 15156-3, Sanicro 28 (UNS N08028) in solution annealed and cold worked condition is categorized in the solid solution nickel based alloy group, 4c. The use in down hole equipment is recommended for any application which falls under these conditions, as described in Table 2 which is taken from NACE MR0175-ISO15156-3 table A.14 In H2S environments, solution annealed and cold worked Sanicro 28 (UNS N08028) showed excellent resistance to SCC/SSC attacks. Previous research by Sandvik Materials Technology Research & Development (R&D) to investigate its performance was conducted under laboratory conditions created a diagram shown in Figure 03. Any condition below the line is a ‘no- corrosion attack region’. The condition given by the client falls in a safe region. Based on these literature findings, Sanicro 28 (UNS N08028) should be sufficient for optimum performance in the client’s required well condition. Table 1. Sanicro™ 28 chemical composition C Si Mn P S Cr Ni Mo Cu max. max. max. max. 0.020 0.6 2.0 0.025 0.015 27 31 3.5 1.0 3
  • 4. Table 2. Taken from NACE MR0175-ISO 15156-3 table A.14 Material type Temperature Partial pressure Chloride pH Sulfur Remarks oC (oF) H2S,pH2S kPa (psi) mg/l resistant ? Max. Max. Max. 232 (450) 200 (30) See “Remarks” See “Remarks” No column column Any combination of Cold worked alloys of types 4c, 4d and 4e 218 (425) 700 (100) See “Remarks” column 204 (400) 1000 (150) See “Remarks” column 177 (350) 1400 (200) See “Remarks” column See “Remarks” No column See “Remarks” No column See “Remarks” No column chloride concentration and in situ pH occurring in production environment is acceptable Any combination of hydrogen sulfide, 132 (270) See “Remarks” column See “Remarks” column See “Remarks” column Yes chloride concentration and in situ pH production environment is acceptable Material selection process - Laboratory test PH2S kPa psi 10000 Gas field conditions. 1000 Corrosion Following good code of conduct practices, the company that owns the project and its location will not be mentioned in this paper. However, the company has allowed us to show the well condition where the tube will be used. It is the basis of this test, described as follows: 1000 100 100 10 No corrosion Client’s field conditions Test temperature: 150o C (302o F) CO2 partial pressure: 41 Bar (594.65 psi) H2S partial pressure: 5.5 Bar (79.77 psi) Chlorides: 75,000 mg/l (as NaCl) Bicarbonate: 0.1 (as sodium bicarbonate) pH at temperature*: 3.75 – 4.25 Total pressure at temp: 54 Bar (783.20 psi); including 7.5 bar (108.78 psi) vapor pressure 10 1 1 0.1 100 200 300 400 500 ˚F * pH at temperature estimated from data in EFC 16, using H2S and CO2 partial pressure and the bicarbonate addition. 0 5% NaCl 15% NaCl 100 Failure Pitting, no failure No corr, attack 200 ˚C Temperature 1000 psi CO2 and stressed to 100% Figure 3. Sanicro™ 28 laboratory sour test result 4
  • 5. Test procedure ‘U’bend specimen Test specimens were made of two sections of pipes representing tube. The two sizes were: 114.3 mm OD x 6.45 mm wall thickness produced with lot number 34672-6; and coupling stock 126 mm OD x 14 mm w/t produced with lot number 34594-2. Five ‘U’ bend specimens were machined from each product form, prepared in accordance with ISO 7539-3. The ‘U’ bend specimens were identified by stamping an identification number, of C120 (A- E) for tube material and C121 (A-E) for coupling stock material, to keep the traceability. The sulfide stress corrosion cracking tests were performed in accordance with ISO 7539-1 and ISO 7539-3. The tests were undertaken using Cortest Inc. ¼ liter autoclaves and calibrated proof rings, and were performed at a stress level of 90% of the actual 0.2% proof stress of the material at test temperature, equaling a stress level of 712.8 N/mm2. Each specimen was placed in an autoclave filled with 250 ml of de-aerated test solution to fully immerse the test specimen gauge section. The autoclave was sealed and placed in the proof ring and each specimen was stressed to the desired test stress. The autoclave was de-aerated with oxygen-free nitrogen for two hours and then pressure tested to 60 bars with nitrogen. Following the pressure test, the nitrogen gas was vented from the autoclave. The solution was then saturated with 3.8 bar H2S gas at 100–200 ml per minute for two hours at room temperature (the pressure required to achieve 5.5 bar H2S partial pressure at the test temperature). The autoclave was then over-pressured with 28.4 bar of CO2, left for one hour to allow CO2 gas to absorb into the test solution, and re-pressured at 28.4 bars. The autoclave was then heated to 150°C ± 3°C and any excess pressure was bled from the autoclave. The autoclave pressure at the test temperature was 54 bars. The overall test duration was 720 hours. During this period, both autoclaves were monitored for temperature and pressure. Figure 3. Autoclave for ‘U’ bend specimen sour test with its schematic picture Table 3. Details of cut-piece samples sent to laboratory Grade Pipe dimension Lot no. Certificate no. Pipe test no. Sanicro™ 28 114.3 mm OD x 6.45 mm w/t 34672-6 A-03-008470 C121 Sanicro 28 (UNS N08028) 126 mm OD x 14 mm w/t 34594-2 A-03-008304 C120 5
  • 6. On completion of the test period, the autoclave was cooled down to room temperature, depressurized and the ‘U’ bend specimens were removed for examination. The ‘U’ bends were cleaned and assessed under a low power binocular microscope at 20X magnification. Test procedure tensile sour test The sulfide stress corrosion cracking tests were undertaken in accordance with ISO 7539-1 and ISO 7539-4. The tests were undertaken using Cortest Inc. ¼ liter autoclaves and calibrated proof rings, performed at a stress level of 90% of the actual 0.2% proof stress of the material, equaling a stress level of 787.5 N/mm2. Each specimen was placed in an autoclave filled with 250 ml of de-aerated test solution in order to fully immerse the test specimen gauge section.The autoclave was sealed and placed Test specimens were made of two sections of pipes representing tube: 114.3 mm OD x 6.45 mm w/t produced with lot number 34672-6; and coupling stock 126 mm OD x 14 mm w/t produced with lot number 34594-2. Two sub-sized specimens were machined for each pipe in accordance with ISO 7539-4:1989. The tensile specimens were identified by stamping with identification numbers, C123 and C125 for tube material and C122 and 124 for coupling stock material, to keep the traceability. in the proof ring, and each specimen was stressed to the desired test stress. The autoclave was de-aerated with oxygen-free nitrogen for two hours and then pressure tested to 60 bar with nitrogen. Following the pressure test, the nitrogen gas was vented from the autoclave. The solution was then saturated with H2S gas at 100 – 200 ml per minute for two hours at room temperature, and at 3.8 bar pressure (the pressure required to achieve 5.5 bar H2S at the test temperature). The autoclave was then over-pressured with 28.4 bar of CO2, left for 1 hour to allow the CO2 gas to absorb in the test solution and re-pressurized at 28.4 bars. The autoclave was then heated to 150°C ± 3°C and any excess pressure bled from the autoclave. The total pressure at the test temperature was 54 bars. The overall test duration was 720 hours. During this period, both autoclaves were monitored for temperature and pressure. Observation Test specimens were made of two sections of pipes representing tube: 114.3 mm OD x 6.45 mm w/t produced with lot number 34672-6; and coupling stock 126 mm OD x 14 mm w/t produced with lot number 34594-2. Two sub-sized specimens were machined for each pipe in accordance with ISO 7539-4:1989 (dimension as CTS-27). The tensile specimens were identified by stamping with identification numbers, C123 and C125 for tube material and C122 and 124 for coupling stock material, to keep the traceability. On completion of the test period, both autoclaves were cooled down to room temperature and vented to atmospheric pressure. Test specimens were removed, cleaned and examined under binocular microscope at 20X magnification. Result As we have predicted from literature studies, solution annealed and cold worked Sanicro 28 (UNS N08028) had performed very well under the test conditions. There were no cracks in all of the specimens tested after 720 hours exposure. Figure 4. Sour environment tensile test with proof ring and autoclave and its schematic diagram 6
  • 7. Specimen C122 (report TR 3030128A) Figure 5. Tensile test specimen view after 720 hours exposure in the test conditions. Specimens C120 A - E (report TR 3030128C) Figure 6. ‘U’ bend specimens after 720 hours exposure in the given test condition Purging the testing solution to remove oxygen is very important considering that oxygen could increase the corrosion rate very significantly, and this would not represent the actual operating condition in the oil/gas well, where oxygen content could be as low as 5 - 8 ppb. Consequently, this testing process was conducted very carefully to achieve optimum results. Sanicro 28 (UNS N08028) – with nickel content between 30.3 – 34 w.t.% and a Pitting Resistance Equivalent (PRE)** minimum of 38 – is suitable for medium to highly sour gas fields. Using a Sanicro 28 (UNS N08028) SSC diagram and NACE MR0175/ISO15156 guidelines as an initial stage of material selection is therefore very useful in order to identify whether solution annealed and cold worked Sanicro 28 (UNS N08028), can be used in the specified environment. For any CO2 partial pressure below 1,000 psi and/or pH higher than 2.9, it is possible to accept higher partial pressure of H2S in the environment. This also works for lower chloride content, so we can accept higher H2S partial pressure. Hence, returning to the Sanicro 28 (UNS N08028) SSC/SCC diagram at figure 3, the border line will move upwards to accept the higher partial pressure of H2S while considering the above pre-conditions. However, it is advised to perform sour corrosion test according to NACE TM 177 to qualify the material for such case(s). Due to a lengthy testing time of 720 hours, in addition to all other preparations, the total time required to complete the test report could be as long as 2 months or even more. This must be considered as part of the procurement timeframe by a project manager. Nevertheless, this step could help the company to make a decision on material selection and avoid premature failure of the production string. Hardness has an important role in the sensitivity of the corrosion resistant alloy to SSC phenomena. In this respect, NACE MR 0175/ISO 15156 also specifies maximum hardness acceptable for each type of material. Materials with slightly harder are still very much affected by the way the tube is produced in cold processes. Even though the average hardness of the material meets the specification, the variation of hardness in different locations within the tube wall – especially close to the skin – might be so high as to detrimentally effects SSC resistance. Sanicro 28 (UNS N08028) – 110 psi SMYS, which falls in ISO 13680/API 5CRA - 2010 category 27-31-4, gives different values depend on its Product Specification Level (PSL). ISO 13680/API 5CRA - 2010 PSL 1 gives a value of maximum HRC 35 according to table A.3. On the other hand, ISO 13680/API 5CRA - 2010 PSL 2 gives a value of maximum HRC 33 according to table A.27 and C.27. After gas production running for years, normally there would be some changes in the gas composition where pH2S and pCO2 would increase in some extent. However, considering there are so many margins between the current well conditions and service borderline of Sanicro 28 (UNS N08028), we can expect that Sanicro 28 (UNS N08028) is able to cope with SSC attacks in the longer run. Conclusion From the above findings and discussions, we can conclude: 1. Sanicro 28 (UNS N08028) – 110 ksi CRA material provided for the test is sufficient to resist corrosion attack in the client’s field environment, as described in the test condition, though there might be changes in gas composition for long run. 2. ISO 7539-1/3/4 test procedures are viable to be part of a project as long as there is sufficient time allocated for the test. In fact, this test was completed in 2.5 months due to a very busy test schedule at the laboratory. 7
  • 9. Appendix 1 LAB DATA CHART FOR MATERIAL Sanicro™ 28 (126 mm O.D. X 14 mm wt) TESTED PER NACE STANDARD TM0177-96 (Method A, Tensile test) (1) SPECIMEN GEOMETRY [ ] STANDARD [ √ ] SUB-SIZE TENSILE NOMINAL DIAMETER 3.08/3.81mm GAUGE LENGTH TEST EQUIPMENT[ √ ] SUSTAINED LOAD - PROOF RING [ ] POSTTEST PROOF RING DEFLECTION MEASUREMENT CHEMISTRY [ ] SOLUTION A [ ] SOLUTION B [ √ ] OTHER SOLUTION [ √ ] OUTLET TRAP TO EXCLUDE OXYGEN? [ √ ] TEMPERATURE MAINTAINED 150˚C ± 3˚C SPECIMEN PROPERTIES TIME (HOURS TO FAILURE AT % YIELD) NF = No Failure at 720 hours Solution pH (5) Heat Treat Applied Remarks Material Identification (2) Ioc (3) Orn Y.S.(4) (N/mm²) T.S. (N/mm²) EI % RA % Hardness HRC 70 80 90 Start Finish C 122 792 N.F. 5.5 bar H2S 41 bar CO2 C 124 792 N.F. 5.5 bar H2S 41 bar CO2 NOTES: (1) Test method must be fully described if not in accordance with NACE Standard TM0177. (2) Location of specimen from test piece may be O.D., Mid-Radius (MR), Centre (C), Edge (E). (3) Orientation may be longitudinal (L) or transverse (T). (4) Yield strength is assumed to be 0.2% offset unless otherwise noted. (5) Enter pH for test conducted on passing specimen at highest stress if summarizing data. 1
  • 10. Appendix 2 LAB DATA CHART FOR MATERIAL Sanicro™ 28 (114 mm O.D. X 6.45 mm wt) TESTED PER NACE STANDARD TM0177-96 (Method A, Tensile test) (1) SPECIMEN GEOMETRY [ ] STANDARD [ √ ] SUB-SIZE TENSILE NOMINAL DIAMETER 3.79/3.80mm GAUGE LENGTH TEST EQUIPMENT [ √ ] SUSTAINED LOAD - PROOF RING [ ] POSTTEST PROOF RING DEFLECTION MEASUREMENT CHEMISTRY [ ] SOLUTION A [ ] SOLUTION B [ √ ] OTHER SOLUTION [ √ ] OUTLET TRAP TO EXCLUDE OXYGEN? [ √ ] TEMPERATURE MAINTAINED 150˚C ± 3˚C SPECIMEN PROPERTIES TIME (HOURS TO FAILURE AT % YIELD) NF = No Failure at 720 hours Solution pH (5) Heat Treat Applied Remarks Material Identification (2) Ioc (3) Orn Y.S.(4) (N/mm²) T.S. (N/mm²) EI % RA % Hardness HRC 70 80 90 Start Finish C 123 875 N.F. 5.5 bar H2S 41 bar CO2 C 125 875 N.F. 5.5 bar H2S 41 bar CO2 NOTES: (1) Test method must be fully described if not in accordance with NACE Standard TM0177-96. (2) Location of specimen from test piece may be O.D., Mid-Radius (MR), Centre (C), Edge (E). (3) Orientation may be longitudinal (L) or transverse (T). (4) Yield strength is assumed to be 0.2% offset unless otherwise noted. (5) Enter pH for test conducted on passing specimen at highest stress if summarizing data. 2
  • 12. Appendix CHEMICAL ANALYSIS Material Test Plan Acceptance criteria ASTM B 668 UNS N08028 Element required C % Si % Mn % P % S % Cr % Ni % Mo % Cu % Fe % N % Test frequency Min 26.0 30.3 3.0 0.6 Remain der ISO 13680 para 10.4 Max 0.020 0.6 2.5 0.025 0.020 28.0 34.0 4.0 1.4 0.10 1 test/heat Tolerances on product analysis as per ASTM B829. Test frequency of product analysis 2 tests/lot (ISO 13680 para 10.4) Type of test Specification MECHANICAL TESTS Number of tests Type of sample Acceptance criteria Tensile test at room temperature ISO 13680 para 11.2 referring to ISO 6892 and table 3 para 8.3.1, 10.5.2, 10.5.3.1 1 test/lot (lot max 50 pipes, ISO 13680 tab 13) STRIP LONGITUDINAL DIRECTION min max Yield strength 0.2% (Rp 02) Tensile strength (Pm) Elongation on 2” Mpa 760 (110 ksi) 965 (140 ksi) Mpa 795 (115 ksi) % 11 Hardness test ISO 13680 PARA 8.3.1 table 3 four quadrants 1 test/lot ISO 13680 para 11.3 figure 5, 10.5.3.3 on ring HRC 33 Hardness variation among values ISO 13680 PARA 8.3.1 table 4 HRC 3 (will be applied on quadrants at the same sample lot only) Type of test Specification LABORATORY TESTS Number of tests Type of sample Acceptance criteria Micrographic examination ISO 13680 para 11.6.1 ASTM E 562 1 test/lot Polished test piece hold in bakelit. ISO 13680 para 10.5.36 Microstructure test ISO 13680 Para 8.5.3 Mass correction factor from the manufacturer: α = 1.0204 refer to ISO 13680:2010(E) para 9.1.1 ** Pitting Equivalent Number = %Cr + 3.3 x %Mo + 16 x %N is a number to rank CRAs against Pitting corrosion attacks which correspond to Stress Corrosion Cracking attacks in chloride environments. 10
  • 13. References 1. Hans Eriksson and J, Michael Nicholls Sandvik Materials Technology AB R&D Center, S81181 Sandviken Sweden Testing and selection of duplex stainless steels for sour environments NACE Corrosion conference, Corrosion 91, March 91, Houston, TEXAS 2. Hans Eriksson and Sven Bernhardsson Sandvik Materials Technology AB R&D Center, S81181 Sandviken Sweden Testing and selection of duplex stainless steels for sour environments NACE Corrosion conference, Corrosion 91, March 91, Houston, TEXAS 3. C. Bradshaw and M.Peet. Sheffield Testing Laboratory, Sheffield, United Kingdom Report on Autoclave Testing of Sanicro 28 (UNS N08028) material Report number TR 3110428 A/B/C 17 November 2003 for Sandvik Materials Technology UK 4. Sven Bernhardsson, Jan Oredsson and Carl Carlborg Sandvik Materials Technology AB R&D Center, S81181 Sandviken Sweden Performance of Ni-Fe-Cr-Mo alloy in sour Oil and Gas applications Paper 225, NACE Corrosion Conference, Corrosion 85, Boston, MA, March 25-29, 1985 5. Jean-Louis Crolet and Michel R. Bonis Elf Exploration Production, France. How to pressurize autoclaves for corrosion testing under CO2 and H2S pressure Paper 102 Corrosion 98, NACE Corrosion conference, June 9-11, 1998 San Diego, CA. 6.Guocai Chai Sandvik Materials Technology AB R&D Center, S81181 Sandviken Sweden Tensile properties, Sanicro 28 (UNS N08028), High temperature Technical report document no. T010690 7. NACE INTERNATIONAL, Houston Texas. NACE MR 0175/ISO 15156-1:2001 Specification Petroleum and natural gas industries – Materials for use in H2S-containing Environments in oil and gas production Part 1 : General principles for selection of cracking-resistant materials. ISBN 1-5759-1765 8. NACE INTERNATIONAL, Houston Texas. NACE MR 0175/ISO 15156-3:2003 Specification Petroleum and natural gas industries – Materials for use in H2S-containing Environments in oil and gas production Part 3 : Cracking-resistant CRAs (corrosion-resistant alloys) and other alloys ISBN 1-5759-1765 9. NACE INTERNATIONAL, Houston Texas NACE TM 177-96 Standard test method: “ Laboratory testing of metals for Resistance to Sulfide stress cracking and Stress corrosion cracking in H2S environment” ISBN 1-57590-036 Sandvik and Sanicro are trademarks owned by Sandvik Intellectual Property AB. 11
  • 14. SANDVIK MATERIALS TECHNOLOGY SE-81 I 81 Sandv1 ken, Sweden, Phone +46 26 26 00 00, Fax +46 26 26 02 20 www.smt.sandv1k.eom