Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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A SEAMLESS STEEL TUBE FOR THE APPLICATION AS WORK-
OVER RISER
FIELD OF THE INVENTION
This invention relates to a seamless steel tube for risers
used in work-over operations.
BACKGROUND OF THE INVENTION
The requirements for operating a well in the seabed involve
a plurality or systems and equipment including drilling,
production and work-over risers.
A drilling riser is a pipe between a seabed blow-out
preventer (BOP) and a floating drilling rig which is a drilling unit
not permanently fixed to the seabed such as a drillship, a semi-
submersible or jack-up unit. A drilling rig is meant to be the
derrick and its associated machinery.
A production riser is a pipeline carrying oil or gas that joins
a seabed wellhead to a deck of a production platform or a tanker
loading platform.
A work-over riser is a flowline which is used to carry on a
well work-over, which is performed on an existing well and may
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involve re-evaluating the production formation, clearing sand
from producing zones, jet lifting, replacing downhole equipment,
deepening the well, acidizing or fracturing or improving the drive
mechanism.
In recent years such work-over operations have been
increasingly carried out using coiled or continuous reel tubing as
disclosed in US4281716 (Standard Oil Co. Indiana).
However, according to W09816715 (Kvaerner Eng.), there
are several advantages using a continuous single tube when
entering a live oil or gas well. This means the well does not have
to be killed, (i.e. a heavy fluid does not have to be pumped down
the production tubing to control the oil or gas producing zone by
the effect of its greater hydrostatic pressure). Continuous tubing
has the advantage of also being able to pass through the tubing
through which the oil and/or gas is being produced, without
disturbing the tubing in place.
Taking in account that work-over risers are subjected to
fatigue and load stresses besides of corrosion attack, pipes used
in this environment are likely to have fatigue and corrosion
resistance properties to accomplish a good performance, reduce
both, the weight of the riser string and the bending loads in the
wellhead and the platform interface.
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Also, these pipes need to have a good welding performance
just to be welded to weld-on-connectors to build the string.
OBJECT OF THE INVENTION
A first object of the invention is to provide a seamless steel
tube to be used as a riser in work-over operations with a specific
chemistry design and microstructure consisting of a geometry in
which ends of the tube have an increased wall thickness and
outer diameter to reduce the weight of the riser string.
A second object is to provide a seamless steel tube for the
application as a work-over riser with a specific chemistry design
and microstructure consisting of a geometry in which ends of the
tube have an increased wall thickness and outer diameter to
reduce the bending loads in the wellhead and the platform
interface.
A third object of the invention is to provide a method of
manufacturing of a seamless steel tube for the application as a
work-over riser with a specific chemistry design and
microstructure consisting of a geometry in which ends of the tube
have an increased wall thickness and outer diameter using
upsetting techniques.
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A fourth object of the invention is to provide a method of
manufacturing of a seamless steel tube for the application as a
work-over riser with a specific chemistry design and
microstructure consisting of a geometry in which ends of the tube
have an increased wall thickness and outer diameter using
machining techniques.
A fifth object of the invention is to provide a method of
manufacturing of a seamless steel tube for the application as a
work-over riser with a specific chemistry design and
microstructure consisting of a geometry in which ends of the tube
have an increased wall thickness and outer diameter able to
guarantee the mechanical characteristics to have high fatigue
and corrosion resistance and a good welding performance.
Also, the tubes used as work-over risers may be reused
meaning an economical saving.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 illustrates a preferred embodiment of the work over
riser of the present invention with upset ends.
Figure 2 shows a graphical representation of the Tensile
test results (YS and UTS) from upset and pipe body sections from
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material in the as-quenched and tempered condition of the
different industrial trials.
Figure 3 shows a graphical representation of the HRC
hardness values from upset and pipe body sections showing the
achievement of the minimum % of martensitic transformation from
material in the as-quenched condition of the production of both
dimensions.
Figures 4 and 5 show a graphical representation of the HRC
hardness values from upset and pipe body sections showing the
individual hardness readings dispersion as a function of the
location through the thickness (OD, MW & ID) from material in the
as- tempered condition of the production of 7"OD x 17.5 mm WT
dimension and 8 5/8" OD x 15.9mm WT dimension, respectively.
Figure 6 shows a graphical representation of the transverse
CVN impact testing results at -20 C from upset and pipe body
sections of the production of both dimensions showing the
individual toughness values dispersion as per specification from
material in the as-tempered condition.
Figure 7 shows the austenitic grain size reported in 9/10
ASTM in the pipe body and 8/9 ASTM in the upset end.
Figure 8 shows transverse section photomicrographs
showing a microstructure constituted by martensite through the
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wall thickness of the pipe body section of quenched material for
Nital 2% in 300X magnification.
Figure 9 shows transverse section photomicrographs
showing a microstructure constituted by martensite in the upset
end of as-quenched material for Nital 2% in 300X magnification.
Figure 10 shows transverse section photomicrographs,
showing a microstructure constituted by tempered martensite in
the pipe body of quenched & tempered material for Nital 2% in
300X magnification.
Figure 11 shows transverse section photomicrographs,
showing a microstructure constituted by tempered martensite in
the upset end of quenched & tempered material for Nital 2% in
300X magnification.
Figure 12 shows microstructural observations of as
quenched material at the pipe machined body and the end zones
revealing a prior austenitic grain size of 8/9 in both zones
measured by the saturation method as per ASTM E-1 12.
Figure 13 shows transverse section photomicrographs
showing a microstructure constituted by martensite through the
wall thickness of the machined pipe body section of quenched
material for Nital 2% in 300X magnification.
Figure 14 shows transverse section photomicrographs
showing a microstructure constituted by martensite through the
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wall thickness of the pipe end section of quenched material for
Nital 2% in 300X magnification.
Figure 15 shows transverse . section photomicrographs
showing a microstructure constituted by tempered martensite
through the thickness of the pipe body section of quenched and
tempered material. for Nital 2% in 300X magnification.
Figure 16 shows transverse section photomicrographs
showing a microstructure constituted by tempered martensite
through the thickness of the pipe end section of quenched and
tempered material for Nital 2% in 300X magnification.
BRIEF SUMMARY OF THE INVENTION
The present invention describes a seamless steel tube to
be used as a riser in work-over operations with a specific
chemistry design and microstructure consisting of a geometry in
which ends of the tube have an increased wall thickness and
outer diameter. The alloy design is based on high strength
requirements. The main features of the chemical composition of
the tube include 0.23-0.28 wt % C, 0.45 -0.65 wt % Mn, and other
alloying elements such as Mo, and Cr to achieve the required
percentage of martensitic transformation. In addition,
microalloying elements such as Ti and Nb are used as grain
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refiners. Low content of residual elements such as S and residual
elements such as Cu and P are used to avoid any corrosion
problem related to inclusions promotion and segregation at grain
boundaries which decrease the corrosion performance, the
hydrogen content was kept below 2.4 ppm to avoid any problem
related to hydrogen entrapment and decrease of the corrosion
performance.
The production route for manufacturing the upset seamless
pipe for the application of as Work Over Riser, includes the
following steps: steel casting (Continuous Cast Bar), seamless
pipe rolling (MPM process), pipe ends upsetting, heat treatment,
destructive testing (including microcleanliness, austenitic grain
size, calculate % of martensitic transformation, tensile, hardness,
toughness, SSC testing), dimensional control of pipe body and
upset ends (outside diameter, out of roundness, excentricity,
straightness, internal diameter, length), machining of external
and internal upset end, dimensional control (internal diameter,
outside diameter and machined length), drift testing at the upset
ends, non-destructive testing (NDT) of upset ends, weighing,
measuring and marking, external surface visual inspection, UT
inspection of pipe body and UT inspection of upset ends
(cylindrical section only).
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The production route for manufacturing the machining
seamless pipe for the application of as Work Over Riser includes
the following steps: steel casting (Continuous Cast Bar),
seamless pipe rolling (MPM process), heat treatment, destructive
testing (including microcleanliness, austenitic grain size,
calculate % of martensitic transformation, tensile, hardness,
toughness, SSC testing), dimensional control of pipe body
(outside diameter, out of roundness, straightness, internal
diameter, length), machining from external surface the complete
length of the pipe by programming CNC lath machine in order to
achieve final dimensions at the ends, dimensional control
(internal diameter, outside diameter, out of roundness,
straightness, and length) of pipe body and machined ends, drift
testing at the ends, non-destructive testing (NDT) of ends,
weighing, measuring and marking, external surface visual
inspection, UT inspection of machined pipe body and UT
inspection of ends (cylindrical section only).
The combination of chemical composition and tight control
of heat treatment parameters allows achieving the adequate
microstructure after quench and temper in order to achieve the
mechanical properties and pass the SSC Method A tests
requirements described above.
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DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
OF THE INVENTION
The chemical composition of the seamless steel tube of the
present invention comprises in weight per cent: carbon 0.23-0.29,
manganese 0.45-0.65, silicon 0.15-0.35, chromium 0.90-1.20,
molybdenum 0.70- 0.90, nickel 0.20 max, nitrogen 0.010 max,
boron 0.0010-0.0030, aluminum 0.010-0.045, sulfur 0.005 max,
phosphorus 0.015 max, titanium 0.005-0.030, niobium 0.020-
0.035, copper 0.15 max, arsenic 0.020 max, calcium 0.0040 max,
tin 0.020 max, hydrogen 2.4 ppm max, the rest are iron and
inevitable impurities.
A more preferred composition comprises: carbon 0.25-0.28,
manganese 0.48-0.58, silicon 0.20-0.30, chromium 1.05-1.15,
molybdenum 0.80- 0.83, nickel 0.10 max, nitrogen 0.008 max,
boron 0.0016-0.0026, aluminum 0.015-0.045, sulfur 0.0030 max,
phosphorus 0.010 max, titanium 0.016-0.026, niobium 0.025-
0.030, copper 0.10 max, arsenic 0.020 max, calcium 0.0040 max,
tin 0.015 max, hydrogen 2.0 ppm max, the rest are iron and
inevitable impurities.
The seamless steel tubes have a geometry, in which ends
of tubes have an increased wall thickness and outer diameter,
and following mechanical properties:
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In the as-quench condition
90% of martensitic transformation when evaluated
according to the following formulae: HRCmin = (58 x %C) + 27
Austenitic grain size as per ASTM minimum 5 or finer
In the as-quench and temper condition
Longitudinal Tensile Test (round standard specimens when
wall thickness equal or above 1" and longitudinal strip specimens
when wall thickness below 1").
Minimum Yield Strength: 90ksi (620 MPa)
Maximum Yield Strength: 105ksi (724 MPa)
Minimum Ultimate Tensile Strength: lOOksi (690 MPa)
Minimum Elongation (L = 4D): 18%
Yield to Tensile Ratio < 0.92
Transverse Charpy Test (using 10x10 mm specimen)
Minimum individual Absorbed Energy: 30 Joules
Minimum Average Absorbed Energy: 40 Joules
Maximum Hardness value: 25.4 Hrc (value as per API 5CT
means average per row)
Microcleanliness acceptance criteria as per ASTM E-45 A:
A, B, C, D all below 2
Compliance with NACE, acceptance criteria: Passing SSC
Method A test as per NACE TM0177-2005, using test solution (A),
testing at 85%SMYS, test period 720 hours.
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The geometry of seamless steel tube of the present
invention and the mechanical characteristics are obtained by two
methods of manufacturing: upsetting and machining.
The upsetting manufacturing method comprises the
following steps:
(a) providing a steel tube containing a composition in
weight per cent, carbon 0.23-0.29, manganese
0.45-0.65, silicon 0.15-0.35, chromium 0.90-1.20,
molybdenum 0.70- 0.90, nickel 0.20 max, nitrogen
0.010 max, boron 0.0010-0.0030, aluminum 0.010-
0.045, sulfur 0.005 max, phosphorus 0.015 max,
titanium 0.005-0.030, niobium 0.020-0.035, copper
0.15 max, arsenic 0.020, calcium 0.0040 max, tin
0.020 max, hydrogen 2.4 ppm max, the rest are
iron and inevitable impurities, obtained by rolling
process (MPM process)
(b) upsetting of tube ends;
(c) austenitizing between 850-930 C the full length of
the tube; and
(d) quenching and tempering between 630-720 C
(e) destructive testing (including microcleanliness,
austenitic grain size, calculate % of martensitic
transformation, according to the formulae HRCmin
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_(58 x %C) + 27 , tensile, hardness, toughness,
SSC testing)
(f) dimensional control of pipe body and upset ends
(outside diameter, out of roundness, eccentricity,
straightness, internal diameter, length)
(g) machining of external and internal upset end
(h) dimensional control (internal diameter, outside
diameter and machined end)
(i) drift testing at the upset ends
(j) non-destructive testing of upset ends, weighing,
measuring and marking, external surface visual
inspection, UT inspection of pipe body and UT
inspection of upset ends.
The machining manufacturing method comprises the
following steps:
(a) providing a steel tube containing a composition in
weight per cent, carbon 0.23-0.29, manganese
0.45-0.65, silicon 0.15-0.35, chromium 0.90-1.20,
molybdenum 0.70- 0.90, nickel 0.20 max, nitrogen
0.010 max, boron 0.0010-0.0030, aluminum 0.010-
0.045, sulfur 0.005 max, phosphorus 0.015 max,
titanium 0.005-0.030, niobium 0.020-0.035,
copper 0.15 max, arsenic 0.020, calcium 0.0040
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max, tin 0.020 max, hydrogen 2.4 ppm max, the
rest are iron and inevitable impurities, obtained by
rolling process (MPM process
(b) heat treatment o pipes (austenitizing between
850-930 C the full length of the tube; and
quenching and tempering between 630-720 C)
(c) destructive testing (including microcleanliness,
austenitic grain size, calculate % of martensitic
transformation according to the formulae , tensile,
hardness, toughness, SSC testing)
(d) dimensional control of pipe body (OD, out of
roundness, straightness, ID, length)
(e) machining from external surface the complete
length of the pipe by programming CNC lath
machine in order to achieve final dimensions at
the ends,
(f) dimensional control (ID, OD, out of roundness,
straightness and length) of pipe body and
machined ends
(g) drift testing at the ends,
(h) non destructive testing (NDT) of ends, weighing,
measuring and marking, external surface visual
inspection, UT inspection of machined pipe body
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and UT inspection of machined ends (cylindrical
section only).
Both methods are also performed providing a seamless
steel pipe with the preferred composition, as disclosed above.
The seamless steel tube of the present invention may be
divided into two zones. As shown in Figure 1, there is an
increased wall thickness and diameter end with internal and
external length (upsetting or machined zone) and the tube body.
Due to a combination of the manufacturing methods and the
chemistry design, both the whole tube body and the ends have
the same yield strength of at least 620 MPa (90 ksi) (YS) and at
most 724 MPa (105 ksi), a Yield to Tensile Ratio not greater than
0.92, also, the same ultimate tensile strength (UTS) of at least
690 MPa (100 ksi), elongation of at least 18%, hardness Rockwell
of at most 25.4 HRC (value as per API 5CT means average per
row) and corrosion resistance (Compliance with NACE,
acceptance criteria: Passing SSC Method A test as per NACE
TM0177-2005, using test solution (a), testing at 85%SMYS, test
period 720 hours). Prior Austenitic Grain Size is 5 or less. The
product after the quench heat treatment process shall comply
with Prior Austenitic Grain Size (PAGS) is 5 or less a
microstructure of at least 90% martensite in the as-quench
condition.
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The tubes may be utilized in sour and non-sour service.
The tubes' nominal diameter to be upsetted ends may be
from 4'/z" to 10 W.
The tubes' nominal diameter which ends will to be
machined may be from 4'/z" to 18" due to the manufacturing
facilities.
The tubes' thickness ranges from 10 mm to 50 mm.
Examples
Example 1
Two industrial development trials for two dimensions of
tubes (8 5/8" ODx15.9 mm WT and 7" OD x 17.5 mm WT) were
carried on. The chemistry design is shown in Table 1 and the
desired ranges of mechanical properties are shown in Table 2.
Table 1
Element Minimum Maximum
C 0.25 0.28
Mn 0.48 0.58
Si 0.20 0.30
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P 0 0.010
S 0 0.0030
Mo 0.80 0.83
Cr 1.05 1.15
Nb 0.025 0.030
Ni 0 0.10
Cu 0 0.10
Sn 0 0.015
Al 0.015 0.045
Ti 0.016 0.026
As 0 0.020
Ca 0 0.0040
B 0.0016 0.0026
N 0 0.008
H 0 2.0
Table 2
Property Min Max
Yield Strength EUL 0.5% (MPa) 620 724
Ultimate Tensile Strength (MPa) 690 n/a
Yield to Tensile Ratio (Y/T) 0.92
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Elongation (%) (L=4D) 18 -
Individual Absorbed Energy At -20 C (J) 30 -
Average Absorbed Energy At -20 C (J) 40 -
Hardness Rockwell HRC-value (tempered n/a 25.4*
condition)
Microcleanliness (acceptance criteria as - 2
per ASTM E-45A: A, B, C, D)
Corrosion Test Solution
period
NACE TM0177-2005 SSC Method A- 85% 720 hrs. A
SMYS
*API 5CT: value= average per row
The upsetting manufacturing operation was performed
following the steps of:
a) The pipe ends in the as-rolled condition were heated up
to the appropriate forging temperature heating the
calculated pipe length. The upsetting operation takes
place at a minimum temperature of 1000 C.
b) Once the heating cycle was accomplished, pipe ends
were upset with the appropriate die and tooling design
for each particular dimension.
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C) Inspection was then made on pipes' external and
internal surfaces after each strike/punch in order to find
any possible defect generated by the upsetting
operation.
Special care was taken into consideration when designing
the heating curve to be use during the heat treatment process in
the austenitizing furnace (860-940 C) and the tempering furnace
(640-720 C) for the upset ends of the 8 5/8"OD product. After
austenitizing heat treatment process, the pipe must enter the
quenching process above AC3 to guaranteed through-wall
transformation. Then, for the 7"OD product, a few heat treatment
adjustments were made on the heating curves based on the
results obtained from the other dimension 8 5/8" OD pipe.
The actual temperatures from the pipe body and upset ends
outer surface were carefully measured throughout the trial stages
right at the entrance of the pipes into the quenching head by
using a manual pyrometer in addition to the furnace pyrometers.
After the heat treatments, a mechanical characterization
was performed. From the as-quenched material, the % of
martensitic transformation was calculated. Tensile, hardness, and
toughness tests were performed on the quenched and tempered
material on both upset and pipe body sections. Specifications
were met; good hardenability, yield strength values of over 92 ksi
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as-tempered HRC values below the maximum allowed (25.4 HRC)
and absorbed energy higher than 100 Joules at the specified
temperature of -20 C.
Extensive destructive characterization and corrosion SSC
Method A (NACE Standard Tensile Test, TM0177-96) were also
conducted.
Homogeneity in tensile properties, hardness and toughness
test results are a consequence of a very homogenous
microstructure through the wall on both upset end and pipe body
in the as quenched and tempered condition. Figures 2 through 5
illustrate several graphical representations of the mechanical
properties including hardness.
The austenitic grain size was measured on as-quenched
material by the saturation method as per ASTM E-112. As shown
in Figure 6, the grain size reported on the samples were 9/10 in
the pipe body which was above the required size since the
minimum required was 5. The upset samples showed a grain size
of 8/9 and 9/10 complying with the specifications as illustrated in
Figure 6.
The transversal face to the rolling axis was
metallographically prepared and etched with Nital 2% to perform
microstructural observations with an optical microscope. (Nital:
Solution of 2% of Nitric acid in Ethyl Alcohol).
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In the as-quenched samples, a martensitic microstructure
was observed on OD, ID and MW sections through the thickness
achieving a martensitic transformation of over 90% measured
from the HRC hardness values as shown in Figures 8 and 9.
In the as-quench and tempered material, a microstructure
constituted by tempered martensite was observed through the
thickness as shown in Figures 10 and 11.
The microstructures observed in as-quenched material were
mainly martensitic with over 95% of martensitic transformation
through the entire thickness of the pipe on both pipe body and
upset which indicates that the temperature at which the pipe
entered the quenching stage and the quenching itself were
homogeneous. On the other hand, the microstructures observed
in tempered material, tempered martensite was present through
the thickness.
The material passed the SSC Method A test at 85%SMYS
as per NACE TM0177-96 accomplishing the 720 hours.
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Corrosion Testing Results as per NACE Method A
NACE TM-0177-96 Method A
Initial Final Stress
Sample Location Heat Specimen Diameter Initial PH Diameter Final PH Applied
Result
SMYS %
98449 Upset 19874 A 6,39 2,69 6,21 3,64 85 NF*
98449 Upset 19874 B 6,42 2,69 6,33 3,62 85 NF*
98449 Upset 19874 C 6,4 2,69 6,29 3,69 85 NF*
8448 Pipe Body 19874 A 6,36 2,66 6,24 3,53 85 NF*
8448 Pipe Body 19874 B 6,41 2,66 6,31 3,51 85 NF*
8448 Pipe Body 19874 C 6,4 2,66 6,29 3,52 85 NF*
98448 Upset 19874 A 6,37 2,66 6,22 3,5 85 NF*
98448 Upset 19874 B 6,37 2,66 6,2 3,5 85 NF*
98448 Upset 19874 C 6,4 2,66 6,33 3,49 85 NF*
*NF: Not failed
Example 2
An industrial development trial for a dimension of tube
(8.26" OD x 44 mm WT and 9.97" OD x 41 mm WT) were carried
on. The chemistry design is shown in Table 1 and the desired
ranges of mechanical properties are shown in Table 2 of Example
1.
The pipe was rolled in a heavy wall condition. The wall
thickness was about 44 mm.
After rolling, heat treatment is performed. Similar
considerations about this step were made such as in Example 1
to obtain through wall transformation.
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After heat treatment of pipes, detail mechanical
characterization was performed such as in Example 1.
Dimensional control of the outside diameter (OD), out of
roundness, inside diameter (ID) and length of pipes was carried
on followed by the UT inspection.
In order to achieve final dimensions, the complete length of
pipe body was machined from external surface by programming
CNC lath machine.
Once again, a dimensional control of pipes after machining
was carried out.
For quality purposes, non destructive inspection of straight
pipe body section using automatic UT and manual for the
cylindrical ends.
As in Example 1, a mechanical characterization was
performed, calculating the % of martensitic transformation from
the as-quenched material. On the quenched and tempered
material, tensile, hardness, and toughness tests were performed
on both machined ends and pipe body sections. Specifications
were met; good hardenability, yield strength values of over 94 ksi
as-tempered HRC values below the maximum allowed (25.4 HRC)
and absorbed energy higher than 100 Joules at the specified
temperature of -20 C.
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Extensive destructive characterization and corrosion SSC
Method A (NACE Standard Tensile Test, TM0177-96) were also
conducted.
Homogeneity in tensile properties, hardness and toughness
test results are a consequence of a very homogenous
microstructure through the wall on both machined ends and pipe
body in the as quenched and tempered condition.
Microstructural observations of as-quenched material at the
pipe machined body and the ends zones reveal a prior austenitic
grain size of 8/9 in both zones measured by the saturation
method as per ASTM E-112. The modified end on the analyzed
sample showed a grain size of 8/9 complying with the
specifications as shown in Figure 12.
The transversal face to the rolling axis was
metallographically prepared and etched with Nital 2% to perform
microstructural observations with an optical microscope. (Nital:
Solution of 2% of Nitric acid in Ethyl Alcohol).
In the as-quenched sample, a martensitic microstructure
was observed on OD, ID and MW sections through the thickness
achieving a martensitic transformation of over 90% measured
from the HRC hardness values as shown in Figures 13 and 14.
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In the as-quench and tempered material, a microstructure
constituted by tempered martensite was observed through the
thickness as shown in Figures 15 and 16.
The material passed the SSC method A test at 85%SMYS
as per NACE TM0177-2005 accomplishing the 720 hours.
