Note: Descriptions are shown in the official language in which they were submitted.
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A SEAMLESS STEEL TUBE FOR USE AS A STEEL CATENARY
RISER IN THE TOUCH DOWN ZONE
FIELD OF THE INVENTION
This invention relates to seamless steel tubes for use as steel
catenary riser.
BACKGROUND OF THE INVENTION
In recent years, the interest in exploiting deeper water off-
shore oilfields has increased sensibly. As a consequence, various
solutions of marine production systems have been developed. The
currently-available solutions are directed generally to semi-floating
and floating production systems which are subjected to various
movements with respect to seabed, mainly due to marine waves,
currents and tides phenomena. The aforementioned systems are
complemented by compliant riser systems compatible with mobile
surface stations.
Steel Catenary Risers (SCR) represents one of the most
outstanding riser systems to be adopted in these challenging
situations. Such component is normally subjected to complex
spectra of fatigue loading related to both the mobility of the floating
platform and to the very large free span of unconstrained line from
the seabed to surface. As a consequence, a big concern in the
design of a SCR is related to the fatigue resistance. Since the cyclic
loading is predominately in the axial direction, it directly stresses
the welded joints between abutting pipes. Such joints generally
represent the weakest point with respect to fatigue resistance, and
the design life of the whole riser is determined by the capability of
this component to resist the fatigue loading.
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Steel Catenary Riser is a proven and economic riser system
solution, as a tie-back production riser and as an export riser from
Floating Production Systems (FPS) in the development of oil and
gas fields in deepwater and ultra-deepwater. The application of
SCRs is challenged by, in some cases, the high fatigue damage at
the Touch Down Zone (TDZ) from a combination of field specific
parameters such as riser size, fluid characteristics, vessel motions,
metocean parameters, soil conditions, and water depth.
The most severe design requirement for SCRs is the fatigue
life of the girth welds at the Touch-Down Zone (TDZ) region where
the riser touches the seafloor and it connects with the rest of the
pipeline, as is illustrated in Figure 1. In this zone, the riser
experiences the highest level of cumulative fatigue damage. This is
due to the fact that in said zone the highest bending of the catenary
line is experienced, contrary to the total absence of bending of the
portion of the line lying on the seabed. Due to the various
movements of FPS (waves, tides, currents, etc.), the line segment in
the TDZ experiences cycles of bending between maximum riser
bending and zero bending (straight). The severity of fatigue loading
in the TDZ is further complicated by the presence of continuous
impacts of the portion of the line when entering in contact with the
ground. Moreover, it has to be considered that the same impact of
the line could dig a hole just in correspondence of the TDZ,
amplifying the amplitude of bending cycle.
In other words, constant motion by the topside floating vessel
results in cyclic pounding for the riser against the sea-floor that, if
not properly designed, can result in fatigue failure. In addition to the
riser motion, other factors that can increase the severity of the TDZ
fatigue include large pipe diameter, deep water depth, high currents,
and sour service (corrosion degradation).
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Various possible solutions for the improvement of fatigue life
at SCR TDZ have been devised and studied. SCRs are utilized as
riser systems in ongoing semi-submersible projects.
Alternative options to obtain an increase in fatigue life at the
TDZ in the deepwater field developments have been devised to
enable the use of SCR. These solutions include: ID machining for
better fit-up and the use of improved welding techniques; the use of
thick forged ends welded onshore to ensure better fit-up and to
reduce the Stress Concentration Factor (SCF); the periodic
movement of the floating vessel to distribute fatigue damage over
longer length at the TDZ; and the use of clad steel.
The upsetting process is commonly used in the industry for
casing and riser joints with threaded ends. Steel grades with higher
carbon content are normally used for these applications. The
upsetting process has not been used so far for weldable pipe of SCR
quality. In most of threaded cases, though, the increase in fatigue
life has been limited to a factor between 2 to 3. In the case of clad
steel applications, a higher increase in fatigue life can be achieved.
In addition, alternative catenary riser design has been developed by
changing the riser pipe material (composite, titanium) or by hybrid
designs (titanium and steel), or by changing the shape near seabed
through provision of significant buoyancy (W097/06341).
The alternative designs have focused on the improvement of
the catenary riser strength near and above the seabed, thus
enabling their use in harsher environment and more challenging
applications.
Thus, there is a need to enhance conventional Steel Catenary
Risers for Touch Down Zone (SCR TDZ) design for achieving
significant increase in fatigue life, particularly, increasing fatigue life
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in SCR TDZ above 3 under sour and non-sour service environments
with a pipe consisting of three regions: pipe body, transition zone
and upset end, as is illustrated in Figure 2.
To accomplish this need, upset pipes to be used in welded
joints have been developed. The simple concept for the improved
fatigue performance consists, in this case, in locally decreasing the
stress experienced by the welding with respect to the stress range
generally experienced by the pipe body and, hence, the section of
the riser in the TDZ. An upset SCR of novel low carbon chemical
composition and microstructure was thus devised to achieve higher
improvement in the fatigue life as it is comprised with the riser pipe
section.
The feasibility of manufacturing thick upset end Riser for the
Touch Down Zone with improved fatigue resistance varies,
nevertheless, with the grade of steel that can be welded for offshore
applications. The feasibility to manufacture a thick end Riser for the
Touch Down Zone with improved fatigue resistance is the key to
ensure that the upset SCR has practical value in application at the
TDZ.
Several Steel Catenary Riser (SCR) solutions have included
mild sour service requirements. Sour Service is the performance of
the Riser in H2S environments. Metallurgical properties known to
affect performance in H2S containing environments include:
chemical composition, steel cleanliness, method of manufacturing,
strength, amount of cold work, heat treatment conditions and
microstructure. Since the upset pipe manufacturing process involves
additional steps subsequent to the manufacture of the seamless
pipe, the end product has to accomplish these requirements.
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SUMMARY OF THE INVENTION
The present invention describes an upset SCR of novel low
carbon chemical composition and microstructure which achieves
higher improvement in the fatigue life as it is integral with the riser
pipe section at the Touch Down Zone. The low carbon upset SCR
achieves its desired properties by the thermal treatment which it is
subjected to. The novel low carbon chemical composition and
microstructure comprises in weight per cent, carbon 0.04-0.10,
manganese 0.40-0.70, silicon 0.15-0.35, chromium 0.40-0.70,
molybdenum 0.40- 0.70, nickel 0.10-0.40, nitrogen 0.008 max,
aluminum 0.010-0.045, sulfur 0.005 max, phosphorus 0.020 max,
titanium 0.003-0.020, niobium 0.020-0.035, vanadium no more than
0.10, copper 0.20 max, tin 0.020 max, and carbon equivalent 0.43
max and PCM no more than 0.23 and having a yield strength of at
least of 65000 psi, the ultimate tensile strength of at least 77000 psi
and YS/UTS ratio below 0.89 in material representing the pipe body,
the transition zone and the upset end.
The present invention also describes a method for
manufacturing a seamless steel tube for steel catenary riser with
upset ends having a yield strength at least of 65000 psi both in the
pipe body, transition and the upset-zone comprising the steps of: (a)
providing a steel tube comprising in weight per cent, carbon 0.04-
0.10, manganese 0.40-0.70, silicon 0.15-0.35, chromium 0.40-0.70,
molybdenum 0.40- 0.70, nickel 0.10-0.40, nitrogen 0.008 max,
aluminum 0.010-0.045, sulfur 0.005 max, phosphorus 0.020 max,
titanium 0.003-0.020, niobium 0.020-0.035, vanadium no more than
0.10, copper 0.20 max, tin 0.020 max, and carbon equivalent 0.43
max and PCM no more than 0.23; (b) upsetting the tube ends in
multiple steps with intermediate heating cycles in between to
achieve the required thickness (c) quenching and tempering between
630-710 C; (d) machining the upset ends.
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BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 shows the Steel Catenary Riser Configuration of a
preferred embodiment of the present invention.
Figure 2 illustrates an embodiment of the tube with an upset
end of a preferred embodiment of the present invention.
Figure 3 shows typical macro sections of RP2Z welds for
different welding conditions of the tube of a preferred embodiment of
the present invention.
Figures 4 (a) and (b) show the tensile test results for the
longitudinal direction and the transverse direction of a preferred
embodiment of the present invention.
Figure 5 illustrates the longitudinal and transverse Y/T ratio
results of a preferred embodiment of the present invention.
Figure 6 shows the Hardness Vickers HV10 of a preferred
embodiment of the present invention.
Figure 7 illustrates the Transverse Charpy V Notch Impact Test
at -30 C of a preferred embodiment of the present invention.
Figure 8 shows the Mean curve for specimens 10 3/4" x 0.866"
X65 of a preferred embodiment of the present invention.
Figures 9 (a) and (b) show the tensile test results for the
longitudinal direction and the transverse direction of a preferred
embodiment of the present invention.
Figure 10 illustrates the longitudinal and transverse Y/T ratio
results of a preferred embodiment of the present invention.
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Figure 11 shows the Hardness Vickers HV10 of a preferred
embodiment of the present invention.
Figure 12 illustrates the Transverse Charpy V Notch Impact
Test at -30 C of a preferred embodiment of the present invention.
Figure 13 shows the Mean curve for specimens 10 3/4" x
1.250" X65 of a preferred embodiment of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
As illustrated in Figure 1, the present invention describes an
upset SCR of novel low carbon chemical composition and
microstructure which achieves higher improvement in the fatigue life
as it is integral with the riser pipe section at the Touch Down Zone.
The low carbon upset SCR achieves its desired properties by the
thermal treatment which it is subjected to.
The steel grade contemplated for use in the upset SCR of the
present invention is X-65 (a yield strength of at least 65000 psi in
the pipe body and in the upset ends).
The alloy design consists of a low-C (0.13 max), low-Mn (1.5
max) steel with additions of microalloying elements such as
Niobium, Titanium (Nb+Ti 0.1 max), Chromium and Molybdenum
(Cr+Mo 1.2 max). The purpose of adding these last two alloying
elements is to increase hardenability and promote a martensitic-
bainitic transformation on thick upset ends and pipe body achieving
high strength. The carbon equivalent (CE) is designed not to exceed
0.43 as requested by API 5L. More preferably, the carbon equivalent
is limited to 0.41. The most preferred embodiment of the present
invention is not to exceed 0.39.
Pipes are hot rolled using a recrystallization controlled rolling
scheme manufactured from round billets obtained by continuously
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cast (CC) process. After hot rolling, the pipes are then inspected
with non-destructive methods such as electromagnetic inspection,
wet magnetic particle inspection and ultrasonic testing with the
purpose of finding any longitudinal or transverse defects on internal
or external surfaces and to verify wall thickness. The pipes are then
upsetted by reheating the pipe ends above the dissolution
temperature of Nb (C, N) to provide adequate plastic flow during
each upset operation whilst controlling austenite grain size by
precipitation of fine TiN particles. The optimum radius at the upset-
pipe body transition is modeled thru Finite Element Analysis (FEA),
where the Stress Concentration Factor (SCF) resulted 1.135 and
1.12 for Case 1 (273.1 mm OD by 22.0 mm WT Pipe body, 28 mm
WT as machined Upset Ends and 35 mm as upset ends, steel grade
X65 for non-sour service application, 10.75" x 0.866") and Case 2
(273.1 mm OD by 31.8 mm WT Pipe body, 45 mm WT as machined
Upset Ends and 53 mm as upset ends, steel grade X65 for sour
service application, 10.75" x 1.250"), respectively. After upsetting
both ends of the pipes, a critical quench and temper heat treatment
is designed and used to provide the final mechanical properties.
Non-destructive testing is again carried out in the pipe body, and the
OD and ID surface of the upset ends are machined and then
inspected with wet magnetic particle inspection and manual
ultrasonic testing. Finally, the pipes are bevel machined for girth
welding. Welding and fatigue behavior are thoroughly characterized.
After the quench and temper heat treatment, the material is
then fully characterized. The Yield Strength (YS), the Ultimate
Tensile Strength (UTS) and the YS/UTS ratio at room temperature
are evaluated using both longitudinal and transverse round
specimens taken from the Upset End, Slope Transition and Pipe
Body regions in two quadrants, 00 and 180 .
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Hardness Vickers HV10 are measured on the OD (outside
diameter), MW (mid-wall) and ID (internal diameter) sections in 4
quadrants are taken from the Upset End, Slope Transition and Pipe
Body regions. The hardness readings are taken at 1.5 mm from OD
and ID. In addition, transverse Charpy V notch impact testing is
carried out at -30 C and -40 C for case 1 and case 2 respectively
using 10x10 mm specimens. Sour service resistance is assessed in
both pipe body and upset ends by the Hydrogen Induced Cracking
(H IC) and Four Point Bend Tests (FPBT).
The present invention thus describes a seamless steel tube for
a steel catenary riser with upset ends comprising in weight per cent,
carbon 0.04-0.10, manganese 0.40-0.70, silicon 0.15-0.35,
chromium 0.40-0.70, molybdenum 0.40-0.70, nickel 0.10-0.40,
nitrogen 0.008 max, aluminum 0.010-0.045, sulfur 0.005 max,
phosphorus 0.020 max, titanium 0.003-0.020, niobium 0.020-0.035,
vanadium no more than 0.10, copper 0.20 max, Tin 0.020 max, and
carbon equivalent 0.43 max and PCM no more than 0.23 and having
a yield strength of at least of 65000 psi in material representing the
pipe body, the transition zone and the upset end.
The novel microstructure of the upset SCR which enables the
seamless steel tube to achieve a higher improvement in the fatigue
life includes the following mechanical properties and corrosion
requirements for Upset SCR as shown in Table 1. The minimum
requirements are following the API 5L, 43rd edition specification.
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Table 1 - Mechanical properties and corrosion requirements for
Upset SCR
Requirements Non Sour Service Casel Sour Service Case 2
Yield Strength 0.5% EUL 65000 psi (minimum), 65000 psi (minimum),
80000 psi (maximum) 80000 psi (maximum)
Ultimate Tensile Strength 0,5%EUL 77000 psi (minimum) 77000 psi (minimum)
Yield/Tensile strength ratio 0.89 (maximum) 0.89
(maximum)
Elongation (% in 2") 18% (minimum) 18% (minimum)
Hardness Vickers (HV10) 269 (maximum) 250 (maximum)
70 minimum Individual, 70 minimum Individual,
Absorbed energy value for 3
individual specimens (Joules) 90 minimum Average 90
minimum Average
at - 30 C at -40 C
0.510 minimum Individual, 0.510 minimum Individual,
Crack Tip Opening Displacement L-
C direction at -10 C (mm), 3
0.635 minimum individual specimens Average 0.635 minimum Average
CTR 3.0% (maximum)
HIC as per NACE TM0284 using CLR 10.0% (maximum)
solution "A". Test period 96 hrs.
CSR 1.0% (maximum)
FPBT as per ASTM G48, test
solution "A" of NAGE TM0177. No cracks after 720 hrs
Testing stress 95% of SMYS. Test
period 720 hrs.
Table 2 shows a summary of observed microstructures. All
microstructures are homogeneous at midwall, which is the most
critical section where mainly bainite, and a mixture of acicular and
non-polygonal ferrite is observed independent of the section (pipe
body, transition or upset). There is a slight presence of martensite
close to the OD and ID sections.
Table 2 - Microstructure of the Upset SCR Seamless Steel Tube
Pipe Body Transition Upset
Bainite, Tempered Bainite, Tempered Martensite Bainite and
presence of
ID Martensite and Acicular and Acicular Ferrite
acicular and non-polygonal
Ferrite Ferrite
Bainite and presence of Bainite, Acicular and non- Bainite and
Acicular and
MW acicular and non-polygonal polygonal Ferrite non-
polygonal Ferrite
Ferrite
Bainite, Tempered Bainite, Tempered Martensite Bainite and
presence of
OD Martensite and Acicular and Acicular Ferrite
acicular and non-polygonal
Ferrite Ferrite
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A specific alloy design is developed and heat treatment
parameters are set to obtain the desired microstructural
characteristics in both pipe body and heavy wall upset sections. The
combination of the above mentioned parameters results in excellent
mechanical properties which meet the strength and corrosion
objectives.
The present invention also describes a method for
manufacturing a seamless steel tube for steel catenary riser with
upset ends having a yield strength at least of 65000 psi both in the
pipe body, transition and the upset-zone comprising the steps of: (a)
providing a steel tube comprising in weight per cent, carbon 0.04-
0.10, manganese 0.40-0.70, silicon 0.15-0.35, chromium 0.40-0.70,
molybdenum 0.40-0.70, nickel 0.10-0.40, nitrogen 0.008 max,
aluminum 0.010-0.045, sulfur 0.005 max, phosphorus 0.020 max,
titanium 0.003-0.020, niobium 0.020-0.035, vanadium no more than
0.10, copper 0.20 max, tin 0.020 max, and carbon equivalent 0.43
max and PCM no more than 0.23; (b) quenching and tempering
between 630-710 C.
Multiple steps of upsetting and heating cycles in between each
upsetting operation are used to achieve required thickness at the
upset ends for each dimension (35 mm wall thickness and 53 mm
wall thickness for the case 1 and 2 above mentioned) to obtained
final as machined upset ends mentioned above.
Weldability and full fatigue tests are performed to a large
number of pipes to establish fatigue performance. These tests are
described as follows:
Welding program
The properties of the upset pipes subject to different thermal
cycles induced by welding operations are evaluated initially by
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welding on a 35 mm wall thickness pipe with the chemistry as the
upset ends.
The conditions are summarized in Table 3, and have been
applied on a welding bevel configuration as recommended in the
standard API RP2Z; Preproduction Qualification for Steel Plates for
Offshore Structures [1].
This specific welding preparation with one of the bevel at 00
enables to quantify the toughness (impact and CTOD testing) of the
HAZ in conditions more severe than with the conventional V or U
bevel (the fatigue crack is placed in the prescribed coarse-grain HAZ
material for at least 15% of the central two thirds of the specimen
thickness).
Table 3 ¨ API RP2Z welding conditions
API RP2Z welding conditions on 35mm thick pipe X70
Heat Input Preheat lnterpass Temp. lnterpass Temp.
(kJ/mm) Temp. ( C) ( C) Fill passes (CC) Cap passes
0.6 100 100 100
0.6 200 200 200
0.8 150 150 150
0.8 200 200 200
0.8 200 200 250
2.0 250 250 250
3.0 250 250 250
The weldability test requires characterization of the HAZ for
two cases subject to different combinations of heat using an API
RP2Z bevel: Preproduction Qualification for Steel Plates for
Offshore Structures [8]. All tests passes or exceeds the
requirements including hardness HV10 below 250 for the sour
service case (Case 2).
The HAZ characterization has been run on both upset pipes
with 28 mm and 45 mm thickness at the upset ends, with the welding
conditions listed in Table 4. The consumables and heat input used
are:
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- Lincoln STT for the root pass, heat input 0.55-0.75
kJ/mm,
- P-GMAW for fill and cap passes with heat input 0.6
kJ/mm,
SAW for fill and cap passes with heat input equal or
greater than 0.8 kJ/mm.
Table 4 ¨ API RP2Z welding conditions on both upset pipes X65
API RP2Z welding conditions on both upset pipes X65
Heat Input Preheat Interpass Temp. Interpass Temp.
(Um) Temp. ( C) ( C) Fill passes ( C) Cap passes
0.8 200 200 250
1.5 250 250 250
3.0 250 250 250
HAZ characterization: testing and results
- Hardness:
On the 35 mm thick pipe, hardness indentations in HAZ are
located in lines parallel to the pipe body, at 1.5 mm from inner and
outer diameter of pipe and each 4 mm across the thickness.
To meet the requirements of 250 Hv10 maximum in HAZ (from
root to cap) for sour service application, the welding conditions are:
a heat input of minimum 0.65 kJ/mm combined with a
preheat temperature of 200 C for root pass,
a heat input of minimum 0.8 kJ/mm combined with an
interpass temperature of 200 C for fill passes,
a heat input of minimum 0.8 kJ/mm combined with an
interpass temperature of 250 C for cap passes.
In addition, for the capping, the last bead is not on a side of a
bevel but is deposited within the width of the weld preparation so
that each cap passing at the edges of the bevel gets the benefit of a
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tempering effect of the subsequent cap passes. On the upset ends
28 and 45 mm thick, by applying the above mentioned welding
conditions, the hardness in HAZ does not exceed 250 HV10.
The typical macro sections of the API RP2Z welds produced for
two heat inputs are shown in Figure 3. These welds are then tested
for hardness and toughness (Charpy and CTOD) properties.
- Toughness:
Impact testing is run at -40 C, from fusion line + 1mm to fusion
line + 3mm, on welds run on 35 mm thick pipe and high heat input (2
and 3 kJ/mm). Absorbed energy obtained is above 200 J for each
specimen
On the upset ends welds, these very high absorbed energy
values in HAZ are duplicated, regardless of the wall thickness and
the welding conditions: minimum value achieved 200 J, maximum
value achieved 450 J.
In addition, CTOD testing (SENB, Bx2B specimens) in HAZ as
per API RP2Z is run at -10 C. With the range of heat input from 0.8
to 1.5 kJ/mm, which is typical of field welding, the achieved CTOD
values are from 1.0 to 1.5 mm, which shows an excellent ductility of
the HAZ.
Development of the Welding Procedure Specification (WPS)
In order to force the fatigue crack to initiate away from the
weld area and so to better quantify the fatigue resistance of the
upset design, a specific welding procedure specification is
developed and used for the welds to be full scale fatigue tested:
selection of a welding consumable with very high toughness,
removal of weld root and reinforcement of cap.
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Full scale testing shows excellent fatigue behavior of upset
girth joints. In both cases, the data correspond to failure, or run-
outs, well beyond the target mean curve for the sets of tests,
demonstrating that both geometries of girth welded upset qualify as
top class (B1 in DNV ¨RP-C203) component for fatigue resistance.
Mean curve results can be seen in Figures 8 and 13 for case 1 and
case 2 respectively.
Examples
Heavy Wall Upset seamless steel tubes with the following
characteristics are used:
Case 1: 273.1 mm OD by 22.0 mm WT Pipe body, 28 mm WT
as machined Upset Ends and 35 mm as upset ends, steel grade X65
for non-sour service application (10.75" x 0.866").
Case 2: 273.1 mm OD by 31.8 mm WT Pipe body, 45 mm WT
as machined Upset Ends and 53 mm as upset ends, steel grade X65
for sour service application (10.75" x 1.250").
Case (1) Upset SCR TDZ 10.75"OD x 0.866" WT X65 Non Sour
Service
Figures 4 (a) and (b) and 5 show the Yield Strength (YS),
Ultimate Tensile Strength (UTS) and the YS/UTS ratio evaluated at
room temperature for quenched and tempered material. Longitudinal
and transverse round specimens taken from sections representing
the Upset End, Slope Transition and Pipe Body are tested in two
quadrants, 0 and 180 . All specimens are standard round except by
those from the pipe body in the transverse direction which are sub-
size round. Figure 4 (a) and (b) show all the YS and UTS values
obtained from the tensile test in the longitudinal and transverse
directions, respectively.
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Figure 4 (a) and (b) show that all Yield Strength values
obtained are above 65,000 psi minimum and do not exceed the
80,000 psi maximum. All the Ultimate Tensile strength values
obtained are above 77,000 psi minimum established.
Figure 5 shows that, for the YS/UTS ratio, all the values are
below 0.89 which is established as maximum YS/UTS specification.
The values of YS/UTS ratio are shown in Figure 5 for both the
longitudinal and transverse directions.
Hardness test
For the material in the "as quenched and tempered condition",
Hardness Vickers HV10 (3 readings per row) are measured on the
OD, MW and ID sections in 4 quadrants taken from the Upset End,
Slope Transition and Pipe Body regions. The hardness readings are
taken at 1.5 mm from outer diameter (OD) and inner diameter (ID).
As quenched and tempered material HV10 test results are shown in
Figure 6.
Even as the material from case 1 is not initially considered for
sour service application, as shown in Figure 6, all hardness readings
are below 250HV10 (22 HRc) complying with NACE requirement for
material to be used in sour environments.
Toughness test
The fracture mechanics characteristic is evaluated using the
Transverse Charpy V Notch Impact Test. The test temperature is -
C. Sets of three full size specimens (10x1Omm) are taken from
25 upset end,
slope transition and pipe body regions in two quadrants,
0 and 180 , for each sample of quenched and tempered material.
Figure 7 shows that all the individual values of Absorbed
Energy are above 70 Joules which is established as minimum target
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and 90 Joules as minimum average of 3 specimens. The transition
temperature obtained in the transverse direction using Charpy V-
notch 10x10 specimens in material representing pipe body and upset
end are below -60 C as is shown in Tables 5 (a) and (b).
Table 6 ¨ Transition Temperature Curve. (a) Pipe body and (b)
Upset End
Transverse Charpy V-Notch test results (Joules , 10x10 mm specimen
Test
Average Average
% % % Absorbed Shear
Sample Pipe/End Location Temperature 1
Sh.A 2 Sh.A 3 Sh.A Energy Area
C
(J) , (T)
-30 439 100 419 100
443 100 434 100
Pipe 10
64283 North Pipe -40 440 100 408 100 415 100 421
100
End body -50 435 100 355 100
437 100 409 100
-60 357 100 451 100
280 100 363 100
(a)
Transverse Charpy V-Notch test results (Joules , 10x10 mm specimen
Test %
Average Averag
% cyo
Sampl Pipe/En Locatio Absorbe e Shear
Temperatur 1 Sh. 2 Sh. 3 Sh.
e d n d Energy Area
e C A A A
(J) _ (%) .
42 43
-30 100 42 100 100 428 100
5 8 1
38 37 43
Pipe 15 -40 100 100 100 399 100
Upset 8 4 5
64286 South
End 42
End -50 100 100 100 427 100
4 2 5
34
-60 100 38 100 100 374 100
4 4 439
(b)
CTOD results representing the pipe body and upset end, as
shown in Table 6, show exceptional results above 0.6 mm at -30 C.
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Table 6 ¨ CTOD Results Representing (a) Pipe Body (b) Upset
End
PIPE BODY ¨ CTOD TEST RESULTS
LONGITUDINAL ORIENTATION
RECTANGULAR BX2B SPECIMEN
Test Average Minimum
Sample Pipe End Temperature Delta (mm) CTOD
Delta CTOD Delta
C 1 2 3 Value
(mm) Value (mm)
64283 10 North -10 1.54 1.51 1.49 1.51 1.49
64286 915 South -30 1.49 1.52 1.39 1.47 1.39
Minimum Specification 0.635 0.510
(a)
UPSET END ¨ CTOD TESTS RESULTS
LONGITUDINAL ORIENTATION
COMPACT BX2B SPECIMEN
Test Average Minimum
Sample Pipe End Temperature Delta (mmi
CTOD Delta CTOD Delta
C 1 2 3 Value (mm) Value (mm)
64283 10 North -10 1.13 1.11 1.10 1.11 1.10
64286 15 South -30 1.15 1.11 1.13 1.13 1.11
Minimum Specification 0.635 0.510
(b)
Microstructural analysis
Samples from as-quenched and as-quenched and tempered
material are prepared for microstructural analysis. The transverse
face to the rolling axis is metallographically prepared by sanding
down to 600 sand paper and polished to a mirror-like appearance
with diamond paste and etched with Nital at 2% to carry out
microstructural observations by optical microscope.
Microstructures are observed on OD, MW and ID sections of
pipe body, slope transition and upset end regions. Two quadrants,
0 and 180 , photomicrographs at 500X representing the
microstructure from OD, MW and ID are obtained.
In this case, the observed microstructure in the pipe body after
quenching consists of a mixture of predominantly bainite and
acicular ferrite through the wall thickness and a slight presence of
martensite close to the outer and inner surface. Similarly, bainite
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and acicular ferrite and some regions of non-polygonal ferrite are
observed through the wall thickness at the upset section.
The prior austenitic grain size (PAGS) are measured using
image analysis on as-quenched material etched with saturated
aqueous picric acid on samples from the pipe body and the upset
end at 0 and 180 Quadrants, resulting in an average size of 9/10
ASTM.
The microstructure after the tempering treatment consists of
predominantly bainite and acicular ferrite are observed through the
wall thickness on material representing pipe body, slope transition
and upset end.
Fatigue Test Results
The fatigue test results are shown in Figure 8. The test results
show very high fatigue performance at upset ends, transition and
pipe body.
Case (2) Upset SCR TDZ 10 1/4"OD x 1.250"WT X65 Sour Service
For case (2), in addition to all the destructive testing including
tensile, hardness toughness performed in case (1), the Sour Service
Hydrogen Induced Cracking Test as per NACE TM0284 and Sulphide
Stress Cracking by using the Four Point Bend Test is performed.
Figure 9 shows the tensile results where it can be seen that Yield
Strength values obtained are above 65,000 psi and do not exceed
the maximum value of 80,000 psi. All the Ultimate tensile strength
values obtained are above 77,000 psi which is established as the
minimum specified.
All the YS/UTS ratio values are below 0.89 as shown in Figure
10 for both longitudinal and transverse direction.
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As shown in Figure 11, all the hardness readings are below
250 HV10 (22 HRc) complying with NACE MR0175 requirements for
materials to be used in sour environments.
For this case (2), the Charpy test temperature is -40 C. Sets of
three full size specimens (10x1Omm) are taken from midwall of upset
end, slope transition and pipe body regions in two quadrants 0 y
180 , from quenched and tempered material. As shown in Figure 12,
all results are above the expected minimum absorbed energy values
of 70 Joules minimum individual and 90 Joules as minimum average
of 3 specimens.
Transverse Charpy V-Notch impact transition curves are
obtained from 2 samples, one representing upset end and another
one representing pipe body from quenched and tempered material
for each case.
The transition temperature obtained in the transverse direction
using Charpy V-notch 10x10 specimens is between -50 C and -60 C
for the material representing the upset end and below -70 C for
material representing pipe body.
As shown in Figure 12, all results were above the expected
minimum values of 70 Joules minimum individual and 90 Joules as
minimum average of 3 specimens.
Transverse Charpy V-Notch impact transition curves are
obtained from 2 samples representing upset end and another
representing pipe body of quenched and tempered material for each
case.
The transition temperature obtained in the transverse direction
using Charpy V-notch 10x10 specimens is between -50 C and -60 C
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for the material representing the upset end and below -70 C for
material representing pipe body as shown in Table 7.
Table 7 ¨ Transition Temperature Curve. (a) Pipe body and (b)
Upset End
Transverse Charpy V-Notch test results (Joules), 10x10 mm specimen
Average Average
Test % 0/0 % Absorbed Shear
Sample Pipe/End Location Temperature 1
Sh.A 2 Sh.A 3 Sh.A Energy Area
C
(J) (%)
-20 436 100 450 100
439 100 442 100
-30 432 100 440 100
422 100 431 100
Pipe 10
64521 North Pipe -40 434 100 442 100 446 100 441
100
body -50 446 100 436 100 449 100 444 100
End
-60 384 100 440 100
439 100 421 100
-70 398 100 424 100
435 100 419 100
(a)
Transverse Charpy V-Notch test results ,Joules), 10x10 mm specimen
,
Test
Average Averag
/0 % %
Sampl Pipe/En Locatio
Temperatur 1 Sh. 2 Sh. 3 Sh. Absorbe e
Shear
e d n
e C A A A
d Energy Area
(J) (%)
42 44 40
-20 100 100 100 426 100
2 _
43 43 45
-30 0 100 100 100 437 100
0 2
42 42 42
Pipe 6 -40 100 100 100 427 100
Upset 9 8 4
64518 North
End 44 44 40
End -50 100 100 100 432 100
3 9 5
43 43
-60 9 0 100 100 294 67
9 2
44
-70 6 0 41 100 100 288 67
5 4
(b)
CTOD results from material representing pipe body and upset
end are above 0.6 mm at -10 C as shown in Table 8.
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Table 8 ¨ CTOD Results Representing (a) Pipe Body (b) Upset
End
PIPE BODY ¨ CTOD TEST RESULTS
LONGITUDINAL ORIENTATION
BX2B SPECIMEN
Test Average Minimum
Sample Pipe End Temperature Delta (mm) CTOD
Delta CTOD Delta
C 1 2 3 Value
(mm) Value (mm)
64577 9 North -10 1.50 1.55 1.54 1.53 1.50
64578 9 South -10 1.61 1.56 1.57 1.58 1.56
Minimum Specification 0.635 0.510
(a)
UPSET END ¨ CTOD TESTS RESULTS
LONGITUDINAL ORIENTATION
COMPACT SPECIMEN
Test Average Minimum
Sample Pipe End Temperature Delta
(mm) CTOD Delta CTOD Delta
C 1 2 3 Value (mm) Value (mm)
64577 9 North -10 1.13 1.14 1.07 1.11 1.07
64578 9 South -10 1,14 1.15 1.17 1.15 1,14
Minimum Specification 0.635 0.510
(b)
Corrosion test only case (2)
Hydrogen Induced Cracking
HIC test is performed on 1 sample representing upset end and
another representing pipe body for Case 2. Each set of 3 specimens
(3 quadrants, 0 , 120 and 2400) representing pipe body and another
set representing upset end is tested as per NACE TM0284 using
Solution "A", test period was 96 hours. The results show that neither
cracks nor blisters are found after test period showing that all the
requirements for the Hydrogen Induced Cracking test are met.
Sulfide Stress Cracking
SSC Four Point Bend Test is performed on 1 sample
representing upset end and another representing pipe body. Each
set of 3 specimens (3 quadrants, 0 , 120 and 240 ) representing
pipe body and another set representing upset end is tested as per
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ASTM G48. Test solution "A" of NACE TM0177 is considered.
Testing stress is 95% of Specified Minimum Yield Strength (SMYS)
and two test periods of 96 hours and 720 hours. The results are
shown in Tables 9 and 10.
Table 9 ¨ SSC Four Point Bend Test Results Representing
Material From Pipe Body (a) After 96 Hrs. Exposure (b) After 720
Hrs. Exposure
SULFIDE STRESS CRACKING ¨ FOUR POINT BEND TEST
SOLUTION "A" NACE 0177-96- TEST DURATION: 96 HRS.
PIPE BODY
Stress
Specimen Initial Values Final Values Applied
No. Result
SATi PHI SATf pHf (Y0SMYS
1 2418.32 2.72 2503.61 3.57 95 Not failed
2 2418.32 2.72 2503.61 3.57 95 Not failed
3 2418.32 2.72 2503.61 3.57 95 Not failed
(a)
SULFIDE STRESS CRACKING ¨ FOUR POINT BEND TEST
SOLUTION "A" NACE 0177-96- TEST DURATION: 720 HRS.
PIPE BODY
Stress
Specimen Initial Values Final Values Applied
No. Result
SATi PHi SATf pHf (Y0SMYS
1 2809.95 2.70 2980.25 3.62 95 Not failed
2 2809.95 2.70 2980.25 3.62 95 Not failed
3 2809.95 2.70 2980.25 3.62 95 Not failed
(b)
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Table 10 ¨ SSC Four Point Bend Test Results From Upset End
(a) After 96 Hrs. Exposure (b) After 720 Hrs Exposure
SULFIDE STRESS CRACKING ¨ FOUR POINT BEND TEST
SOLUTION "A" NACE 0177-96- TEST DURATION: 96 FIRS.
UPSET END
Stress
Specimen Initial Values Final Values Applied
No. Result
SATi PHi SATf pHf %SMYS
1 2418.32 2.72 2503.61 3.57 95 Not failed
2 2418.32 2.72 2503.61 3.57 95 Not failed
3 2418.32 2.72 2503.61 3.57 95 Not failed
(a)
SULFIDE STRESS CRACKING ¨ FOUR POINT BEND TEST
SOLUTION "A" NACE 0177-96- TEST DURATION: 720HRS.
UPSET END
Stress
Specimen Initial Values Final Values
Applied
No. Result
SATi PHi SATf pHf %SMYS
1 2809.95 2.70 2980.25 3.62 95 Not failed
2 2809.95 2.70 2980.25 3.62 95 Not failed
3 2809.95 210 2980.25 3.62 95 Not failed
(b)
Tables 9 and 10 show that all Four Point Bend specimens
passed successfully the SSC test after the test period, stressed at
95%SMYS, no cracks are observed after 96 hours and even after
720 hours.
Microstructural Characterization
Optical Microscopy and Scanning Electron Microscopy is used
for material characterization. Microstructural analysis is performed
on OD, MW and ID sections of pipe body, slope transition and upset
end regions in two quadrants 0 and 180 for samples in the as-
quenched condition and quench and tempered condition.
The pipe body as-quenched microstructure consists of
predominantly bainite and acicular ferrite at midwall and, close to
the outer and inner surface, a slight presence of martensite is
observed.
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The upset as-quenched microstructure consists of
predominantly bainite and acicular ferrite through the wall thickness.
The PAGS is measured using image analysis on as-quenched
material etched with saturated aqueous picric acid on samples from
pipe body and upset end. An average PAGS size of 7/8 ASTM is
obtained for both pipe body and upset end respectively.
The microstructure at mid-wall after tempering consists of
predominantly bainite and acicular ferrite at the pipe body and slope
transition; and bainite, acicular ferrite, and non-polygonal ferrite at
the upset ends.
Fatigue results
The fatigue test results are plotted in Figure 13. The test
results show very high fatigue performance at upset ends, transition
and pipe body.
The invention has been fully described and experimental
fatigue results obtained shows that the fatigue performance for
these two Upset Solutions described above in case (1 and 2) has
been increased with a factor ranged between 3 and 15.
