High-strength large-diameter pipe for
long-distance high pressure gas pipelines
M. K. Gräf
H.-G. Hillenbrand
C. J. Heckmann
K. A. Niederhoff
Europipe GmbH
Europipe GmbH
Mannesmann Forschungsinstitut GmbH
Mannesmann Forschungsinstitut GmbH
ISOPE 2003
May 26-30, 2003, Honolulu, Hawaii, USA
TP53
High-strength large-diameter pipe for long-distance high pressure gas pipelines
M. K. Gräf1 , H.-G. Hillenbrand 2 , C. J. Heckmann3 , K. A. Niederhoff3
1
2
Europipe GmbH
Mülheim, Germany
Europipe GmbH
Ratingen, Germany
ABSTRACT
Mannesmann Forschungsinstitut
Duisburg, Germany
PROJECT COST REDUCTION
The ever-increasing demand for natural gas will further influence the
type of its transportation in the future, both from the strategic and
economic point of view. Long-distance pipelines are a safe and
economic means to transport the gas from production sites to end users.
The energy scenario has been changing quickly in recent years.
International studies forecast that the demand for natural gas will be
nearly doubled by 2030. The distance between gas production sites and
end users increases, implying the need for the construction of complex
gas transportation pipeline networks, when the use of LNG tankers is
impossible or uneconomical. This will make the high pressure natural
gas transportation via pipelines increasingly interesting.
The use of grade X 80 linepipe has already been shown to result in
substantial cost savings. Results of tests on grade X 80 production pipe
supplied for onshore and offshore projects are presented in this paper.
But the economic transport of gas over very long distances requires
additional cost cuts. The use of grade X100 and/or X120 could be a
solution. Therefore, the benefits of using high-strength linepipe and the
present-day technical limitations on its production are addressed.
Project cost reduction may be a result of the sum of the different
benefits that can be derived by using high-strength steels /1/, even
when the price per tonne of the pipe increases as the material grade
increases. The benefits include:
•
•
•
reduced quantity of steel required
lower pipe transportation costs
lower pipelaying costs.
The use of grade X 80 linepipe in the construction of the first Ruhrgas
X80 pipeline led to a material saving of about 20 000 t, compared with
grade X 70 pipes (Figure 1), through a reduction of the wall thickness
from 20.8 mm for X 70 to 18.3 mm for X 80. This resulted also in a
reduction of the pipelaying costs because of reduced pipe transportation
costs and greatly reduced welding costs through reduced welding times
needed with thinner walls. The use of materials with still higher
strength, such as grade X 100 or grade X 120 could lead to further
material savings as it is further illustrated in Figure 1.
Laboratory and production results on high-strength large-diameter
pipes are presented to describe the materials properties as well as the
service behaviour. Girth welding procedures covering mechanised and
manual methods have already been developed.
This paper gives an overview of the development of high-strength lowalloy linepipe grades. Some of the current projects for pipelines in
grade X 80 and the benefits of using X 80 pipe are presented. Also,
important aspects of the properties of base material and welds are
discussed. The development of material grades up to X 100 or X 120
represents one of the big challenges and opportunities in the future.
Special attention is focused on the effect of boron on the mechanical
properties of the material grades between >X 80 and X 120.
Furthermore, the various aspects of production welds and field
weldability are dealt with.
Gräf
165000
170000
160000
145000
150000
Pipe line weight [t]
INTRODUCTION
Paper No. 2003-SYMP-03
3
140000
126000
130000
120000
101000
110000
100000
90000
80000
70000
60000
50000
X70
X80
X100
X120
API steel grade
Figure 1: Possible material savings through the use of high strength
material
1
A preliminary economic evaluation /2/ highlighted that high pressure
X 100 pipelines could give investment cost savings of about 7%
compared with grade X 80 pipeline. This study claims cost savings of
up to 30 % when X 70 and X 100 are compared. Given that, in a
complex pipeline network operating at high pressure, the capital
expenditure is very high, it becomes understandable how much more
attractive the high strength steel option could be.
On the other hand, it becomes clear from Figure 2 that the reduction in
the manufacturing cost per tonne of the pipe at a given transport
capacity of a pipeline is enhanced not just by the increase in the
material grade of the steel but also by the reduction in pipe wall
thickness. From the point of view of pipe manufacturers, reduction of
pipe wall thickness is not a preferred option. A reduction in pipe
diameter at constant pipe thickness and a simultaneous increase in
pipeline operating pressure would represent, in our opinion, a more
favourable solution to the problem.
Manufacturing cost per metric tonne
1250
Since 1984 longitudinal seam submerged-arc welded grade X 80 pipe
has been used in the implementation of several pipeline projects in
Europe and North America (Figure 3). In 1984, EUROPIPE produced
the grade X 80 linepipe installed, for the first time in history, in the
Megal II pipeline. A manganese-niobium-titanium steel, additionally
alloyed with copper and nickel, was used for the production of the
44” OD x 13.6 mm WT pipe. Subsequent optimisation of the
production parameters enabled the CSSR order to be executed using a
manganese-niobium-titanium steel without the additions of copper and
nickel.
YEAR
ORDER
PIPE GEOMETRY
PIPELINE LENGTH
1984
Megal II
44" x 13.6 mm
3.2 km
1985
CSSR
56" x 15.5 mm
1.5 km
12.7 mm
1991/92 Ruhrgas
48" x 18.3 mm
250 km
15.9 mm
2001-03 CNRL
24" x 25.4 mm
12.7 km
2001-03 Transco
48" x 14.3/15.1 mm
158 km +
1150
1050
19.1 mm
950
25.4 mm
Figure 3: Europipe Projects executed with linepipes made of grade
X80
850
750
650
550
450
X60
X80
X100
X120
API steel grade
Figure 2: Manufacturing cost per tonne of pipe for different steel
grades and wall thicknesses to be used at a constant
transportation capacity
DEVELOPMENT OF HIGH-STRENGTH STEEL GRADES
The improved processing method for currently used high-strength
steels like X 80 and higher, consists of thermomechanical rolling
(emerged in the 1980s) followed by accelerated cooling. By this
method, it has become possible to produce high-strength NbTi
microalloyed material, having a reduced carbon content and thereby
excellent field weldability. Additions of molybdenum, copper and
nickel enable the strength level to be raised to that of grade X100,
when the steel is processed to plate by thermomechanical rolling plus
modified accelerated cooling. The development of high strength steel
for pipes in grade X 120 consists of further optimisation of the
thermomechanical treatment and the use of niobium, titanium and
boron as microalloying elements. First results of this development as
regards the mechanical properties of the new material are very
encouraging.
GRADE X 80
X 80 Projects and relevant pipe properties
In the past two decades, EUROPIPE has carried out extensive work to
develop high-strength steels in grades X 80 and X 100 to assist
customers in their endeavour to reduce pipe weight and pipelaying
costs.
Paper No. 2003-SYMP-03
Gräf
The first pipeline using GRS 550 (X 80) for its entire length of 250 km
was the Ruhrgas Werne-to-Schlüchtern pipeline project implemented in
Germany in 1992. EUROPIPE supplied all 48” diameter pipe with up
to 19.3 mm wall thickness and the necessary induction bends. Since the
strength decreases as the wall thickness increases, it had been necessary
at that time to raise the carbon and manganese levels marginally. The
concentrations of all other elements remained unchanged.
The measured tensile strength and impact energy values conformed
fully to the specification requirements in all cases. The standard
deviation for the yield and tensile strength values was very low. The
impact energy values measured on Charpy V-notch impact specimens
at 0°C was very high, averaging to about 180 J. The 85% shear area
transition temperatures determined in the drop weight tear (DWT) tests
were far below 0°C.
In 2001, 2002 and 2003, X 80 (L555MB) pipes were manufactured
again for Transco projects in the UK. Linepipe for several parts of gas
pipeline networks of about 158 km length in total was produced.
EUROPIPE supplied pipe of 48” diameter with the thicknesses of
14.3 mm and 15.1 mm. Another 52 km are ordered for 2004.
Figure 4 shows a view of the Transco pipeline construction site. After
finishing welding, non destructive examination and field joint coating,
the girth welded pipeline sections were lowered onto the prepared
trench bottom.
The results of the tests performed by EUROPIPE on production pipe in
the context of certification of the pipe are shown in Figures 5 and 6.
All results of the tensile and impact tests performed were within the
specification for grade X 80. The standard deviation was 15 MPa for
the yield strength values and 13 MPa for the tensile strength values.
The average value of impact energy was 227 J for base metal and 134 J
for weld metal.
2
tankers, X 80 linepipe material with 33 mm wall thickness. Figures 7
and 8 give an idea of the installation of such a PNG tanker. About
40.000 tonnes of gas can be shipped per vessel and there is no need to
treat or cool the gas. An approval of this concept was given by DNV.
Figure 4: View of a pipelaying operation (Transco project)
Design pressure, 250 bar
Incidental pressure, 262.5 bar
Height: appr. 36 meter
I.D.: 1000 mm
Volumes:
Weight of each cylinder: appr. 31 Mt
No. of cylinders: 3600
Total weight of cylinders: 112.000 Mt
Design premises:
X80 line pipe material
33 mm WT.
Figure 7: Design of containment cylinders for PNG tankers
Figure 5: Tensile properties of Transco grade X 80 pipe (48” OD x
15.1 mm WT)
Figure 8: Design of a PNG tanker
The mechanical properties of the X 80 pipes used for the cylinders are
summarised in Figure 9. All values of the tensile and impact tests met
the requirements. The Charpy V-notch impact energy measured at
-10°C was in excess of 200 J. Because this is not an application under
arctic conditions, neither a high toughness at low temperatures nor
BDWT tests are required. The pipe forming and welding operations did
not cause any problems.
Field welding of grade X 80 pipe
Pipeline construction needs welding operations by manual SMAW and
automatic GMAW. These welding methods are well-established now
and regarded as sufficiently validated for large-scale use /4-6/.
Figure 6: Toughness properties of Transco grade X 80 pipe (48”OD x
15.1 mm WT)
One of the most challenging projects encountered in 2001 was a hot
steam system for CNRL in Canada /3/. The longitudinally welded
linepipe was qualified for use at temperatures up to 354°C. The high
temperature properties were determined and found satisfactory. For a
new hot steam pipeline section, further 7.7 km of pipe have been
ordered recently.
To demonstrate the manufacturability of heavy wall grade X 80 pipe,
EUROPIPE produced for the design of containment cylinders for PNG
Paper No. 2003-SYMP-03
Gräf
Besides manual SMAW, automatic GMAW became increasingly
important as an economic process because of a reduced welding time
required with narrow gaps. Narrow gaps require a reduced number of
individual passes. One of the very efficient automatic GMA welding
processes used is the CRC process that was also partly used for the
construction of the Werne–to–Schlüchtern pipeline and the recent
Transco projects. Figure 10 describes a welding procedure applied to
X 80 pipes. Figure 11 shows the mechanical properties and the
toughness of the girth welds, which conform to typical specification
requirements comfortably.
3
DEVELOMENT OF GRADE X100/X120
To cope with the market requirements for enhanced pipe strength,
EUROPIPE put its effort to the development of grade X 100. No
technological breakthroughs in TM rolling and accelerated cooling had
been necessary. Only optimisation of the existing technology was
required for the production of grade X 100 plate. As a result, the
production window became narrower. Heat treatment of plate or pipe
was obviously not necessary.
Since 1995, EUROPIPE has developed different approaches to produce
high strength materials /1/. As can be seen in Figure 12, three different
approaches are generally possible in selecting the chemical
composition and plate rolling conditions.
Figure 9: Mechanical properties of heavy wall grade X 80 pipe for
PNG containment cylinders
Pass
Welding
Consumables
Current Voltage speed Oscil [A]
[V]
[cm/min] lation
dia.
Trade name [mm] Shielding Gas
Root
Pass
Hot
Pass
Filler
Passes
Thyssen
K Nova
Thyssen
NiMo 80
Thyssen
NiMo 80
Cap
Pass
Thyssen
NiMo 80
0.9
Ar/CO 2 75/25
190/220 19/21
75
n
0.9
CO2
240/260 24/26
127
n
0.9
CO2
210/250 22/25
36/45
y
0.9
Ar/CO 2 75/25
200-230 20/22
26/41
y
Figure 10: Typical welding parameters for GMAW of grade X 80 by
the CRC process
Figure 12: Different approaches to reach the strength level of grade
X 100 by varying the steel chemistry as well as the cooling
parameters during plate manufacture /7/
Approach A (Table 1), which employs a relatively high carbon
equivalent, at 0.49, has the disadvantage that the crack arrest toughness
properties are not good and therefore requirements to prevent longrunning cracks may not be fulfilled. Moreover, this approach is also
detrimental, e.g. to field weldability. A typical result of this approach
was follows:
Approach A
Strength Properties
(Flat Specimen crossweld )
Strength [MPa]
Heat
I
CVN Toughness
800
pipe size
OD X WT
C
Mn
Si
Mo
Ni
Cu
Nb
Ti
N
CEIIW
PCM
30" x 19.1 mm 0 . 0 8 1.95 0.26 0.26 0.23 0.22 0.05 0.018 0.003 0 . 4 9 0.22
300
700
270
690
240
600
500
Fracture Toughness
210
550
180
400
150
300
120
Heat
WM
-30°C
WM
0°C
HAZ
0°C
I
yield t o
yield strength tensile strength
tensile ratio
R t0.5 *
Rm *
R t0.5 / R m *
739 MPa
792 MPa
Elongation
A5*
CVN
(20°C)
DWTTtransition
temperature
18.4%
235
- 15 °C
0.93
90
200
60
100
* transverse tensile tests by round bar specimens
30
0
0
YS
Table 1: Approach A for the production of plate in API grade X100
TS
Figure 11: Test results on X 80 girth welds (CRC process)
Paper No. 2003-SYMP-03
Gräf
Approach B (Table 2), which adopts a carbon equivalent of only 0.43
and which is used in combination with fast cooling rates in the plate
mill down to a very low cooling-stop temperature, results in the
formation of large fractions of martensite in the microstructure, which
4
has a detrimental effect on the toughness properties of base metal. This
effect cannot be adequately compensated for by using extremely low
carbon contents.
In addition, softening of the heat affected zone was observed.
Approach B
Heat
II
Heat
II
pipe size
OD X WT
C
Mn
3 0 " x 1 5 . 9 m m 0 . 0 7 1.89
Si
Mo
Ni
0.28 0.15 0.16
yield to
yield strength tensile strength
tensile ratio
R t0.5 *
Rm *
R t0.5 / R m *
755 MPa
820 MPa
0.92
Cu
-
Nb
Ti
N
C EIIW
excess of 200 J in all cases. It seems to be impossible to guarantee
values in excess of 300 J at low temperatures on a production basis. In
Figure 14, the DWT test results at –20°C are shown for the different
wall thicknesses. Typically, the shear area values are higher for thinwall X 100 material. Because of the relatively high carbon equivalent
and the high strength level, the toughness of the longitudinal seam weld
metal and the HAZ is limited. The X 100 material produced responds
favourably to manual and mechanized field welding, a finding which
can be attributed to its reduced carbon content /8, 9/.
PC M
0.05 0.015 0.004 0.43 0.19
Elongation
A5 *
CVN
(20°C)
DWTTtransition
temperature
17.1 %
240
- 25 °C
Table 2: Approach B for the production of plate in API grade X100
Experience gained meanwhile indicates that Approach C (Table 3) is
the best choice. This approach enables the desired property profile to be
achieved through an optimised two-stage rolling process in conjunction
with a medium carbon content, a medium carbon equivalent and an
optimised cooling process. The special potential of the existing rolling
and cooling facilities contributes significantly to the success of this
approach.
Figure 13: Tensile properties of X 100 pipes with different wall
thicknesses
The medium carbon content employed in Approach C ensures excellent
toughness as well as fully satisfactory field weldability, despite the
relatively high carbon equivalent, at about 0.46. The chemical
composition should therefore be considered acceptable for the purpose
of current standardisation.
EUROPIPE has already produced hundreds of tonnes of grade X 100
pipe adopting Approach C. Recent trials have covered the wall
thickness range between 12.7 and 25.4 mm. It was demonstrated that
the same steel composition could be used and only slight changes in the
rolling conditions would be necessary.
Figure 14: Influence of wall thickness on DWT test results at –20°C
(X 100 pipes)
Approach C
Heat
pipe size
OD X WT
C
Mn
Si
Mo
Ni
Cu
Nb
Ti
N
C EIIW PCM
III
56" x 19.1 mm 0.07 1.90 0.30 0.17 0.33 0.20 0.05 0.0180.005 0.46 0.20
IV
36" x 16.0 mm 0.06 1.90 0.35 0.28 0.25
-
0.05 0.0180.004 0.46 0.19
Heat
yield strength
R t0.5 *
tensile
strength
Rm *
yield to
Elongation
tensile ratio
A5 *
R t0.5 / R m *
III
737 MPa
800 MPa
0.92
18 %
200 J
- 20 °C
IV
752 MPa
816 MPa
0.92
18 %
270 J
200270 J
∼ - 50 °C
CVN
(20°C)
DWTTtransition
temperature
* transverse tensile tests by round bar specimens
** -60°C for WT 12.7mm -10°C for WT 25mm
Table 3: Approach C for the production of plate in API grade X100
As can be seen in Figure 13, the results on production pipes show
uniform strength properties for all the wall thicknesses tested. Tensile
tests were performed using round bar specimens. Yield-to-tensile ratios
were still relatively high. The elongation values are lower than those
known for grade X 70. The impact energy (CVN) measured was in
Paper No. 2003-SYMP-03
Gräf
Figure 15: Charpy test results on 36” OD x 16 mm WT grade X 100
pipe in the as delivered and aged conditions
5
For reasons of technical feasibility and cost-effective production, it is
necessary in the context of grade X 100 to reassess and redefine some
of the requirements for mechanical properties, giving consideration to
anticipated service conditions.
The pipes produced were subjected to different tests to evaluate the
service behaviour. Figure 15 shows the influence of an ageing
treatment on the Charpy transition curve. There was only a slight
decrease in toughness properties after a thermal treatment for 30min at
250°C.
Field cold-bending trials were also completed with satisfactory results.
Figure 16 shows photographs of full scale burst tests, which were
conducted by CSM as part of an ECSC funded research project /10/. So
far, our experience has shown that it is impossible to install a grade
X100 pipeline in arctic regions without the use of crack arrestors.
EUROPIPE offers different types of crack arrestors to the industry.
Figure 16: View of full scale burst tests carried out on 56” x 19.1 mm
and 36” x 16.0 mm grade X 100 pipes
Figure 17: Influence of boron on the yield strength of high strength
linepipe material (15-18 mm wall thickness)
Microalloying with boron also enabled grade X 120 material to be
produced. The alloy design that enables this ultrahigh-strength material
to be produced is also characterised by a reduced carbon content. It
contains besides Cu, Ni, Cr, Nb and Ti, additions of V and B. The
carbon equivalent CEIIW of the chemical composition used in initial
investigations was 0.55 %. By using narrow temperature ranges for the
individual rolling stages, which were based on precisely measured Ar3
temperatures, a very high strength level could be achieved.
Furthermore, impact energy values ≥ 215 J were measured at –30°C.
The mechanical properties are listed in Figure 18.
Effect of boron on high-strength linepipe steels in grades
X 80 to X 120
It is of paramount importance to the pipe producer, and eventually to
the customer, to ensure that the required properties are attained with a
minimum of alloying additions, in order to control pipe production
costs and to make the use of high strength steel pipelines for longdistance transportation of gas under high pressure more attractive. A
suitable combination of pipe chemical composition and
thermomechanical treatment parameters ensuring a correct balance
between strength, toughness and weldability was necessary. Besides
niobium, titanium and vanadium, the micro-alloying element boron was
thought to be effective. Therefore, a series of laboratory plate rolling
trials were performed with the well-known chemical composition for
grade X 80 material starting from an extremely low CEIIW , at only
0.38 %. Besides the cooling rate (ca. 15 and 25 °C/s) all rolling and
cooling conditions were kept constant.
Figure 17 illustrates the influence of boron on the yield strength of
plate in comparison with boron-free heats. As can be seen from the
figure, grade X 100 plate properties for 20 mm wall thickness were
achieved with a CEIIW of about 0.41%, which is very low. The increase
in the yield strength achieved by adding boron is about 70 to 100 MPa,
compared with boron-free material. In all cases, the base material was
characterised by a predominately bainitic microstructure. The Charpy
V-notch energy measured at –40 °C was in excess of 200 J. Only
boron-microalloyed heats containing 0.06 % C exhibited lower Charpy
values, between 100 and 170 J at –40 °C.
Paper No. 2003-SYMP-03
Gräf
Figure 18: Mechanical properties of plate material in grade X 120
Aspects to be solved with respect to welding of the
longitudinal seam
The multi-wire submerged-arc welding process used universally to
deposit the two-pass longitudinal seam weld in pipe is associated with a
high heat input and leads to aspects that cannot be underestimated in
the case of grades X 100 and X 120 aimed at.
The first problem is the softening of the base material adjacent to the
longitudinal seam weld. This problem is existent to some extent also in
the case of materials in grades X 80 and X 100. But, the extent of the
problem here is such that it can be easily managed.
6
The second problem is associated with continuing the use of the proven
submerged-arc welding and achieving adequate strength and toughness
for the weld metal of the two-pass longitudinal seam weld in the
highest strength material X 120. This problem cannot be resolved by
selecting a matching chemical composition for the weld metal alone. It
would be rather necessary to reduce the heat input per pass. The
average heat input per pass, which is at 2 kJ per centimetre of the weld
and per millimetre of the pipe wall thickness, needs to be reduced
considerably (e.g. to 1.5 kJ per centimetre of the weld and per
millimetre of the pipe wall thickness). Production experience available
today in this connection is not sufficient enough to permit an
assessment of the softening that occurs in the base material adjacent to
the weld. This depends also on the pipe wall thickness. Finally, such an
approach is limited by the need for a sufficiently overlapped welding
and therefore adequate production safety.
If it is not possible to reduce the heat input with the two-pass
submerged-arc welding to the extent necessary without compromising
on production safety, alternative welding methods involving multilayer welding should be sought for. These methods, in turn, would
invariably lead to high cost of investment in the pipe mills. Also, a
quick changeover from the current welding methods to the required
new methods would not be easy.
The necessary decisions in this context are therefore fraught with
uncertainties for the pipe manufacturer. Plate production and field
welding (development of welding consumables) have been already well
developed.
Field girth welding of X 100/X 120
Manual SMA and mechanised GMA field welding of high strength
linepipe in grades X 100 and X 120 do not pose any severe problems.
The chemical composition of grade X100 would be practically the
same as that for heavier-wall grade X 80 pipe (additionally alloyed with
molybdenum). With grade X 120, the same low C content can be used
but at a marginally higher C equivalent (0.50 to 0.55% according to
IIW).
Figure 19: Factors affecting the cold cracking susceptibility during
pipeline construction (field welding)
The carbon equivalent of high-strength linepipe steel grades on itself
has no significant effect on the peak hardness under typical field
welding conditions any more (short t8/5 cooling times, Figures 20 and
21). In girth welds, which are always characterised by cooling times of
t 8/5 = 2 to 6 s, the peak hardness of the root pass HAZ is initially
governed by a 100 % martensitic structure and therefore dependent
only on the carbon content. This aspect should be taken into account
when stipulating restricted carbon equivalents in standards and
specifications for high-strength steels under discussion. The same is
true of grade X 120, representing the highest strength level aimed at.
Therefore, there is no difference in the base material’s cold cracking
behaviour between grade X 100 and grade X 120.
The peak hardness in the HAZ of the girth welds plays an important
role in the susceptibility to cold cracking (Figure 19). High residual
stresses developed in the weld area during the critical period between
root pass welding and hot pass welding have also a significant effect.
As the hot pass is deposited, the HAZ of the root pass undergoes
hardness reduction as a result of reheating (normalising and tempering
effects) so that the risk of cold cracking, which preferably may initiate
at the toe notches of the root pass, is significantly reduced.
Theoretically speaking, the residual stresses increase as the materials
strength increases. This problem can be coped with by using soft
cellulosic electrodes to deposit the root pass. This aspect and the
increased HAZ hardness will not however have any significance,
provided that the weld is maintained at a temperature ≥ 50°C during the
critical initial stage and any unscheduled interruptions during
subsequent welding. It is well established that cold cracking in girth
welds can occur only when the interpass temperature falls significantly
below plus 50°C.
Figure 20: Comparison of the hardenability of an older X 70 linepipe
material with a modern X 100 linepipe material in respect
of typical girth welding conditions (calculation acc. to
Mannesmann formulas)
Therefore, it has to be emphasised that it is not the base material, but it
is the filler weld metal deposited with ultra-high-strength basic vertical
down electrodes that is more sensitive and therefore, plays the major
role in respect of avoiding cold cracking when welding grade X 100
and particularly grade X 120 material. The preheating temperature to be
selected must be appropriate to the weld metal’s chemistry and the
Paper No. 2003-SYMP-03
Gräf
7
hydrogen input during welding.
This implies that the preheating temperature has to be such that
hydrogen can adequately effuse from the ultra-high strength basic weld
metal in the filling and cap passes before the weld cools to room
temperature.
All these measures are commonplace today and do not imply very high
additional costs. The manufacture of welding consumables matching
grades X 100 and X 120, should be possible in principle for both SMA
and GMAW.
The enormous pressure on the price of natural gas forces the pipeline
operators to explore all possibilities to reduce the cost of pipeline
projects in future. The pipe manufacturer can assist him in his
endeavour by supplying high quality pipe. The effect of pipe quality on
the reduction of project costs will be more substantial when the pipeline
is constructed to the limit state design.
Finally, the pipe manufacturers make contributions to reducing
operational costs of a pipeline over its life by determining through
investigations the fatigue, corrosion and ageing behaviour of pipe and
pipe materials. These properties have a significant bearing on the
integrity of a pipeline and consequently the operating costs. These
properties are currently being extensively studied. The knowledge
gained from these studies can be made available to assist the pipeline
operators when planning a new pipeline project or when estimating the
residual life of ageing pipelines.
REFERENCES
/1/ M. K. Gräf and H.-G. Hillenbrand: “High Quality Pipe – a
Prerequisite for Project Cost Reduction”, 11th PRCI-EPRG Joint
Technical Meeting, Arlington, Virginia, April 1997
/2/ L. Barsanti, H.-G. Hillenbrand, G. Mannucci, G. Demofonti, and D.
Harris: “Possible use of new materials for high pressure linepipe
construction: An opening on X100 grade steel”, International Pipeline
Conference, Calgary, Alberta, September 2002
Figure 21: Hardenability of linepipe steel grades X 100 and X 120
(calculation acc. to Mannesmann formulas)
/3/ M. D. Bishop, O. Reepmeyer, H.-G. Hillenbrand, J. Schröder and A.
Liessem: “Longitudinal welded X80 pipes for a high temperature, high
pressure steam pipeline”, 3 R international 41 (2002) No. 2
CONCLUSIONS
/4/ H. Engelmann, A. Engel, P. A. Peters, C. Düren and H. Müsch:
“First use of large-diameter pipes of the steel GRS 550 TM (X80)”; 3R
International 25 (1986), No. 4, 182 - 193
The predicted growth in energy consumption in the coming decades
necessitates severe efforts for transporting large amounts of natural gas
to end users economically. Large-diameter pipelines serve as the best
and the safest means of transport. This paper presents an overview of
the current requirements for high strength steels and the associated
developments. The technical possibilities are described. Also in the
future, additional substantial improvements can be realised.
Several pipelines installed in Europe and North America in the past two
decades show that the use of X 80 linepipe causes no problems with
respect to mechanical properties and welding. The development work
led to the conclusion that grade X 100 mechanical properties can be
achieved. Crack arrest properties for certain pipe sizes were verified in
full scale burst tests. The initial results of the work directed to
developing grade X 120 are encouraging with respect to the properties
of the base material.
Not only the steel grade, but also the usage factor and the operating
pressure are increasing steadily. From the manufacturers’ point of view,
certain points must be observed when using higher-strength material
grades. The minimum thickness should be 12 mm and for grade X 80
pipe and 16 mm for grade X 100 pipe. An increase of the operating
pressure combined with a smaller diameter and a constant wall
thickness should be preferred to reducing the wall thickness. In any
case, the thickness-to-diameter ratio of high strength large-diameter
pipe should be in excess of 1% or better 1.5%.
Paper No. 2003-SYMP-03
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/5/ V. Chaudhari, H. P. Ritzmann, G. Wellnitz, H.-G. Hillenbrand and
V. Willings: “German gas pipeline first to use new generation
linepipe”; Oil & Gas Journal, January 1995
/6/ H.-G. Hillenbrand, K. A. Niederhoff, G. Hauck, E. Perteneder and
G. Wellnitz: “Procedure, considerations for welding X80 linepipe
established”; Oil & Gas Journal, Sept 15, 1997
/7/ V. Schwinn, P. Fluess and J. Bauer: "Production and progress work
of plates for pipes with strength level of X80 and above", International
Conference on the Application and Evaluation of high-grade linepipes
in hostile Environments, Yokohama, Japan, November 2002
/8/ L. Barsanti, G. Pozzoli and H.-G. Hillenbrand: “Production and
Field Weldability Evaluation of X100 Linepipe”, 13th Joint Meeting
PRCI-EPRG, New Orleans, USA 2001
/9/ H.-G. Hillenbrand, A. Liessem, G. Knauf, K. A. Niederhoff and J.
Bauer: “Development of large-diameter pipe in grade X100 – State of
the art report from the manufacturer’s point of view“, International
pipeline technology conference, Brugge, Belgium, May 2000
/10/ G. Demofonti, G. Mannucci, D. Harris, H.-G. Hillenbrand and L.
Barsanti: “Fracture behaviour of X100 gas pipeline by full scale tests”,
International Conference on the Application and Evaluation of highgrade linepipe in hostile Environments, Yokohama, Japan, November
2002
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