Possible use of new materials for high pressure line pipe construction: The experience of SNAM RETE GAS and EUROPIPE on X 100 grade steel

Transcription

1 Possible use of new materials for high pressure line pipe construction: The experience of SNAM RETE GAS and EUROPIPE on X 100 grade steel L.Barsanti, SNAM RETE GAS SpA H.G. Hillenbrand, EUROPIPE GmbH EUROPIPE. The world trusts us.

2 Proceedings of IPC: The International Pipeline Conference September, 2002, Calgary, Alberta, Canada POSSIBLE USE OF NEW MATERIALS FOR HIGH PRESSURE LINEPIPE CONSTRUCTION: THE EXPERIENCE OF SNAM RETE GAS AND EUROPIPE ON X100 GRADE STEEL L. Barsanti SNAM RETE GAS SpA Viale De Gasperi 2, San Donato Milanese 20097, Milano, Italy H.G. Hillenbrand EUROPIPE GmbH Formerstrasse 49, Ratingen, Germany ABSTRACT The increasing needs of natural gas, foreseen for the next years, makes more and more important the type of transportation chosen, both from strategic and economic point of view. The most important gas markets will be Northern America, Europe, Asia and Russia but the demand shall be fulfilled also by emerging producers as Kazakhstan, Turkmenistan and Eastern Siberia that at the moment are developing their resources in order to be competitive on Gas market. In this way producers and customers will be placed at greater and greater distances implying realization of complex gas transportation pipeline network, when use of LNG tankers is impossible or uneconomic. On the base of these considerations Eni group sponsored in 1997 a feasibility study on X100 steel, given that, comparing different design approaches, it has been observed that consistent savings could be obtained by means of using high grade steel and high pressure linepipes. In this project, involving CSM and Corus group for the laboratory and full-scale pipes testing, played an important part also Europipe: the pipes producer. No technical breakthrough, but only improvements in the existing expertise were involved in the X100 production; consequently, the production window is very narrow. However optimized steelmaking practices and processes enabled the material to reach the desired properties: strength, toughness and weldability. This paper is intended to present the general results arising from this project, in terms of steel properties (chemical composition, mechanical properties), ductile and brittle fracture resistance (results of full scale burst tests, West Jefferson tests) and field weldability, but above all the know-how stored till now on high grade steel and its possible use from a Gas company and a Pipe maker point of view. INTERNATIONAL SCENARIO The energetic scenario has been changing quickly in these last years. International studies foresaw an increasing demand of natural gas till doubling in This statement is based on several issues: The availability of natural gas fields is greater than that of verified oil fields. The exploitation of these reserves is yet limited. The need of substituting polluting fuels according Kyoto agreement with the consequent increasing use of natural gas for electric energy production with combined cycles. This increasing demand will be satisfied not only by major producers (Russia, Norway, Northern America etc.) but also by emerging countries like Kazakhstan, Turkmenistan and Eastern Siberia, that at the moment are developing their resources in order to be competitive on Gas market. Also for this reason, producers and customers will be placed at greater and greater distances implying construction of complex gas transportation pipeline network, when use of LNG tankers is impossible or uneconomic. This makes high pressure natural gas transportation via pipelines more and more interesting for gas companies. On the base of these considerations Eni group sponsored in 1997 a feasibility study on X100 steel grade because this high strength steel could give consistent savings in terms of CAPEX comparing it to an X80 high pressure solution. Also other gas companies tried to Copyright 2002 by ASME 1

3 compare transportation costs and qualities of conventional pipeline steels in contrast to new grades like X100. Costs have been evaluated under several hypothesis: Unit steel cost has been estimated according trend extrapolated from lower grades. Costs of fittings and valves have been considered as a constant portion of the total steel cost. Transportation costs have been evaluated as dependent from the steel weight. Laying costs have been analyzed completely: trenching and field bending have been considered constant for both solutions, instead welding costs have been divided in two parts, one constant and the other proportional with the thickness; moreover it has been taken care of the possible higher costs of consumables and of the possible greater difficulties for welders. The other costs (coatings, cathodic protection) have been considered equal for both solutions. This preliminary economic evaluation highlighted that X100 steel high pressure pipes could give investment costs savings of about 7% with respect to X80 grades (See Fig.1 for costs options comparison). Other studies claim cost savings of up to 30% when X70 and X100 is compared. Given that in a complex pipeline network operating at high pressure, capital expenditure is very high, it is understandable how much attractive could be high strength steel option. A research program was conducted by Snam Rete Gas (on behalf of Eni group) together with Europipe and Centro Studi Materiali. This last actor also assured partial contribution from ECSC. MATERIALS In the last 7 years, Europipe developed three different approaches with respect to the selection of chemical composition. Approach A, which involves a relatively high carbon content, has the disadvantage that the crack arrest toughness requirements to prevent long-running cracks, may not be fulfilled. Moreover, this approach is also detrimental, e.g. to field weldability. Results of that approach are as follows: Heat pipe size OD X WT Approach A C Mn Si Mo Ni Cu Nb Ti N CEIIW PCM I 30" x 19.1 mm Heat I yield strength R t0.5 tensile strength R m yield to tensile ratio R t0.5 / R m CVN (20 C) DWTTtransition temperature 739 MPa 792 MPa % C transverse tensile tests by round bar specimens Elongation A 5 Approach B, which was used in combination with fast cooling rates in the plate mill down to a very low cooling-stop temperature, results in the formation of uncontrolled fractions of martensite in the microstructure, which have a detrimental effect on toughness properties of base metal and leads additionally to the softening in the heat affected zone. This effect cannot be adequately compensated for extremely low carbon contents, without adversely affecting productivity. Approach B To cope with market requirements for enhancing strength Europipe put its effort to the development of grade X100. No technological breakthroughs, such as TM rolling and accelerated cooling which increased the strength and toughness respectively, but only improvements in the existing technology were involved in the production of grade X100 plate. As a result, the production window is quite narrow. Heat treatment of plate or pipe is obviously not advisable. Heat II Heat II pipe size OD X WT C Mn Si Mo Ni Cu Nb Ti N CEIIW PCM 30" x 15.9 mm yield strength R t0.5 tensile strength R m yield to tensile ratio R t0.5 / R m Elongation A 5 CVN (20 C) DWTTtransition temperature 755 MPa 820 MPa % C transverse tensile tests by round bar specimens right 2002 by ASME 2

4 Experience gained meanwhile indicates that Approach C is the best choice. This approach enables the desired property profile to be achieved through an optimized two-stage rolling process in conjunction with a reduced carbon content, a relatively high carbon equivalent and optimized cooling conditions. The special potential of the existing rolling and cooling facilities contributes significantly to the success of this approach. Approach C, which involves a low carbon content, ensures excellent toughness as well as fully satisfactory field weldability, despite the relatively high carbon equivalent of the chemical composition. The chemical composition should therefore be considered acceptable for the purpose of current standardization. Europipe already produced hundreds of tons of grade X100 according Approach C. The latest trials were covering 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 are necessary. (See Fig.2 for approaches comparison) Heat III IV V Heat III pipe size OD X WT Approach C C Mn Si Mo Ni Cu Nb Ti N CEIIW PCM 56" x 19.1 mm " x 16.0 mm "x mm yield strength R t0.5 tensile strength R m yield to tensile ratio R t0.5 / R m Elongation A 5 CVN (20 C) DWTTtransition temperature 737 MPa 800 MPa % 200 J - 20 C IV 752 MPa 816 MPa % 270 J ~ - 50 C 200- V MPa MPa ~ % ~ C 270 J transverse tensile tests by round bar specimens -60 C for WT 12.7mm -10 C for WT 25mm All production results have shown that the strength properties can be easily reached when using round bar specimens. Yield/Tensile ratios are still high and elongation values lower than for grade X70.. Charpy toughness was measured in excess of 200 J but it seems to be impossible to guarantee values in excess of 300 J for a big project. Due to the relatively high carbon equivalent and the high strength level, the toughness of the longitudinal weld seam and the HAZ is limited. BRITTLE AND DUCTILE BEHAVIOUR One of the paramount issues in terms of safety is the assessment of the Battelle criteria regarding ductile and brittle behaviour of high strength steel: The fitness of 85% shear area Battelle criterion, based on the DWT Test, to define the ductile to brittle transition temperature. The existing predictive formulae for arresting ductile propagation fracture behavior. In order to do that laboratory DWT Tests have been compared with four full scale West Jefferson tests, for the first point, and two full-scale burst tests have been carried out at the CSM Perdasdefogu shooting Test Station in Sardinia. Brittle Fracture In these last years the Battelle approach for brittle fracture assessment has been confirmed on large diameter pipes built in steel grades from API X65 to X80. In order to verify these results for the prediction of full scale behaviour in X100 steel pipes, the ductile to brittle transition curves have been measured and the results compared with those obtained by four West Jefferson (WJ) tests carried out on two 56 x19.1mm and two 36 x16mm samples; the test temperatures have been chosen in order to have both full ductile and transition behaviour. The ductile/brittle transition curves have been measured interpolating data from both Charpy V and full thickness DWTT specimen with a pressed notch in accordance with the API RP 5L3 Recommendations. The WJ tests were carried out by CSM at a pressure equivalent to about 72% of the SMYS. The tests were performed using water as a pressurising medium, with a small percentage of air (about 5 %) to assure enough energy to propagate the fracture. In Figs. 3-4 the transition curves obtained by DWT tests and Charpy V tests are compared with the WJ tests results. It can be noted the Battelle criterion is completely fulfilled and the DWT Test allows the determination of the pipe transition temperature in a right 2002 by ASME 3

5 conservative way, even if the full-scale results show a little spread. Ductile fracture propagation In order to assess the existing predictive formulae for arresting ductile propagation fracture behavior of API X100 pipeline, two full-scale burst tests have been carried out at the CSM Perdasdefogu shooting Test Station in Sardinia. Seven pipes have been used for each full-scale burst test: one initiation pipe, six test pipes and two reservoirs to avoid the reflection of the pressure waves and their interaction with fracture propagation. In Figs. 5-6 the two tests lay-out, Charpy V shelf energy at room temperature and predictive Battelle formulae fracture behaviour, in terms of arrest (A) and propagation (P) event of a running crack, are shown. The main full-scale burst tests conditions were: 1 test 2 test Nominal diameter Nominal thickness 19.1 mm 16 mm Pressurizing medium air air Test pressure 126 bar 181 bar Usage Factor 68% 75% In order to collect every data necessary for analysis was installed instrumentation fit for purpose: timing wires, internal pressure transducers and thermocouples. The paths followed by the two fractures are shown also in figures 5 and 6. 1 test After the initiation, obtained by means of an explosive shaped charge, the fracture propagated on the upper pipe generatrix at a very high speed in both test line sides. West side : The crack, after the initiation, propagated in the first pipe, but in correspondence of the girth weld with the adjacent pipe it split in two causing the severance of the test line and the ejection of the pipe itself. So no information about West test side were available. East side :The crack propagated through the initiation pipe and arrested at the end of the third pipe ( 260 J of Charpy V energy) in correspondence of the girth weld. 2 test In this case two propagations and two clear arrests were observed. West side: the crack, after initiation, propagated with a maximum speed of about 310 m/s and arrested eventually in the last pipe (297 J of Charpy V energy) after about meters. East side: the crack, after the initiation, propagated with a maximum speed of about 300 m/s and entered in the following pipe (259 J of Charpy V energy) where it arrested after about 5 meters. On the base of these results, especially for the second burst test, where we had two valid arrests, it can be said a toughness level of about 260 J is sufficient to arrest a long ductile propagating fracture in the tests conditions chosen. To tell the truth, on the west side, it arrested in a pipe characterised by 297 J, but considering that in the previous pipe (252 J ) we had a lower DWTT energy and that fracture arrested at the very beginning of the last pipe, we can subscribe previous statement. This result is in agreement with previous tests performed on high grade/high hoop stress pipelines. Therefore in order to use the conventional Battelle Two Curves Approach, based on CharpyV values, several correction factors according the tests should be used: 1.5 for the first test and 1.7 for the second one (see Fig. 7). FIELD WELDABILITY One of the most important issue in gas transportation industry is not only development of the steel but also appropriate welding procedures. So in the present paper will be presented results obtained by means of laboratory and full scale concerning three main items: Review on commercial availability of consumables with suitable chemical composition and mechanical properties in terms of tensile strength and hardness to fulfil overmatching criterion ; Definition of minimum welding requirements with reference to pre-heating temperatures in order to right 2002 by ASME 4

6 avoid cold cracking problems. Execution of test girth welds both with manual (SMAW) and mechanised (GMAW) welding methods in order to collect as much information as possible about every technical problems arising from full scale welding of high grade steel. In order to define suitable preheating temperatures laboratory tests have been performed: Implant and Tekken type. Implant tests, cause of the more severe costraint conditions, gave temperatures too high in order to be applied in field instead Tekken tests gave more interesting results as can be observed in the following table. ROOT ELECTRODE IMPLANT TEKKEN Basic el. E C 100 C Cellulosic el. E C 200 C Cellulosic el. E6010 n. d. 150 C Table 1: Minimum Preheating Temperatures established from laboratory tests Once chosen pre-heating temperatures two field welding trials have been performed on two pipes (56"x19mm and 36"x16mm) investigating on both most spread techniques: GMAW (PASSO system) and SMAW. In the tables 2-3 can be observed the welding procedures followed for each geometry. Both techniques gave good results even if GMAW resulted less problematic because of its lower impact on welder s skill and training, in Fig.8-9 the appearance of welds can be observed for each technique. CONCLUSIONS On the base of last previsions, gas quantities to be transported will increase significantly making more and more attractive natural gas transportation by means of long distance high pressure pipelines. X100 steel could be a material suitable for this type of construction: it could combines high pressure and reduced thickness of the pipe in order to minimize CAPEX. But it will be necessary to reassess and redefine some of the material requirements Research developed by Snam Rete Gas, Europipe and CSM showed it was possible also from the point of view of safety: main results obtained are the following. The pipe material shows a full ductile fracture behavior down to -20 C. The validity of the Battelle criterion, in order to evaluate the full scale pipe ductile to brittle transition temperature, has been assessed. The toughness characteristics of the API X100 steel grade line pipes, in terms of Charpy V energy, proved enough to warrant the arrest of a long running shear in the test conditions chosen. As regard the correction factor to be used with the Battelle two curves approaches for the API X100 grade steel pipes tested in these burst tests, two different correction factors must be used (1.5, 1.7). For the weldability issue it is surely possible welding X100 pipes with both manual and mechanised technique. Best results have been obtained with the mixed procedure which allowed to decrease cold cracking susceptibility without any meaningful softening of the joint. However the most important item is the welder s skill. On the other hand GMAW gave good results without any problems and this seems very promising considering the type of application suitable for X100 pipes. After results of this research and those that will arise from Demopipe project (demonstrative project on behalf of EPRG about X100 steel line pipes) the following step could be creating specification and codification of the steel. ACKNOWLEDGMENTS This research was performed also with the help of Esab and Bohler for the consumables supplying and with the collaboration of Bonatti and Sicim for pipe welding. right 2002 by ASME 5

7 REFERENCES H.-G. Hillenbrand et al. High Strength Line Pipe for Project Cost Reduction, World pipelines, Vol.2 No.1, 2002 L. Barsanti, H.G. Hillenbrand Production and Field Weldability Evaluation of X100 Line Pipe PRCI-EPRG Meeting, New Orleans Louisiana USA, G. Mannucci, G. Demofonti, L. Barsanti, H.G. Hillenbrand, D. Harris FRACTURE PROPERTIES OF API X100 GAS PIPELINE STEELS PRCI-EPRG Meeting, New Orleans Louisiana USA, G. Mannucci, G. Demofonti, L. Barsanti, C.M. Spinelli, H.G. Hillenbrand, Fracture behaviour and defect evaluation of large diameter, HSLA steels, very high pressure linepipes IPC, Calgary Alberta Canada, Mannucci, G., Demofonti, G., Galli, M.R., Spinelli, C. Structural Integrity of API 5L X70-X80 Steel Grade Pipeline for High Pressure Long Distance Transmission Gas Lines 12 th EPRG/PRCI Biennial Joint Technical Meeting on Pipeline Research. Groningen, 1999, paper 13. G. Demofonti, G. Junker, V. Pistone Transition Temperature Determination for Thick-Wall line Pipe, 11 th EPRG/PRCI Biennial Joint Technical Meeting on Pipeline Research, Arlington, 1997, paper 5. H.G. Hillenbrand et al. Development of linepipe in grade up to X100, 11 th EPRG/PRCI Biennial Joint Technical Meeting on Pipeline Research, Arlington, 1997, paper 6. API RP5 L3, Third edition February 1996, Recommendation Practice for Conducting Drop Weigth Tear Tests on Line Pipe. Maxey, W. Fracture Initiation, Propagation and arrest Pipeline Research Committee of the American Gas association. 5 th Symposium on Line Pipe Research. Houston, Demofonti, G., Pistone, P, Re, G., Vogt, G., Jones, D.G. EPRG Recommendation for Crack Arrest Toughness for High Strength Line Pipe Steels. 3R International 34, J.F. Kiefner, W.A. Maxey, R.J. Eiber, A.R. Duffy Failure stress levels of flaws in pressurised cylinders ASTM STP 536 (1973). right 2002 by ASME 6

8 APPENDIX Costs [USD/m] Common costs Welding Laying Materials API 5L X80 API 5L X100 Fig.1: Comparison between costs associated to X80 and X100 options for the same project construction. Fig.2: Comparison between A, B, C approaches in order to obtain X100 steel target. right 2002 by ASME 7

9 Brittle fracture (%) DWTT Charpy V WJ Results Shear Area (%) Battelle Criterium Temperature ( C) Fig.3: Comparison between WJ and DWTT results on pipe 56 x 19mm DWTT Charpy V Brittle fracture (%) WJ Results Shear Area (%) Battelle Criterium Temperature ( C) Fig.4: Comparison between WJ and DWTT results on pipe 36 x 16mm right 2002 by ASME 8

10 X100, 56"x19.1mm Burst Test Layout WEST Severance EAST Reservoir Reservoir Initiation pipe Pipe number Tensile and YS (MPa) Fracture toughness TS (MPa) Path properties Y/T ratio CharpyV (Joule) Arrest predicted CharpyV toughness values with P=126 bar (hoop stress=469 MPa) Battelle simpl. formula 188 J A A A P P A A "A" = predicted arrest Battelle Two Curve appr. 176 J A A A P P A A "P" = predicted propagation Fig.5: X100, 56 x19.1mm burst test layout and results X100, 36"x16mm Burst Test Layout WEST EAST Reservoir Reservoir Initiation pipe Pipe number Tensile and YS (MPa) Fracture toughness TS (MPa) Path properties Y/T ratio CharpyV (Joule) Arrest predicted CharpyV toughness values with P=181 bar (hoop stress=517 MPa) Battelle simpl. formula 186 J A A A P A A A "A" = predicted arrest Battelle Two Curve appr. 154 J A A A A A A A "P" = predicted propagation Fig.6: X100, 36 x16mm burst test layout and results right 2002 by ASME 9

11 Actual CharpyV energy (J) Actual CharpyV energy Vs. Predicted by Battelle Two Curve Approach [CSM Database 10 tests: grade=api X80, OD=42-56"; thick=16-26mm, P=80-161bar, Hoop stress= mpa, air and natural gas (not rich)] Database Arrest Database Propagation X100 56"x19.1mm Arrest X100 56"x19.1mm Propagation X100 36"X16mm Arrest X100 36"x16mm Propagation 1:1.7 1:1.5 1:1.43 1:1 50 Fig.7: Predicted CharpyV energy by Battelle Two Curve Approach (J) Actual vs. Predicted CharpyV energy (Battelle Two Curve Approach) for high-grade steel linepipes (CSM database) Fig.8: Appearance of a weld (test n.3 SMAW 36 x16mm, mixed weld joint, vertical up welding) right 2002 by ASME 10

12 Fig.9: Appearance of a weld (test n.10 GMAW 36 x16mm, wire A 5.28 ER 100 S-G) Snam specifications Sal 1: SMAW Line welding Test N. Root pass (AWS) Hot pass (AWS) Filler (AWS) 1 E6010 E9010 E10018-G 2 E8018-G E10018-G E10018-G 7 E6010 E10018 E E7016 E10018 E10018-G Sal 2: SMAW 3 E6010 E10018-G E10018-G Joining welding (es: tie in) 4 E6010 E9010 E10018-G Sal 1: GMAW ( PASSO type) 9 ER 100 S-G / / 5 ER 90 S-G / / 6 ER 100 S-G / / Table 2: Types of welding procedures, wires and electrodes used for 56 x19mm pipe. right 2002 by ASME 11

13 Snam specification Sal 1: SMAW (line welding) Sal 2: SMAW (linking welding) Test N. Root pass (AWS) Second pass (AWS) Filling (AWS) 1 E6010 E11018-G E11018-G 2 E8018-G E10018-G E10018-G 6 E6010 E10018 E E6010 E10018-G E10018-G 4 E6010 E10018-G E10018-G 9 E7016 E10018 E10018-G Sal 1: GMAW 5 ER 90 S-G / / ( PASSO type) 10 ER 100 S-G / / Table 3: Types of welding procedures, wires and electrodes used for 36 x16mm pipe. right 2002 by ASME 12