Production and field weldability evaluation of X 100 line pipe

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1 Production and field weldability evaluation of X 100 line pipe L. Barsanti, SNAM SpA G. Pozzoli, SNAM SpA H. G. Hillenbrand, Europipe GmbH EUROPIPE. The world trusts us.

2 Production and Field Weldability Evaluation of X100 Line Pipe L. Barsanti, G.Pozzoli SNAM SpA Viale De Gasperi 2, San Donato Milanese 20097, Milano, Italy H.G. Hillenbrand Europipe GmbH Formerstrasse 49, Ratingen, Germany ABSTRACT In order to demonstrate technical and economical feasibility of long distances natural gas transportation through large-diameter, high-pressure pipelines using X100 grade steel, Eni and ECSC (European Community for Steel and Carbon) sponsored a research program in The results arising from this research, summarised in a paper presented at this Conference, seem to be very promising with respect to both operator's and pipe manufacturer's perspectives although the use of high-strength steel (X80 to X100) in the construction of gas transmission pipelines has not progressed at a pace probably predicted in the beginning. This is probably due also to the fact that the traditional manual welding processes became unsuitable for advanced steels either for metallurgical or economical reasons (associated for example to the in field productivity point of view). Consequently the primary challenges in the gas transportation industry are the development of the steel together with the appropriate welding procedures. In order to explain the developments achieved till now this paper wants to summarise and discuss the work carried out by Snam and Europipe in order to find the optimum balance, both from the producer and the operator point of view, between high strength, high toughness and good weldability, particularly in field conditions. Regarding the last point SNAM decided to start activities focussed on weldability aspects of grade X100 using 56 x 19mm pipe supplied by Europipe. The first part of the paper gives a review of product development of high strength steels. The results of 4 mill production trials are presented and discussed.the second part of the paper presents results obtained by means of laboratory and full scale field welding tests executed on the pipes produced concerning three main aspects: Review on commercial availability of electrodes and 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 temperature in order to avoid cold cracking problems: this part of the activity has been executed out by means of laboratory tests, Implant and Tekken type; 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. 1

3 1. INTRODUCTION The production of longitudinally submerged-arc welded high-strength linepipe has been made possible through the introduction of thermomechanical (TM) rolling of plate. TM rolling was introduced about 30 years ago, i.e. in the late 60s. Prior to that, the hot rolled plate was normalised and only strength levels up to grade API 5L X 60 had been possible (Figure 1). The TM rolling in conjunction with accelerated cooling from finish rolling temperature, which has been introduced later, eventually enabled linepipe steels up to grade X 100 to be produced in one heating cycle. The refinement of the rolling and cooling processes over these years has enabled the carbon content of the steel to be decreased despite increasing strength levels (Figure 1). At the same time, the product properties have also been improved. For instance, the technological development has resulted in: good consistency in the strength of pipe good toughness of the base material (high impact energy values at common design temperatures and below) fulfilling fracture arrest criteria (impact energy and transition temperature as measured in DWT tests). improved toughness of weld metal and HAZ in longitudinal seam welds improved resistance to cold cracking in field welding. This situation has led the customer to specify the most exacting requirements for the pipe. Moreover, the transition from grade X 70 to grade X 80 was associated with additional requirements, particularly with respect to impact toughness. These are likely to become still more exacting when pipelines in grade X 90 or grade X 100 will be designed. These requirements are not yet standardised today. 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 X 100 plate. As a result, the production window is quite narrow. Moreover, heat treatment of plate or pipe is obviously not advisable. Optimised steelmaking practices and processes enabled the base material to achieve toughness values enough good but there are yet limitations on the weldability point of view. Consequently the primary challenges in the gas transportation industry are the development of appropriate welding procedures and the choosing of suitable wires and consumables that allow the economical laying of pipelines using X100 grade steel avoiding all the typical problems associated to high strength microstructures and chemical compositions: cold cracking, weld joint toughness, hydrogen susceptivity. So the weldability activity, carried out by Snam in co-operation with Europipe which furnished the pipes and with some contractors, is developed in three main points: Investigation on commercial availability of electrodes and consumables with suitable chemical composition and mechanical properties in terms of tensile strength and hardness in order to fulfil overmatching criterion ; Definition of minimum welding requirements with reference to pre-heating temperature in order to avoid cold cracking problems: this part of the activity has been executed out by means of laboratory tests, Implant and Tekken type; 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. 2

4 2. REVIEW OF PRODUCT DEVELOPMENT This part of the paper reviews the current status of technological development at Europipe to produce grade X 100 material. Two publications [1,2] have preceded this paper with respect to steel development. The major objective of this new work was to optimise further the chemical composition in conjunction with improved rolling and cooling conditions to achieve the goals defined in Figure 2 within an adequately large window of production parameters. As can be seen in Figure 3, three main different approaches are possible with respect to the selection of chemical composition and cooling conditions. Approach A, which involves a relatively high carbon content, has the disadvantage that the requirements for toughness to ensure crack arrest, i.e. prevention of long running cracks, may not be fulfilled. Moreover, this approach is also detrimental, e.g. to field weldability. Approach B, which is practically the same as direct quenching with fast cooling rates 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. This effect cannot be adequately compensated for even with extremely low carbon contents, without adversely affecting productivity. Moreover, it is very difficult to produce pipe with adequate uniformity of strength properties. This difficulty cannot be attributed only to the Bauschinger effect associated with the variation in local deformation occurring during the intensive straightening operation needed in the case of thin section plate, which distorts heavily during direct quenching. Experience gained meanwhile indicates that Approach C is the best choice (Figure 3). This approach enables the desired property profile to be achieved through an optimised two-stage rolling process in conjunction with a reduced carbon content, a relatively high carbon equivalent and optimised 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 standardisation (Figure 4). 3. MECHANICAL PROPERTIES OF PRODUCTION PIPE 3.1 PIPE BODY Based on the experience gained from previous trials of X 100 pipe production [1,2], two new trials were made, which involved further optimisation of the chemical composition on the one hand and further optimisation of rolling and cooling conditions on the other hand (Approach C, Figure 3). As can be seen from Table 1, the carbon content of the newest heat IV was reduced to 0.06 %. The carbon equivalent of the new heats III and IV was 0.46 % (CE IIW ) and about 0.20 % (P CM ). Table 2 shows, for comparison, the mechanical properties determined on pipes from the four trials. As can be seen, Approach C (heats III and IV) enable pipe to be produced with average properties that are above the specified minimum values. Compared to the previous two trials, consistently good strength properties could be achieved in the recent trials. Especially, there is an improvement in the upper shelf energy and the ductile-brittle transition temperature. For instance, transverse impact energy values in excess of 270 J could be achieved on 36" OD pipe. The 85 % shear area transition temperature determined in the BDWT tests is about -50 C. The smaller section thickness, at 16 mm, has also played a favourable role in achieving such a good value. 3

5 Furthermore, the results show the strong Bauschinger effect associated with this higher strength steel. This effect resulting from specimen flattening decreased the yield strength determined on the flattened rectangular specimen by 90 MPa on average, compared to round bar specimen. The yieldto-tensile (Y/T) ratio determined on the round bar specimen is about 0.92 on average, while that determined on the flattened rectangular specimen is Therefore, the flattened rectangular specimen is not the right specimen type to determine the yield strength on grade X 100 pipe. 3.2 LONGITUDINAL SAW SEAM WELD The possibilities to improve the strength and toughness of the longitudinal seam weld have been extensively discussed [2]. No aspects that are fundamentally new have been identified since then. Additional experience has however been gathered in connection with HAZ toughness. The effects of aluminium and silicon were studied extensively in this context. It was shown that the HAZ can be rendered sufficiently tough by the use of currently favoured chemical composition, with a low carbon content [see 3, 4]. A low carbon content in conjunction with a relatively high carbon equivalent has been found optimum with respect to reducing the softening of HAZ. This aspect gains in significance as the material grade increases. Figure 5 shows the weld metal properties reported in refs. [1,2]. Both conventional C-Mn-Mo and C- Mn-Mo-Ti-B weld metals result in adequate toughness and strength for the weld. 4. FIELD WELDABILITY ASSESSMENT 4.1 CURRENT STATUS The experience with manual field welding so far [5-8] shows that cellulosic electrodes are not suitable for making the filler and cap passes of the welds in the high strength, grade X 80/grade X 90 material. The use of cellulosic electrodes with a further increased strength (greater than or equal to that of type E 9010-G) cannot be considered any more. The use of them would result in: Unacceptably low weld metal toughness Increased susceptibility to cold cracking of the weld metal itself (but not of the low-carbon high-strength base material!) Following the introduction of grade X 80 into the market, a mixed manual welding procedure has been proposed for use in field welding. This procedure consists of making the root and hot pass welding with soft cellulosic electrodes and the filler and cap passes with high strength vertical-down basic electrodes of the types E G and E G. This procedure has been successfully used now in making the field girth welds in grades X 80/X 90 [7, 8]. Matching/Overmatching strength electrodes with strength up to (and sometimes over) that of grade X 100 are also now available for use in mechanised narrow-gap gas metal arc welding (GMAW). 4.2 INVESTIGATIONS With a view to developing a procedure for depositing field girth welds in grade X 100 linepipe, the following aspects have been studied in this work: i) Cold cracking behaviour (Implant and Tekken tests) [10, 11] ii) Mechanical properties of the girth welds [12, 13] 4

6 Strength and toughness properties of the weld metal for: - different filler materials - different welding methods, namely: - mechanised narrow-gap GMAW - manual vertical-down welding with basic-coated electrodes (root and hot pass preferably cellulosic) - manual vertical-up welding with basic coated electrodes Toughness of the heat-affected zone of the different girth welds, as measured in Charpy V-notch impact tests and CTOD tests Hardness of the weld The individual results of this work are too extensive to be presented within the scope of this paper. Therefore, only a summary of the results is presented below. 4.3 RESULTS COLD CRACKING TESTS The investigations included both Implant tests and Tekken tests. In the course of these tests, it was found that laboratory tests of this kind on high-strength steels lead to results too much conservative especially with respect to Implant tests. In fact Implant sample doesn t represent a real joint because the stress state in the girth weld is mainly due to residual stresses while in an Implant sample is caused by an external load. Since that Implant tests are more severe then root pass of a girth weld the results coming out the tests have been checked using the Tekken testing, a method more fit for purpose, even if it doesn t allow to derive a numerical relationship between the applied load and the cooling time. One of the difficulties associated with both these tests methods is that in order to avoid the occurrence of fracture in the weld metal, it is necessary on the one hand to use high-strength or highest-strength electrodes for the simulation of the root pass welding. On the other hand, this is just what must to be avoided in practice. The other difficulty is associated with the fact that in the above-mentioned tests, the root pass, in general, is cooled to room temperature from welding temperature (conservative test conditions). However, in practice, cooling of the weld to room temperature shall be invariably avoided. It is therefore not surprising that the Implant and Tekken tests led to the requirement of very high minimum preheat temperatures (Table 3) [11]. It should also be noted that at least the high-strength basic weld metals appear to be more susceptible to cold cracking than are the low-carbon, high-strength base materials. Therefore, the minimum preheat and interpass temperatures really needed can only be determined by field welding trials on the pipe string in practice. Probably to use a preheat temperature of 100 C to 120 C would be sufficient, when it is ensured that the weld is finished without interruption VISUAL INSPECTION SMAW welding All the tests have been executed by a welder for each half circumference on spools enough long in order to be representative of the field conditions. Test n.1 Test n.2 The overall evaluation is positive. Root pass is enough good, finish seems to be not homogeneous: it s poor in some points and plentiful in others. Welder s cleverness has still to be perfected. The evaluation is negative respect to root pass, a strong root concavity, due to welder s lack of experience and manual joint preparation, has been observed. Finish is not completely homogeneous, poor in some points and plentiful in others. Welder s cleverness has still to be perfected. 5

7 Test n.3 Test n.4 The appearance of root pass is very good, but finish presents some tract with a lot of indentations. Three final beads technique has to be perfected. The appearance of root pass is very good, but finish is not completely homogeneous, poor in some points and plentiful in others. Welder s cleverness has still to be perfected. GMAW welding All welding tests have been executed by two welders. Test n.5 and 6 The overall evaluation is positive. Both the appearance and finish of all root passes are very good RADIOGRAPHIC INSPECTION SMAW welding The radiographic response respect to defects arising from welder s cleverness and filler material was positive for each test. Some metallurgical defect has been found in test n.4. Test n.1 Test n.2 Test n.3 Test n.4 Isolated porosity clusters Porosity clusters, wormholes, lack of side wall fusion and concavities. Without defect Crack in direction transversal to weld between h 4 and h 5. This crack has been impossible to detect with visual inspection because in that point the weld has been ground superficially. The formation of a transversal crack is an unusual event in the lower steel pipeline laying, but for X100 steel is a more likely phenomenon because of the strong residual stresses in the longitudinal direction that can reach yield strength. On the base of visual inspection the crack has been likely caused by the incorrect welding sequence executed in that point. The correct welding procedure foresees to start continuously from h 12 to h 6, while in this case the welder began to weld always from the same point. Another problem arose during the execution of test n.4. There was a blackout causing the switching off of the closed electrode container. The electrodes may have absorbed some moisture that enhanced hydrogen embrittlement. GMAW welding The radiographic response on all welds executed with mechanised system is very good. It has not been found any type defect and any difference respect to a traditional weld executed on lower grade steel MECHANICAL PROPERTIES OF THE GIRTH WELDS Table 4 shows the welding methods and the welding consumables studied. The weld metals of all the welds deposited in the vertical-down position, also in combination with the softer root pass welds, have sufficient strength (Tables 5 and 6). In contrast, the weld metal of the weld made with basiccoated electrodes in the vertical-up position did not achieve the minimum strength specified for the base material because of the high heat input associated with vertical-up welding. Both the weld metals and the heat-affected zones exhibited sufficiently large Charpy V-notch impact energy values at 30 C (Figures 6 and 7). This finding is valid for the manual vertical-down welding with basic-coated electrodes as well as for the mechanised gas metal arc welding procedure used. In the CTOD tests performed at a test temperature of -20 C and with the notch located in the HAZ, low CTOD values were measured in isolated cases. On the whole, the CTOD values measured at test temperatures (- 10 C) are quite satisfactory even if the values aren t so high with respect to those required by Snam recommendations. It should be noted that on the one hand the low carbon content of the base material had a favourable effect. On the other hand, it was however difficult to establish whether the crack initiation was in the weld metal or in the HAZ close to the fusion line in the CTOD specimens. 6

8 Examples of hardness distribution across the welds (for the macro sections see Figures 8 to 10) deposited with the vertical-down basic electrodes and those deposited by the narrow gap GMAW are given in Table 7. On examining the data, it appears that peak hardness values up to about 300 HV 10 are to be anticipated in these welds because of the low heat inputs. Cap passes are expected to have the highest hardness values. Isolated hardness values up to about 320 HV 10 may occur in these passes. 5. CONCLUSIONS Europipe has produced large-diameter grade X100 pipes on a trial basis for the third and fourth time. Beside other investigations the pipes were used as test pipes to determine the behaviour of grade X 100 material in full-scale burst tests, which are conducted as part of an ECSC-funded research project [ 9 ] and presented in another paper at this Conference. The mechanical properties determined on the pipes are quite appreciable, although they do not fully comply with the requirements currently specified for lower-strength material grades. The current requirements particularly for Y/T ratio and elongation, which are applicable to material grades up to X80, are too severe to be fulfilled for grade X100 on a statistical basis. This difficulty is attributable to the basic finding that as the strength increases, the Y/T ratio increases and the elongation decreases. For reasons of technical feasibility and cost-effective production, it is necessary in the context of grade X100 to redefine some of the requirements for the mechanical properties, considering the anticipated service conditions for the pipe. Close co-operation between the pipeline designer and the pipe manufacturer in this respect would be conducive to finding cost-effective solutions for the use of grade X100 material in pipeline construction. Another aim of this development work was to prove the possibility to weld X100 steel with appropriate care and this result has been completely sufficient. The activities were focussed on the X100 field welding behaviour by means of laboratory tests (cold cracking tests) and, using the indications coming out with respect to preheating temperatures, on developing standard welding procedures for field girth welding of X100 (heat III, 56 x 19 mm) pipes using SMAW and GMAW techniques. With respect to SMAW techniques a special skilling of welders must be taken in to consideration. Beside the manual vertical-down methods the GMAW results are very promising considering the fact that this technique will be much more involved in the applications suitable for X100 steel grade: long distances natural gas transportation over large diameter, high pressure-pipelines. The weld metal strength (yield and ultimate tensile strength) can be considered satisfactory for all the procedures used, except the test executed with basic vertical-up welding that presented an yield strength value lower than 700 MPa. In tests n. 1 and 6 the weld metal achieved strength properties much higher than necessary with the indication of a simultaneous toughness decrement. But the impact energies measured can be considered as adequate high and the investigation shows the well known correlation between strength properties and toughness properties of the weld metals. This is especially indicated in respect of the CTOD values of weld metals. The CTOD results obtained with GMAW were satisfactory down to 20 C for all wires used. On the base of results obtained, preheating temperatures heat input, interpass times, materials and procedures used proved enough satisfactory, even if the number of test executed cannot be considered sufficient for the full scale welding qualification of X100 steel. However this research can be judged a good starting point for studying the problem more in detail. 7

9 6. REFERENCES 1. H.-G. Hillenbrand, E. Amoris, K. A. Niederhoff, C. Perdrix, A. Streisselberger and U. Zeislmair: "Manufacturability of Linepipe in Grades up to X 100 from TM Processed Plate"; Pipeline Technology Conference, Oostende (Belgium), September 11-14, H.-G. Hillenbrand, K. A. Niederhoff, E. Amoris, C. Perdrix, A. Streisselberger and U. Zeislmair: "Development of Linepipe in Grades up to X 100"; EPRG/PRC biennial joint technical meeting on linepipe research, April 97, Washington D.C., USA 3. M. K. Gräf and K. A. Niederhoff: "Toughness behaviour of the heat-affected zone (HAZ) in double submerged-arc welded large-diameter pipe"; Pipeline Technology Conference, Oostende (Belgium), October 15-18, M. K. Gräf, and K. A. Niederhoff: "Properties of HAZ in two-pass submerged-arc welded largediameter pipe - Means of influencing, specified and necessary tests accompanying pipe production -"; Pipeline Technology Conference, May 22-24, 2000, Brugge, Belgium 5. M. Matoušu, Z. Škarda, I. Béder, J. Lombardini, H. G. Schuster and C. Düren: "Large-Diameter pipes of steel GRS 550TM (X80) in the 4th transit gaspipeline in Czechoslovakia"; 3R international, volume 8, Oct M. K. Gräf, H.-G. Hillenbrand and K. A. Niederhoff: "Production of large diameter linepipe and bends for the world s first long-range pipeline in grade X80 (GRS 550)"; 8th Symposium on Line Pipe Research, Houston (Texas), September 26-29, V. Chaudhari, H. P. Ritzmann, G. Wellnitz, G. H. Hillenbrand and V. Willings: "German gas pipeline first to use new generation line pipe"; Oil & Gas Journal, January, 2, H. G. Hillenbrand, K. A. Niederhoff, G. Hauck, E. Perteneder and G. Wellnitz: "Procedures, considerations for welding X80 line pipe established"; Oil & Gas Journal, September, 15, G. Demofonti, G. Mannucci, C. M. Spinelli, L. Barsanti, H.-G. Hillenbrand: "Large diameter API X 100 Gas Pipelines: Fracture Propagation evaluation by full scale burst test"; Pipeline Technology Conference, May 22-24, 2000, Brugge, Belgium 10. G. Pozzoli, A. Soldi: Prove di saldabilità su acciaio di grado X100 di produzione Europipe ; Instrum-Snam, G. Pozzoli, A. Soldi: Weldability tests on X100 grade steel ; Instrum-Snam, G. Pozzoli: X100 Prove di saldabilità ; Instrum-Snam, L.Barsanti, G. Pozzoli: Weldability evaluation of steel grade linepipes (DN 56 x 19 mm); Instrum-Snam,

10 7. ACKNOWLEDGMENTS Thanks to Sicim, Bohler and Esab for the fruitful contribution given during the work. The authors thank Dr. K. Niederhoff and C. Spinelli for the fruitful discussions. Heat Pipe size ODxWT C Mn Si Mo Ni Cu Nb Ti N CE W P CM I 30" x 19.1 mm II 30" x 15.9 mm III 56" x 19.1 mm IV 36" x 16.0 mm Table 1: Chemical compositions and carbon equivalents of industrial heats (X100 base materials) in wt. % Pipe 30" x 19.1 mm (Heat I) Pipe 30" x 15.9 mm (Heat II) Pipe 56" x 19.1 mm (Heat III) Pipe 36" x 16.0 mm (Heat IV) round bar flat bar round bar flat bar round bar flat bar round bar flat bar Yield strength R t0,5 (transverse) Tensile strength R m (transverse) 739 MPa 665 MPa* 755 MPa 681 MPa* 737 MPa 643 MPa* 752 MPa 649 MPa* 792 MPa 785 MPa 820 MPa 816 MPa 800 MPa 805 MPa 816 MPa 811 MPa R to.5 /R m 93% 84% 92% 83% 92% 80% 92% 80% Elongation A 5 : 18.4% A 2" : 32.5 % A 5 : 17.1 % A 2" : 27.7 % A 5 : 18% A 2" : 30% A 5 : 18% A 2" : 28% CVN (-20 C) 235 J 240 J 200 J 270 J DWTT-transition temperature -15 C -25 C -20 C -50 C * Specified minimum values not fulfilled due to the Bauschinger effect Table 2: Mechanical Properties (pipe body) 9

11 TYPE OF ROOT ELECTRODE IMPLANT TEKKEN Basic vertical-down electrode E C 100 C Cellulosic electrode E C 200 C Cellulosic electrode E6010 n. d. 150 C Table 3: Minimum Preheating Temperatures established from laboratory tests Welding code (joint preparation API standard) Test N. Root Pass (AWS) Hot Pass (AWS) Filler and Cap Passes (AWS) Notes Manual welding 1 E6010 E9010 E11018-G 2 E8018-G E11018-G E11018-G First and second passes cellulosic vertical-down, rest basic vertical-down welded All passes basic vertical-down welded Manual welding 3 E6010 E11018-G E11018-G 4 E6010 E9010 E11018-G First pass cellulosic vertical-up, rest basic vertical-up welded First and second passes cellulosic vertical-up, rest basic vertical-down welded Mechanised welding (GMAW Passo system) 5 ER 90 S-G / / 6 ER 100 S-G / / On a quarter of circumference (from h 9 to h 12) following passes have been executed from the root to cap Table 4: Welding test programme 10

12 Test No. Type of filler electrode (AWS) verticaldown All-weld metal test (two samples) Transverse weld tensile test * (two samples) vertical-up YS (MPa) UTS (MPa) UTS (MPa) Fracture position 1 E HAZ-BM 1) 2 E BM 3 E BM 4 E HAZ 1) * Weld reinforcement not removed 1) due to toe notches Table 5: Strength properties of SMAW girth welds All-weld metal test Transverse weld tensile Type of wire (two samples) test * (two samples) Test No. (AWS) Fracture YS (MPa) UTS (MPa) UTS (MPa) position 5 ER 90 S-G BM 6 ER 100 S-G BM * Weld reinforcement not removed Table 6: Strength properties of GMAW girth welds Test No. Maximum HV 10 (average values at 3 positions) Weld sequence HAZ WM BM 1 SMAW (see table 5) SMAW (see table 5) GMAW (see table 6) GMAW (see table 6) Table 7: Hardness Survey (Peak values) 11

13 Fig. 1: History of the development in linepipe steels (large-diameter pipe) 12

14 Fig 2: X100 requirements for onshore use Fig. 3: Principle of modifying steel chemistry and major cooling parameters to achieve the strength level of API X100 by optimized two step TM rolling. 13

15 Fig. 4: Maximum permitted carbon equivalents (acc. to EN and DNV'99) Fig. 5: Strength and toughness properties of longitudinal seam weld metal 14

16 Transition curve - Test n 1 Energy [J] -WELD Absorbed Energy [J Energy [J] -HAZ Temperature [ C] Fig. 6: SMAW welding (Type of filler electrode AWS E11018) 100 Transition curve - Test n 6 Energy [J].-WELD 80 Absorbed Energy [J] Temperature [ C] Fig. 7: GMAW welding (wire AWS ER 100 S-G) 15

17 Fig. 8: Macrograph from 3 o'clock position (test n.3, SMAW, vertical-up) Fig. 9: Macrograph from 3 o'clock position (test n.5, mechanised GMAW, wire AWS ER 90 S-G) 16

18 Fig. 10: Macrograph from 3 o'clock position (test n.1, SMAW, vertical-down) 17

19 Biography Mrs. Barsanti was born in Livorno on the 12/11/71. Has taken a degree in Chemical Engineering with a specialisation in material behaviour at the University of Pisa with a discussion about microstrucure of Line Pipe steel. She worked in Pisa at the Metal Science department in order to perform microstrucural analysis by means of T.E.M. on steels and special aluminium alloys. Since 1999 she has been working for Snam as Material Engineer dealing with ductile/brittle fracture propagation problems, corrosion, weldability of line pipe steel, particularly respect to X100 steel grade." Dr. Hans-Georg Hillenbrand hold a MS in mechanical engineering (1979) and a PhD in material science (1983), both from Ruhr-University, Bochum. In 1983 he started his career in the Mannesmann Research Institute developing steels for largediameter pipes. From 1986 to 1994 he was first QA/QC Manager of Mannesmann heavy plate mill, later Senior Manager quality for plates and welded pipes of Mannesmannröhren. Since 1994 he is a Senior Manager and head of Technical Sales of Europipe GmbH. He is the author of more than 40 papers relating to HSLA steels. 18