Patent Publication Number: US-2010129680-A1

Title: Uoe steel pipe and a method for its manufacture

Description:
TECHNICAL FIELD 
     This invention relates to a high strength UOE steel pipe having a tensile strength of at least 900 MPa and a method for its manufacture. 
     BACKGROUND ART 
     A UOE steel pipe is manufactured by forming a steel plate having a thickness of around 6-40 mm into an open pipe using a UO press, then welding the abutting end portions of the open pipe by submerged arc welding to form a longitudinal weld (referred to in this description simply as a weld), and then after welding, performing a pipe expansion step with the object of straightening the pipe and removing residual stresses. 
     The weld of a UOE steel pipe is normally formed by welding a total of two layers including one layer on the inner side and one layer on the outer side of the pipe. 
     Such a UOE steel pipe is primarily used as piping for long distance transport of fluids such as petroleum and gas. 
     At present, the principal grade of UOE steel pipes is API (American Petroleum Institute) X65 grade. In order to decrease transport costs by increasing the transport pressure and reducing construction costs at the time of pipe installation, there is a demand for further increases in the strength and decreases in the wall thickness of UOE steel pipe. 
     In recent years, UOE steel pipe of X120 grade having a tensile strength of at least 900 MPa (referred to below as high strength UOE steel pipe) is being investigated. 
     This high strength UOE steel pipe has a strength which reaches nearly twice that of conventional pipe. Therefore, it has various problems not only with respect to its performance such as securement of the strength and toughness of the base metal and of the welds but also with respect to its manufacture. 
     One of the problems which occur at the time of manufacture of a high strength UOE steel pipe is delayed hydrogen cracking which develops in welds. As the strength of a steel pipe increases, it becomes desirable to increase the strength of welds in accordance with the increase in strength of the base metal. However, if the strength of a weld is made too high, the susceptibility of the weld to cracking increases, and delayed hydrogen cracking occurs. If the strength of a weld is decreased, the occurrence of delayed hydrogen cracking is suppressed, but if the strength is decreased too much, the weld fractures during pipe expansion after welding. Thus, in the manufacture of a high strength UOE steel pipe, preventing fracture during pipe expansion and preventing delayed hydrogen cracking are mutually opposed goals, and solving this problem is a manufacturing challenge. 
     In the past, in Patent Document 1, for example, an invention was disclosed which prevents the occurrence of delayed hydrogen cracking by limiting the oxygen content of a weld to at least 0.035% to at most 0.050% (in this specification, unless otherwise specified, % with respect to a composition means mass %) and decreases is susceptibility of welds to cracking by hydrogen. 
     Patent Document 1: JP 10-306348 A1 
     DISCLOSURE OF INVENTION 
     However, in the invention disclosed in Patent Document 1, increasing the oxygen content of a weld not only does decreases the toughness of weld but also may increase the occurrence of weld defects, such as an increase in blow holes or slag inclusion. 
     The object of the present invention is to provide a method of manufacturing a UOE steel pipe having a high strength of at least 900 MPa and having welds and heat affected zones with excellent toughness without delayed hydrogen cracking in welds or fracture during pipe expansion. It is another object to provide a UOE steel pipe which is manufactured by this method. 
     In contrast to the consideration in Patent Document 1, the present inventors focused on decreasing the oxygen content of weld metal in order to improve the low temperature toughness of welds. At the same time, it is necessary to impede the occurrence of hydrogen cracking. Upon investigating the cause of hydrogen cracking, it was found that preheating treatment of welds promotes the evolution of hydrogen, thereby making it possible to prevent effectively the occurrence of delayed hydrogen cracking caused by decreasing the oxygen content in weld metal. 
     Based on such knowledge, a method of manufacturing a high strength UOE steel pipe which can simultaneously prevent fracture during a pipe expansion step and prevent delayed hydrogen cracking was completed. 
     Namely, the present invention is a method of manufacturing a UOE steel pipe comprising press forming a base metal steel plate so as to form an open pipe, welding the abutting end portions of the open pipe initially from the inner side and then from the outer side, and subjecting the resulting welded pipe to pipe expansion, characterized in that a steel plate with a tensile strength of at least 900 MPa is used as the base metal steel pipe, the weld obtained by welding from the inner side is preheated to a temperature of 75-250° C. before it is welded from the outer side, and the weld obtained by welding from the inner and outer sides is made to have a tensile strength which is 95-110% of the tensile strength of the base metal and an oxygen content of at most 0.035 mass %. 
     From another aspect, the present invention is a UOE steel pipe which is manufactured by the above-described method, characterized in that the tensile strength of the base metal is at least 900 MPa, the tensile strength of the weld is in the range of 95-110% of the tensile strength of the base metal, and the oxygen content of the weld is at most 0.035 mass %. 
     According to the present invention, a high strength UOE steel pipe which has a weld and a heat affected zone of excellent toughness, which has a tensile strength of at least 900 MPa, and which does not experience delayed hydrogen cracking of the weld or fracture during pipe expansion is provided as well as a method for its manufacture. 
     BEST MODE FOR CARRYING OUT THE INVENTION 
     Embodiments of the present invention will be explained in detail. 
     In the present invention, the composition of a base metal steel plate for a high strength UOE steel pipe having a tensile strength of at least 900 MPa does not need to be limited to a specific composition. Any composition known as a composition of a high strength UOE steel pipe can be employed. 
     An example of a steel composition in a preferred embodiment of the present invention consists essentially of C: at least 0.02% and at most 0.12%, Si: at most 0.35%, Mn: at least 0.5% and at most 2.0%, Ni: at least 0.02% and at most 4%, at least one of Cr and Mo in a total amount of at least 0.1% and at most 4%, optionally Cu: at most 1.50% and/or at least one of Al, Ti, Nb, V, and B in a total amount of at most 1%, and a remainder of Fe and impurities (including P: at most 0.04% and S: at most 0.03%). The reasons for the limits on the listed elements are as follows. 
     C: 
     It is possible to inexpensively increase strength by adding at least 0.02% of C. If the C content exceeds 0.12%, martensite-austenite constituent develops in the heat affected zones at the time of welding, and the toughness of welds decreases. In the examples of the present invention, the C content is at least 0.02% and at most 0.12%. Preferably, it is at least 0.03% and at most 0.06%. 
     Si: 
     If Si is contained in excess of 0.35%, martensite-austenite constituent easily develops in the heat affected zone at the time of welding. Therefore, the S content is at most 0.35%. Preferably it is at most 0.15%. 
     Mn: 
     The addition of at least 0.5% of Mn increases hardenability, leading to an increased strength and toughness. However, if the Mn content exceeds 2.2%, manufacturing problems such as cracks of an ingot develop. Therefore, the Mn content is at least 0.5% and at most 2.2%. Preferably it is at least 0.6% and at most 2.0%. 
     Ni: 
     Like Mn, the addition of at least 0.02% of Ni contributes to strength and toughness. However, Ni is an expensive element, and if the Ni content exceeds 4%, manufacturing costs increase. Therefore, the Ni content is at least 0.02% and at most 4%. Preferably it is at least 0.3% and at most 1.0%. 
     Cr and/or Mo: 
     Cr and Mo are also useful for increasing strength and toughness, but if too much thereof is added, the toughness of heat affected zones decreases. Therefore, one or both of Cr and Mo is added in a total amount of at least 0.1% and at most 4%. 
     Cu: 
     Cu is an element which is also effective at increasing strength and toughness, so it can be added if necessary. However, if it is added in excess of 1.5%, problems such as surface cracks develop at the time of producing a slab. Therefore, its upper limit is 1.5%. Preferably it is at most 1.0%. 
     In the present invention, one or more of Al, Ti, Nb, V, and B in a total amount of at most 1% may be added as optional elements for increasing strength and toughness. 
     The remainder other than the above-described elements is Fe and impurities. In particular, P and S are both impurities which are unavoidably incorporated during the melting stage. In view of a considerable increase in manufacturing costs involved in reduction of the contents of these elements to extremely low levels and in order to guarantee toughness, the P content is at most 0.04% and the S content is at most 0.03%. 
     Next, a method of manufacturing a high strength UOE steel pipe according to the present invention will be explained. 
     A thick steel plate normally having a thickness of around 6-40 mm is used as a starting material. After both ends in the widthwise direction of the steel plate undergo beveling, the plate undergoes press forming in a C press, a U press, and a O press to form an open pipe. 
     The abutting portions at both ends in the widthwise direction of the steel plate are then tack welded by gas shielded arc welding, and one layer of submerged arc welding is carried out from the inner side. Subsequently, at least a region including both ends, namely, the weld formed by welding from the inner side is preheated to a predetermined temperature, and one layer of submerged arc welding is then carried out from the outer side. 
     For the purposes of pipe straightening and removal of residual stresses, the resulting welded steel pipe is subjected to pipe expansion in which plastic deformation on the order of 1% elongation in the circumferential direction is normally applied to the pipe over its entire length to manufacture a UOE steel pipe. The pipe expansion step can be carried out by mechanical pipe expansion or hydraulic pipe expansion, and there is no particular limitation on this step in the present invention whichever method is used. 
     Methods of manufacturing a UOE steel pipe are well known in the art, and in the present invention, pipe manufacture may be carried out according to such conventional methods with no particular limitations except concerning the following points. 
     According to the present invention, prior to pipe expansion, the weld has a tensile strength which is in the range of at least 95% to at most 110% of the tensile strength of the base metal and the oxygen content of the weld metal in the weld is at most 0.035%. 
     If the tensile strength of the weld is less than 95% of the tensile strength of the base metal, fracture may occur at the time of pipe expansion, whereas if it exceeds 110% of the tensile strength of the base metal, susceptibility of the weld to cracking increases and delayed hydrogen cracking may occur. 
     The oxygen content of the weld metal of a weld greatly affects the toughness of the weld. If the oxygen content of the weld metal exceeds 0.035%, there is a marked decrease in the toughness of the weld. In the present invention, in order to guarantee the toughness of the weld metal, the oxygen content of the weld metal is at most 0.035%. 
     The tensile strength and the oxygen content of a weld can be arbitrarily varied by adjusting the composition of the base metal, and the types of welding rod and/or flux which are used for welding. 
     As stated above, in order to guarantee the toughness of the weld metal of a weld, the oxygen content of the weld metal is made at most 0.035%. This increases susceptibility to cracking of the weld and may result in the occurrence of delayed hydrogen cracking. Therefore, in the present invention, before carrying out welding from the outer side, the pipe having a weld formed by welding from the inner side is preheated such that at least this weld portion of the pipe is preheated. 
     For the following reasons, the timing of this preheating is limited to being carried out before welding from the outer side. 
     The cause of the occurrence of delayed hydrogen cracking in a high strength UOE steel pipe is thought to be that at the time of welding from the outer side, diffusible hydrogen which is incorporated into the weld metal is trapped inside minute cracks in the weld metal formed by welding from the inner side which was reheated by the heat of welding from the outer side. By carrying out preheating prior to welding from the outer side, the cooling time is prolonged and evolution of the diffusible hydrogen can be promoted. if preheating is not carried out, such diffusible hydrogen remains trapped inside the weld metal on the inner side during welding from the outer side, and it may cause delayed hydrogen cracking afterwards. 
     The preheating temperature is at least 75° C. in order to sufficiently cause evolution of diffusible hydrogen and prevent the occurrence of delayed hydrogen cracking with certainty. Preheating heats not only the weld but also the base metal and the heat affected zone. Therefore, if preheating is carried out at a temperature exceeding 250° C., there is the possibility of a deterioration in the toughness of these portions. Accordingly, the preheating temperature is at most 250° C. as a temperature which can guarantee an impact energy of at least 84 J in a Charpy impact test at −30° C. Preferably it is 80-240° C. 
     A means for preheating can be any heating means which can heat the weld to a prescribed temperature such as heating with a gas burner or heating with an induction heater, and it is not limited to a specific heating means. Heating can be carried out such that at least the weld is successively heated over its entire length. The heated region in the circumferential direction may extend around the entire periphery of the steel pipe, but it may be limited to a local region including the weld such as a region within 10 mm of the bevel of the weld. 
     In this manner, according to the present invention, a high strength UOE steel pipe which has a high tensile strength of at least 900 MPa and preferably higher and which has a weld and a heat affected zone both having excellent toughness (Charpy absorbed energy at −30° C. of at least 84 J) can be stably manufactured without delayed hydrogen cracking in the weld or fracture at the time of pipe expansion. 
    
    
     The present invention will be more concretely explained while referring to examples. 
     EXAMPLES 
     In this example, three types of thick steel plates (Steels A, B, and C) having different compositions as shown in Table 1 were manufactured and tested. 
     Using each of these steel plates as a starting material, beveling was carried out on both ends of a plate in the widthwise direction, and then working was carried out on the steel plate with a C press, a U press, and an O press to form an open pipe. After tack welding was carried out on the abutting portions of both ends of the open pipe by gas shielded arc welding, a first layer of submerged arc welding was carried out from the inner side, and then one layer of submerged arc welding was carried out from the outer side either immediately or after preheating the weld in a region including both end portions to a predetermined temperature. 
     A welded steel pipe which was obtained in this manner was subjected to pipe expansion over its entire length with plastic deformation of in the form of 1% circumferential elongation to manufacture a UOE steel pipe with an outer diameter of 30 inches (762 mm), a wall thickness of 16 mm, and a length of 12 m. 
     Pipes which experienced fracture of the weld during pipe expansion (Comparative Examples A-1 through A-3, B-1 through B-3, and C-1 through C-3 in Table 1) could not be used as products, so testing of these pipes was stopped at that point. 
     For the pipes which did not experience fracture of the weld during pipe expansion (Comparative Examples A-4 through A-10, B-4 through B-10, C-4 through C-10, Examples A-1 through A-3, B-1 through B-3, C-1 through C-3), an ultrasonic flaw test was carried out over the entire length of the weld, when 48 hours elapsed after submerged arc welding from the outer side, to ascertain whether delayed hydrogen cracking had occurred. In order to evaluate the toughness of the weld metal of the weld zone and the heat affected zone, a test piece was cut from the UOE steel pipe after pipe expansion and it was subjected to a Charpy impact test at −30° C. 
     The test results are shown in Tables 2 through 4. 
     In Tables 2, 3, and 4, Comparative Examples A-1 through A-3, B-1 through 3-3, and C-1 through C-3 each had a ratio of the tensile strength of the weld with respect to that of the base metal which was lower than the range prescribed in the present invention, so fracture occurred during pipe expansion. Therefore, subsequent tests were not carried out. 
     Comparative Examples A-4, B-4, and C-4 did not undergo the preheating which is prescribed by the present invention before welding from the outer side, and for Comparative Examples A-5, B-5, and C-5, the preheating temperature was lower than the range prescribed by the present invention. Therefore, delayed hydrogen cracking developed in the welds after the passage of 48 hours after welding from the outer side. 
     Comparative Examples A-6, B-6, and C-6 underwent preheating before welding from the outer side, so delayed hydrogen cracking of the weld could be prevented. However, due to the preheating temperature which was above the range prescribed by the present invention, the toughness of the heat affected zone deteriorated. 
     Comparative Examples A-7, A-8, B-7, B-8, C-7, and C-8 had a ratio of the tensile strength of the weld with respect to that of the base metal which was above the range prescribed by the present invention, so susceptibility to cracking increased, and after welding was carried out from the outer side, delayed hydrogen cracking occurred in the weld after the passage of 48 hours. Particularly in Comparative 
     Examples A-8, B-8, and C-8, delayed hydrogen cracking developed even though preheating was carried out at 250° C. before welding from the outer side. 
     In Comparative Examples A-9, A-10, B-9, B-10, C-9, and C-10, the oxygen content of the weld metal in the weld was above the range prescribed by the present invention, so the toughness of the weld metal deteriorated. 
     In contrast, for Examples A-1 through A-3, B-1 through B-3, and C-1 through C-3, the tensile strength of the weld was at least 95% and at most 110% of the tensile strength of the base metal, so pipe expansion by 1% was possible. In addition, since preheating at 75-250° C. was carried out prior to welding from the outer side, delayed hydrogen cracking could be prevented without a deterioration in the toughness of the weld heat affected zone. Furthermore, due to the oxygen content of the weld metal which was suppressed to at most 0.035%, the toughness of the weld metal could satisfy target values. 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 Steel Compositions (mass %) 
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
               
            
               
                 Steel 
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
               
               
                 Type 
                 C 
                 Si 
                 Mn 
                 P 
                 S 
                 Cu 
                 Ni 
                 Cr 
                 Mo 
                 Nb 
                 V 
               
               
                   
               
               
                 Steel A 
                 0.04 
                 0.09 
                 1.63 
                 0.006 
                 0.001 
                 0.28 
                 0.62 
                 0.29 
                 0.40 
                 0.018 
                 0.032 
               
               
                 Steel B 
                 0.05 
                 0.12 
                 1.95 
                 0.004 
                 0.001 
                 — 
                 0.50 
                 0.25 
                 0.30 
                 0.014 
                 0.020 
               
               
                 Steel C 
                 0.06 
                 0.10 
                 0.60 
                 0.005 
                 0.001 
                 1.00 
                 0.60 
                 0.45 
                 0.45 
                 0.032 
                 0.040 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 2 
               
             
            
               
                   
               
               
                 Examples (Steel A) 
               
            
           
           
               
               
               
               
               
            
               
                   
                 Ratio of 
                   
                 Evaluation 
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
            
               
                   
                   
                   
                 tensile 
                   
                   
                   
                 Delayed 
                   
                   
                   
               
               
                   
                   
                   
                 strength 
                   
                 Preheating 
                   
                 hydrogen 
                   
                   
                   
               
               
                   
                   
                   
                 of weld 
                 Oxygen 
                 temperature 
                   
                 cracking 
                 Weld metal 
                 Toughness 
               
               
                   
                 Tensile 
                   
                 to base 
                 content 
                 before outer 
                   
                 of weld (UST 
                 toughness 
                 of 
               
               
                   
                 strength 
                 Tensile 
                 metal 
                 of weld 
                 side welding 
                 Fracture during pipe 
                 after 48 
                 (CVN at 
                 HAZ (CVN 
               
               
                   
                 of base 
                 strength 
                 (weld/ 
                 metal 
                 (° C.) 
                 expansion 
                 hours) (◯: 
                 −30° C.) 
                 at −30° C.) 
               
               
                   
                 metal 
                 of weld 
                 base 
                 (mass 
                 (—: no 
                 (◯: success, X: 
                 no cracking, 
                 (◯: ≧84 J, 
                 (◯: ≧84 J, 
                 Overall 
               
               
                 No. 
                 (MPa) 
                 (MPa) 
                 metal) 
                 %) 
                 preheating) 
                 fracture) 
                 X: cracking) 
                 X: &lt;84 J) 
                 X: &lt;84 J) 
                 evaluation 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                 Comp. A-1 
                 1010 
                 942 
                  93% 
                 0.034 
                 160 
                 X (weld fracture) 
                 No further testing 
                 X 
               
               
                 Comp. A-2 
                 1053 
                 949 
                  90% 
                 0.033 
                 250 
                 X (weld fracture) 
                   
                 X 
               
               
                 Comp. A-3 
                 1032 
                 939 
                  91% 
                 0.031 
                  75 
                 X (weld fracture) 
                   
                 X 
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
            
               
                 Comp. A-4 
                 951 
                 962 
                 101% 
                 0.034 
                 — 
                 ◯ (1% pipe expansion) 
                 X 
                 ◯ (96 J) 
                 ◯ (165 J) 
                 X 
               
               
                 Comp. A-5 
                 954 
                 923 
                  97% 
                 0.029 
                  70 
                 ◯ (1% pipe expansion) 
                 X 
                 ◯ (120 J) 
                 ◯ (140 J) 
                 X 
               
               
                 Comp. A-6 
                 942 
                 999 
                 106% 
                 0.028 
                 260 
                 ◯ (1% pipe expansion) 
                 ◯ 
                 ◯ (118 J) 
                 X (80 J) 
                 X 
               
               
                 Comp. A-7 
                 915 
                 1020 
                 111% 
                 0.033 
                 — 
                 ◯ (1% pipe expansion) 
                 X 
                 ◯ (92 J) 
                 ◯ (153 J) 
                 X 
               
               
                 Comp. A-8 
                 920 
                 1031 
                 112% 
                 0.034 
                 250 
                 ◯ (1% pipe expansion) 
                 X 
                 ◯ (93 J) 
                 ◯ (89 J) 
                 X 
               
               
                 Comp. A-9 
                 936 
                 915 
                  98% 
                 0.037 
                 — 
                 ◯ (1% pipe expansion) 
                 ◯ 
                 X (79 J) 
                 ◯ (172 J) 
                 X 
               
               
                 Comp. A-10 
                 945 
                 960 
                 102% 
                 0.036 
                 250 
                 ◯ (1% pipe expansion) 
                 ◯ 
                 X (81 J) 
                 ◯ (91 J) 
                 X 
               
               
                 Ex. A-1 
                 960 
                 980 
                 102% 
                 0.021 
                  75 
                 ◯ (1% pipe expansion) 
                 ◯ 
                 ◯ (112 J) 
                 ◯ (125 J) 
                 ◯ 
               
               
                 Ex. A-2 
                 1010 
                 990 
                  98% 
                 0.019 
                 160 
                 ◯ (1% pipe expansion) 
                 ◯ 
                 ◯ (102 J) 
                 ◯ (105 J) 
                 ◯ 
               
               
                 Ex. A-3 
                 983 
                 1005 
                 102% 
                 0.034 
                 250 
                 ◯ (1% pipe expansion) 
                 ◯ 
                 ◯ (95 J) 
                 ◯ (92 J) 
                 ◯ 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 3 
               
             
            
               
                   
               
               
                 Examples (Steel B) 
               
            
           
           
               
               
               
            
               
                   
                 Evaluation 
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
            
               
                   
                   
                   
                   
                   
                   
                   
                 Delayed 
                   
                   
                   
               
               
                   
                   
                   
                 Ratio of 
                   
                 Preheating 
                   
                 hydrogen 
                 Weld 
                 Toughness 
               
               
                   
                   
                   
                 tensile 
                 Oxygen 
                 temperature 
                   
                 cracking of 
                 metal 
                 of HAZ 
               
               
                   
                 Tensile 
                   
                 strength of 
                 content 
                 before outer 
                   
                 weld (UST 
                 toughness 
                 (CVN at 
               
               
                   
                 strength 
                 Tensile 
                 weld to 
                 of weld 
                 side welding 
                 Fracture during pipe 
                 after 48 hours) 
                 (CVN at 
                 −30° C.) 
               
               
                   
                 of base 
                 strength 
                 base metal 
                 metal 
                 (° C.) 
                 expansion 
                 (◯: no 
                 −30° C.) 
                 (◯: 
               
               
                   
                 metal 
                 of weld 
                 (weld/base 
                 (mass 
                 (—: no 
                 (◯: success, X: 
                 cracking, X: 
                 (◯: ≧84 J, 
                 ≧84 J, 
                 Overall 
               
               
                 No. 
                 (MPa) 
                 (MPa) 
                 metal) 
                 %) 
                 preheating) 
                 fracture) 
                 cracking) 
                 X: &lt;84 J) 
                 X: &lt;84 J) 
                 evaluation 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                 Comp. B-1 
                 1100 
                 939 
                  85% 
                 0.031 
                 110 
                 X (weld fracture) 
                 No further testing 
                 X 
               
               
                 Comp. B-2 
                 1092 
                 951 
                  87% 
                 0.035 
                 190 
                 X(weld fracture) 
                   
                 X 
               
               
                 Comp. B-3 
                 1041 
                 922 
                  89% 
                 0.025 
                  80 
                 X (weld fracture) 
                   
                 X 
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
            
               
                 Comp. B-4 
                 1030 
                 1051 
                 102% 
                 0.030 
                 — 
                 ◯ (1% pipe expansion) 
                 X 
                 ◯ (90 J) 
                 ◯ (143 J) 
                 X 
               
               
                 Comp. B-5 
                 1093 
                 1049 
                  96% 
                 0.027 
                  70 
                 ◯ (1% pipe expansion) 
                 X 
                 ◯ (107 J) 
                 ◯ (121 J) 
                 X 
               
               
                 Comp. B-6 
                 990 
                 1000 
                 101% 
                 0.030 
                 260 
                 ◯ (1% pipe expansion) 
                 ◯ 
                 ◯ (120 J) 
                 X (75 J) 
                 X 
               
               
                 Comp. B-7 
                 941 
                 1063 
                 113% 
                 0.031 
                 — 
                 ◯ (1% pipe expansion) 
                 X 
                 ◯ (89 J) 
                 ◯ (139 J) 
                 X 
               
               
                 Comp. B-8 
                 984 
                 1092 
                 111% 
                 0.025 
                 250 
                 ◯ (1% pipe expansion) 
                 X 
                 ◯ (99 J) 
                 ◯ (96 J) 
                 X 
               
               
                 Comp. B-9 
                 1022 
                 1012 
                  99% 
                 0.038 
                 — 
                 ◯ (1% pipe expansion) 
                 ◯ 
                 X (70 J) 
                 ◯ (139 J) 
                 X 
               
               
                 Comp. B-10 
                 955 
                 993 
                 104% 
                 0.039 
                 250 
                 ◯ (1% pipe expansion) 
                 ◯ 
                 X (77 J) 
                 ◯ (93 J) 
                 X 
               
               
                 Ex. B-1 
                 1010 
                 1015 
                 100% 
                 0.030 
                 240 
                 ◯ (1% pipe expansion) 
                 ◯ 
                 ◯ (91 J) 
                 ◯ (108 J) 
                 ◯ 
               
               
                 Ex. B-2 
                 920 
                 980 
                 107% 
                 0.015 
                  80 
                 ◯ (1% pipe expansion) 
                 ◯ 
                 ◯ (119 J) 
                 ◯ (115 J) 
                 ◯ 
               
               
                 Ex. B-3 
                 1062 
                 1019 
                  96% 
                 0.021 
                 190 
                 ◯ (1% pipe expansion) 
                 ◯ 
                 ◯ (99 J) 
                 ◯ (97 J) 
                 ◯ 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 4 
               
             
            
               
                   
               
               
                 Examples (Steel C) 
               
            
           
           
               
               
               
            
               
                   
                 Evaluation 
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
            
               
                   
                   
                   
                   
                   
                   
                   
                 Delayed 
                   
                   
                   
               
               
                   
                   
                   
                 Ratio of 
                   
                 Preheating 
                   
                 hydrogen 
                   
                 Toughness 
               
               
                   
                   
                   
                 tensile 
                 Oxygen 
                 temperature 
                   
                 cracking of 
                 Weld metal 
                 of HAZ 
               
               
                   
                 Tensile 
                   
                 strength of 
                 content 
                 before outer 
                   
                 weld (UST 
                 toughness 
                 (CVN at 
               
               
                   
                 strength 
                 Tensile 
                 weld to 
                 of weld 
                 side welding 
                 Fracture during pipe 
                 after 48 hours) 
                 (CVN at 
                 −30° C.) 
               
               
                   
                 of base 
                 strength 
                 base metal 
                 metal 
                 (° C.) 
                 expansion 
                 (◯: no 
                 −30° C.) 
                 (◯: 
               
               
                   
                 metal 
                 of weld 
                 (weld/base 
                 (mass 
                 (—: no 
                 (◯: success, X: 
                 cracking, X: 
                 (◯: ≧84 J, 
                 ≧84 J, 
                 Overall 
               
               
                 No. 
                 (MPa) 
                 (MPa) 
                 metal) 
                 %) 
                 preheating) 
                 fracture) 
                 cracking) 
                 X: &lt;84 J) 
                 X: &lt;84 J) 
                 evaluation 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                 Comp. C-1 
                 990 
                 911 
                  92% 
                 0.030 
                 120 
                 X (weld fracture) 
                 No further testing 
                 X 
               
               
                 Comp. C-2 
                 965 
                 907 
                  94% 
                 0.029 
                  76 
                 X (weld fracture) 
                   
                 X 
               
               
                 Comp. C-3 
                 980 
                 921 
                  94% 
                 0.033 
                 210 
                 X (weld fracture) 
                   
                 X 
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
            
               
                 Comp. C-4 
                 922 
                 950 
                 103% 
                 0.035 
                 — 
                 ◯ (1% pipe expansion) 
                 X 
                 ◯ (89 J) 
                 ◯ (170 J) 
                 X 
               
               
                 Comp. C-5 
                 914 
                 960 
                 105% 
                 0.026 
                  68 
                 ◯ (1% pipe expansion) 
                 X 
                 ◯ (111 J) 
                 ◯ (130 J) 
                 X 
               
               
                 Comp. C-6 
                 945 
                 936 
                  99% 
                 0.031 
                 260 
                 ◯ (1% pipe expansion) 
                 ◯ 
                 ◯ (103 J) 
                 X (82 J) 
                 X 
               
               
                 Comp. C-7 
                 978 
                 1095 
                 112% 
                 0.029 
                 — 
                 ◯ (1% pipe expansion) 
                 X 
                 ◯ (115 J) 
                 ◯ (165 J) 
                 X 
               
               
                 Comp. C-8 
                 940 
                 1062 
                 113% 
                 0.030 
                 250 
                 ◯ (1% pipe expansion) 
                 X 
                 ◯ (98 J) 
                 ◯ (93 J) 
                 X 
               
               
                 Comp. C-9 
                 955 
                 917 
                  96% 
                 0.038 
                 — 
                 ◯ (1% pipe expansion) 
                 ◯ 
                 X (75 J) 
                 ◯ (160 J) 
                 X 
               
               
                 Comp. C-10 
                 969 
                 1017 
                 105% 
                 0.037 
                 190 
                 ◯ (1% pipe expansion) 
                 ◯ 
                 X (79 J) 
                 ◯ (100 J) 
                 X 
               
               
                 Ex. C-1 
                 935 
                 1019 
                 109% 
                 0.024 
                  80 
                 ◯ (1% pipe expansion) 
                 ◯ 
                 ◯ (118 J) 
                 ◯ (132 J) 
                 ◯ 
               
               
                 Ex. C-2 
                 1003 
                 993 
                  99% 
                 0.018 
                 183 
                 ◯ (1% pipe expansion) 
                 ◯ 
                 ◯ (121 J) 
                 ◯ (111 J) 
                 ◯ 
               
               
                 Ex. C-3 
                 975 
                 1014 
                 104% 
                 0.032 
                 244 
                 ◯ (1% pipe expansion) 
                 ◯ 
                 ◯ (92 J) 
                 ◯ (98 J) 
                 ◯