ESSO Test Research Articles

Brittle crack arrestability of thick steel plate welds in large structure

Recently, there has been such a critical issue in shipbuilding industry that much larger and stronger ships are required to develop oil and gas in the Arctic region. Attention has been paid to obtaining high strength, good toughness at low temperature, and good weldability. An experimental study was performed to evaluate the brittle crack arrest toughness value (Kca) and brittle crack arrest method of welded joints using EH40 grade steel with a thickness of 80 mm. The test specimens were made by both flux cored arc welding (FCAW) and combined welding (EGW+FCAW) processes. Temperature gradient ESSO test was performed to measure the Kca of the base metal. Also, a constant temperature (−10 °C) ESSO test was performed to establish a brittle crack arrest method using high toughness welding consumable with real structural specimens. The research aims in this study were to investigate the effect of joint design and welding consumable for the crack arrestability of thick steel plates using EH40 grade shipbuilding steel of straight block joint weld line with two kinds of welding processes.

Development of 7%Ni-TMCP Steel Plate for LNG Storage tanks

LNG storage tanks made of 9%Ni steel plate have safely been operated at the many LNG export and import terminals in the world for the last half-century. Over the years extensive improvement and enhancement have been achieved on the 9%Ni steel plate in terms of toughness in steel to withstand the cryogenic temperatures under an operating condition with LNG.This paper reports research and development of the 7%Ni - TMCP steel plate. As nickel is an expensive and valuable rare metal, it was aimed to reduce nickel content to 7% to save investment costs for constructions of LNG storage tanks. Inferiority of the lower nickel content was compensated by adjusting chemical contents of Mn, Si, Cr etc. and by Thermo-Mechanical Controlled Process (TMCP) with an intermediate heat treatment.In order to evaluate fitness of the 7%Ni - TMCP steel plate and its weld for LNG storage tanks a series of testing was conducted. Three different kinds of plate thicknesses of 40, 25 and 10 mm were chosen to run large scale fracture toughness tests such as duplex ESSO tests, cruciform wide plate tests as well as small scale tests. Those mechanical tests showed excellent quality of the steel and demonstrated safety of the steel which was considered the same safety level as the conventional 9%Ni steel plate.Hence, it is considered that the 7%Ni - TMCP steel plate warrants serious consideration for use in LNG storage tanks.

Effect of unwelded length on behaviour of brittle crack arrest in T-joint structure

In the large heat input weld joint of heavy gauge steel plate used for large container carriers, a brittle crack possibly propagates straight along a weld joint without diverging to the base metal. This phenomenon is discussed for its application to the large heat input weld of heavy gauge plate to ship structures. In this study, to arrest a brittle crack at the T-joint embedding unwelded face, the effect of the unwelded face on behaviour of brittle crack propagation/arrest in the T-joint structure was investigated and analysed. The ESSO test of the T-joint structure was carried out, supposing that a brittle crack which propagates along a weld joint of hatch coaming rush into T-joint of hatch coaming and strength deck. The test results showed that the brittle crack arrested at the T-joint embedding the unwelded face, and the brittle crack arrested easier, the longer the unwelded face. The results of static FEM analysis showed that the stress intensity factor of the brittle crack was increased by the unwelded face, until the brittle crack reached a flange. However, when the brittle crack propagated into the flange, the stress intensity factor of the brittle crack was decreased by the unwelded face. The crack-arrest effect of the unwelded face appears after the brittle crack propagates into the flange.

TEMPERATURE DEPENDENT FRACTURE MODEL AND ITS APPLICATION TO ULTRA HEAVY THICK STEEL PLATE USED FOR SHIPBUILDING

In this study, experimental and numerical studies were performed to examine the effects of thickness of steel plate on the arrest fracture toughness. The ESSO tests were performed with the steel plates having temperature gradient along the crack propagation direction. A temperature dependent crack initiation criterion was proposed as well. A series of three-dimensional FEA was then carried out to simulate the ESSO test while the thickness of the steel plate varies. Results reveal that a temperature dependent brittle criterion proposed in this study can describe the fracture behavior properly.

Fracture Toughness of Thick Steel Plates for Shipbuilding

In this study, the effect of thickness on the fracture toughness of the steel plate with the thickness of 80mm has been investigated by the wide plate tensile test and ESSO test. The fracture toughness for crack initiation and propagation was evaluated quantitatively for the full thickness specimen. It was found that EH-36 grade steel with the thickness of 80mmt showed the KIC value of 164kgf/mm1.5 at -145°C. Also, large-scale ESSO test result showed that the steel with the thickness of 80mm had 520kgf/mm1.5 at -10°C. Although it was known that the fracture toughness decreases with the increase of the plate thickness, EH-36 grade steel with the thickness of 80mm had enough values of fracture toughness to prevent the crack initiation and arrest the brittle crack propagation.

T継手部の脆性き裂伝播停止挙動に及ぼす未溶着寸法の影響

In the large heat input weld joint of heavy gauge steel plate used for large container carrier, a brittle crack possibly propagates straightly along a weld joint without diverging to base metal. This phenomenon is being discussed for its application to the large heat input weld of heavy gauge plate to ship structures. In this study, to arrest a brittle crack at Tee joint embedding un-welded face, the effect of un-welded face on behavior of brittle crack propagation/arrest in Tee joint structure was investigated and analyzed. The ESSO test of Tee joint structure was carried out, supposing that a brittle crack which propagates along a weld joint of hatch coaming rush into Tee joint of hatch coaming and strength deck. The test results exhibited that the brittle crack arrested at the Tee joint embedding un-welded face, and the brittle crack arrested easier, the longer un-welded face was. The results of static FEM analysis showed that stress intensity factor of brittle crack was increased by un-welded face, until brittle crack reached a flange. However, when brittle crack propagate into the flange, stress intensity factor of brittle crack was decreased by un-welded face for instance. The crack-arrest effect of un-welded face appears remarkably after brittle crack propagates into the flange.

表層超細粒化による高アレスト鋼板の諸特性

A new type of steel plate with high crack arrestability has been developed by controlling its microstructure especially in surface layers of the plate. The microstructure of the surface layers of the plate is ultra-fine grained (so-called SUF), which provides excellent fracture toughness even at a cryogenic temperature. Crack arrestability of the plate has been further improved by the enhanced formation of side-ligaments (shear-lips) due to SUF, since unstable running crack behaviour is strongly affected by these shear-lips, which are formed in the surface layers of the plate after the unstable brittle crack has propagated in the mid-section of the plate.In the present report, the practical properties of the developed plate (so-called SUF plate) are investigated. Fracture tests confirm that the SUF plate possesses ultra high crack arrestability. The improved value of arrestability due to the SUF effect can be predicted by fracture mechanics.For practical use of the SUF plate, the damage to the surface layers in actual service should be considered, since the SUF region (surface layers) is essential for obtaining ultra high arrestability in the SUF plate. Considering corrosion loss on an un-painted surface of the plate, the SUF plate, which is prepared by cutting down one side surface to remove 'SUF', is evaluated for crack arrestability by ESSO tests. To simulate the welding damage to the SUF plate, bead-on-SUF plate specimens are tested for crack arrestability by ESSO tests. Both test results suggest that the SUF plate possesses sufficient crack arrestability even in actual service.Furthermore, it is also confirmed that the SUF plate has other characteristics, such as weldability and workability, which make it suitable for ship-building use, such characteristics being similar to those of a conventional-steel plate, including TMCP steel plate.

Unstable Brittle Crack-Arrest Toughness of Newly Developed Steel Plate with Surface Layers having Ultra Fine Grain Microstructure (2)

A new type steel plate with ultra fine grain surface layers (SUF plate) has been developed to improve crack arrestability. In order to prevent the catastrophic damage of hull, which might cause ocean pollution and casualties, caused by serious accidents such as collisions and/or grounding of VLCCs (Very Large Crude oil Carriers), application of SUF plates with ultra-high crack arrestability has been investigated using both computer simulation for a collision of VLCCs and large scale fracture testings for crack arrestability in emergency cases.The computer simulation results suggest that a collision generates significant plastic strain in surroundings of a struck part. For example, the plastic strain reached a 5-10% level before an inner-hull of the VLCC was ruptured at sheer strake plates near the struck part.Therefore, the effect of plastic strain (10% level) on crack arrestability in steel plates (the SUF plate and a conventional TMCP plate) was examined by standard ESSO test, ultra-wide plate duplex ESSO test, and sheer strake model fracture test. The test results suggest the followings : 1) Plastic strain deteriorates crack arrestability.2) Sufficient crack arrestability at 0 deg. C cannot be expected in the conventional TMCP steel plate with 10% plastic strain induced.3) The SUF plate with 10% plastic strain induced possesses high crack arrestability against emergency cases for ships.Therefore it is expected that application of SUF plates can prevent serious accidents in which a large amount of oil flows out through hull structural plates damaged by brittle fracture.

Statistical analysis of fracture arrest toughness of various structural steel plates

A statistical investigation was made relating to the brittle fracture arrest properties of various steel plates for ship and bridge structures, low-temperature storage tanks and pressure vessels. Fracture arrest toughness ( K a ) data obtained by means of the temperature gradient type of ESSO tests on around 200 steel plates were collected and analyzed. It was found that K a transition curves in terms of temperature for a set of steel plates possessed a ‘pivot’ on the temperature versus K a diagram when the data were grouped according to their chemical composition and production methods. It was also found that this pivot is moved to lower temperatures or to higher K a directions following the application of production processes and selection of the chemical composition such as the following: normalizing heat treatment; quenching and tempering heat treatment; rolling at intercritical temperature; reduction in carbon content and increase in nickel content. It was also found that the new production method of Thermomechanically Controlled Process (TMCP) for plate rolling provides an effective measure to improve the fracture arrest properties of steel plates.

Crack Arrest Toughness of Structural Steels Evaluated by Compact Test

Crack arrest tests such as compact, ESSO and DCB tests were made on SA533B Cl. 1, HT80 and KD32 steels to evaluate the crack arrest toughness. The main results obtained are as follows:(1) The crack arrest toughness could be evaluated by KIa which was obtained by the static analysis of compact test.(2) KID determined by the dynamic analysis of compact test was greater than KIa, though KID became close to KIa as KIa/KQ became a unity where KQ is the stress intensity factor at the crack initiation.(3) No significant difference was observed between KIa and Kca obtained by ESSO and DCB tests, though Kca obtained by DCB test tended to be smaller than KIa at lower temperatures.(4) KIa was smaller than KIc in the transition temperature range, while it was greater than KId. In the temperature range where KIc, which was determined from JIc, decreased with temperature increase, however, it was smaller than KIa.(5) The fracture appearance transition temperature and the absorbed energy obtained by 2mm V-notch Charpy test were appropriate parameters for representing the crack arrest toughness, while the NDT temperature was not.

コンパクト試験による構造用鋼材の脆性き裂伝播停止靱性の評価

Crack arrest tests such as compact, ESSO and DCB tests were made on SA533B Cl. 1, HT80 and KD32 steels to evaluate the crack arrest toughness. The main results obtained are as follows:(1) The crack arrest toughness could be evaluated by KIa which was obtained by the static analysis of compact test.(2) KID determined by the dynamic analysis of compact test was greater than KIa, though KID became close to KIa as KIa/KQ became a unity where KQ is the stress intensity factor at the crack initiation.(3) No significant difference was observed between KIa and Kca obtained by ESSO and DCB tests, though Kca obtained by DCB test tended to be smaller than KIa at lower temperatures.(4) KIa was smaller than KIc in the transition temperature range, while it was greater than KId. In the temperature range where KIc, which was determined from JIc, decreased with temperature increase, however, it was smaller than KIa.(5) The fracture appearance transition temperature and the absorbed energy obtained by 2mm V-notch Charpy test were appropriate parameters for representing the crack arrest toughness, while the NDT temperature was not.

On a Modified Three Point Bend Test for Determining Brittle Fracture Arresting Properties

Robertson type test method such as double tension test or ESSO test is very popular for the assessment of propagating and arresting properties of brittle fracture of steel plates with fracture mechanics approach. This is a so-called large scale test, requiring large amount of material, the test pieces being very expensive. Thus it is not suitable as a material test method.Recently, double cantilever beam (DCB) test has been proposed as a small scale fracture mechanics test for this purpose. However, it is necessary to machine very sharp grooves on the specimen surfaces in order to guide the crack path on the symmetric axis of specimen. Because of grooves, specimens tend to be expensive, and full thickness properties of plates can not be obtained.Therefore, it is required to develop a new test method which has following advantages ;(1) Specimen is small and not expensive.(2) Test method is simple and convenient.(3) Full thickness properties can be obtained ; i. e. crack propagates straightly on the symmetric axis without any surface grooves.(4) Test result can be evaluated with the fracture mechanics.In this paper, triangle specimens which were subjected to three point bending load were examined. Then, it was found that full thickness properties of crack arresting can be determined with the triangle bend specimens which have a pressed notch and gradient temperature distribution.Furthermore, using finite element method, crack paths of DCB specimen and triangle bend specimen were analyzed with a criterion of maximum strain energy release rate. As a result, it was found that the crack path of DCB specimen is unstable. Namely, in case of ideally symmetric specimen, the crack would propagate along the symmetric axis. However, if any small disturbances exist, the crack deviates from the symmetric axis. On the other hand, the crack path of triangle bend specimen is stable, the crack propagating along the axis even if small disturbances exist.

鋼材溶接継手の低温加熱急冷疲れ強さ改善処理のじん性におよぼす影響

It was already reported that quenchings from a temperature under A1 point improved the fatigue strength of steel welded joints, and the reasons of this fatigue strength improvement was attributed to quench aging effect and compressive residual stress in surface layer.On the other hand, aging of steel has a liklihood to make a embrittlement of steel. This experiment was carried out to clarify the effect of this fatigue strength improving heat treatment (low temperature quenching) on the toughness of welded joint.Each welded joint of rimmed steel, 50 kg/mm2 and 60 kg/mm2 steel was heated by hot dip galvanizing, at 500°C and 700°C in furnace, followed by quenching into about 20°C water. Toughness of toe of welded joint was investigated by i) Standard V notch Charpy Impact Test ii) COD Test and iii) ESSO Test.The following results were obtained, 1) The results of Charpy impact test and COD test showed that toughness of SS41, SM50 and HT60 steel welded joints did not decreased remarkably compared with as welded joint by a low temperature quenching.2) The ESSO test result showed that crack arrest temperature of SM50 steel welded joint slightly increased by low temperature quenching, but crack arrest temperature of SS41 and HT60 steel welded joints were nearly same compared with as welded joints.

Effect of Fabricating Method at Assembly Stage on Notch Toughness of Steel Plates (Report No. 3)

It is inevitable that high-strength steels of the 50 kg. per sq. mm. class suffer from some embrittlement when they are subjected to bending by the line-heating process. The embrittlement, however, is localized in some limited zone of the plate thickness. Therefore, it is a problem to estimate the notch toughness of the line-heated zone by the Charpy V-notch impact test as generally performed.In this study, an investigation was made to find the behaviour of the full thickness of the plates to the characteristics of brittle fracture initiation (by the Deep Notch test) and crack propagation-arrest (by the Double Tension and ESSO tests) at the line-heated zone, using large-sized test specimens including full thickness plate.The results of the above-mentioned tests are examined about criterions of vTrs, 16TiC=10, 16TaKc=220 and 16TaKc=439. Consequently, having control of cooling condition, the more efficient conditions of line-heating than the actually suggested ones are obtained without the much embrittlement of plate. The line-heating conditions are outlined as follows;1) In air-cooling after heating, there is no unfavourable effect observed even if the heating temperature is as high as 800 or 900°C.2) In water-cooling immediately after heating, there is no unfavourable effect observed when the heating temperature is as high as 650°C.3) In water-cooling during air-cooling after heating, there is comparatively little unfavourable effect observed when the heating, temperature is 800 or 900°C, as long as the temperature at the start of water-cooling is below 500°C.

Effects of Specimen Size and Loading Condition on the Brittle Fracture Propagation Arrest Characteristics

The Double Tension Test or the ESSO Test with temperature gradient has been carried out to estimate the brittle fracture propagation arrest characteristics of the steel used in the welded structures. However the effects of specimen size and loading condition on these tests have been considered vaguely.In this report, the authors have investigated these effects by the statical elastic analysis using the simple spring model and by the systematical experiments. In fact they have been carried out for the 5 test series changing the parameter of the loading condition and the aspect ratio of the test specimen, the distance of pin-to-pin to the specimen breadth.In the test results these effects have been found as was expected and explained by the above-mentioned analysis satisfactorily.Then the one of the experimental methods to avoid these effects in the test of the brittle fracture propagation arrest are proposed.

ごく薄板の脆性破壊特性

Recently, the demand for constructing welded structures for low temperature materials such as LPG, LMG, liquid oxygen and nitrogen has increased. Low temperature structural steels such as aluminum killed steel (QT), 2.5, 3.5 and 9% Ni steels have been employed for these structures. The brittle fracture initiation and arresting characteristics of these steels are very important for their application. It is wellknown that the thinner plate has the lower transition temperature on account of the decreased triaxiality and the improved metallurgical factors such as the fine grain and the lower finishing temperature, etc.In this paper, thin mild steel plates or sheets were investigated to evaluate the brittle fracture initiation and the arresting characteristics by using the large size tests such as the deep notch test, the welded and notched wide plate test and the ESSO test with temperature gradient.Two scmikilled steels and two killed steels 3.2 mm thick were tested. The brittle faacture characteristics of plate in the directions parallel and nomal to rolling were investigated.From the results of these large size tests, the excellent notch toughness or brittle fracture initiation and arresting characteristics were proved. In addition, the effect of welding residual stress on brittle fracture initiation characterestics was discussed.

Effectiveness of Crack Arrester (First Report)

The crack arrester is used for prevention of welded steel structures from brittle fracture. In the latest mammoth tankers, the welded crack arrester of high quality steel such as grade E steel is used instead of the riveted seam.In this paper, the brittle crack arresting characteristics for welded crack arrester was investigated by using large size specimens in 1, 300 mm width. Then the correlation between the characteristics in large size specimen and in standard ESSO test with temperature gradient as a substitute of double tension test was examined.From the test results, it was found that the modified gross stress-arresting temperature curves for arrested crack length of 500, 750 and 1, 000 mm, respectively, were common, and the effective crack length was approximately 250 mm which was obtained from the ESSO test or the double tension test with temperature gradient.In addition, the effect of width of arrester plate on the crack arrest in which the distribution of residual stress was taken into account, was found.

シャルピー衝撃試験における遷移挙動および破壊靭性の評価について

Analysis of the transition behaviour of mild steel in the Charpy impact test was made over a wide temperature range (100°∼−196°C) by observing the relationship between load and time during impact. As a result of this study, the transition behaviour in the Charpy impact test may be divided into six temperature regions. And it appears that usual transition temperatures such as Charpy-V 15 ft-lb energy. Charpy-V 0 percent shear and Charpy-V 15 mil lateral expansion are the yield point fracture criteria. On the other hand, Charpy-V 30∼35 ft-lb energy or Charpy-V 25 percent shear is the initiation (ductility) transition temperature at which no ductile crack can propagate after che maximum bending load is attained and rapid transition to brittle fracture occurs. It seems that this temperature correlates with NRL drop weight test NDT. Another important transition temperature is the cleavage initiation temperature at which first cleavage fracture appears in the load/time curve and this temperature coincides with nearly 100 percent cleavage fracture appearance temperature in the brittle boundary specimens (i.e. carburized specimens). And it appears that this temperature is a measure of estimating the brittle crack propagation arresting temperature of a large scale test. Furthermore we made attempt to obtain fracture toughness Gc values proposed by Irwin et al. from a small scale test such as the Charpy impact test in this case. For this purpose, we used brittle boundary specimens prepared by carburizing the free surface layers of Charpy specimens and measured load/time curves during fracture of these specimens. By these procedures we obtained some agreement with temperature gradient type ESSO test results. And estimates of Gc values relative to onset and arrest of brittle crack propagation were made and discussed.

On the Brittle Crack Propagation and Arrest with Special Reference to ESSO Test with Temperature Gradient

The mechanism of propagation and arrest of a brittle crack, which was governed by the plastic surface energy, the temperature, the crack length and the applied stress, was investigated from a viewpoint of crack speed.The ESSO test with temperature gradient was conducted and analyzed theoretically.A crack propagating in a field of gradient temperature reduces its speed gradually with the increasing crack length, and then is arrested abruptly after the speed downs to lower than the critical crack speed of 250_??_400m/sec.The effect of shear lip on the plastic surface energy was found by using a specimen with hardened surface.The stress-arresting temperature curve for a given temperature distribution was approximately estimated from the crack speed data under a stress level.

A Proposal Concerning Propagation Test of Brittle Crack

As a testing method to obtain critical temperature-stress curve for propagation of brittle crack, the author proposes a notch tensile test of cross welded steel plate. An experiment has been carried out for the quenched and tempered steel “2 H”, having high notch toughness and high tensile strength, such as, 60 kg/mm2, and the test result was compared with those of ESSO test and of double tension test with each gradient and flat temperature distribution. The result obtained by the test was very similar to that of double tension test with flat temperature distribution. (cf. Fig. 7) The distinctive features of this test are summarized as follows : 1) The cross welded specimen, having a sharp notch in its high tensile residual stress field, may cause single stage complete fracture under lower applied stress than yield stress.2) When a brittle transverse weld metal is provided at the location of notch, running crack may propagate to the base metal at the temperature above critical temperature for crack propagation without gradient temperature destribution on the specimen. Therefore, it is easy to apply this test for the steel of excellent notch toughness.3) By adjusting the length of brittle transverse welded joint, sufficient speed of running crack may be obtained.4) Fracture stress level of the specimen may be adjustable by preloading at the temperature above critical temperature of crack initiation under low applied stress level.Further investigations should be performed about stress destributions at the propagation field under various loading conditions and also about stress re-destribution during crack propagation.