API 2W Research Articles

Estimation of Fracture Toughness of API 2W Gr.50 Steel in Ductile to Brittle Transition Behavior Using Master Curve Approach

Welding is used as the main joining method in various industries, including the shipbuilding industry. In the case of welded structures, structural integrity assessment is essential to ensure the safety of the structure because many defects inevitably exist during the manufacturing process. The value of reliable fracture toughness is required for structural integrity assessment. It is obtained by the fracture toughness test, but the fracture toughness test requires a lot of time and effort. Therefore, many studies have been conducted on efficient methods to evaluate fracture toughness. Among the various studies that estimate fracture toughness, some have been conducted using the Charpy impact test, which is relatively simple compared to the fracture toughness test. This study conducted a series of experimental investigations on API 2W Gr.50 steel applied with different welding conditions. Based on the Charpy impact test results, the fracture behavior was well estimated in the ductile to brittle transition region according to the temperature. However, there was a difference in the accuracy of predicting fracture behavior depending on the welding process. Therefore, additional consideration reflecting the various welding conditions is required to ensure the safety of welded structures.

Effect of grain size on the resistance to hydrogen embrittlement of API 2W Grade 60 steels using in situ slow-strain-rate testing

This study investigated the grain size effect on the resistance to hydrogen embrittlement (HE) of API 2W Grade 60 steels using in situ slow-strain-rate testing. Hydrogen was electrochemically charged into specimens and the hydrogen content evolved from diffusible hydrogen-trap sites was measured by thermal desorption spectrometry (TDS). The fine-grained (14μm) steel showed superior HE resistance despite exhibiting higher total hydrogen content than the coarse-grained (35μm) steel. Decreasing grain size resulted in a larger grain boundary area, thereby better reducing the normalized amount of diffusible hydrogen trapped per unit length of grain boundary.

CTOD Evaluation for HAZ Toughness of Offshore Structure Steels with Heavy Thickness Based on API RP 2Z

The CTOD (Crack Tip Opening Displacement) evaluation and control for HAZ (Heat Affected Zone) toughness of welded joints are the most effective measures to the security of steel structures. This paper address the problem of the newly developed offshore structure steel API 2W 50Z with heavy thickness of 100mm. In accordance with the American Petroleum Institute standard Recommended Practice 2Z (API PR 2Z), the CTOD tests of two critical positions of HAZ in three kinds of heat inputs were carried out in low temperature (-10°C). All of these CTOD testing and assessments are finished under the witness of American Bureau of Shipping (ABS). The result shows that all of the CTOD values are greater than the required value (0.38mm) in API RP 2Z. This indicates that the newly developed offshore structure steel (API 2W 50Z) meet the requirement of the toughness. Further, the CTOD testing and assessments in several international standards about weld joints of steel plates are also compared and discussed in this paper.

API 2W Gr. 50 강재 용접부의 피로균열전파거동의 거시적 및 미시적 관찰

It is well known that a considerable amount of scatter is shown in experimental results relating to fatigue crack growth even under identical and constant amplitude cyclic loading conditions. Moreover, flux cored arc welding (FCAW) is a common method used to join thick plates such as the structural members of large scale offshore structures and very large container ships. The objective of this study was to investigate the macro- and microscopic observations of the fatigue crack growth (FCG) behavior of the FCAWed API 2W Gr. 50 steel joints typically applied for offshore structures. In order to clearly understand the randomness of the fatigue crack growth behavior in the materials of three different zones, the weld metal (WM), heat affected zone (HAZ), and base metal (BM), experimental fatigue crack growth tests for each of five specimens were performed on ASTM standard compact tension (CT) specimens under constant amplitude cyclic loading. Special focus was placed on the fatigued fracture surfaces. As a result, a different behavior was observed at the macro-level, depending on the type of material property: BM, HAZ, or WM. The variability in the fatigue crack growth rate for WM was higher than that of BM and HAZ.

Evaluation of fracture behavior of the reheated weld zone in API 2W Gr. 50 steel weld metals

In this study the effect of martensite-austenite (M-A) constituents on the fracture behaviour of the reheated weld zone formed by subsequent weld passes in API 2W Gr. 50 steel welds was evaluated. For the weld thermal cycle simulation process with the Geeble thermal simulator, the actual single-pass weldment was used rather than the base metal. The reheated weld zone in the weld metal was categorized into four typical areas according to the peak temperature. The test results indicated that toughness is closely related to the fraction of the martensite-austenite constituents.In particular, the intercritical reheated weld zone with a high fraction of M-A as well as a coarse-grained reheated zone can be considered as local brittle zones of weld metal.

Variability of Fatigue Crack Initiation Life in Flux Cored Arc Welded API 2W Gr.50 Steel Joints

Flux Cored Arc Welding (FCAW) is a common practice to join thick plates such as the structural members of large scale offshore structures and very large container ships. The objective of this study was to investigate the mechanical properties and variability of the fatigue crack initiation life in the flux cored arc welded API 2W Gr.50 steel joints typically applied to offshore structures with a focus on the effect of the materials in fatigue crack growth life from the notch root of a compact tension specimen. Offshore structural steel (API 2W Gr.50) plates (60-mm thick) were used to fabricate multi-path flux core arc welded butt welded joints to clearly consider fatigue fractures at the weld zone from the notch. Fatigue tests were performed under a constant amplitude cyclic loading of R = 0.4. The mean fatigue crack initiation life of the HAZ specimen was the highest among the base metal (BM), weld metal (WM), and heat affected zone (HAZ). In addition, the coefficient of variation was the highest in the WMl specimen. The variability of the short fatigue crack growth rates from the notch tips in the WM and HAZ specimens was higher than in BM.

EFFECT OF LOAD RANGE ON PROBABILISTIC FATIGUE CRACK GROWTH RESISTANCE IN FLUX CORED ARC WELDED API 2W GR. 50 STEEL

The aim of this paper is to investigate the effects of the load range on the spatial variation of fatigue crack growth resistance in three different zones, WM, HAZ and BM for flux cored arc welded API 2W Gr. 50 steel using the stochastic model based on reliability theory. Experimental fatigue crack growth tests were performed on ASTM standard CT specimens. The results indicates that the load range has strong dependency on probabilistic fatigue crack growth for the three different zones WM, HAZ and BM, and also the spatial variation of fatigue crack growth resistance.

DOGAL API 2W GRADE 50

Abstract DOGAL API 2W GRADE 50 is thermomechanical control processed plate produced to meet specifications for API 2W Grade 50 Steel. This datasheet provides information on composition and tensile properties as well as fracture toughness. It also includes information on forming. Filing Code: SA-620. Producer or source: SSAB Swedish Steel Inc..

Fatigue crack in large-scale tubular joints for offshore structures

Tubular members have been used for constructing offshore structures. Large-scale fatigue tests of welded tubular K-joints under the balanced in-plane bending brace were carried out to investigate the fatigue behavior of API 2W Gr.50 steel produced by POSCO. The experimental results were verified by numerical approaches and compared with the IIW, DnV RP-C203 and API RP 2A-WSD design curves. The test results based on the hot spot stress were in agreement with the design curves. The SCF factor for tubular K-joint was also obtained. The numerical parametric study of the K-joint (using the finite element program) was described and its results were compared with experimental results. The stress effects of various parameters including α, β, γ, τ and θ on the stress in the K-joint were investigated. The stress distribution for each parameter was introduced. The study showed that the maximum stress of the joint varied according to the variation of joint parameters.

입열량에 따른 FCAW용접부 파괴인성에 미치는 미세조직의 영향

This paper is to evaluate fracture characteristics of API 2W Gr.50 TMCP steel weldment typically applied for offshore structures, with the focus on the influence of heat input arising from flux cored arc welding. Based on the results and insights developed from this study, it is found that the toughness for both CTOD and impact exhibits a tendency to decrease as the weld heat input increases. The reheated zone of weldmetal exhibit lower hardness than solidified zone and microstructure that are liable to affect the toughness are acicular ferrite and martensite-austenite constituents (M-A). In particular, M-A is a more effective micro-phase for CTOD toughness than impact toughness.

Fracture characteristics of TMCP and QT steel weldments with respect to crack length

This experimental investigation focuses on an evaluation of fracture characteristics of API 2W Gr.50 (TMCP) and 580 MPa class high-strength steel (QT) weldments with respect to crack length to width ratio. Crack tip opening displacement (CTOD) values from single edge notched bending (SENB) specimen are associated with the Charpy toughness of root weld located at the middle of the specimen thickness and showed lower toughness values according to the increasing crack length to width ratio. In fractography analysis, there is no significant effect of crack tip constraint on fracture mode. The hardness values of the reheated zone in weld metal are lower than the solidified zone, and fractures are initiated at the reheated zone with low hardness values within the center third of section thickness.

해양구조용강재의 SA용접부에서 입열량이 파괴인성에 미치는 영향에 관한 실험적 연구

The influence of heat input on fracture toughness was investigated in SAW weldments, which were prepared at two different welding conditions in API 2W Gr.50 and EN10225 5420. By examining the fracture initiation point, refined areas(ICHAZ and SCHAZ) in weld metal was identified as local brittle zone, in which M-A constituents and coarsed grain size were observed. Impact values showed the most significant difference at root portion, and CTOD transition temperature was related with impact values obtained at root portion. Hardness values in refined area were less than columnar microstructure about 20 HV5.