Cracks In Welded Joints Research Articles

Ultraviolet excitation for thermography inspection of surface cracks in welded joints

Infrared thermography is a non-contact and full field inspection method which has proven to be suitable for automatic surface crack detection. For automatic analysis of the inspection results, a high signal-to-noise ratio (SNR) is required. In this paper an alternative excitation method, using ultraviolet (UV) illumination, is presented and evaluated. Artificial surface defects, so-called notches, in a titanium plate are detected both in the weld seam and in the heat affected zone. Notches with a size from 80 μm in width and 250 μm in length are detected. The SNR using UV illumination is compared with that using flash lamp excitation. The results show that UV illumination using a mercury lamp is a good alternative as excitation source for thermography when detecting surface cracks. To validate the excitation method, results from real surface cracks are included.

Characterization of cracks of welded joint of ferritic stainless steel pipe AISI 430

This paper presented the main objective characterization of cracks in welded joints of ferritic steels, since these are considered one of the most serious types of discontinuities in welds of these steels. These discontinuities are formed when tensile stresses are developed in a fragile material, unable to plastically deform the absorbing it. High tensile stresses are created and developed in the weld region as a result of thermal expansion and contractions located ( associated with non-uniform heating of the weld ), the volume changes due to phase transformations and as a result of links between pieces being welded and the rest of the structure. To induce cracking of the sample Varestraint test was used, as well as to measure the fracture toughness testing we performed Charpy Impact. However, in this study we observed that microfissures solidification in HAZ (heat affected zone), cracks in the center of the weld cracking due to thermal expansion and overhead imposed by the test were prevalent in these steels AISI/ASTM 430 specification. There was also the toughness of the weld proved always above to the base material.

Analysis of the elastic-plastic behavior of pressurized internal cracks in welded joints of low carbon steel pipes

It was analyzed the elastic-plastic behavior of areas with pressurized planar internal cracks extending from the pattern metal region in the heat affected zone to the welding metal in welding joints of low carbon pipes subject to internal pressure. Using the ANSYS 8.0[TM] software, three-dimensional simulation of geometrical models of pipes containing the internal pressurized cracks was performed. The finite element method with non linear strain conditions was employed, considering the kinematic hardening rule and the real material properties for every location. The fracture paths and expressions to calculate the pressure in the crack and in the pipe that lead to fracture of the cracked area were obtained.

Ways of ensuring regulatory resource of bridge spans

The structural features of welded railway bridges of the last century were considered. The basic causes of appearance of fatigue cracks in welded joints of railway bridges were assessed. Structural and technological ways of provision of the design life of operated and new-built welded railway bridges are discussed.

シェルーソリッド混合解析を用いた船体構造部材に発生する表面き裂の三次元破壊力学解析に関する研究

Applications to three-dimensional fracture mechanics analyses for surface cracks in welded joints of ship structure are presented. To evaluate mechanical behaviors of ship structures, shell finite elements are often used in finite element analyses (FEA). It is difficult to solve three-dimensional crack problems such as surface cracks using the shell elements because the plate thickness is assumed in the shell element formulation. A shell-solid mixed analysis is performed to evaluate stress intensity factors (SIFs) of three-dimensional surface cracks in ship structural members. The whole analysis region is modeled by triangle or quadrilateral shell elements, and the local region near the surface crack is modeled by tetrahedral solid elements. The shell model and the solid model are connected using RBE3 (Rigid Body Element 3) connection in MSC.Nastran. In addition, a semi-auto RBE3 connection technique is developed to enhance the shell-solid mixed analysis. VCCM (Virtual Crack Closure-integral Method) using tetrahedral finite elements are adopted to calculate the SIFs of the three-dimensional surface cracks. The SIFs calculation and the evaluation of the surface cracks in the welded joints of the ship structure are demonstrated.

Cracking of welded joints at elevated temperatures

Cracking of welded joints at elevated temperatures

Corrosion cracking of welded joints of pipelines from steel 08Kh18N10T in power units with RBMK-type reactors

The effect of coolant parameters (temperature, content of oxygen and chlorine ions, acidity parameter pH) and of residual stresses on the susceptibility of welded joints of pipelines from steel 08Kh18N10T at power units with RBMK-type reactors to intercrystalline corrosion cracking is studied. It is shown that the endurance of the pipelines depends on the heat treatment of welded joints and on the deaerated rise of the reactor to the operating conditions.

Reduction of air inflows in condensers of 200-MW power units

Results of updating the reducer between the LPC and the condenser involving removal of lens compensators and stiffening of the bar and rib frames are presented. Air inflows into the vacuum system through cracks in welded joints of flexible elements with total welded length of 240 m are lowered considerably by replacing them by stiff sheet structures. Computations of the thermal and stress-strain states of the system are performed.

Intercrystalline Corrosion Cracking of Welded Joints of the Austenitic Pipelines of Nuclear Power Plants

We consider the character of damages of welded joints of Du300 pipelines in the course of operation of nuclear power plants with RBMK reactors and determine the principal causes of intercrystalline corrosion cracking. We describe in detail the kinetics of sensitization of the metal in the near-weld zone of welded joints of 08Kh18N10T steel.

Strengthening fatigue-cracked steel bridge decks

In slender orthotropic decks of steel bridges, the dynamic interaction between vehicle tyres on flexible asphaltic pavement and the deck structure plays an important role on stress amplitudes. This involved interaction mechanism is brought into the discussion on the main causes of the pavement disruption and of the observed cracks in a large steel bridge, which has been frequently damaged by fatigue cracks in welded joints and geometric details under random stresses produced by traffic loading. Numerical modelling and experimental strain measurements performed both in situ and in the laboratory on a prototype scale model of the actual steel deck. Proposed solutions include adding a reinforced concrete pavement, either as a sandwich structure with a visco-elastic layer in between the steel plate and the concrete slab, or as a composite deck formed by fixing the concrete slab to the steel plate with stud connectors. It is shown that visco-damping and composite stiffness properties led to substantial reduction of both longitudinal and transverse bending stresses, enhancing the fatigue performance of these bridge decks.

Strengthening fatigue-cracked steel bridge decks

In slender orthotropic decks of steel bridges, the dynamic interaction between vehicle tyres on flexible asphaltic pavement and the deck structure plays an important role on stress amplitudes. This involved interaction mechanism is brought into the discussion on the main causes of the pavement disruption and of the observed cracks in a large steel bridge, which has been frequently damaged by fatigue cracks in welded joints and geometric details under random stresses produced by traffic loading. Numerical modelling and experimental strain measurements performed both in situ and in the laboratory on a prototype scale model of the actual steel deck. Proposed solutions include adding a reinforced concrete pavement, either as a sandwich structure with a visco-elastic layer in between the steel plate and the concrete slab, or as a composite deck formed by fixing the concrete slab to the steel plate with stud connectors. It is shown that visco-damping and composite stiffness properties led to substantial reduction of both longitudinal and transverse bending stresses, enhancing the fatigue performance of these bridge decks.

Observation of type IV cracking in welded joints of high chromium ferritic heat resistant steels

Type IV cracking in welded joints of high Cr ferritic heat resistant steels at 923 K is investigated in the present study. First, internal pressure creep tests were performed to investigate the features of cracking at 923 K and at stresses of 108–167 MPa. Results showed that at low stresses cracks occurred in the fine grained heat affected zone (FGHAZ), showing low deformation, a vast amount of creep voids and short creep life: these were identified to be type IV cracks. However, as the stress was increased the crack locations moved further away from the fusion line, the creep void area density decreased, and the slope of the main crack ratio curve increased. At high stress, cracks occurred in the base metal and were identified to be normal cracks. Second, creep tests were carried out on one pass welded specimens to clarify the relationship between the creep property deterioration in the FGHAZ and the weld thermal cycle. Type IV cracking was repeated successfully and results showed good correspondence with the position of cracks among the softened region, the highest creep void area density and the fracture location. Both internally pressurised and one pass welded specimens showed that at low stress the FGHAZ was the weak zone and creep voids played an important role in type IV cracking.

Analysis of factors affecting type IV cracking in welded joints of high chromium ferritic heat resistant steels

In the present work, creep tests on single pass welded joints were carried out to investigate the factors affecting the deterioration of the creep strength of weldments of high Cr heat resistant steels. In creep tests at a temperature of 923 K and stresses of 90 and 120 MPa, creep fracture occurred in the fine grained heat affected zone (FGHAZ) and was identified as type IV cracking. It was found that a peak temperature between Ac1 and Ac3 in the FGHAZ caused the observed creep property deterioration. The factors identified as leading to the deterioration are a fine grain structure, low hardness, and large precipitates. Further investigations confirmed the influence of the fine grain structure as a critical factor decreasing the creep rupture time. The hardness difference between the FGHAZ and the base metal is insignificant, especially at 923 K. However, SEM investigations revealed that many large precipitates are distributed on the boundaries of the martensite laths and prior austenite grain boundaries. It is considered that the large precipitates also have a significant influence on the creep strength deterioration.

Effect of welding and weld repair on crack propagation behaviour in aluminium alloy 5083 plates

Aluminium alloy 5083 is used in the fabrication of lightweight, high-speed marine vessels. The high cyclic service stresses on such structures render welded joints in them fatigue-critical. This paper presents experimental investigations on fatigue crack behaviour of welded 5083-H321 aluminium alloy plates. Crack propagation in the heat-affected zone of welded specimens was determined from tests conducted on single edge-notched tension specimens. Three-dimensional finite-element analysis was employed to determine stress intensity factors for cracks in the weld line. The crack closure effects of weld residual stresses were evaluated. The residual stresses significantly influence the crack growth rates. Fatigue behaviour of weld repairs in cracked plates was also investigated. The weld-repair process significantly increases the grain size and the size of defects in the heat-affected zone. The results indicate that weld repair of cracks in welded joints provides little improvement in residual life.

Formation of hot cracks in welded joints in alloys of aluminium-magnesium-lithium and aluminium-copper-lithium systems

Formation of hot cracks in welded joints in alloys of aluminium-magnesium-lithium and aluminium-copper-lithium systems

Prevention of damage to welded joints of 12Kh18N10T steel in production of potassium nitrate

We analyzed damage to welded joints of pipes made of 12Kh18N10T steel in working media for the production of potassium nitrate. We showed that the corrosion cracking of objects was caused by the action of chlorides in technological solutions under a high level of residual postwelded stresses in welded joints. We give some recommendations for the prevention of the corrosion cracking of welded joints of pipelines and pressure filters.

Fatigue notch factor of gaps in welded joints reconsidered

The fatigue notch factor of short gaps or cracks in welded joints determined by the notch stress approach with fictitious notch rounding is modified on the basis of theoretical relations for notch stresses and stress intensity factors. The accuracy of the derived correction factors is proven by application to a cruciform welded joint with short internal gaps.

Effect of lateral load on fatigue growth rate of surface cracks in welded joints

The fatigue growth rates of surface cracks in welded joints subjected to uniaxial and biaxial loads are studied for two common types of pressure vessel steels. The equations of crack growth rates with survival probabilities equal to 50% and 97·73% are developed. The effect of lateral load on fatigue growth rate is discussed. The rate of fatigue crack growth in welded joints is compared with those of parent materials.

Distinctive features of sulfide cracking of welded joints of pipe steel

We present the results of investigations aimed at the determination of susceptibility of welded joints in low-alloy 14GB pipe steel to sulfide cracking in the presence of technological defects. We established that these joints exhibit no susceptibility to cracking at stresses below −0.5σ0.2 for the base metal, and thatK Iscc in the NACE solution is equal to 28MPa√m.

A probabilistic model for initiation and propagation of surface cracks in welded joints: Lecsek, R.L., Yee, R., Lambert, S.B. and Burns, D.J. Fatigue Fract. Engng. Mater. Struct. (July–August 1995) 18 (7–8), 821–831

A probabilistic model for initiation and propagation of surface cracks in welded joints: Lecsek, R.L., Yee, R., Lambert, S.B. and Burns, D.J. Fatigue Fract. Engng. Mater. Struct. (July–August 1995) 18 (7–8), 821–831