Austenitic Stainless Steel Pipe Welds Research Articles

Study on effectiveness of education and training for ultrasonic examiner in austenitic stainless steel piping welds

Study on effectiveness of education and training for ultrasonic examiner in austenitic stainless steel piping welds

Fatigue Crack Growth Studies on Narrow Gap Pipe Welds of Austenitic Stainless Steel Material

The objective of the present study is to understand the Fatigue Crack Growth (FCG) behavior in austenitic stainless steel pipe welds. The tests have been carried out on Compact Tension (CT) specimens machined from the actual narrow gap pipe welds. The notch was located in Weld Centre Line (WCL), Heat Affected Zone (HAZ), HAZ-Fusion Line (FL) interface and the parent metal. The comparisons have been made for the FCG rate for different locations of the crack. The tests were carried out using standard procedure of ASTM E647. The results of FCG rate of narrow gap welds (HAZ, WCL, HAZ-FL interface and parent material) have been compared with that of conventional V-groove welds of Shielded Metal Arc Welding (SMAW) process. The comparison shows that the fatigue crack growth resistance of narrow gap welds is better than conventional groove welds. The FCG resistance of weld and parent material is better than HAZ location in the Paris regime. However, parent material shows superior threshold crack driving force range.

Improvement in Welding of Austenitic Stainless Steel Thick Pipe: Metallurgical, Mechanical & Full Scale Pipe Weld Tests

The paper aims at demonstration of reduction in residual stress, distortion and sensitisation in austenitic stainless steel pipe welds. The welding processes considered are Gas Tungsten Arc Welding (GTAW) and Shielded Metal Arc welding (SMAW) along with Hot wire GTAW with narrow gap welding technique. It was shown that residual stress is significantly reduced in case of hot wire GTAW. The reduction in residual stress is due to the low heat input and high deposition rate. Lower heat input leads to higher cooling rate giving more margins on sensitization in heat affected zone (HAZ). This has been confirmed by measuring temperature and cooling rate during welding in HAZ of the weld joints. Susceptibility to sensitization of the welds has been compared by carrying out ASTM E262 Practice A and E along with Electo-Potentiokinetic Reactivation (EPR) method. The results of the tests show that values are within acceptable limit for both the cases. However, hot wire GTAW has marginally better sensitization resistance. Fatigue crack growth rate and fracture resistance behavior of the above mentioned weld joints have been compared by carrying out tests on the specimens (Compact Tension) and full scale pipe welds with crack. Fatigue crack growth rate and fracture toughness of the weld joints (hot wire GATW) is superior to conventional GTAW and SMAW. The paper presents the details of the above mentioned studies.

Analytical Study of the Relaxation of Welding Residual Stress by Excessive Loading for Austenitic Stainless Steel Piping Welds

Welding residual stress is one of the most important factors of stress corrosion cracking (SCC) for austenitic stainless steels of the pressure boundary piping in nuclear power plants. For the assessment of the integrity of piping particularly for a long-term operation, it is necessary to understand the effect of excessive loading, such as an earthquake, on the residual stress. Three-dimensional finite element analyses were performed using three-dimensional model for a 250A pipe butt weld of low-carbon stainless steel of type 316L. The welding simulation method considering the moving heat source with the double ellipsoid model was confirmed by comparing with some experimental measurements. After conducting the welding simulation and residual stress analysis, several loading patterns of bending moment and axial displacements have been applied to the model by varying amount of moment and displacement in order to study the effect of excessive loading. The analyses indicated that higher loading of bending and axial stresses caused higher relaxation on welding residual stress near piping welds. The difference in the effect of loading direction was observed for both cases. It is concluded that excessive loading to piping butt-welds has an influence on the suppression of SCC growth due to the decrease in tensile residual stress at the inner surface.

Optimization of residual welding stresses in austenitic steel piping: prooftesting and numerical simulation of welding and postwelding processes

The development/modification and qualification of welding technology for generating compressive stresses in austenitic stainless steel piping welds are discussed. The following welding processes are considered: 1. A modified, orbital gas tungsten arc (GTA) narrow-gap welding process with significant improvements over conventional and standard narrow-gap orbital pipe welding, 2. The heat sink welding (HSW) process with internal cooling of the pipe with water or liquefied CO 2 gas, and 3. The postwelding process. Last pass heat sink welding (LPHSW) for altering residual stresses in an existing weld. Residual stresses have been measured by using the so-called ring-core as well as radiographic procedures. In support of experimental work required to qualify these welding techniques a numerical simulation effort was undertaken.

Discrimination of ultrasonic indications from austenitic stainless-steel pipe welds

The inspection of butt-welded stainless-steel pipe joints in nuclear power plants is routinely performed using ultrasonic non-destructive evaluation methods. Field experience, based on conventional ultrasonic signal-amplitude criteria, shows that a large number of indications are recorded. Most of these are not due to cracks, but are inherent in the geometry of the specimen. Discrimination between crack and geometric/weld (malignant versus benign) indications is principally based on operator experience, variations in signal amplitude, and the location of the reflector. Significant differences in performance exist due mainly to operator experience, fatigue, concentration, and conventional signal-amplitude evaluation criteria. In addition, the process of distinguishing the type of indications is very time consuming, as field experience and round-robin tests have shown. In response to this inspection problem, a pattern-recognition methodology has been developed to discriminate intergranular stress-corrosion cracking from geometric/weld reflectors in austenitic stainless-steel pipes. Results demonstrate that this algorithm can provide discrimination comparable to or better than those supplied by well trained operators. Preliminary results show that the pattern-recognition algorithm approach yields a better than 90% index of performance.

高温水中における各種オーステナイトステンレス鋼管溶接継手部の応力腐食割れ感受性

高温水中における各種オーステナイトステンレス鋼管溶接継手部の応力腐食割れ感受性