Austenitic Stainless Steel Piping Research Articles

Crack resistance of austenitic stainless steel pipe and pipe welds with a circumferential crack under monotonic loading

ABSTRACTThis paper describes the experimental studies carried out on cracked austenitic stainless steel pipe and pipe welds under bending loads. Pipe welds were produced by gas tungsten arc welding (GTAW) and shielded metal arc welding (SMAW). Fracture resistance curves for pipe and pipe welds were compared. Results indicate that the fracture resistance of pipe and pipe weld (GTAW) is comparable but that of pipe weld (GTAW+SMAW) is inferior. Cracks do not deviate from their original plane during propagation as observed in the cases of carbon steel pipe and pipe welds. The fracture resistance of pipe welds does not depend on the loading histories to which it has been subjected prior to fracture test. Initiation and crack propagation were observed prior to the maximum moment. An existing limit load expression is applicable for the pipe base material but gives non‐conservative results for the pipe welds. Multiplication factors have been suggested for the pipe welds for evaluation of limit loads using the existing expression. Fracture resistance for the pipe and compact tension specimens have also been compared for base material and welds.

Lésion verruqueuse du dos de la main

Water leakage occurred in hot-water pipes made of 304 stainless steel of an antiburning boiler after usage for 8 months. The detection revealed that the 304 austenitic stainless steel in a combustion chamber cracked on the side of the hot water outflow. This study analyzed the cause of cracking of the 304 austenitic stainless-steel hot water pipe by using microstructural, intergranular corrosion, and corrosion product analyses. Results showed that the 304 stainless steel, which met the material requirements, fractured via a mixed cracking that included transgranular and intergranular cracking (mainly transgranular). Moreover, a large amount of single copper accumulated on the crack surface, which indicated that the crack was induced by stress corrosion involving copper ions and mechanical stress. High temperature was another factor that induced cracking because the passive film of 304 stainless steel weakened in hot water. The copper ions came from the inferior brass valves when immersed in hot water with oxygen exposure. Basing on the above results, this type of cracking can be prevented by using 2205 duplex stainless steel (DSS) instead of 304 stainless steel. The stress corrosion behaviors of 304 stainless steel and 2205 DSS in aqueous solution with a certain concentration of copper chloride were analyzed using four-point bending test. Results showed that 2205 DSS did not crack, whereas 304 austenitic stainless failed in the test.

Evaluation of the Degradation Characteristics of CF-8A Cast Stainless Steel Using Indentation Techniques and EDS

Cast austenitic stainless steel piping pump, valve casings and elbows are susceptible to reductions in toughness and ductility because of long term exposure at the operating temperatures in the LWR (light water reactor). In this study, the three classes of thermally aged CF-8A cast austenitic stainless steel specimens were prepared using an artificially accelerated aging method for 0, 2,679 and 3,572 hours at 400oC. An indentation technique was applied to evaluate of the thermal aging of CF-8A cast austenitic stainless steel. We have performed indentation tests (automated ball indentation and nano-indentation) and EDS (energy dispersive spectroscopy) in order to characterize the micro-structural changes of the phase with aging. The fracture toughness of aged CF-8A cast stainless steel was determined by standard fracture toughness tests and automated ball indentation techniques.

2807 オーステナイトステンレス鋼管継手へのろう付圧接技術の適用性(S35-2 溶接・接合の動向とその展開(2),S35 溶接・接合の動向とその展開)

Braze Pressure Welding (BPW) with high frequency induction heating is a newly developed pressure welding technique using interlayer metals for welding the general steel pipes for pipe arrangement in buildings. At a joining temperature in this method, the melted interlayer removes contaminations from the joining surface of the base metal. Then the liquid filler is discharged from the joining interface by the joining pressure, and forms fillets at the gaps around the joint. The fillets have the effects both on relaxing the stress concentration at the joint and on increasing the joining area, which contribute to the strengthening of the joint. Thus, the high quality pipe joining without the dispersion in joint properties due to welder's skill can be performed. In this report, applicability of the BPW technology to austenitic stainless steel pipe joint is investigated and discussed on the results of microscopy and tensile tests of the joints.

In-situ eddy current monitoring of structural components in nuclear power plants

This paper discusses the feasibility of Eddy Current Monitoring (ECM) system as a in-situ evaluation method of crack propagation in a Boiling Water Reactor (BWR) environment. For the purpose, we review an ECM experiment conducted at a System Safety Benchmark Facility (SSBF) with a large-scale austenitic stainless steel pipe specimen. Several slits were prepared at the Heat Affected Zones (HAZs) and weld lines from the inner surface. After exerting the load, Eddy Current Testing (ECT) probes attached on the outer surface of the specimen provide the crack propagation signal. Numerical simulation of eddy current signals based on the experimental conditions indicate that this system is capable of monitoring the crack growth in BWR environments.

Authors's reply to `Generation of surface degraded layer on austenitic stainless steel piping exposed to flowing sodium in a loop: inter comparison of long term exposure data', by S. Rajendran Pillai

This is an elaborate author's reply to a comment `Generation of surface degraded layer on austenitic steel piping exposed to flowing sodium in a loop: inter comparison of long term exposure data' by S. Rajendran Pillai appearing in this proceedings. The basic misunderstanding as seen in the above comment about the mass loss due to sodium exposure, which is reflected throughout the above comment, has been explained in detail in this reply for better understanding of the phenomenon. It is precisely mentioned and understood that Thorley and Tyzack model deals with complete mass loss and not mere degradation. The total mass loss corresponds to mass loss due to wall thinning and that due to degraded layer formation. Though Thorley and Tyzack model is the most pioneering model in the field of sodium corrosion, the inadequacies of this model for materials without molybdenum such as SS 304 with very long exposure in sodium is clearly brought out in this paper. This model has been successfully applied to calculate life of clad tubes, which have relatively short stay in reactor core. Yoshida models are highlighted and compared with our experimental results. Yoshida models are not valid below certain durations owing to the empirical nature of such expressions. Thorley and Tyzack model can be used for SS 316 LN as this alloy contains molybdenum and nitrogen both of which imparts corrosion resistance in sodium. What is required is that one needs to establish the extent to which this model can be applied for materials exposed to high temperatures and very long durations. The details are discussed in this reply.

Generation of surface degraded layer on austenitic stainless steel piping exposed to flowing sodium in a loop: intercomparison of long-term exposure data

Exposure of austenitic stainless steels to high temperature sodium causes leaching of the constituent elements. Different elements are leached to different extent on account of the difference in their solubility in sodium. Nickel is having the highest solubility and hence would be leached out preferentially. The leaching of nickel causes the destabilization of the austenite and promote the generation of ferrite phase. The layer containing ferrite is referred to as `surface degraded layer'. This layer may have undergone the leaching of other elements like chromium also. The paper compares the thickness of surface degraded layer reported by different investigators. An ambiguity in the literature in explaining the observed corrosion behaviour and need to distinguish between complete metal loss and generation of degraded layer has been clarified in this paper.

Technical note Corrosion and cracking under insulation of type 304 stainless steel at ambient temperature

Corrosion pitting was found under insulation on type 304 austenitic stainless steel pipes used in an ethylene plant since 1980 to transport hydrocarbon products at – 170 ° C. Preliminary investigations established that the corrosion was confined to areas adjacent to the circumferential weld seams. Chlorides were present on the external surface of the pipes owing to ingress through defective insulation. Detailed examination of specimens from the affected pipes revealed that stress corrosion cracks had initiated in the corroded areas near the welds where defects and high residual stresses can be encountered. The cracks had initiated intergranularly before changing to a transgranular mode of crack propagation, typical of stress corrosion cracking of austenitic stainless steels in chloride environments. The evidence suggests that the cracks developed while the plant was not operating when the pipework would have been at ambient temperature.

OS12W0465 Strength evaluation of centrifugally cast steel pipes for gas equipment

Austenitic stainless steel pipes made by centrifugal casting have been used as burner material for heat-treatment furnaces and other industrial furnaces. This material has a high heat resistance, but brittle fracture can occur earlier than expected. Brittle fracture may start in the final solidification layer with micro cavitated structure formed on the inner surface of centrifugally cast pipes during manufacturing. In the present study, the strength of the specimens of an austenitic stainless steel machined from centrifugally cast pipes was studied with attention to the final solidification layer on the inner surface of the pipe. The strength decreased with increasing area of the final solidification layer. In order to predict the fracture strength of pipes with solidification layers under a variety of yielding scales, two-parameter method was proposed based on the combination of the stress intensity factor criterion and the gross sectional yielding stress criterion.

802 ステンレス鍛鋼品の疲労き裂進展特性について

LBB evaluation guide in Nuclear Power Plants (NPP) was developed based on material properties of austenitic stainless steel piping in Japan. On the other hand, we use stainless steel forging in piping systems of NPPs. On the LBB evaluation, both the estimation of fatigue crack propagation and evaluation of crack instability play important roles. So we prepared stainless steel forging to obtain material properties such as strength, fracture toughness and fatigue crack propagation data in the simulated primary coolant of PWR. As for the strength and fracture toughness, stainless steel forging is as same as stainless steel pipes. On the fatigue crack propagation, experimental data of stainless steel forging is slower than the estimation formula in LBB evaluation guide. Taking these data of stainless steel forging account, we can treat stainless steel forging same as stainless steel pipes on LBB evaluation

Corrosion behaviour of stainless steel surfaces formed upon chemical decontamination

In the VVER-type pressurised water nuclear reactors, the so-called AP-CITROX method (AP: alkaline permanganate; CITROX: citric and oxalic acids) is widely used for the chemical decontamination of the austenitic stainless steel piping in steam generators. In the present work we report some new findings obtained by voltammetric, gravimetric, γ-spectrometric, surface spectroscopic (SEM-EDX) and in situ radiotracer studies of the passive layers formed on austenitic stainless steel type 08X18H10T (GOST5632-61) during the surface decontamination by the AP-CITROX procedure. The experimental results reveal that the AP-CITROX decontamination procedure, performed even in three consecutive cycles, does not exert detrimental corrosion effects, but rather substantially improves the passivity of the surface oxide layer.

Numerical weld modeling — a method for calculating weld-induced residual stresses

In the past, weld-induced residual stresses caused damage to numerous (power) plant parts, components and systems (Erve, M., Wesseling, U., Kilian, R., Hardt, R., Brümmer, G., Maier, V., Ilg, U., 1994. Cracking in Stabilized Austenitic Stainless Steel Piping of German Boiling Water Reactors — Characteristic Features and Root Causes. 20. MPA-Seminar 1994, vol. 2, paper 29, pp.29.1–29.21). In the case of BWR nuclear power plants, this damage can be caused by the mechanism of intergranular stress corrosion cracking in austenitic piping or the core shroud in the reactor pressure vessel and is triggered chiefly by weld-induced residual stresses. One solution of this problem that has been used in the past involves experimental measurements of residual stresses in conjunction with weld optimization testing. However, the experimental analysis of all relevant parameters is an extremely tedious process. Numerical simulation using the finite element method (FEM) not only supplements this method but, in view of modern computer capacities, is also an equally valid alternative in its own right. This paper will demonstrate that the technique developed for numerical simulation of the welding process has not only been properly verified and validated on austenitic pipe welds, but that it also permits making selective statements on improvements to the welding process. For instance, numerical simulation can provide information on the starting point of welding for every weld bead, the effect of interpass cooling as far as a possible sensitization of the heat affected zone (HAZ) is concerned, the effect of gap width on the resultant weld residual stresses, or the effect of the ‘last pass heat sink welding’ (welding of the final passes while simultaneously cooling the inner surface with water) producing compressive stresses in the root area of a circumferential weld in an austenitic pipe. The computer program feresa (finite element residual stress analysis) was based on a commercially available abaqus code (Hibbitt, Karlsson, Sorensen, Inc, 1997. abaqus user's manual, version 5.6), and can be used as a 2-D or 3-D FEM analysis; depending on task definition it can provide a starting point for a fracture mechanics safety analysis with acceptable computing times.

Failure Assessment Curves for Austenitic Stainless Steel Pipes with a Circumferential Crack at a Welded Joint.

Failure Assessment Curves for Austenitic Stainless Steel Pipes with a Circumferential Crack at a Welded Joint.

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.

Laser cladding technology to small diameter pipes

A laser cladding method which produces a highly corrosion-resistant material coating layers (cladding) on the austenitic stainless steel (Type 304 SS) pipe inner surface was developed to prevent SCC (stress corrosion cracking) occurrence. This technology is applicable to a narrow and long distance area from operators, because of the good accessibility of the YAG (Yttrium–Aluminum–Garnet) laser beam that can be transmitted through an optical fiber. In this method a mixed paste metallic powder and heating-resistive organic solvent are firstly placed on the inner surface of a small pipe, and then a YAG laser beam transmitted through an optical fiber irradiates to the pasted area. A mixed paste will be melted and form a cladding layer subsequently. A cladding layer shows as excellent corrosion resistance property. This laser cladding (LC) method had already applied to several domestic nuclear power plants and had obtained a good reputation. This report introduces the outline of laser cladding technology, the developed equipment for practical application in the field, and the circumstance in actual plant application.

A Study of Effects of Pipe Geometry on FAD Curves for Austenitic Stainless Steel and Ferritic Steel Piping Materials

A comprehensive study of failure assessment diagrams for circumferentially surface-cracked austenitic stainless and ferritic steel pipes was conducted with the use of the finite element method (FEM). While the majority of the analyses were conducted using the line-spring/shell finite element method, some three-dimensional finite element analyses, conducted independently, are also reported in this paper. Comparison of the predictions of the line-spring/shell and three-dimensional analyses reinforce the validity of the former approach for surface-cracked pipes. The results indicated that the ASME Code Case N-494-2 applicable for ferritic steel piping appears reasonably conservative even for pipes with mean radius-to-wall thickness ratios of 20, whereas the results showed that the newly adopted Code Case N-494-3 for austenitic stainless steel piping requires a limit for pipe with mean radius-to-wall thickness ratios larger than 15. For consistency, the limitation of Rm/t ≤ 15 was incorporated in the approved final version of Code Case N-494-3, and was incorporated in Code Case N-494-2 as well. Because these Code cases are applicable only to Class 1 primary nuclear piping, which typically has values of Rm/t ≤ 15, this is not a significant limitation. It was also shown that the choice of definitions of membrane and bending stresses as well as the choice of F1 function values in calculating the elastic part of the J integral have a profound effect on the resulting FAD curves.

Cracking in stabilized austenitic stainless steel piping of German boiling water reactors—characteristic features and root cause

Cracks have been found in the welds of piping systems made from stabilized austenitic stainless steels in German boiling water reactors (BWR). In the course of the intensive failure analysis metallographic examinations, microstructural investigations by electron microscopy, corrosion experiments and welding tests have been performed. The results show that cracking under the given medium conditions is due to intergranular stress corrosion cracking (IGSCC) in those parts of the heat affected zone (HAZ) which are overheated during welding and where solution of titanium carbides and subsequent precipitation of chromium carbides and depletion of chromium along the affected grain boundaries could occur.

Pipe break testing of primary loop piping similar to the Department of Energy's new production reactor-heavy water reactor

This paper provides information about and results from specific tests completed at Oak Ridge National Laboratory (ORNL) in support of the Department of Energy's (DOE's) new production reactor-heavy water reactor (NPR-HWR) program. The paper also provides detailed analytical studies completed by Battelle Columbus Laboratory. All of this information is presented in a demonstration that the primary piping of the NPR-HWR, with its relatively moderate temperature and pressure should not suffer an instantaneous double-ended guillotine break (DEGB) under design basis loadings and conditions. The first ORNL test series obtained pipe crack extension data representative of large dynamic loads applied to a flawed stainless steel 316LN pipe weldment. The results of that testing were reviewed by a special Piping Integrity Review Group (PIRG) established by DOE. Members of this group are identified in this paper. The PIRG review comments were such as to necessitate a second series of tests. This paper provides results of that second series of pipe tests. An aged section of 304 stainless steel pipe, obtained from the C-reactor at Savannah River, was subjected to large fully reversed cyclic bending loads. An initial flaw size was based on leakage flow testing at prototypic NPR-HWR pressure and temperature. The detectable leakage flaw was cycled in bending at large loads for 40 cycles. The members of the PIRG assessed these results together with analytic work by Battelle and stated that, provided the caveats cited in this paper are in force, the following conclusion is applicable: • For DOE low-pressure (≤1·72 MPa), low-temperature (100°C) reactors with austenitic stainless steel piping, the DEGB should not be a design basis condition.

Intergranular corrosion resistance of stainless steel diffusion‐bonded joints with B‐containing amorphous insert metal

Summary This paper describes an investigation of the intergranular corrosion resistance of austenitic stainless steel joints diffusion‐bonded with an amorphous insert metal containing 1.5 mass% boron, in order to clarify optimum bonding conditions for austenitic stainless steel pipes joined by a high‐speed diffusion bonding system. The sulphuric acid/copper sulphate test is conducted to evaluate the intergranular corrosion of bonded joints caused by a Cr depletion zone. Joints diffusion‐bonded with lower bonding pressure and shorter bonding time are more sensitive to intergranular corrosion. Under such bonding conditions, Cr boride and Cr carboboride precipitates causing selective corrosion are found in the bonding layer. Joints diffusion‐bonded under higher bonding pressure and with longer bonding time, however, show no intergranular corrosion and few precipitates in the bonding layer. With regard to the B‐containing amorphous insert metal used in the present investigation, the optimum bonding conditions...

Laser Surface Modification for Structural Materials.

Much attention is recently paid to laser surface modification (LSM) techniques forproviding an approach in controlling compositions and structure of matal surface. IHI has been performing reseach activity for bringing LSM techniques to a degree of development such that they can be used industrially. One of these LSM techniques was actually applied to austenitic stainless steel pipes put in practical use to prevent stress corrosion cracking.In this paper, our recent laser beam technology related to LSM and details of LSM technique applied to actual component in our company are introduced.