Welding Procedure Qualification Research Articles

Semi-supervised learning for real-time anomaly detection in pulsed transfer wire arc additive manufacturing

In Wire-Arc Additive Manufacturing (WAAM), ensuring the quality and integrity of components is of key importance and performing anomaly detection during production is an efficient strategy for preventing defects and maintaining an acceptable quality with lower costs compared to the development of complex supervised learning techniques. This paper presents an approach based on semi-supervised learning for real-time anomaly detection in the production of Inconel 718 components via the Pulsed Transfer WAAM process. The workflow is based on the use of training data obtained by employing established process parameters, similar to what is done in Welding Procedure Qualification Records (WPQRs), to develop a semi-supervised anomaly detection application. The proposed approach involves depositing material using the already established process parameters and collecting the corresponding welding data in terms of welding current and voltage sensor signals. The collected data are then employed to train an unsupervised algorithm by using solely good deposition data to learn hidden complex patterns of normality and hence detect anomalies based on deviations from these patterns. With this aim, global and local features are extracted from the welding current and voltage sensor signals in both time and time-frequency domains via Wavelet Transform technique and a deep learning approach based on a residual convolutional autoencoder. To showcase the effectiveness of the proposed approach, a case study involving wire arc additive manufacturing of Inconel 718 components was conducted. The proposed algorithm was tested and achieved an F-score of 0.895, representing a 30 % improvement over state-of-the-art methods that rely on time domain features for anomaly detection. This research work contributes to the improvement of anomaly detection methodologies, offering substantial advantages over alternative techniques for quality control and reliability of additive manufacturing processes such as WAAM.

Reviewing Welding Procedures—Checklists for Nuclear Power Systems

Abstract To ensure effective control of the welding process, nuclear power architecture and engineering (AE) companies routinely undertake the review of procedure qualification records (PQRs) and welding procedure specifications (WPSs) for safety-related structures, systems, and components (SSCs), as qualified by manufacturers and construction contractors. Given the substantial quantity of PQRs and WPSs necessitating evaluation, along with the multitude of variables inherent in these documents, a set of review checklists has been devised. These checklists, developed from the perspective of AE companies' welding engineers, transform welding procedure qualification rules and requirements into intuitive descriptions, assessments of correctness, or numerical comparisons of scale. AE companies' welding engineers employ these review checklists to scrutinize PQRs and WPSs, facilitating a comprehensive, accurate, and efficient review process.

Experience in the Fabrication of Tube Grade 7CrMoVTiB10-10 with Inconel 625 Weld Overlay for Use in Steam Superheaters Exposed to Highly Corrosive Environments

Problems with corrosion in boilers and their parts can be solved by the application of different nickel alloys like 622, 625 or 686 by a variety of welding processes. This solution is used mostly in Waste-to-Energy plants or biomass stations burning waste wood, but it can also be found in the recovery boilers used in the paper industry. The most common material grades include low alloyed boiler steels like 16Mo3, 13CrMo4-5 and 10CrMo9-10. When there is a need to increase steam temperature and pressure more complicated alloys to become a natural choice. This paper focuses on the fabrication experience of welding of 7CrMoVTiB10-10 base tube with Inconel 625 weld overlay and presents a welding solution of matching filler metal used for root pass and S Ni 6625 filler metal for a fill-up and the cap performing a full strength weld without the need of overlay peeling and manual tie-in overlay. This method of welding saves a lot of time during execution in the workshop and on-site during installation and assures much better quality in the end. All examinations were performed to allow welding procedure qualification according to ASME and EN standards.

Effect of thickness on mechanical properties of modified 9Cr 1Mo steel welds made by narrow gap hot wire gas tungsten arc welding process

Hot wire Gas Tungsten Arc Welding (GTAW) process is selected for fabrication of thick section modified 9Cr 1Mo steel components of Steam Generators (SGs) for 500MWe Prototype Fast Breeder Reactor (PFBR) at Kalpakkam, India. During the welding procedure qualification for fabrication of SGs, the 30 mm and 62 mm thick modified 9Cr 1Mo steel welds were subjected to chemical analysis, visual examination, liquid penetrant examination, radiography examination, micro-hardness tests, longitudinal and transverse tensile tests (at ambient temperature and 525 °C), bend tests, drop weight tests and impact tests (at 0 °C and +18 °C). Literature reveals both positive and negative view on the welding of thick section steel components. Limited information is available in open literature on the effect of thickness on material properties of modified 9Cr 1Mo steel welds made by hot wire GTAW method. In view of the above, authors attempted to systematically investigate the influence of thickness on mechanical properties of modified 9Cr 1Mo steel welds made by hot wire GTAW process. In this paper, the chemical compositions, hardness, tensile strength, bending strength and impact properties of 30 mm and 62 mm thick welds produced by narrow gap hot wire GTAW process are characterized and compared. It is found that the mechanical properties of 30 mm and 62 mm thick welds are comparable except the impact properties at 0 °C. The impact strength at 0 °C for 62 mm thick weld was found inferior in comparison with 30 mm thick weld.

Welding procedure qualification record (WPQR) for welds fabricated at proximity

Maintaining the minimum allowable distance between proximity welds has always been considered a subject of debate among design engineers, welding engineers/inspectors and fabricators/engineering contractors. The scattered nature of guidelines available in welding codes and standards for maintaining the minimum allowable distance poses a significant challenge in the welding procedure and inspection criteria development process. This is especially critical for complex welded joints on submerged sections of offshore structures, in compact layouts/branched connections of topside piping components, and on topside structural joints (depending on the complexity). This manuscript presents the findings of an experimental study that was performed by fabricating two girth welds at proximity on an S355 steel tubular section with diameter of 219.1 mm and thickness of 8.18 mm. Proximity girth welds were fabricated on S355 tubular sections at three different distances between their weld toes, 5, 10, and 15 mm, respectively, using two different welding procedures. Welding procedure qualification record (WPQR) was performed, and all prescribed mechanical tests were recorded as per NORSOK M-101, a structural steel fabrication code. Although all results from the mechanical test met the minimum specified values as defined in the NORSOK code, the research findings revealed a noticeable difference in Charpy and hardness values for proximity region between adjacent welds. Considerable changes in final microstructure morphology were observed between proximity welds due to varying thermal cycles. These observations can form the basis for the future welding procedure qualification of critical welded joints, especially for proximity welds on critical welded joints of offshore structures and welds fabricated during replacement/repair procedures in compact piping layouts.

Liquid Metal Embrittlement in Narrow Gap Welds

Abstract Failure analysts are sometimes surprised to find well-known metallurgical failure mechanisms at work in completely unexpected places. This contribution is an eloquent example for just such an incidental convergence of well-known failure mechanism and fabrication process where it was not reported to have previously occurred. Liquid Metal Embrittlement (LME) was observed in Narrow Gap Welds (NGW) produced for Welding Procedure Qualification (WPQ). The embrittling liquid metal was copper in this case. It is believed to have originated from copper backing used for weld pool protection. It was recommended to replace copper backing with ceramic weld pool protection.

Effect of Post-Weld Heat Treatment Conditions on Mechanical Properties, Microstructures and Nonductile Fracture Behavior of SA508 Gr.1a Thick Weldments

This study analyzes the effects of post-weld heat treatment (PWHT) on the mechanical properties and microstructures of SA-508 Gr.1a welds and proposes a new PWHT exemption criterion based on nonductile fracture evaluation considering welding residual stress. The welding coupons were prepared with submerged-arc welding, gas-tungsten arc welding, and shielded-metal arc welding, using ferritic steel, SA-508 Gr.1a. The microstructure of the heat-affected zone (HAZ) was analyzed using optical microscopy, electron-back-scatter diffraction and Vickers hardness testing. The mechanical properties of the welds were evaluated by uniaxial tensile test, transverse side bend test, Charpy V-notch impact test and side bend test. Bainite and ferrite structures formed mainly in the HAZ, and the grain size became coarser with proximity to the surface and fusion line. The mechanical properties did not depend strongly on PWHT, weldment thickness or welding techniques, and they satisfied the welding procedure qualification test specified in the ASME Boiler & Pressure Vessel code. Welding residual stresses were considered in assessing structural integrity using nonductile fracture evaluation. A margin of safety against nonductile fracture with residual stress was calculated for Korean Standard Nuclear Power Plant steam-generator welds, using its design parameters and operating conditions, and this safety margin is suggested as an acceptance criterion for residual stress for exemption from PWHT.Graphic abstract

REPLACEMENT OF MANUAL GMAW WELDING BY FCAW SEMI-AUTOMATIC WELDING

The article describes a replacement and benefits between manual gas metal arc welding (GMAW) with solid wire and semi-automatic flux-cored arc welding (FCAW) with metal flux-cored wire for a specific application of a welded steel compensator used for connecting piping systems to form larger units. For the replacement of the technologies and improvement of the welding efficiency and productivity a specific type of carbon steel mounting insert, DN300 PN16, was selected. Since these pressure parts are subject to the directive 2014/68/EU, both the welding processes have to meet the same welding quality requirements. In particular, they are the welding procedure qualification report (WPQR) and the welder’s or welding operator’s qualification in accordance with valid European standards. Based on this requirement, a sample was selected so that it would cover the widest possible range of carbon steel mounting inserts produced. This article describes the whole experiment including the selection of the right equipment and filler material, finding the ideal welding parameters, and the subsequent qualification of the welding procedure and the operator with emphasis on the largest possible increase in the welding speed and productivity for these specific weldments.

Welding procedure qualification of small diameter thin-walled titanium pipes

The small diameter thin-walled TA2 titanium tubes are used in a technical renovation project. In order to ensure the performance of the product, the automatic GTAW welding process is adopted by analyzing the weldability of TA2 titanium tubes. The process qualification tests such as appearance inspection, nondestructive testing, mechanical properties and metallographic examination are carried out. The test results show that the welding joint with good performance can be obtained by reasonable welding procedure parameters and strict gas protection measures. The welding procedure and related measures can be used as a reference for manufacture and installation of titanium pipes.

Welding procedure research of zirconium tube-to-tubesheet

The welding characteristics of zirconium tube-to-tubesheet, the joint structure and quality influencing factors are analyzed in the paper. The automatic pulsed GTAW procedure are formulated and examined by welding sample test. The tube-to-tubesheet procedure is qualified by joint surface inspection, joint sections observation, height measurement of the weld metal and metallographic examination. It has the great significance of the successful welding procedure qualification to guide the actual manufacture of R60702 zirconium heat exchanger.

Welding procedure qualification of Q345 grade fire-resistant steel based on Jmat-pro calculation

The welding process of two Q345 grade low Mo (about 0.25 wt.%) fire-resistant steels will be calculated and evaluated in this paper. The continuous cooling transformation (CCT) curve and isothermal transformation (TTT) curve of test steel were calculated by Jmat-pro software. The welding processes of steels were evaluated by measuring the continuous cooling transition (SH-CCT) curves of welding heat affected zone. The test results show that when the actual cooling time of Q1 steel is t 8/5>43s, cracking does not occur in the HAZ of welding and near the fusion zone, while when t 8/5<43s, cracking may occur in the HAZ or fusion zone; When the actual cooling time of Q2 steel is t 8/5>44s, cracking does not occur in the welding heat affected zone and the vicinity of the fusion zone, while when t 8/5<44s, cracking may occur in the heat affected zone or the fusion zone. In addition, Jmat-pro software has a certain accuracy for the calculation of Ac 3, but has a large error for the continuous cooling transformation (CCT) curve, especially the difference between the calculated value and the measured value of Q2 steel is larger, which only has reference value.

Welding procedure research of R60702 zirconium pressure vessels

In order to improve efficiency and reduce costs, the new PAW plus GTAW method for R60702 zirconium plates used in acetic acid production unit is analyzed. The microstructure and mechanical properties are tested by PAW procedure. Through the test analysis and the measured data in the practical application, the butt joint welded by the PAW procedure can satisfy the standard requirements of mechanical properties, corrosion resistance. The success of the welding procedure qualification shows that the new PAW plus GTAW method has great advantages over the traditional GTAW method.

Manufacturing of molten salt reactor heat exchangers using inner hole welding

ABSTRACT Inner hole welding was applied to weld UNS N10003 nickel-based alloy tubes (φ13.72*1.65 mm) to heat exchanger tubesheet in the Thorium Molten Salt Reactor for the first time. Welding defects were eliminated after the welding technology optimization after a great deal of trials and errors. And proper inner hole welding procedure and good butt joints were obtained. Welding procedure qualification shows that the strength of the welded joints at room temperature, 650°C and 700°C was higher than the qualified values of the base metal. After the confirmation of exact welding conditions on full-size mockup, the first batch of two heat exchangers of Thorium Molten Salt Reactor was fabricated by using inner hole welding technics in the world. The tube bundles containing 58 tubes (116 joints) were welded to tubesheet successfully. Penetration and radiation inspection revealed all the welds had no defects and were 100% qualified. Finally the completed unit passed 0.85 MPa hydrostatic testing. The successful development and application of inner hole welding process also establish a good foundation for the manufacture of high-temperature heat exchangers of other reactors besides Molten Salt Reactor.

Development and application of knowledge-based software for railcar frame welding process

As main welded components of the rail vehicle, the railcar frames have specific needs in preparing a suitable welding document for each welded joint to guide the welding process during the manufacturing process. In this paper, the expert system and database technology are introduced into the field of rail vehicle welding process preparation, and a knowledge-based software for railcar frame welding process is developed. This system could maintain the normal operation of the enterprise rail welding system based on knowledge base and database. The numerous paper-based and fragmented electronic documents are stored in a unified format within the system’s database, and a reasoning mechanism based on Rule-Based Reasoning (RBR) and Case-Based Reasoning (CBR) is designed to intelligently match the welding procedure specification (WPS) and welding procedure qualification report (WPQR) online. Furthermore, the system supports multiple departments and personnel by integrating the function of workflow to carry out the WPS prepare and review process. Thousands of welded joints with various structures and complex positions in the same vehicle body can be aggregated into a welding summary table to reduce the repeated welding procedure qualifications (WPQ) of the same or similar welding joint. This method not only saves manpower and resources, but also ensures the accuracy of these process documents. In the end, the future development trend of this kind of application software is prospected.

Design and Implementation of Welding Procedure Qualification Expert System

Welding process evaluation is an important link to ensure the quality of welding engineering and determine the welding process specification. It is also the main procedure to evaluate the welder’s examination results. In the traditional way of processing WPS documents, the test results are usually judged manually by experts based on experience. However, the evaluation of welding process is often very complex, involving the base material, sample type, process parameters and a large number of international standards. Therefore, how to utilize the software engineering method and experience, make the welding process evaluation program accurate and efficient information, make the welding process evaluation program easier and more efficient, is very important to the whole field of welding.

A simulation-based approach to characterise melt-pool oscillations during gas tungsten arc welding

Development, optimisation and qualification of welding and additive manufacturing procedures to date have largely been undertaken on an experimental trial and error basis, which imposes significant costs. Numerical simulations are acknowledged as a promising alternative to experiments, and can improve the understanding of the complex process behaviour. In the present work, we propose a simulation-based approach to study and characterise molten metal melt pool oscillatory behaviour during arc welding. We implement a high-fidelity three-dimensional model based on the finite-volume method that takes into account the effects of surface deformation on arc power-density and force distributions. These factors are often neglected in numerical simulations of welding and additive manufacturing. Utilising this model, we predict complex molten metal flow in melt pools and associated melt-pool surface oscillations during both steady-current and pulsed-current gas tungsten arc welding (GTAW). An analysis based on a wavelet transform was performed to extract the time-frequency content of the displacement signals obtained from numerical simulations. Our results confirm that the frequency of oscillations for a fully penetrated melt pool is lower than that of a partially penetrated melt pool with an abrupt change from partial to full penetration. We find that during transition from partial to full penetration state, two dominant frequencies coexist in the time-frequency spectrum. The results demonstrate that melt-pool oscillations profoundly depend on melt-pool shape and convection in the melt pool, which in turn is influenced by process parameters and material properties. The present numerical simulations reveal the unsteady evolution of melt pool oscillatory behaviour that are not predictable from published theoretical analyses. Additionally, using the proposed simulation-based approach, the need of triggering the melt-pool oscillations is expendable since even small surface displacements are detectable, which are not sensible to the current measurement devices employed in experiments.

Cyclic loading tests on welded connections of stainless-clad bimetallic steel and modelling

Bimetallic steel is an advanced high-performance (HP) laminated steel that may balance well performance against production cost, and has great potential for practical use in structural engineering, particularly for stainless-clad (SC) ones. Welding is the most important connection technique for fabrication of such steel members because preparation of holes within the steel plate for mechanical fasteners may expose the substrate and thus destroy the corrosion resistance. The present paper aims to clarify mechanical performance of butt welded connection of the SC bimetallic steel that requires special welding configurations, particularly under seismic loadings. The butt welded connections are firstly tested for welding procedure qualification. Based on subsequent monotonic and cyclic test results, failure modes are clarified, and their mechanical properties are analysed in terms of cyclic and envelop curves. It is indicated that welded connections of the SC bimetallic steel plate are adequate for structural usage under earthquake; their cyclic hardening effects are remarkable, and the envelop curves can be well described by using the Ramberg-Osgood (R-O) model. An adapted cyclic constitutive model based on the Chaboche model is proposed with parameters being determined through non-linear fitting of cyclic test results, and its accuracy and adequacy are verified. Additionally, the butt welded connections exhibit more significant isotropic and kinematic hardening effects compared with the SC bimetallic steel plate. Research findings herein provide important evidence for adequacy of the SC bimetallic steel welded connections applied in seismic regions, and also provide accurate constitutive models for predicting their cyclic behaviour.

20 kW laser welding applied on the international thermonuclear experimental reactor correction coil case welding

International thermonuclear experimental reactor correction coil cases are made of heavy, thick, high strength, and high toughness austenitic stainless steel 316LN. The BTCC (bottom and top correction coils) case has the dimension of 2.5 × 7 m2 and cross section of 239.8 × 146.7 mm2, side correction coil case has the dimension of 7.2 × 7.6 m2 and cross section of 147.8 × 168 mm2, and they will be closure welded after winding pack insertion. The 20 mm welding depth, dozens of meter of welding length, strict welding requirements, large size, and complex configuration bring a big challenge to this closure welding work. 20 kW high power laser welding is selected as the main welding method because of the advantage of potential welding deformation control and its penetrating ability and cracking resistance. The welding parameter is developed that can cover the assembly gap from 0 to 0.5 mm with a good welding quality. A special test coupon is designed for the welding procedure qualification, and related tests are carried out to qualify the joint properties of bend, tensile, and impact. Finally, a full-scale BTCC case is welded. After welding, ultrasonic testing confirms that almost all welds satisfy the weld seam quality requirement. The recorded temperatures less than 250° indicate that the temperature induced by welding will not harm the internal winding pack. The dimensional deviation of the inner face is less than 4 mm and also satisfies the tolerance requirement of ±2 mm for the BTCC case.

New Low Alloy High Strength Steel Welding Procedure Evaluation

In order to determine the weldability of a new type of low alloy high strength steel, the feasibility of the proposed welding process was examined and the welding procedure qualification of a new type of ultrahigh strength steel WELDOX 1100 was carried out through the weldability test of the welded joint, the small iron research and the highest hardness test. . The test result satisfies the specification requirements and proves that the proposed welding process plan is correct and feasible. It provides a reliable basis for the preparation of welding process documents and ensures the smooth development of the company's new products.

Methods for the measurement of ferrite content in multipass duplex stainless steel welds

The phase balance is commonly determined as a part of the duplex stainless steel (DSS) welding procedure qualification. In this work, the aim was to find a reliable, but still fast method to measure the ferrite content of DSS welds. Four methods were compared: image analysis with light optical metallography, magnetic measurements with Feritscope and Magne-Gage, and X-ray diffractometry (XRD). Image analysis with a magnification of ×500 was concluded to be most accurate on condition that the image quality was sufficiently high. The best contrast for image analysis was achieved by covering all surfaces apart from the part of interest with adhesive tape and etching the sample in a modified Beraha II solution. The Feritscope systematically underestimated the average ferrite volume fraction compared with image analysis, and a correction factor of 1.1 is suggested. Magne-Gage in turn resulted in considerably higher ferrite numbers as compared with the Feritscope and would require a correction factor of 1.18. Besides the long duration of XRD measurements, the method proved unsuitable for ferrite measurement due to the coarse texture of the microstructure.