Search Results for high temperature welded components

The paper describes methods for practical high temperature weldment life assessment, and their application to the analysis of notable high energy piping weldment failures and interpretation of cross-weld data. The methods described in the paper are simplified versions of full continuum damage mechanics (CDM) analysis techniques which have been developed over the last 20 years. The complexity of the CDM methods and their data requirements has been a barrier to their more widespread use. The need for simplified methods has been driven by the need for risk assessment of in-service high temperature welded piping and headers around the world, the need to connect cross-weld data to weld joint design and assessment, and in general, the need to develop suitable guidelines for evaluating the strength of weldments relative to that of base metal.

Qualifying welding procedures for repair of components in high temperature service requires careful consideration of factors including identification of the materials involved, existing mechanical properties and service operating parameters such as temperature, pressure and environment. Selection of weld metals to match, under match or overmatch base material as well as direct and indirect consequences on the heat-affected zone also require evaluation. Application of post weld heat treatment and ramifications where dissimilar base materials are involved are discussed plus the necessity of conducting tests at the operating temperatures and conditions where information is not available from the literature. Each of these factors is discussed and examples provided.

This paper describes the steps necessary for consideration of weld behavior in order to be used in modern design procedures. Specific behavior of similar and dissimilar welds in the creep regime are described as well as procedures and criteria to be used for the assessment of welded joints.

Simplified or reference stress techniques are described and demonstrated for high temperature weld design and life assessment. The objective is the determination of weld life under steady and cyclic loading in boiler headers and piping systems. The analysis deals with the effect of cyclic loading, constraint and multiaxiality in a heterogeneous joint. A common thread that runs through most high temperature weld reports and failure analyses is the existence of a relatively creep-weak zone somewhere in the joint. This paper starts with the assumption that the size and creep strength of this zone are known, in addition to parent metal properties. Life prediction requires an efficient analysis technique (such as the reference stress method), which separates the structural and material problems, and does not require complex constitutive models. The approach is illustrated with a simple example of an IN617 main steam girth weld, which could be present in an advanced plant concept with 700°C steam temperature.

Metallographic tests, micro-hardness tests, mechanics performance tests and Energy Dispersion Spectrum (EDS) were conducted for a 2.25Cr-1Mo main steam pipe weldment served for more than 32 years. Microstructural evolution of the 2.25Cr-1Mo base metal and weld metal was investigated. Degradation in micro-hardness and tensile properties were also studied. In addition, the tensile properties of subzones in the ex-service weldment were characterized by using miniature specimens. The results show that obvious microstructural changes including carbide coarsening, increasing inter lamella spacing and grain boundary precipitates occurred after long-term service. Degradation in micro-hardness is not obvious. However, the effects of long term service on tensile deformation behavior, ultimate tensile strength and yield stress are remarkable. Based on the yield stress of micro-specimens, the order of different subzones is: WM>HAZ>BM, which is consistent with the order of different subzones based on micro-hardness. However, the ultimate tensile strength and fracture strain of HAZ are lower than BM.

High gamma prime Ni-based superalloys comprising ≥3.5 % Al are difficult to weld due to high propensity of these materials to weld solidification, heat affected zone liquation, and stress-strain cracking. In this study the root cause analysis of cracking and overview on the developed weldable Ni-based superalloys for repair of turbine engine components manufactured from equiaxed (EA), directionally solidified (DS), and single crystal (SX) materials as well as for 3D AM is provided. It is shown that the problem with the solidification and HAZ liquation cracking of turbine engine components manufactured from EA and DS superalloys was successfully resolved by modification of welding materials with boron and silicon to provide a sufficient amount of eutectic at terminal solidification to promote self-healing of liquation cracks along the weld - base material interface. For crack repair of turbine engine components and 3D AM ductile LW4280, LW7901 and LCT materials were developed. It is shown that LW7901 and LCT welding materials comprising 30 - 32 wt.% Co produced sound welds by GTAW-MA on various SX and DS materials. Welds demonstrated high ductility, desirable combination of strength and oxidation properties for tip repair of turbine blades. Examples of tip repair of turbine blades are provided.

Advanced martensitic 9% chromium steels have been identified as the most favored group of materials for high temperature applications in thermal power plants. To extend the temperature range of martensitic steels up to 650°C large effort was put on the development of new alloy concepts. The so-called MARBN concept (Martensitic steel with defined Boron/Nitrogen relation) provides increased creep rupture strength due to higher solid solution strengthening and improved microstructural stability. The major improvement is the reduction of type IV cracking in welded joints, which shifts the focus to the creep rupture strength of the weld metal. This paper illustrates the process experience of the steel foundry for production of heavy cast components in latest state of the art 9-12%Cr-MoCoVNbNB-alloyed cast steel grades and the newest state of development and prototype components in MARBN cast steel grades. Metallurgy, solidification, heat treatment and welding are main items to be considered for development of new, complex steel grades for foundry processing with the help of empiric processing in test programs and thermo-physical simulation. As welding is an essential processing step in the production of heavy steel cast components a good out-of-position weldability is required. Moreover a stress-relieve heat-treatment takes place subsequently after welding for several hours. This contribution also deals with the development of matching welding consumables for the production of heavy cast components and discusses the challenges of defining appropriate welding and heat treatment parameters to meet the requirements of sufficient strength and toughness at ambient temperature. Additionally, first results of creep rupture tests are presented.

Along with rapid development of thermal power industry in mainland China, problems in metal materials of fossil power units also change quickly. Through efforts, problems such as bursting due to steam side oxide scale exfoliation and blocking of boiler tubes, and finned tube weld cracking of low alloy steel water wall have been solved basically or greatly alleviated. However, with rapid promotion of capacity and parameters of fossil power units, some problems still occur occasionally or have not been properly solved, such as weld cracks of larger-dimension thick-wall components, and water wall high temperature corrosion after low-nitrogen combustion retrofitting.

Development activities initiated over a decade ago within the COST 522 program and continuing through the COST 536 Action have yielded significant progress in constructing a new generation of steam power plants capable of operating under advanced steam conditions. These innovative plants promise substantially improved thermal efficiency, with steam temperatures reaching up to 620°C (1150°F). Recent successful power plant orders in Europe and the United States stem from critical advancements, including the development, testing, and qualification of 10% Cr steels with enhanced long-term creep properties for high-temperature components such as turbine rotors and valve casings. Extensive in-house development efforts have focused on fabrication, weldability, mechanical integrity, and fracture mechanics evaluations of full-sized forged and cast components. These materials will be implemented in several new coal-fired power plants, notably the Hempstead plant in the USA, which will operate with live steam temperatures of 599°C (1111°F) and reheat steam temperatures of 607°C (1125°F). The improved creep properties enable the construction of casings with reduced wall thicknesses, offering greater thermal flexibility at lower component costs and facilitating welded turbine rotors for high-temperature applications without requiring cooling in the steam inlet region. Looking forward, further efficiency improvements are anticipated through the introduction of nickel alloys in steam turbine and boiler components, with the European AD700 project targeting reheat steam temperatures of 720°C (1328°F) and the US Department of Energy project aiming even higher at 760°C (1400°F). The AD700 project has already demonstrated the technical feasibility of such advanced steam power plants, with engineering tasks progressing toward the construction of a 550 MW demonstration plant, while DOE activities continue to address boiler concerns and focus on rotor welding, mechanical integrity, and steam oxidation resistance.

In order to improve thermal efficiency of fossil-fired power plants through increasing steam temperature and pressure high strength martensitic 9-12%Cr steels have extensively been used, and some power plants have experienced creep failure in high temperature welds after several years operations. The creep failure and degradation in welds of longitudinally seam-welded Cr- Mo steel pipes and Cr-Mo steel tubes of dissimilar metal welded joint after long-term service are also well known. The creep degradation in welds initiates as creep cavity formation under the multi-axial stress conditions. For the safety use of high temperature welds in power plant components, the complete understanding of the creep degradation and establishment of creep life assessment for the welds is essential. In this paper creep degradation and initiation mechanism in welds of Cr-Mo steels and high strength martensitic 9-12%Cr steels are reviewed and compared. And also since the non-destructive creep life assessment techniques for the Type IV creep degradation and failure in high strength martensitic 9-12%Cr steel welds are not yet practically established and applied, a candidate way based on the hardness creep life model developed by the authors would be demonstrated as well as the investigation results on the creep cavity formation behavior in the welds. Additionally from the aspect of safety issues on welds design an experimental approach to consider the weld joint influence factors (WJIF) would also be presented based on the creep rupture data of the large size cross-weld specimens and component welds.

Early supercritical units such as American Electric Power (AEP) Philo U6, the world’s first supercritical power plant, and Eddystone U1 successfully operated at ultrasupercritical (USC) levels. However due to the unavailability of metals that could tolerate these extreme temperatures, operation at these levels could not be sustained and units were operated for many years at reduced steam (supercritical) conditions. Today, recently developed creep strength enhanced ferritic (CSEF) steels, advanced austenitic stainless steels, and nickel based alloys are used in the components of the steam generator, turbine and piping systems that are exposed to high temperature steam. These materials can perform under these prolonged high temperature operating conditions, rendering USC no longer a goal, but a practical design basis. This paper identifies the engineering challenges associated with designing, constructing and operating the first USC unit in the United States, AEP’s John W. Turk, Jr. Power Plant (AEP Turk), including fabrication and installation requirements of CSEF alloys, fabrication and operating requirements for stainless steels, and life management of high temperature components

Components exposed to the highest temperatures and mechanical loading in 700°C power plants are predominantly manufactured from nickel-based alloys, with ongoing material development for boiler and turbine components in this challenging temperature regime. This paper presents comprehensive investigations of various components, including tubing, membrane walls, and thick-walled structures constructed from nickel-based alloys. Qualification programs for boiler components have demonstrated the applicability of Alloy 617, with similar extensive programs and investigations currently underway for Alloy 263 and Alloy 740. Researchers have conducted detailed experiments and investigations to optimize and qualify welding consumables, aiming to transfer critical knowledge directly to component manufacturing processes. Recognizing the complexity of material performance, the study emphasizes the necessity of long-term material qualification, which extends beyond traditional creep behavior assessments to include detailed investigations of deformation capabilities following extended aging periods. These comprehensive evaluations are crucial for ensuring the reliability and performance of advanced high-temperature power plant components under extreme operational conditions.

The inspection and evaluation of defects in the welds of P92 high temperature reheater header with a diameter of about 1000mm and a wall thickness of about 100 mm have been done by means of hardness test, nondestructive testing on the surface, ultrasonic testing, metallographic and component sampling. By analyzing the results of on-site test and samples removed from the component, it is found that cracks existing in the welds are hydrogen induced delayed cracks. During the welding process and post-heating treatment (hydrogen bake-out), dehydrogenation was insufficient. This fact, combined with welding residual stresses resulted in the observed hydrogen induced cracking.

In order to reduce CO 2 emissions and improve power generation efficiency, a development project involving an advanced USC (A-USC) plant has been carried out in Japan since 2008. Nibased alloys are candidate materials for boiler components with high temperature steam conditions, which are much stronger than conventional heat resistant steel. However, Ni-based alloys have never been applied with respect to the high pressure parts and thick walled components of USC coal-fired power plants. In this study, therefore, fabrication and characteristic properties, such as weldability, the weld joint and bent part properties, and weld cracking susceptibilities of Ni-based alloys such as HR6W, HR35 and two types of Alloy617 (High B and Low B) pipes were evaluated. Additionally, two types of HR6W header mock-ups and a HR6W tube element mock-up were fabricated. With the exception of Alloy617 (High B), the fabrication trials of Ni-based alloy pipes were conducted successfully, and the long-term creep strength of weldments and bends of Ni-based alloy pipes were found to be nearly equivalent to those of base metal. In the case of Alloy617 (High B), hot cracking was observed.

Martensitic steel P91 with higher creep strength was first introduced as thick section components in power plants some 18 years ago. However, more recently a number of failures have been experienced in both thick and thin section components and this has given rise to re-appraisal of this steel. Thick section components are generally known to have failed due to Type IV cracking. Furthermore, due to the restructuring of the electricity industry worldwide many of the existing steam plant are now required to operate in cycling mode and this requires the use of materials with high resistance to thermal fatigue . Here high strength P91 is assumed to offer an additional benefit in that the reduced section thickness increases pipework flexibility and reduces the level of through wall temperature gradients in thick section components. Because of this envisaged benefit a number of operators/owners of the existing plant, especially in the UK, have been substituting these new higher strength steels for the older materials, especially when a plant is moved from base load to cyclic operation. There has also been a perceived advantage of higher steam side oxidation resistance of superheater tubes made from high Cr steels. For the Heat Recovery Steam Generators (HRSGs) used in Combined Cycle Gas Turbines (CCGTs) there is a requirement to produce compact size units and thus high strength steels are used to make smaller size components. This paper discusses these issues and compares the envisaged benefits with the actual plant experience and more recent R&D findings. In view of these incidents of cracking and failures it is important to develop life assessment tools for components made from P91 steel. ETD has been working on this through a ‘multi-client project' and this aspect will be discussed in this paper.

Advanced ultra-supercritical fossil plants operated at 700/725 °C and up to 350 bars are currently planned to be realized in the next decade. Due to the increase of the steam parameters and the use of new materials e.g. 9-11%Cr steels and nickel based alloys the design of highly loaded components is approaching more and more the classical design limits with regard to critical wall thickness and the related tolerable thermal gradients. To make full use of the strength potential of new boiler materials but also taking into account their specific stress-strain relaxation behavior, new methods are required for reliable integrity analyses and lifetime assessment procedures. Numerical Finite Element (FE) simulation using inelastic constitutive equations offers the possibility of “design by analysis” based on state of the art FE codes and user-defined advanced inelastic material laws. Furthermore material specific damage mechanisms must be considered in such assessments. With regard to component behavior beside aspects of multiaxial loading conditions must be considered as well as the behavior of materials and welded joints in the as-built state. Finally an outlook on the capabilities of new multi-scale approaches to describe material and component behavior will be given.

In several material qualification programs tubes and thick-walled components mainly from Alloy 617 and Alloy 263 were investigated. Results as low cycle fatigue and long term creep behavior of base materials and welds are presented. Numerical models to describe the material behavior have been developed and verified by multiaxial tests. In order to ensure the feasibility of A-USC plants two test loops have been installed in GKM Mannheim – one for tube materials and a new one for thick-walled piping and components. The latter consists of a part with static loading and a part subjected to thermal cycles and is in operation since November 2012. First results of measurements and numerical calculations for a pipe bend (static loading) as well as pipes and a header (thermal cycles) are presented.

A material test loop has been installed at GKM Mannheim, which enables thick-walled components of future highly-efficient power plants to be exposed to steam temperatures of up to 725 °C. The project goal was to demonstrate the feasibility of a 700 °C power plant.

CO 2 emission reduction from coal power plants is still a serious issue to mitigate the impact of global warming and resulting climate change, though renewables are growing today. As one of the solutions, we developed A-USC (Advanced Ultra Super Critical steam condition) technology to raise the thermal efficiency of coal power plants by using high steam temperatures of up to 700℃ between 2008 and 2017 with the support of METI (Ministry of Economy, Trade and Industry) and NEDO (New Energy and Industrial Technology Development Organization). The temperature is 100℃ higher than that of the current USC technology. Materials and manufacturing technology for boilers, turbines and valves were developed. Boiler components, such as super heaters, a thick wall pipe, valves, and a turbine casing were successfully tested in a 700℃-boiler component test facility. Turbine rotors were tested successfully, as well, in a turbine rotating test facility under 700℃ and at actual speed. The tested components were removed from the facilities and inspected. In 2017, following the component tests, we started a new project to develop the maintenance technology of the A-USC power plants with the support of NEDO. A pressurized thick wall pipe is being tested in a 700℃ furnace to check the material degradation of an actual sized component.

The voestalpine foundry group, operating at locations in Linz and Traisen, Austria, specializes in heavy steel casting components ranging from 1 to 200 tons for power generation, oil and gas, chemical processing, and offshore applications. Their manufacturing expertise encompasses high-alloyed martensitic 9-12% Cr-steels and nickel-based Alloy 625, particularly for ultra-supercritical (USC) and advanced USC power generation systems operating at temperatures from 600°C to over 700°C. The production of these complex, thick-walled components relies on advanced thermodynamic calculation and simulation for all thermal processes, from material development through final casting. The foundries’ comprehensive capabilities include specialized melting, molding, heat treatment, non-destructive testing, and fabrication welding, with particular emphasis on joining dissimilar cast, forged, and rolled materials. Looking toward future innovations, the group is exploring additive manufacturing for mold production and robotic welding systems to enhance shaping and surface finishing capabilities.