Finite element thermal analysis of the fusion welding of a P92 steel pipe

Fusion welding is common in steel pipeline construction in fossil-fuel power generation plants. Steel pipes in service carry steam at high temperature and pressure, undergoing creep during years of service; their integrity is critical for the safe operation of a plant. The high-grade martensitic P92 steel is suitable for plant pipes for its enhanced creep strength. P92 steel pipes are usually joined together with a similar weld metal. Martensitic pipes are sometimes joined to austenitic steel pipes using nickel based weld consumables. Welding involves severe thermal cycles, inducing residual stresses in the welded structure, which, without post weld heat treatment (PWHT), can be detrimental to the integrity of the pipes. Welding residual stresses can be numerically simulated by applying the finite element (FE) method in Abaqus. The simulation consists of a thermal analysis, determining the temperature history of the FE model, followed by a sequentially-coupled structural analysis, predicting residual stresses from the temperature history. <br><br> In this paper, the FE thermal analysis of the arc welding of a typical P92 pipe is presented. The two parts of the P92 steel pipe are joined together using a dissimilar material, made of Inconel weld consumables, producing a multi-pass butt weld from 36 circumferential weld beads. Following the generation of the FE model, the FE mesh is controlled using Model Change in Abaqus to activate the weld elements for each bead at a time corresponding to weld deposition. The thermal analysis is simulated by applying a distributed heat flux to the model, the accuracy of which is judged by considering the fusion zones in both the parent pipe as well as the deposited weld metal. For realistic fusion zones, the heat flux must be prescribed in the deposited weld pass and also the adjacent pipe elements. The FE thermal results are validated by comparing experimental temperatures measured by five thermocouples on the pipe outside surface with the FE temperature history at corresponding nodal points

Gastrointestinal tuberculosis following renal transplantation accompanied with septic shock and acute respiratory distress syndrome:A survival case presentation

Background: Post-transplant tuberculosis (PTTB) is a serious opportunistic infection in renal graft recipients with a 30-70 fold higher incidence compared to the general population. PTTB occurs most frequently within the first years after transplantation, manifesting as pulmonary or disseminated TB. Gastrointestinal TB (GITB) is a rare and potentially lethal manifestation of PTTB and may show delayed onset in renal transplant recipients due to the use of lower doses of immunosuppressants. Further, non-specificity of symptoms and the common occurrence of GI disorders in transplant recipients may delay diagnosis of GITB. Case presentation: Here we report a rare survival case of isolated GITB in a renal transplant recipient, occurring seven years after transplantation. The patient's condition was complicated by severe sepsis with positive blood culture Staphylococcus haemolyticus, septic shock, multiple organ failure including acute respiratory distress syndrome (ARDS) and acute renal failure, requiring mechanical ventilation, vasopressor circulatory support and intermittent hemodialysis. Furthermore, nosocomial infections such as invasive aspergillosis and Pseudomonas aeruginosa occurred during hospitalization. Antituberculosis therapy (rifampicin, isoniazid, ethambutol and pyrazinamide) was initiated upon Mycobacterium confirmation. Moreover, treatment with voriconazole due to the Aspergillus flavus and meropenem due to the Pseudomonas aeruginosa was initiated, the former necessitating discontinuation of rifampicin. After 34 days, the patient was weaned from mechanical ventilation and was discharged to the pulmonary ward, followed by complete recovery. Conclusion: This case offers a guideline for the clinical management towards survival of GITB in transplant patients, complicated by septic shock and multiple organ failure, including acute renal injury and ARDS

Reticular synthesis and the design of new materials

The long-standing challenge of designing and constructing new crystalline solid-state materials from molecular building blocks is just beginning to be addressed with success. A conceptual approach that requires the use of secondary building units to direct the assembly of ordered frameworks epitomizes this process: we call this approach reticular synthesis. This chemistry has yielded materials designed to have predetermined structures, compositions and properties. In particular, highly porous frameworks held together by strong metal-oxygen-carbon bonds and with exceptionally large surface area and capacity for gas storage have been prepared and their pore metrics systematically varied and functionalized.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/62718/1/nature01650.pd

Mapping of Functional Groups in Metal-Organic Frameworks

We determined the heterogeneous mesoscale spatial apportionment of functional groups in a series of multivariate metal-organic frameworks (MTV-MOF-5) containing BDC (1,4-benzenedicarboxylate) linkers with different functional groups - B (BDC-NH2), E (BDC-NO2), F [(BDC-(CH3)2], H [BDC-(OC3H5) 2], and I [BDC-(OC7H7)2] - using solid-state nuclear magnetic resonance measurements combined with molecular simulations. Our analysis reveals that these methods discern between random (EF), alternating (EI and EHI), and various cluster (BF) forms of functional group apportionments. This combined synthetic, characterization, and computational approach predicts the adsorptive properties of crystalline MTV-MOF systems. This methodology, developed in the context of ordered frameworks, is a first step in resolving the more general problem of spatial disorder in other ordered materials, including mesoporous materials, functionalized polymers, and defect distributions within crystalline solids

Comparison of measured and modelled residual stresses in a welded P91 steel pipe undergoing post weld heat treatment

The process of fusion arc welding of steel pipes in power generation plants induces residual stresses which may be detrimental to the integrity and endurance of plant pipelines. P91 is high-grade steel used in the construction of pipelines carrying hot steam at high pressure, conditions which cause creep during service. Welded P91 pipes are usually subjected to post-weld heat treatment (PWHT) to mitigate the magnitude of residual stresses and temper the material, hence improving its resistance to creep. In this paper, the finite element (FE) method of modelling residual stresses due to PWHT in a circumferentially butt-welded P91 pipe is presented. The PWHT hold temperature is 760 °C. The paper describes the X-Ray Diffraction (XRD) and Deep-Hole Drilling (DHD) experimental techniques and how they are applied to measure residual stresses in the welded P91 pipe after PWHT. The material property data, necessary for the FE simulation of PWHT, has been obtained from stress-relaxation tests on P91 uniaxial tensile specimens at 760 °C. Good agreements have been achieved between the results of the FE method and the two sets of experimentally-measured residual stresses

Metal–organic fireworks: MOFs as integrated structural scaffolds for pyrotechnic materials

A new approach to formulating pyrotechnic materials is presented whereby constituent ingredients are bound together in a solid-state lattice. This reduces the batch inconsistencies arising from the traditional approach of combining powders by ensuring the key ingredients are ‘mixed’ in appropriate quantities and are in intimate contact. Further benefits of these types of material are increased safety levels as well as simpler logistics, storage and manufacture. A systematic series of new frameworks comprising fuel and oxidiser agents (group 1 and 2 metal nodes & terephthalic acid derivatives as linkers) has been synthesised and structurally characterised. These new materials have been assessed for pyrotechnic effect by calorimetry and burn tests. Results indicate that these materials exhibit the desired pyrotechnic material properties and the effect can be correlated to the dimensionality of the structure. A new approach to formulating pyrotechnic materials is proposed whereby constituent ingredients are bound together in a solid-state lattice. A series of Metal–organic framework frameworks comprising fuel and oxidiser agents exhibits the desired properties of a pyrotechnic material and this effect is correlated to the dimensionality of the structure

Advances in ab-initio theory of Multiferroics. Materials and mechanisms: modelling and understanding

Within the broad class of multiferroics (compounds showing a coexistence of magnetism and ferroelectricity), we focus on the subclass of "improper electronic ferroelectrics", i.e. correlated materials where electronic degrees of freedom (such as spin, charge or orbital) drive ferroelectricity. In particular, in spin-induced ferroelectrics, there is not only a {\em coexistence} of the two intriguing magnetic and dipolar orders; rather, there is such an intimate link that one drives the other, suggesting a giant magnetoelectric coupling. Via first-principles approaches based on density functional theory, we review the microscopic mechanisms at the basis of multiferroicity in several compounds, ranging from transition metal oxides to organic multiferroics (MFs) to organic-inorganic hybrids (i.e. metal-organic frameworks, MOFs)Comment: 22 pages, 9 figure

Evolution of form in metal-organic frameworks

Self-assembly has proven to be a widely successful synthetic strategy for functional materials, especially for metal-organic materials (MOMs), an emerging class of porous materials consisting of metal-organic frameworks (MOFs) and metal-organic polyhedra (MOPs). However, there are areas in MOM synthesis in which such self-assembly has not been fully utilized, such as controlling the interior of MOM crystals. Here we demonstrate sequential self-assembly strategy for synthesizing various forms of MOM crystals, including double-shell hollow MOMs, based on single-crystal to single-crystal transformation from MOP to MOF. Moreover, this synthetic strategy also yields other forms, such as solid, core-shell, double and triple matryoshka, and single-shell hollow MOMs, thereby exhibiting form evolution in MOMs. We anticipate that this synthetic approach might open up a new direction for the development of diverse forms in MOMs, with highly advanced areas such as sequential drug delivery/release and heterogeneous cascade catalysis targeted in the foreseeable future.ope

Methane adsorption in metal-organic frameworks containing nanographene linkers: a computational study

Metal-organic framework (MOF) materials are known to be amenable to expansion through elongation of the parent organic linker. For a family of model (3,24)-connected MOFs with the rht topology, in which the central part of organic linker comprises a hexabenzocoronene unit, the effect of the linker type and length on their structural and gas adsorption properties is studied computationally. The obtained results compare favourably with known MOF materials of similar structure and topology. We find that the presence of a flat nanographene-like central core increases the geometric surface area of the frameworks, sustains additional benzene rings, promotes linker elongation and the efficient occupation of the void space by guest molecules. This provides a viable linker modification method with potential for enhancement of uptake for methane and other gas molecules

Unveiling thermal transitions of polymers in subnanometre pores

The thermal transitions of confined polymers are important for the application of polymers in molecular scale devices and advanced nanotechnology. However, thermal transitions of ultrathin polymer assemblies confined in subnanometre spaces are poorly understood. In this study, we show that incorporation of polyethylene glycol (PEG) into nanochannels of porous coordination polymers (PCPs) enabled observation of thermal transitions of the chain assemblies by differential scanning calorimetry. The pore size and surface functionality of PCPs can be tailored to study the transition behaviour of confined polymers. The transition temperature of PEG in PCPs was determined by manipulating the pore size and the pore–polymer interactions. It is also striking that the transition temperature of the confined PEG decreased as the molecular weight of PEG increased