Estimation of the resource of pipes of the main circulation pipeline of a NPP by the criterion of crack resistance with account of operational degradation of properties

The results of an experimental determination of the characteristics of cyclic crack growth resistance of specimens made of stainless steel 08Kh18N12T are given. Compact samples 20 mm thick cut from Du 550–30 pipes of the primary circuit of the main circulation pipeline (MCР) were studied under eccentric tension in the initial state and after 100 thousand hours of operation in the conditions of the Novo-Voronezh NPP. Using a new engineering approach based on measuring the specimen tightening and constructing a cyclic elastoplastic fracture diagram for a specimen with a crack in the coordinates “tightening – the stress intensity factor, calculated taking into account the plasticity correction”, a calculated life estimation is given for the pipe of Du 550–30 MCР NPP, made of 08Kh18N12T steel, according to the criterion of cyclic crack growth resistance, taking into account operational degradation of properties caused by the running time of 100 thousand hours. The life (survivability), expressed in a number of cycles of change in internal pressure, for a pipe with the most dangerous defects (surface semi-elliptical crack and combined defect “pitting + crack”) is determined. An analysis of the influence of the level of initial damage and the type of hazardous defect on the survivability of the pipes is made. The results can be used to analyze damage and predict the life of pipes made of ductile metals and alloys, in cooling systems of reactors, as well as main pipelines of hydrocarbon transport.

Mechanism of Degradation of the Properties of Recycled Plaster Mixed Aluminate Cement

This manuscript investigates the degradation of the properties of recycled plaster-mixed aluminate cement (RAP) and analyzes its degradation mechanism by DSC/TG and SEM. The results showed that the setting time of RAP was shortened due to the fast formation of recycled ettringite (AFt) and its strength was decreased relative to the pure recycled plaster (RP) in the absence of aluminate cement. Different from the properties of RP and RAP, the hydration of commercial plaster was slowed down by the addition of aluminate cement for its low hydration rate, and its strength was increased with respect to the pure commercial plaster (CP) without aluminate cement. Therefore, the properties of RP and RAP could be seen to decrease in relation to CP and commercial plaster mixed aluminate cement (CAP). The SEM and DSC/TG analyses confirm the presence of cluster and fine crystals and noncementing AH3 in RAP, which demonstrates its degradation of properties.

Use of Non-Destructive Tests for the Assessment of Integrity and Service Life of Hydro-Mechanical Equipment

Technical diagnostics of hydromechanical equipment, is based on testing procedures including the history of the exploitation with expert knowledge of structures and operating conditions, as well as, on the analysis of results performed by experts with appropriate experience and knowledge in design, exploitation, maintenance, reliability, fracture mechanics etc. Degradation of properties of the material and/or welded joints of hydro-mechanical equipment is being caused by the simultaneous influence of a large number of factors. First of all, it is thought of technological, metallurgical, structural and conditions of exploitation. In this paper, the selection of methodology for the rehabilitation of hydro-mechanical equipment is presented based on the previously conducted assessment of state of equipment using the nondestructive testing methods. Repair welding, repair of damaged surfaces by cold metallization, corrections of existing structural solutions of metallic components in order to improve their technical characteristics and extend the service life are presented.

Modeling galvanic coupling and localized damage initiation in airframe structures

Traditionally, airframe structures are designed for immediate mechanical performance and loads-only structural response; the lifetime of aircraft structures is predicted on these analyses and environmental degradation of properties over the life cycle and during operations is often an afterthought. Although the maintenance of aircraft structures is primarily determined by material degradation, galvanic management of airframe designs and corrosion-resistant material selection have never been done systematically. From end-of-life tear-down inspections, we know that, predominantly, structural failures are initiated from corrosion features, especially those accelerated by dissimilar material coupling. In its most simplistic form, this environmental exposure, “loading”, creates corrosion features, such as pitting, that produce crack initiation morphologies; cracks nucleate from these features and then grow under the combined influence of mechanical stress and corrosion, eventually leading to structural failure. There is clearly a strong correlation between corrosion and structural damage, which we think of as corrosion fatigue and stress corrosion cracking. Office of Naval Research’s Sea-Based Aviation program is developing computational approaches to corrosion activity prediction, crack initiation and crack growth, with the ultimate aim of predicting service life in terms of the combination of mechanical and chemical stress. This approach is intended to be the basis for design of durable aircraft structures, using design principles that will take into account both stress and corrosion in the design phase, rather than designing for stress and then maintaining for corrosion.

Degradation of recycled flame-retardant GFPBT during extrusion: Effect of screw types on the extrudate properties

For both environmental and economic consideration, the use of recycled glass fiber-reinforced flame retardant poly(butylene terephthalate) (RGFFRPBT) is of significant importance. In the study, the mechanical, thermal, rheological, and flame retardant properties of RGFFRPBT granulated by different extruders were evaluated. To explore the relationship between the screw structure and the properties of the extruded RGFFRPBT, the carboxyl content (CC), and intrinsic viscosity ([Formula: see text]) of the processed polymer and the average GF length ([Formula: see text]) were investigated. Increasing the shear force of the extruder caused both [Formula: see text] and [Formula: see text] to decrease, whereas the CC increase. Variations of these parameters had a different effect on the properties of the RGFFRPBT. Both of mechanical and thermal properties of extruded RGFFRPBT deteriorated with the increase of screw shear force, while the thermal flowability improved. Furthermore, all the extruded products were classified as V-0 with LOI of 32.2%, and passed the glow wire ignition temperature test (GWIT). The results confirmed that the degradation of properties of RGFFRPBT can be controlled by screw-type extrusion. RGFFRPBT granulated by a single screw extruder with 30 mm diameter and length to diameter ratio of 30 was found to produce material with properties meeting the requirements for electronic and electrical applications.