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Genova, Italy

Mandina M.,IIS Service | Magnasco M.,Nuovo Pignone | Moracchioli L.,Nuovo Pignone | Giorgini L.,Nuovo Pignone
Rivista Italiana della Saldatura | Year: 2014

This article provides mention of metallurgy and weldability of 13% Cr-4% Ni steel and the results of experimental welding tests aimed to supporting repair process, using covered electrodes and corresponding filler material, of possible imperfections of forging and / or by mechanical processing in crates and stator parts of centrifugal compressors, in accordance with ASTM A182. The effects of chemical composition of base material, filler material, as well as post-weld heat treatment (PWHT) on the mechanical properties of welded joints have been investigated, in order to minimize hardness in the fusion zone and heat affected zone.

Canale G.,IIS Service | De Marco M.,Italian Welding Institute | Pinca S.,IIS Service
Welding International | Year: 2013

The special process of welding still plays a key role in the fabrication of pressurized equipment for the energy processing and generation industry. Similarly, welding is extensively used in repair, modification and overlay/cladding procedures and during the maintenance operations for large plants. However, the harsh statistics relating to faults shows welded joints to be among the most 'at-risk' areas with regard to various active damage mechanisms. Within the framework of the management of plant risk and equipment integrity, the risk-based inspection method, with the aim of prioritizing and optimizing the inspection strategy, focuses attention on the criticality of welded joints with the framework of problems related to both simple mechanical vulnerability and physicochemical aspects such as corrosion and/or stress corrosion. The aim of this paper is to offer an overview of the interactions existing between the various active damage mechanisms in plants and welded joints in addition to indicating the criticality associated with these interactions, with the purpose of optimizing the management of plant risk and inspection strategies for resolving them. © 2013 Copyright Taylor and Francis Group, LLC.

Ranieri S.,University of Genoa | Rizzo C.M.,University of Genoa | Cosso G.L.,IIS Service | Servetto C.,IIS Service
Rivista Italiana della Saldatura | Year: 2015

The main aim of this work is the fatigue strength assessment of a butt joint with weld reinforcement, typically used in steel works and especially in shipbuilding applications when varying different geometric parameters of the welded joint; to this purpose, three different approaches for fatigue strength estimates were applied, i.e. the Effective Notch Stress Approach, which is now commonly used and it is supported by a comprehensive bibliography, the Strain Energy Density approach (SED) and the Peak Stress Method (PSM), the latter ones newly introduced in scientific literature and still being tested within industrial practice. Furthermore, all analyses were carried out using two different finite element codes: ANSYS® and ADINA®. The application of different FEM software allowed verifying the quality of obtained results, disclosing certain essential aspects related to the extrapolation of values from integration points of finite elements and extending the Peak Stress Method to an additional software with respect to that proposed by the author of the method, i.e. ANSYS®.

In the latest edition of the ASME Code, criteria for fatigue assessment in pressure vessels manufactured with 225Cr-IMo-Vsteel are given up to operating temperatures not exceeding 371 °C (700 °F), whilst the design temperature typically adopted (454 °C) is significantly higher. In order to plug this gap, ASME has recently published the Code Case 2605-1, considering the interaction between fatigue and creep phenomena. Material creep behaviour is in particular represented through the "Omega" approach, recently introduced by the API 579-1/ASME FFS-I standard. This article has been written with the aim to present the application of Code Case prescriptions for the fatigue assessment of items F90101AIB (Hot High Pressure Separator), manufactured by ATB Riva Calzoni S.p A. on behalf of ENI R&M. In particular the manufacturing procedures followed in vessels construction and the numerical analyses performed for the assessment of components are described in detail, highlighting, with special attention, those features which mainly affect evaluation results.

We present the results of an experimental program of fatigue tests carried out on two types of butt-jointed, of thickness 20 and 40 mm respectively, characterized by a significant gap between the flaps, not meeting the requirements of the construction specifications. The tests were conducted on specimens taken from the heels of welding joints representative of the site (butt joints between souls and lintels) and made with the same procedures (welding process, welding position, welding consumables, etc.). The test results were statistically processed to determine the category of fatigue in accordance with the requirements of standard EN 1993-1-9 and IIW Recommendations. The calculations took into account both the thickness of the samples (both tests were conducted on specimens in scale, is the true thickness of samples for validation) both components of the bending stress induced by the non-planarity of the specimen.

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