Alfred Dhooge - Academia.edu (original) (raw)

Papers by Alfred Dhooge

Welding in The World, 1986

ABSTRACT Nowadays, intense efforts are made to increase efficiency and thereby minimize harmful e... more ABSTRACT Nowadays, intense efforts are made to increase efficiency and thereby minimize harmful emissions of power plants. This can be achieved by increasing operating pressure and temperature to ultra-supercritical conditions. Presently martensitic 9%Cr-steels, e.g. P91, E911 and P92 are used for power plants with advanced steam parameters. Whilst these materials have the highest creep rupture strength values of ferritic steels, their oxidation resistance is lower than 12%Cr-steels, such as X20CrMoV12-1. With increasing steam temperature (target: 650°C) the lifetime of components made of 9%Cr-steel becomes limited not only by creep but also by oxidation. The present paper reports a new 12Cr martensitic steel developed by Vallourec & Mannesmann, which is designed for use at temperatures up to 650°C. It is the outcome of a normative research project of the Belgian Welding Institute in collaboration with Laborelec and with industrial partners (Carnoy Industrial Piping, Cockerill Mechanical Industries, Fabricom, Stork Mec, Böhler Thyssen Welding Germany, Vallourec & Mannesmann Tubes, AIB-Vinçotte, VCL, Tractebel and WTCM). Base metal properties (creep strength, toughness, reheat cracking susceptibility, oxidation behavior...), welding and high temperature behavior of the new 12%Cr-steel, and welds are addressed.

The incentive for the present study was a brittle fracture that occurred in a 101 mm thick 24” we... more The incentive for the present study was a brittle fracture that occurred in a 101 mm thick 24” welding neck flange of Class 600 according to ANSI B16.5. This component, with a coarse grain microstructure, was installed in a high-density polyethylene (HDPE) loop reactor and failed presumably at a temperature of -16 °C. In this project, a large number of ASTM A105 carbon steel flanges has been investigated with the main purpose of evaluating the material’s fracture toughness and defect tolerance. Investigations revealed large variations in microstructure, grain size and hardness, depending on the manufacturing route and heat treatment. Even multiple small hydrogen cracks were found in two of the investigated 24” flanges. Toughness has been evaluated by notch impact and CTOD fracture toughness tests at different low temperatures. A correlation was made between microstructure, grain size and fracture toughness. A fitness-for-purpose analysis, based on CTOD fracture toughness, allowed to assess the risk for brittle fracture in large (24” / Class 600) carbon steel flanges complying with ASTM A105.

Nowadays, high efforts are undertaken to increase efficiency and thereby minimizing harmful emiss... more Nowadays, high efforts are undertaken to increase efficiency and thereby minimizing harmful emissions of power plants. This can be achieved by increasing the steam temperature and pressure to supercritical conditions. Presently martensitic 9% Cr-steels, e.g. P91, E911 and P92 are used for power plants with advanced steam parameters. While these materials have the highest creep rupture strength values of ferritic steels, their oxidation resistance is lower than 12% Cr-steels, such as X20CrMoV12-1. With increasing steam temperature (target: 650°C) the lifetime of components made of 9% Cr-steel becomes limited not only by creep but also by oxidation.

Materials Science and Engineering, Dec 1, 1985

The minimum creep rate data for a nickelbase superalloy (IN-738) taken from the literature are an... more The minimum creep rate data for a nickelbase superalloy (IN-738) taken from the literature are analysed according to an effective stress model. The internal stress is shown to be determined largely by the stress necessary for bypass of the 7' particles. The stress dependence of the particle back stress can correlate the creep rates at low and high stresses. In an intermediate stress region, time-dependent microstructural changes markedly influence the particle back stress, and the increase in creep rate can be explained by the decreasing particle stress.

International Journal of Pressure Vessels and Piping, 1987

Reheat Cracking--a Review of Recent Studies. A Dhooge, A Vinckier Int. J. Pressure Vessels Piping... more Reheat Cracking--a Review of Recent Studies. A Dhooge, A Vinckier Int. J. Pressure Vessels Piping 27:44, 239-269, 1987. The most recent information on the topic of reheat cracking in low alloy ...

Welding in The World, 1986

ABSTRACT Nowadays, intense efforts are made to increase efficiency and thereby minimize harmful e... more ABSTRACT Nowadays, intense efforts are made to increase efficiency and thereby minimize harmful emissions of power plants. This can be achieved by increasing operating pressure and temperature to ultra-supercritical conditions. Presently martensitic 9%Cr-steels, e.g. P91, E911 and P92 are used for power plants with advanced steam parameters. Whilst these materials have the highest creep rupture strength values of ferritic steels, their oxidation resistance is lower than 12%Cr-steels, such as X20CrMoV12-1. With increasing steam temperature (target: 650°C) the lifetime of components made of 9%Cr-steel becomes limited not only by creep but also by oxidation. The present paper reports a new 12Cr martensitic steel developed by Vallourec & Mannesmann, which is designed for use at temperatures up to 650°C. It is the outcome of a normative research project of the Belgian Welding Institute in collaboration with Laborelec and with industrial partners (Carnoy Industrial Piping, Cockerill Mechanical Industries, Fabricom, Stork Mec, Böhler Thyssen Welding Germany, Vallourec & Mannesmann Tubes, AIB-Vinçotte, VCL, Tractebel and WTCM). Base metal properties (creep strength, toughness, reheat cracking susceptibility, oxidation behavior...), welding and high temperature behavior of the new 12%Cr-steel, and welds are addressed.

The incentive for the present study was a brittle fracture that occurred in a 101 mm thick 24” we... more The incentive for the present study was a brittle fracture that occurred in a 101 mm thick 24” welding neck flange of Class 600 according to ANSI B16.5. This component, with a coarse grain microstructure, was installed in a high-density polyethylene (HDPE) loop reactor and failed presumably at a temperature of -16 °C. In this project, a large number of ASTM A105 carbon steel flanges has been investigated with the main purpose of evaluating the material’s fracture toughness and defect tolerance. Investigations revealed large variations in microstructure, grain size and hardness, depending on the manufacturing route and heat treatment. Even multiple small hydrogen cracks were found in two of the investigated 24” flanges. Toughness has been evaluated by notch impact and CTOD fracture toughness tests at different low temperatures. A correlation was made between microstructure, grain size and fracture toughness. A fitness-for-purpose analysis, based on CTOD fracture toughness, allowed to assess the risk for brittle fracture in large (24” / Class 600) carbon steel flanges complying with ASTM A105.

Nowadays, high efforts are undertaken to increase efficiency and thereby minimizing harmful emiss... more Nowadays, high efforts are undertaken to increase efficiency and thereby minimizing harmful emissions of power plants. This can be achieved by increasing the steam temperature and pressure to supercritical conditions. Presently martensitic 9% Cr-steels, e.g. P91, E911 and P92 are used for power plants with advanced steam parameters. While these materials have the highest creep rupture strength values of ferritic steels, their oxidation resistance is lower than 12% Cr-steels, such as X20CrMoV12-1. With increasing steam temperature (target: 650°C) the lifetime of components made of 9% Cr-steel becomes limited not only by creep but also by oxidation.

Materials Science and Engineering, Dec 1, 1985

The minimum creep rate data for a nickelbase superalloy (IN-738) taken from the literature are an... more The minimum creep rate data for a nickelbase superalloy (IN-738) taken from the literature are analysed according to an effective stress model. The internal stress is shown to be determined largely by the stress necessary for bypass of the 7' particles. The stress dependence of the particle back stress can correlate the creep rates at low and high stresses. In an intermediate stress region, time-dependent microstructural changes markedly influence the particle back stress, and the increase in creep rate can be explained by the decreasing particle stress.

International Journal of Pressure Vessels and Piping, 1987

Reheat Cracking--a Review of Recent Studies. A Dhooge, A Vinckier Int. J. Pressure Vessels Piping... more Reheat Cracking--a Review of Recent Studies. A Dhooge, A Vinckier Int. J. Pressure Vessels Piping 27:44, 239-269, 1987. The most recent information on the topic of reheat cracking in low alloy ...