Fatigue of welded hybrid‐joints

Only for steels up to grade S690QL the well‐known fact is confirmed that the fatigue strength of welded joints is independent of the material. For higher strength steels a remarkable reduction of the fatigue strength is found. Some advice is given for designers in which situations the one or the other of the various approaches for the assessment of the fatigue strength of welds could be applied. In complex, real situations even the highly sophisticated effective notch stress approach might loose its applicability. A new alternative approach is proposed for these situations. It is based on stresses in real notches and an example is presented for the familiar case of a start‐stop position.     

EPR‐Messungen in warmgehenden Anlagen

EPR measurements in heat‐working plants This paper reports about experiences of sensitization behaviour of titanium and niob stabilized steels under practice conditions at operating temperature between 340 and 600°C. Pipes, flanges, welds including heat‐affected zones are examined for sensitization with help of the e lectrochemical‐p otentiodynamic‐r eactivation‐method. Measurements were carried out on‐site during plant stoppage at different pipes with diameter between 150 to 460 mm with a set‐up measuring cell.     

Fatigue crack propagation behavior in AISI 304 steel welded joints for cold‐stretched liquefied natural gas (LNG) storage tank at cryogenic temperatures

AISI304 steel welded joints are used in cold‐stretched liquefied natural gas (LNG) storage tanks used for storing and transporting of liquefied gases. Compared with a conventional liquefied natural gas storage tank, a cold‐stretched liquefied natural gas storage tank has many advantages such as reduced thickness, light weight, low cost and low energy consumption. However, liquefied natural gas storage tanks can be subjected to alternative loads at cryogenic temperatures; thus, it is important to investigate the fatigue crack propagation behavior in AISI 304 steel welded joints at cryogenic temperatures. Specimens were machined from a cold‐stretched liquefied natural gas storage tank with a welding structure. The crack length was determined using compliance method and confirmed by examination with traveling microscope. Fatigue crack propagation rates were evaluated at various stress ratios and temperatures. The fatigue crack growth rate of all specimens a little appears the effect of stress ratio, but it has a great influence at a cryogenic temperature. The fatigue crack growth rate of longitudinal welded joint is the fastest at room and cryogenic temperature. Fracture mechanism in the specimen is examined using a scanning electron microscope.     

Lochkorrosion nichtrostender Stähle und hochlegierte Fe/Ni/Cr/Mo‐Werkstoffe ‐ Entwicklungsstufen und Untersuchungsverfahren

Pitting corrosion of stainless steels and high‐alloyed Fe/Ni/Cr/Mo materials – Stages of development and test methods In relation to the stages of development of pitting the characteristics and factors of influence are explained. After the explanation of distinct pitting potentials different ways of the detection of the stages of pitting are highlighted and their influencing through characteristic featues of the metal, of the chemical composition of the medium, and of the physical conditiones are pointed out. Based upon these facts, loading and methods of analyses and evaluation for the test of pitting resistance are discussed and chemical and electrochemical tests are described which are important to solve technical problems. Furthermore a test for the determination of the pitting resistance of welds directly performed at apparatus and equipments is explained which is still in the development stage.     

Zum Einfluss des Schweißens auf das Kriechverhalten moderner Stähle für die thermische Energieerzeugung

The influence of welding on creep behaviour of modern steels for thermal power generation Un‐ and low alloyed ferritic/bainitic Chromium steels as well as high alloyed ferritic/martensitic 9–12 % Chromium steels are widely used for high temperature components in thermal power generation. Welding in all its variety is the major repair and joining technology for such components. The weld thermal cycle has significant influence on the base material microstructure and its properties. The Heat Affected Zone is often regarded as the weakest link during high temperature service. While weldments of un‐ and low alloyed ferritic Chromium steels can show significant susceptibility to Reheat Cracking in the coarse grained heat affected zone, weldments of high alloyed ferritic Chromium steels generally fail by Type IV Cracking in the fine grained heat affected zone during long term service. In this paper the influence of the weld thermal cycle on the base material microstructure is described. Long‐term creep behaviour of weldments is directly related to the main failure mechanisms in creep exposed ferritic weldments and implications for industries using heat resistant ferritic steels are shown.