Fatigue crack growth and fracture toughness properties of 304 stainless steel pipe for LNG transmission

Abstract

The fatigue crack growth rate and fracture toughness tests of type 304 stainless steel were studied over a temperature range of -162 o C to room temperature. Girth weld metal specimens were fabricated using a combination of gas-tungsten-arc-welding and shielded-metal-arc-welding. The seam weld metal was made with submerged arc welding. Fatigue crack growth rate tests were conducted using compact tension specimens in accordance with ASTM E647. Fracture toughness was evaluated through CTOD tests with three point bend specimens. The CTOD values were affected by crack orientation with respect to the rolling direction, but orientation had no influence on fatigue crack growth rates. The fatigue crack growth rates and the CTOD values decreased with decreasing test temperature. INTRODUTIONThe demand for clean and convenient natural gas has been continuously increasing. Natural gas is more efficiently stored and transported as liquefied natural gas (LNG) below the liquefaction temperature because the volume of LNG is about 1/600 that of the gaseous form. The materials for storage and transmission of LNG should have good mechanical properties at low temperature because the boiling point of LNG is -162 o C under 1 atmosphere [1-3]. The structural materials for cryogenic application should exhibit high strength, ductility, fracture toughness, good weldability and fabrication [4]. Type 304 austenitic stainless steel, which has excellent low temperature performance and is stable, is the most common material for pipes used to carry LNG [2,3]. Type 304 austenitic stainless pipes for LNG transmission are invariably joined by welding and the fracture origins of the welding structures are mainly the degradation of mechanical properties due to variation in microstructure through thermal cycles during welding. The integrity of welded structures is considerably reduced by fatigue in the presence of such weld metal defects as incomplete fusion, gas pore, undercut and slag inclusion. The pipes for LNG transmission are subjected to repeated thermal stress as a result of temperature gradients and pressure fluctuation due to changes in operating conditions [2,3,5]. The coefficient of thermal expansion of 304 austenitic stainless is about one and a half times higher than that of carbon steel [6]. Stainless steel pipes for LNG transmission are subject to significant thermal contraction under cryogenic temperature. The result of this could be increased distortion, buckling and fatigue fracture at the weld joint. There have been a large number of studies of the fatigue and fracture toughness of the weld metal and base metal of austenitic stainless steel [7-10]. Little research, however, has been done on the fatigue and fracture toughness properties at LNG temperature. Mukai et al., investigated the tensile and fatigue properties of the base metal of austenitic stainless steel at temperatures between 20 o C and -162 o C [2]. The authors in ref.[2] did not deal with the fracture toughness of the base metal and the mechanical properties of the we...

Ambient and cryogenic S-N fatigue behavior of Fe15Mn steel and its weld

“…The S-N fatigue tests were conducted on a servo-hydraulic testing machine (Instron Model 8516) at an R ratio of 0.1 under a uniaxial loading condition with a sinusoidal frequency of 30 Hz at 298 K and 110 K, respectively, in accordance with ASTM E466 [34]. The run-out fatigue specimens were defined as those not failed up to 2×10 6 cycles. An environmental chamber was utilized to maintain the testing temperature of 110 K which is the temperature of LNG.…”

“…The steels with Mn contents ranging from 15 to 30 wt% are under consideration for the application in a variety of fields, such as the material for LNG liquified natural gas (LNG) tankage [5][6][7][8] and cryogenic pipelines in offshore industry [4]. While the plastic deformation of high Mn steel is mostly accommodated by the slip mechanism, TRIP/TWIP effect can also contribute the deformation [9,10].…”

Statistical analysis of sub-zero temperature effects on fatigue strength of welded joints

“…While effects of high temperatures on material behavior are well covered in international standards and guidelines, there is no comprehensive guidance for sub-zero temperature fatigue strength assessment of welded joints. This is likely related to the small number of publications concerning fatigue of welded steel joints at sub-zero temperatures, see [6][7][8][9][10][11][12][13][14][15][16][17]. Moreover, the majority of studies focuses on fatigue crack growth (FCG) rate testing for cryogenic applications and butt-welded joints.…”

Experimental fatigue crack growth analysis and modelling in part‐through circumferentially pre‐cracked pipes under pure bending load

“…Fatigue crack growth study in pressure vessels and piping is being carried out by many researchers [13][14][15][16][17][18][19][20][21][22][23] . Darcis et al 18 reported the experimental investigation of fatigue crack growth rates in ferrite-pearlite pipeline steels using curved middle-tension M(T) specimens.…”

“…Darcis et al reported the experimental investigation of fatigue crack growth rates in ferrite–pearlite pipeline steels using curved middle‐tension M(T) specimens. In most of the cases, standard specimens or non‐standard specimens, directly fabricated from actual components, were used for experimentation and/or finite element analysis. It was altogether concluded that the fatigue and fracture properties predicted from these specimens were conservative because of the difference in constraint effect in real structural components.…”