9 research outputs found
Effect of preheating and preplaced filler wire on microstructure and toughness in laser-arc hybrid welding of thick steel
Acicular ferrite (AF) is the most important microstructural constituent to achieve high toughness at low temperatures in weld metal of steels. This is due to the relatively small grain size and large misorientation angles. AF is known to form at non-metallic inclusions (NMIs), but under high cooling rates, as in deep and narrow laser-arc hybrid welding (LAHW), this phenomenon is scarcely studied. In deep and narrow LAHW, insufficient transportation of filler wire to the root results in low amount of NMIs, thus bainite-martensite mainly forms due to fast cooling. In this work, a 45 mm thick high strength low alloy steel was welded by double-sided LAHW using different groove preparations. The effect of different cooling times on the microstructure in the weld metal and the heat-affected zone was studied. A low fraction of AF and high hardness were achieved in the root of weld metal when using standard LAHW. This was related to a rapid cooling time (Δt8/5 35 J) was achieved at −50 °C by combining preheating and preplaced filler wire, and up to 45 % fraction content of AF was reached. However, many NMIs were still inactive due to a small diameter (< 200 nm) and unfavorable chemical composition related to the high cooling rate. The external methods had no influence on the occurrence of weld centerline cracks in the root, which will require further attention to secure mechanical properties and integrity.publishedVersio
OMAE2008-57309 FULL SCALE FATIGUE TESTING OF FATIGUE ENHANCED GIRTH WELDS IN CLAD PIPE FOR SCR'S INSTALLED BY REELING
ABSTRACT H 2 S is reported to degrade the fatigue properties of C-Mn steels with a factor of 10-20 in life, while clad pipes are reported to have a performance close to or as good as in air. Clad pipes could therefore be used in highly fatigue loaded parts of the riser to facilitate design of steel catenary risers (SCRs) that are connected to floaters in deep waters. A literature survey of high quality girth welds intended for SCR is included in this paper and compared with fatigue test data obtained in this project. The first nine full scale 15" clad pipe girth welds out of a program of 24 specimens are fatigue tested in a high frequency resonance test rig and reported. The pipes were tested as welded, hammer-peened and reeled. The 15" OD steel pipes with 316 cladding tested in this work were surplus pipes from the Norne pipeline project. The fatigue test pipes were fabricated using the same welding procedure and welding facilities at Technip's spool base in Orkanger, Norway, as the Norne pipeline project. The Norne pipeline is the world's first reeled clad pipeline. The objective of this work was to test premium quality girth welds with best possible fatigue performance in actual pipes under realistic conditions was. The effect of hammer-peening of the OD was therefore investigated. Post failure examination was performed to determine the type and size of defects at the fatigue crack initiation site
Qualification of the hybrid metal extrusion & bonding (HYB) process for welding of aluminium offshore structures
In the present investigation the aptness of the HYB process for butt welding of 4mm AA6082-T6 profiles is evaluated and benchmarked against one gas metal arc (GMA) weld and one friction stir (FS) weld, representing best practice for both methods. The tensile testing shows that the yield strength of the HYB weld exceeds that of the GMA weld and is comparable with that of the FS weld. When it comes to impact toughness the HYB weld is the superior one of the three. Since the subsequent transverse bend testing did not reveal any evidence of bonding defects or crack formation, it means that the 4mm AA6082-T6 HYB butt weld meets all acceptance criteria being specified by Equinor for offshore use
Influence of sigma-phase precipitation on the impact behaviour of duplex stainless steel pipe fittings
In this study, the effect of sigma-phase precipitation in duplex stainless steel (grade 2205) pipe fittings collected from top-side process systems offshore was investigated under realistic loading conditions. This was done by conducting quasi-static and dynamic impact tests on 3” fittings with a nominal outside diameter of 88.9 mm, nominal wall thickness of 3.05 mm and D/t-ratio of nearly 30. The fittings had a sigma-phase level between 0 and 15 vol.%, and were loaded by a massive steel indenter with a hemispherical nose of 25 mm radius. In the quasi-static tests, the loading rate was 2 mm/min, while in the dynamic tests the impact velocity was varied between 5 and 10 m/s. A few dynamic impact tests on 2” fittings with an increased wall thickness and low sigma-phase levels were carried out for comparison, while some 3” fittings were pre-charged with hydrogen before dynamic testing to examine the effect of sigma phase on cathodic protected subsea components. When the sigma-phase level was low (i.e. σ ⩽ 5 vol.%), no evidence of fracture was found in any of the pipe fittings, whereas at higher sigma-phase levels (σ > 5 vol.%), fracture occurred in all tests. At the highest sigma-phase level (σ ≈ 15 vol.%), extensive fracture and crack growth took place independent of the loading rate
Thermo-mechanical tensile testing of geothermal casing materials
Ultra-high temperature geothermal wells (>450 °C) have a large potential for increased energy yield as compared to conventional high-temperature geothermal wells (200-300 °C), but several research challenges must be resolved before robust operation in this temperature range can be achieved. In this study, yield- and tensile strength data for several relevant carbon steels and corrosion resistant alloys are generated as a step on the way to enable design of collapse- and tensile capacity for geothermal casings exposed to temperatures up to 500-550 °C. The experiments extend the data set listed in NZS 2403:2015 by providing data for higher temperatures and different material classes. It is found that the carbon steels follow the same near linear decay in strength as the NZS 2403:2015 curves up to 350 °C, and then display a significant drop in tensile strength at higher temperatures, particularly for the lower strength steels. The alloys with high nickel content work harden significantly more than the carbon steels at high temperatures and they tend to retain their strength at temperatures above 350 °C. The tested titanium alloy shows high yield strength and low work-hardening at 500 °C and in contrast to the tested nickel alloys, do not display dynamic strain ageing.publishedVersio
Effect of preheating and preplaced filler wire on microstructure and toughness in laser-arc hybrid welding of thick steel
Acicular ferrite (AF) is the most important microstructural constituent to achieve high toughness at low temperatures in weld metal of steels. This is due to the relatively small grain size and large misorientation angles. AF is known to form at non-metallic inclusions (NMIs), but under high cooling rates, as in deep and narrow laser-arc hybrid welding (LAHW), this phenomenon is scarcely studied. In deep and narrow LAHW, insufficient transportation of filler wire to the root results in low amount of NMIs, thus bainite-martensite mainly forms due to fast cooling. In this work, a 45 mm thick high strength low alloy steel was welded by double-sided LAHW using different groove preparations. The effect of different cooling times on the microstructure in the weld metal and the heat-affected zone was studied. A low fraction of AF and high hardness were achieved in the root of weld metal when using standard LAHW. This was related to a rapid cooling time (Δt8/5 35 J) was achieved at −50 °C by combining preheating and preplaced filler wire, and up to 45 % fraction content of AF was reached. However, many NMIs were still inactive due to a small diameter (< 200 nm) and unfavorable chemical composition related to the high cooling rate. The external methods had no influence on the occurrence of weld centerline cracks in the root, which will require further attention to secure mechanical properties and integrity
Effect of preheating and preplaced filler wire on microstructure and toughness in laser-arc hybrid welding of thick steel
Acicular ferrite (AF) is the most important microstructural constituent to achieve high toughness at low temperatures in weld metal of steels. This is due to the relatively small grain size and large misorientation angles. AF is known to form at non-metallic inclusions (NMIs), but under high cooling rates, as in deep and narrow laser-arc hybrid welding (LAHW), this phenomenon is scarcely studied. In deep and narrow LAHW, insufficient transportation of filler wire to the root results in low amount of NMIs, thus bainite-martensite mainly forms due to fast cooling. In this work, a 45 mm thick high strength low alloy steel was welded by double-sided LAHW using different groove preparations. The effect of different cooling times on the microstructure in the weld metal and the heat-affected zone was studied. A low fraction of AF and high hardness were achieved in the root of weld metal when using standard LAHW. This was related to a rapid cooling time (Δt8/5 35 J) was achieved at −50 °C by combining preheating and preplaced filler wire, and up to 45 % fraction content of AF was reached. However, many NMIs were still inactive due to a small diameter (< 200 nm) and unfavorable chemical composition related to the high cooling rate. The external methods had no influence on the occurrence of weld centerline cracks in the root, which will require further attention to secure mechanical properties and integrity
Thermo-mechanical tensile testing of geothermal casing materials
Ultra-high temperature geothermal wells (>450 °C) have a large potential for increased energy yield as compared to conventional high-temperature geothermal wells (200-300 °C), but several research challenges must be resolved before robust operation in this temperature range can be achieved. In this study, yield- and tensile strength data for several relevant carbon steels and corrosion resistant alloys are generated as a step on the way to enable design of collapse- and tensile capacity for geothermal casings exposed to temperatures up to 500-550 °C. The experiments extend the data set listed in NZS 2403:2015 by providing data for higher temperatures and different material classes. It is found that the carbon steels follow the same near linear decay in strength as the NZS 2403:2015 curves up to 350 °C, and then display a significant drop in tensile strength at higher temperatures, particularly for the lower strength steels. The alloys with high nickel content work harden significantly more than the carbon steels at high temperatures and they tend to retain their strength at temperatures above 350 °C. The tested titanium alloy shows high yield strength and low work-hardening at 500 °C and in contrast to the tested nickel alloys, do not display dynamic strain ageing