Materials Science Forum Vol. 850

Abstract: To confirm pipeline designs and validate the weld toughness, extensively works of Curved Wide Plate (CWP) test methods was carried out. The method of Two Clip Gauge-CTOD was firstly introduced in CWP test in this paper. The test results of CWP analyzed by Two Clip Gauge-CTOD method and Compliance—J method was compared. The CTOD-R curves achieved by these methods showed the good consistence with each other. Furthermore, the difference of the test results among SENB(single edge-notched bend), SENT(single edge-notched tensile) and CWP was discussed. It shows that the toughness obtained by SENB is relatively conservative, and CWP and SENT are recommend to be chosen for pipeline steel welds toughness test.

Abstract: In the pipeline construction, the girth welds tend to be the weakness because of defects and microstructure. The importance of suitable assessment of various defects in the weld is not only to prevent the cracks from unstable growth to cause catastrophic accident but also can effectively reduce the weld repair to reduce construction cost. Although many welding defects assessment methods and codes are used in this field, there are many differences among them. In this paper, the welding defect assessment methods, such as API 1104 and BS7910, were studied. The results show the key factors that affect the result of these assessment methods. The application of these methods was also discussed. The results indicate that API 1104 level1 has the highest conservatism, while API 1104 level 2 is next.

Abstract: Tie-in is a very important step on the final stage of pipe construction. The stress of the tie-in girth weld is really one of the key roles that affect the security of the pipeline in service. In this paper, Finite Element Method (FEM) was used to determine the stress of the tie-in girth weld. The factors of stress of tie-in girth weld were analyzed. The results show that uncovered pipe length, tie-in offset and misalignment were the important factors which affect the stress of tie-in girth weld. The maximum Mises stress and axial stress at tie-in girth weld increased with the uncovered pipe length decreasing and the tie-in offset increasing. The stress also increased significantly with girth weld misalignment, especially for axial stress.

Abstract: This paper provided a detailed description of X90 pipeline steel developed in Wuhan Iron and Steel Corporation (WISCO), including its metallurgical design, manufacturing process, structural characteristics and mechanical properties. Some key issues such as the cooling rate and rolling parameters were addressed for the development of X90 pipeline steel. The experimental results showed that the manufacturing process of controlled rolling (for austenite refining) + relaxation (for ferrite phase transformation) +ultrafast accelerated cooling could guarantee very fine microstructure and excellent mechanical properties. The X90 pipeline steel developed in WISCO has a good match of high strength and excellent toughness. Mechanical properties of X90 coils, plates and corresponding SSAW and LSAW pipes comprehensively meet the technical requirements of China National Petroleum Corporation (CNPC).

Abstract: This work presents an investigation of the ductile tearing properties for a pipe with internal and external circumferential cracks using 2D plane strain and axisymmetric models. Crack growth resistance curves were computed using the complete Gurson model. The pipes with various crack depths and internal pressures were analyzed. The results were compared with those of corresponding SENT and SENB specimens. It clearly indicated a significant effect of constraint on the resistance curves for internal and external cracked pipes. A minor effect of hoop stress induced by internal pressure on the CTOD-resistance curves is expected for deep-cracked pipes. The SENT specimen is a better representation of circumferentially flawed pipes and an alternative to the conventional standard SENB specimen for the fracture mechanics testing in engineering critical assessment of high-strength pipeline steels.

Abstract: In this paper, the simulation heat affected zone (HAZ) continuous cooling transformation (SHCCT) curve of X90 pipeline steel was drew by using Gleeble 3500 simulator. The results show that the trend of hardening of the weld HAZ of X90 pipeline steel was moderate, and softening tendency was not significant. When cooling rate was between 1°C/s and 10°C/s, the microstructure of X90 pipeline steel weld HAZ were composed of granular bainite and lath bainite. The recommended welding heat input of X90 pipeline steel was between 21kJ/cm and 66.4kJ/cm, and the weld preheating temperature was controlled about 100°C. In conclusion, optimization control measures on the microstructure and properties of X90 pipeline steel weld HAZ are presented by above comprehensive analysis.

Abstract: Test bends of L415M hot induction bend of 508 mm OD×14.3 mm WT used in –45°C areas were conducted. The bending and tempering process parameters were designed, the influences of bending and tempering process parameters on impact toughness at –45°C and microstructure of tangent weld and bend weld were investigated. Hot induction bend was produced by the process of local induction heating+fast water quenching. After tempering treatment, the weld contained martensite-austenite (M-A) islands, carbide precipitations, welded column crystal structure and little pearlite (P), and the brittle fracture surface contained S segregation, the temper brittleness of the weld occurred, which lead to impact energy of bend weld to be lower than 40 J at –45°C. Without post-bending tempering treatment, the microstructures of bend weld was a composite of polygonal ferrite (PF) and granular bainite (GB) with small size and uniform distribution, the coarse column structure and acicular ferrite (AF) disappeared in the weld, so the impact energy of bend weld was higher than 70 J at –45°C, but the impact energy of tangent weld was very poor. It suggests that the process of overall induction of heating + fast water quenching + no tempering treatment is more reasonable, the process ensures that the impact toughness at –45°C, strength and other properties of bend meet the requirements of CDP-S-OGP-PL-016-2011-2.

Abstract: The microstructural evolution of the high Nb X80 pipeline steel in Continuous Cooling Transformation (CCT) by Gleeble-3500HS thermal mechanical simulation testing system was studied, the corresponding CCT curves were drawn and the influence of some parameters such as deformation and cooling rate on microstructure of high Nb X80 pipeline steel was analyzed. The results show that as cooling rate increased, the phase transformation temperature of high Nb X80 steel decreased, with the microstructure transformation from ferrite-pearlite to acicular ferrite and bainite-ferrite. When cooling rate was between 20°C/s and 30°C/s, the microstructure was comparatively ideal acicular ferrite, thermal deformation accelerates phase transformation notably and made the dynamic CCT curves move upward and the initial temperature of phase transformation increase obviously. Meanwhile the thermal deformation refined acicular ferrite and extended the range of cooling rate accessible to acicular ferrite.

Abstract: P91 heat-resistant steel is widely used in the high temperature of piping components of thermal power plants and nuclear power plants. In these conditions, the typical failure of P91 is mainly caused by creep at low stress. In this investigation the short-term creep behavior in P91 at low stress was investigated by helicoid spring creep test due to its high strain-sensitivity. The helicoid spring creep was based on the assumption of pure torsion. The mechanics field was firstly studied by ANSYS finite-element simulation to find the establishing conditions of pure torsion. Secondly, the creep properties of P91 were studied under the conditions of the temperatures of 0.38T_m<T<0.46T_m and the stresses of 14.6 MPa, 25 MPa, 34 MPa, respectively. The ANSYS finite-element simulation shows that the creep deformation is considered to be pure torsion when the pitch spacing of coil is between 2mm to 4mm. The creep curves show "Normal type ", and “the stress exponent” is n=0.9.

Abstract: In this paper the water absorption properties of polyethylene shrink tape were analyzed for long-distance pipeline. In the water absorption experiments, the normal and high temperature type heat shrinkable tape from six different manufacturers were respectively immersed in water range from 24 h to 28 d. The results show that the water absorption of the normal and high temperature type heat shrinkable tape was steady under the condition of 144 h. Once exceeding 144h, the water absorption increased gradually. Furthermore, the glue layer of heat shrinkable tape had a greater impact on water absorption. And the water absorption of glue layer of heat shrinkable tape decreased with an increase of the hot glue layer thickness,