Ke Tong

Study on FCAW Semi-Automatic Welding Procedure of Girth Weld Joint of Line Pipes

This paper investigate the mechanical property and microstructure of girth weldment of Lan Zhou to Cheng Du crude oil pipeline. The welding joint was bottomed by cellulose electrode E6010 and filled and covered by flux-cored wire AWS A 5.29 E71T8-Ni1. According to SY/T 4103-2006, test results show that the selected process parameters and welding method take on outstanding performance .Microstructure of weld joints is acicular ferrite, polygonal ferrite, proeutectoid ferrite and granular bainite, and widmanstaten ferrite dosn’t exsist in heat affected zone(HAZ). Microstrure of the whole weld joint is mainly polygonal ferrite and granular bainite, this is the reason that mechanical properties can meet the Lan Zhou to Cheng Du crude oil pipeline project requirement.

SEM In Situ Investigation on Fatigue Cracking Behavior of X80 Pipeline Steel with Inclusions

The micro-mechanical behavior of inclusions in X80 pipeline steel under fatigue loading was investigated by means of SEM in situ observation. The influence of sizes and shapes of inclusion on crack initiation and propagation was analyzed. The result shows that for large-size single-particle inclusion, cracks initiate from the interior under the fatigue loading. When a certain circulation cycles are reached, cracks initiate at the matrix near the sharp corner of the inclusion. The cracks extend at the matrix during the stable extension period and unstable extension period following the crack initiation, until fracture occurred. For chain inclusion, cracks first initiate at the interface between inclusion and matrix within the chain area, and the circulation cycles needed for initiation are far less than single inclusion. Cracks steadily extend after the initiation, and then fracture after very short circulation cycles. A chain of inclusion with the shape corners is serious harmful to the fatigue properties.

Properties of X80 Pipeline Girth Welds for Different Welding Procedures

The X80 girth welds were produced by solid-wire gas metal arc welding (GMAW) and shield metal arc welding (SMAW) using two welding consumables respectively, which contained different mass fraction of C, Mo and Ni. The tensile properties, notch toughness, hardness, and microstructures of welded joints were evaluated. The results indicate that high strength and good toughness of welded joints can be achieved. But the tensile properties of all weld metal of GMAW and SMAW process were evidently different because of the difference of mass fraction of C, Mo, Ni. The strength reduced slightly in softening zone of HAZ. Using welding consumable which contain higher Mo additions, the microstructure in filler weld and fusion zones were IAF+GB and GB+M respectively. Furthermore, the mechanical properties of X80 pipeline welded by single wire welding and double wire welding respectively have been compared. The double wire welds exhibited lower yield strength but higher toughness compared to the corresponding single wire welds.

Mechanical Property, HIC and SSCC Test Analysis of L245NS Anti-Sulfur Bending Pipe

Rational utilization of the anti-sulfur tubes is considerable significance to the reliability and service life of oil-gas pipeline system. Unfortunately, there have been no such researches in the field of anti-sulfur bending pipe. In this paper, the mechanical property test, hydrogen induced cracking(HIC) test and sulfide stress-corrosion cracking(SSC) test were conducted to investigate the Φ406.4×10.31mm L245NS anti-sulfur bending pipe with the technique of induction heating bending. And the test result was analyzed combining with microstructure of pipe. The results show that mechanical properties and HIC behavior of L245NS bending pipe reach the standard with the 890~930°C induction quenching and 580-630°C temper process. The strength and Charpy toughness of inner arc and outer arc are higher than base metal. Most HIC crack initiated at the bainite structure and banded structure. The L245NS anti-sulfur bending pipe exhibits good resistance to SSCC under the NACE TM0177-2005 experiment environment.

Micro-Behavior of Inclusions in X80 Pipeline Steel under Tensile Loading

Specially designed SEM in-situ tensile tests have been conducted to trace the entire process of crack initiation and propagation induced by inclusions in X80 pipeline steel. The main inclusions are complex oxides containing aluminum, calcium and magnesium with round or oval shape, and their sizes are in the range of 3~20μm. Cracks initiate firstly in inclusions and also easily initiate among inclusions if they distribute in the steel as an inclusion chain. The size of an inclusion has little effect on the initiation stress of the first crack, which mainly depends on the yield strength of the steel. Once a crack initiates in X80 pipeline steel, it zigzag propagates along the direction of maximum shear stress that orients in about 45° to the loading direction till failure. In the process of crack propagation, the crack experiences propagation, anti-crack, bluntness and new micro-cracks initiation again and again. These valuable experimental results reveal the harmful effect of inclusions in micro-scale and are helpful for understanding failure mechanisms of the advanced steel components.

Structures and Properties of X80 Pipeline Girth Welds for Different Welding Procedures

The X80 girth welds were produced by solid-wire gas metal arc welding (GMAW) and shield metal arc welding (SMAW) using two welding consumables respectively, which contained different mass fraction of C, Mo and Ni. The tensile properties, notch toughness, hardness, and microstructures of welded joints were evaluated. The results indicate that high strength and good toughness of welded joints can be achieved. But the tensile properties of all weld metal of GMAW and SMAW process were evidently different because of the difference of mass fraction of C, Mo, Ni. The strength reduced slightly in softening zone of HAZ. Using welding consumable which contain higher Mo additions, the microstructure in weld seam and fusion zones were IAF+GB and GB+M respectively. Furthermore, the mechanical properties of X80 pipeline welded by single wire welding and double wire welding respectively have been compared. The double wire welds exhibited lower yield strength but higher toughness compared to the corresponding single wire welds.Copyright

Flow Stress Behaviour of TWIP Steel during the Hot Compression Deformation

The hot deformation behavior of Fe-25Mn-3Si-3Al TWIP steel were investigated by isothermal single-pass compression on Gleeble-3500 thermal simulator at the temperature range of 900°C to 1100°C and the strain rate range of 0.01s-1 to 1s-1. The results showed that the true stress-strain curves of Fe-25Mn-3Si-3Al steel had a typical feature which often appears during the hot deformation process of metals and alloys with high stacking fault energies. In true stress-strain curves, No obvious flow stress peak was observed. With the increase of strain, flow stress reaches the saturation value, indicating that the hot deformations of these conditions are dynamic recovery. The hot compression deformation of Fe-25Mn-3Si-3Al steel can be represented by Arrhenius model. The constitutive equation of Fe-25Mn-3Si-3Al steel under hot compression deformation is calculated by a linear regression analysis. The activation energy for hot deformation of the experimental steel is 422.51kJ/mol.

The Micro-Mechanical Behavior of Inclusions under Tensile Load in X80 Pipeline Steel

In-situ tensile tests with specially designed SEM were conducted to trace the entire process of crack initiation and propagation till fracture in X80 pipeline steel. The mode of crack initiation induced by inclusions under tensile load was investigated. The results show that: (1) All the inclusions crazed and fracture was the typical tensile fracture, which indicates that the inclusions have little effect on the tensile properties of the X80 material under tensile load. (2) When the size of inclusion is larger than the critical size, crack initiated at inclusion/matrix interface first, and could easily propagate into matrix，but the long crack cannot form. When the size of inclusion is smaller than the critical size, cracks first formed in the inside of inclusions but not propagate into matrix. (3) If the area of cross section of round inclusion is less than 100μm2, crack initiated firstly in the inside of inclusion. If the area of cross section of round inclusion is larger than 100μm2, crack initiated firstly at the inclusion/matrix interface. For the rectangle inclusion, when its area of cross section is below 150μm2, cracks usually initiate in the center of inclusions.

Research and Prospect on Relationship Between Microstructure Characteristics and Strength-Toughness of High Grade Pipeline Steel

The strength property of high grade pipeline steel has been obviously improved with the rapid development of the constructing of oil and gas pipelines. And the excellent strength-toughness matching of pipeline steel is very important. The major affecting factor on strength-toughness of pipeline steel is microstructure characteristic. In this paper, the research status of pipeline steel microstructure characteristic including effective grain size, non-metallic inclusions and banded structure is summarized at home and abroad. In addition, the shortcomings of former research on the relationship between microstructure characteristics and strength-toughness are also analyzed for this pipeline steel. On this basis, a solution is put forward to investigate the characterization of effective grain size and micro-mechanical behavior of inclusions and banded structure with the method of electron backscatter diffraction and the method of SEM in situ observation. And the necessities and feasibilities of the solution are discussed.Copyright

Effects of M/A Islands Microstructure Characteristic on Mechanic Properties of High Grade Pipeline Steel

The microstructure characteristic of martensite/austenite (M/A) islands of X80-1#, X80-2#, X100-3#, X100-4# steel pipelines come from different manufacturer were investigated by OM and SEM contrastively, and the influence of M/A islands microstructure characteristics of pipelines were studied combining with tests of mechanic properties. The result shows that the effect of the M/A islands volume fraction, average dimension, form and distribution on the material strength, yield ratio and toughness were distinct. When the M/A islands distribute uniformly with small size and spherical or crossed strip form, under the certain volume fraction, the pipeline steel exhibits excellent strength-toughness matching.© 2010 ASME