This paper summarizes a series of the authors’ research in the field of assessing the operational degradation of oil and gas transit pipeline steels. Both mechanical and electrochemical properties of steels are deteriorated after operation, as is their resistance to environmentally-assisted cracking. The characteristics of resistance to brittle fracture and stress corrosion cracking decrease most intensively, which is associated with a development of in-bulk dissipated microdamages of the material. The most sensitive indicators of changes in the material’s state caused by degradation are impact toughness and fracture toughness by the J-integral method. The degradation degree of pipeline steels can also be evaluated nondestructively based on in-service changes in their polarization resistance and potential of the fracture surface. Attention is drawn to hydrogenation of a pipe wall from inside as a result of the electrochemical interaction of pipe metal with condensed moisture, which facilitates operational degradation of steel due to the combined action of operating stresses and hydrogen. The development of microdamages along steel texture was evidenced metallographically as a trend to the selective etching of boundaries between adjacent bands of ferrite and pearlite and fractographically by revealing brittle fracture elements on the fracture surfaces, namely delamination and cleavage, indicating the sites of cohesion weakening between ferrite and pearlite bands. The state of the X52 steel in its initial state and after use for 30 years was assessed based on the numerical simulation method.

https://www.mdpi.com/1996-1944/14/12/3247/pdf

Assessment of Operational Degradation of Pipeline Steels

Flow stress characteristics and design of innovative 3-steps multiphase control thermomechanical processing to produce ultrafine grained bulk steels

A multi-layered plate with robust interfacial strength composed of high-Cr martensitic stainless steel was produced via repetitive hot roll bonding (RHRB) at elevated temperature. The minimum processing temperature required for the production of multi-layered plates turned out to be in the two-phase region between the A1 and A3 temperatures of stainless steel. Decarburization took place on the surface layer of each process cycle and multi-layered plates were produced with a carbon content that fluctuated along the thickness direction that constitutes a composite plate. The multi-layered composite structure revealed an effective combination of strength and ductility. Also, strong bonding results at each interface were validated via tensile testing with in-situ observation from the sides of the specimens during deformation.

Heterogeneities in the microstructure and mechanical properties of high-Cr martensitic stainless steel produced by repetitive hot roll bonding

The ultra-fine-grained ferrite (UFGF) with the size of less than 1 μm is often difficult to be obtained for low-alloyed steel in practical production processing. In this study, considering the rod and wire production process, a new method for preparing the UFGF with submicron scale is proposed by warm deformation of six passes with total strain of 2.6, followed by the cooling process in Gleeble-3500 thermo-mechanical simulator. The results show that the UFGF with an average size of 0.64 μm could be obtained via the phase transformation from austenite grains with an average size of 3.4 μm, which are achieved by the deformation-induced reversal austenization during the high strain rate warm deformation. The main driving force for the reversal transformation is the stress. And the interval between the passes also plays an important role in the reversal austenization.

Ultra-fine-Grained Ferrite Prepared from Dynamic Reversal Austenite During Warm Deformation

The modern industry allows synthesizing and manufacturing composite materials with a wide range of mechanical properties applicable in medicine, aviation, automotive industry, etc [...]

https://www.mdpi.com/1996-1944/13/24/5820/pdf

Special Issue "Advanced Composites: From Materials Characterization to Structural Application"

In this study, the series temperature Charpy impact and drop-weight tear test (DWTT) were investigated, the misorientation angles among structural boundaries where the cleavage crack propagated were identified, and angles of {100} cleavage planes between adjacent grains along the cleavage crack propagated path were calculated in five directions (0°, 30°, 45°, 60°, and 90° to the rolling direction) of high-grade pipeline steel. Furthermore, the effective grain size (grain with misorientation angles greater than 15°) was redefined, and the quantitative influences of the redefined effective grain size on Charpy impact and DWTT is also discussed synthetically. The results showed that the microstructure presented a typical acicular ferrite characteristic with some polygonal ferrite and M-A islands (composed of martensite and retained austenite), and the distribution of the high-angle grain boundaries were mainly distributed in the range of 45°–65° in different directions. The Charpy impact energy and percent shear area of DWTT in the five directions increased with refinement of the redefined effective grain size, composed of grains with {100} cleavage planes less than 35° between grain boundaries. The ductile-to-brittle transition temperature also decreased with the refining of the redefined effective grain size. The redefined effective grain boundaries can strongly hinder fracture propagation through electron backscattered diffraction analysis of the cleavage crack path, and thus redefined effective grain can act as the effective microstructure unit for cleavage.

Influence of Effective Grain Size on Low Temperature Toughness of High-Strength Pipeline Steel.

Fabricating ultrafine grain by advanced thermomechanical processing on low-carbon microalloyed steel

In this study, the effect of pre-deformation at recrystallization and non-recrystallization zone on the grain ultrafining by the subsequent intercritical deformation (ID) was investigated on low-carbon microalloyed steel. The results showed that ultrafine grain microstructure with an average size of ~ 1.0 μm was fabricated through pre-deformation in the recrystallization zone followed by ID. When pre-deformed at the non-recrystallization zone prior to ID, the grain size increased to 1.6 μm with a heterogeneous distribution along with the well-developed dynamic recovery of ferrite. The grain ultrafining mechanism was attributed to the combined action of the deformation-induced ferrite transformation and the continuous dynamic recrystallization. In particular, the continuous dynamic recrystallization process during ID occurred on the pro-eutectoid ferrite as a result of the subgrain rotation mechanism and the absorbing dislocations mechanism.

Effect of Pre-deformation on Grain Ultrafining by Intercritical Deformation in Low-Carbon Microalloyed Steels

The invention relates to steel for bend pipes and pipe fittings for oil and gas transportation in a low-temperature environment and a manufacturing method, belongs to the technical field of high-strength low-alloy steel, and can be used in the field of production of the bend pipes and the pipe fittingsfor a low-temperature field stationwith extremely high requirements for low temperature toughness. The steel for the bend pipes and the pipe fittings is prepared from C: 0.02-0.05 wt%, Si: =180J, and the steel plate can be applied to the bend pipes and the pipe fittings for field stations and suspended span pipe sections in colder latitudes.

Steel for bend pipes and pipe fittings for oil and gas transportation in low-temperature environment and manufacturing method

The invention discloses a heat treatment method for manufacturing low-temperature resistant pipeline steel, and belongs to the technical field of pipeline steel manufacturing. By carrying out two times of heating quenching at different temperatures on a granular bainite structure obtained through controlled rolling and controlled cooling, the granular bainite structure is homogenized and refined significantly, a bainite ferrite matrix with nanoscale battens is obtained, and an extremely good combination of strength and toughness is ensured; and then through tempering, stress is relieved, at the same time, carbides of chromium are precipitated, and the strength is further improved. The prepared low-temperature resistant pipeline steel comprises the chemical components of 0.5-0.15% of chromium and the balance X80 level pipeline steel. The heat treatment method has the advantages that a mixed structure of the bainite ferrite matrix containing the nanoscale superfine battens and the uniformly distributed carbides is obtained, the good low temperature toughness is guaranteed, the strength is improved and the heat treatment method is applicable to the pipeline laying in high and cold areas.

Li Ba

Papers

Influence of Effective Grain Size on Low Temperature Toughness of High-Strength Pipeline Steel.

Fabricating ultrafine grain by advanced thermomechanical processing on low-carbon microalloyed steel

Effect of Pre-deformation on Grain Ultrafining by Intercritical Deformation in Low-Carbon Microalloyed Steels

Steel for bend pipes and pipe fittings for oil and gas transportation in low-temperature environment and manufacturing method

Heat treatment method for manufacturing low-temperature resistant pipeline steel