Low-carbon Pipe Steel Research Articles

Measurement and Prediction of Residual Stresses in Low Carbon Steel Pipes Welded Shielded Metal Arc Welding

Welding is carried out with a very complex thermal cycle, which results in irreversible elastic-plastic deformation, and residual stresses in and around fusion zone and heat-affected zone (HAZ). A residual stress due to welding arises from the differential heating of the pipes due to the weld heat source. However, due to the presence of residual stresses in and around the weld zone the strength and life of the component is also reduced. The objective of this work is to measure the welding residual stress in ASTM (A-106 Gr. b) steel pipes with 4" diameter and 6 mm thickness welded manually (SMAW) in three-pass butt joint where shielded metal arc welding process consists of heating, melting and solidification of parent metals and a filler material in localized fusion zone by a transient heat source to form a joint between the parent metals. The welding process will have accrued without preheating and heat treatment. This measuring of residual stress occurs by using hole-drilling strain gauge method according to (ASTM E-873) then the experimental results for residual stresses obtained from welded carbon steel pipes used to provide validation for finite element simulations. The welding process and welding residual stress distribution is calculated by Ansys Finite Element techniques. Theoretical considerations can be assessed by a mechanical model. The overall, there is good agreement between the predicated and measured distributions of residual stress, but the magnitude of predicted stress tend to greater in welding region.

Determination of fracture toughness in the short transverse direction of low carbon steel pipes by compact-tension specimens completed by welded attachments

An experimental procedure for direct measurement of the fracture toughness values (KIC) in the short transverse directions, of low carbon steel pipes, is proposed. The method consists of enlarging the material strip to be tested, by welding extensions so as to complete the dimensions of a valid compact tension specimen. Validation of the KIC results was done by the comparison between the values obtained from one-piece compact tension specimens and welded-completed specimens, both in the longitudinal direction (CL). Additionally, the effect of the steel microstructure orientation on the KIC in the short transversal direction was studied. The results show that the KIC values in the short transversal direction of low carbon steel pipes is as much as 20% lower than the CL direction. This is directly related to the relative orientation parameter (Ω12) and the banding degree (Ai) of the pearlite bands in the microstructure, and the location of the crack plane with respect to the pearlite banding plane.

Microstructure of intercritical heat affected zone and toughness of microalloyed steel laser welds

Microstructure of laser welds of the X70 low-carbon pipe steel was studied. High cooling rates after laser welding and non-uniform distribution of carbon in the ferrite-pearlite base metal caused formation of regions with increased microhardness (up to 650 НV) in inter-critical heat affected zone (ICHAZ). These regions consisted of finely dispersed degenerate upper bainite and martensite-austenite constituents of a slender shape and small fraction of a massive shape along the boundaries of bainite laths, as well as twinned martensite. High concentration of martensite-austenite constituents (10–16%) and residual stresses in ICHAZ, as well as a dendritic martensitic structure with carbide interlayers along the boundaries of martensite laths in fusion zone were the main reasons of sharp decrease in charpy impact energy of the welded samples. High microhardness of the laser welds was decreased down to 320 HV and their brittleness was improved by annealing. Also, in ICHAZ, degenerate upper bainite and the regions of martensite-austenite constituents decayed forming tempered sorbite and Fe2C and Fe3C carbides, respectively. Charpy impact energy of the welds doubled after annealing compared to the welds without annealing, and ductile-brittle transition temperature decreased down to –60°С.

Vanadium Dispersion Strengthening of Low-Carbon Pipe Steels

The research results of the nitrogen and vanadium influence on the microstructure, fine structure formation and mechanical properties of low-carbon steel pipe are considered. It is shown that it is possible to obtain cold-resistant mill products with strength classes from K48 to K60 with high (26–29%) percentage of elongation by dispersion hardening due to the precipitation of vanadium particles together with hardening of a manganese solid solution in the conditions of the Vyksa Metallurgical Plant casting and rolling complex.

Analysis of Mechanical and Metallurgical Properties of Friction Welded ASTM A106Gr.B Carbon Steel Pipe Joints by Varying Upset Pressures

Friction welding is one of the most common methods employed in the joining of carbon and alloy steel tubular sections. In the present work, the analysis of the effect of upset pressure on mechanical and metallurgical properties of friction welded ASTM A 106 Gr. B low carbon steel pipes has been investigated. The test joints were made using continuous drive welding machine with upset pressures of 5 MPa to 8 MPa and evaluated for microstructure, hardness, tensile strength and impact toughness. The weld joints exhibited mostly ferrite and pearlite microstructure in both fully plastically deformed zone (FPDZ), partially deformed zone (PDZ) on the either side of the weld interface and a distinct dynamically recrystallized ferrite pearlite microstructure was observed in the FPDZ at the weld centre line. Better tensile properties were observed in case of the joints made with upset pressure of 6.4 MPa. It is observed that the weld region is stronger than base metal and the hardness has increased with the increase in the upset pressure. Marginal reduction in the toughness was noted with the increase in the upset pressure.

Production of Heavy Plates of Pipe Steel with Increased Strength and Cold Resistance on the 5000 Rolling Mill at PJSC MMK

Abstract—On the basis of laboratory experiments on an ITs Termodeform-MGTU test system, the production of rolled plates with large thickness from pipe steel of improved strength (Rt 0.5 = 505–610 MPa, Rm = 570–680 MPa) and cold resistance (KV–48 ≥ 170 J, DWTT–55 ≥ 90%) is introduced in the 5000 rolling mill at PJSC MMK. To ensure high cold resistance, the formation of predominantly quasi-polygonal and polygonal (polyhedral) ferrite is optimal. It is found that, if the steel microstructure includes a considerable quantity of bainite, the performance of the steel in drop tests is impaired. By means of the Gleeble 3500 test system, the thermokinetic diagram of supercooled-austenite decomposition is plotted for the new low-carbon pipe steel, with up to 1% Ni.

Decomposition of Supercooled Austenite in Low-Carbon Pipe Steel

Controlled rolling may facilitate the transition from ferrite–pearlite structure to bainite structure and hence improve the strength of low-carbon alloy steel. A literature review shows the lack of detailed research regarding the type of bainite structure that ensures optimal properties of low-carbon alloy steel. To determine the temperature, time, and other parameters of treatment to produce such structure, it is expedient to establish the influence of the cooling rate on the structure and properties of low-carbon alloy steel. In the present work, we investigate the decomposition of supercooled austenite in low-carbon alloy pipe steel with 0.062% C, 1.80% Mn, 0.120% Mo, 0.032% Cr, 0.90% Ni, and other elements (Al, Cu, V, Nb, Ti). The treatment conditions producing bainite structure with elevated steel are determined for such steel. At low cooling rates (no more than 6°C/s), not only ferrite is formed in the microstructure but also granular (or globular) bainite consisting of bainitic α phase and an insular martensite–austenite component (1–6 μm). At a rate of 6°C/s, transition to rack bainite is observed; around the boundaries of the racks, carbides and residual austenite are seen. At cooling rates above 16°C/s, the bainite has packet–rack structure, Between 50 and 150°C/s, the mean rack width of the bainitic α phase declines from 2.24 to 1.32 μm.

Distortion Prediction in Quenching Seamless Pipes of Low-Carbon Steel

Abstract Quenching is an important pipe production step that can also be responsible for geometric distortions in steel parts, depending on cooling heterogeneities, thermal contractions, and changes in the steel microstructure. The quenching stage generally leads to an increase in the outside diameter (OD) of the pipes, and the prediction of the final size becomes key to assuring the quality and dimensional requirements of the product. The objective of this study was to apply simulations based on the finite element method (FEM) to water quenching in tanks to estimate the final OD of a seamless low-carbon steel pipe. This work is a first approach to developing a methodology for predicting quenched pipe distortion that depends on the process parameters used during quenching, e.g., internal and external water jets. In the available scientific literature, there are some approaches to the problem, but a consistent approach was not found, especially concerning the experimental validation of the simulation results, which is always a challenge under industrial conditions. The present research was developed in three stages: temperature measurement at several points of the pipe during the quenching process, heat transfer coefficient (HTC) calculation, and distortion calculation. The first stage was performed on an industrial scale to determine the pipe temperature distribution. Afterwards, a finite element (FE) model was set to conduct the second and third stages. The former covered the HTC prediction for inner and outer pipe surfaces using inverse analysis. Pipe distortions were predicted while taking phase transformations and deformations into account. Finally, experimental temperature profiles during heat treatment were used to predict the HTC and OD growth in the low-carbon pipes. The results of the simulations were compared with the industrial data of a quenched pipe in order to validate the methodology that was used.

The Welding of Dissimilar Joints with Low Temperature Martensitic Transformation Filler Material

Abstract The welding of dissimilar joints is very common in systems used in oil exploration and production in deep waters. This commonly involves welding low carbon steel pipes with valves, pumps or other pipes, all of them made of alloy steel. Inconel has been used in such welding as filler material; however, this welding is preceded by a process of buttering in the low alloy steel side and a stress relief heat treatment. An alternative technique presented in this paper is the use of a welding filler metal that, during the cooling process, undergoes a martensitic transformation at a relatively low temperature, so that the resulting deformation processing offsets the contraction that occurs as a result of the cooling process. This study evaluates the application of Maraging 250 weld in a dissimilar joint of the oil industry. Tests were performed on joints of ASTM steels A516 grade 70 and AISI 8630M welded with Maraging 250. The residual stress profiles, hardness, microstructure, tensile strength and impact energy absorbed were evaluated. The welded joint with Maraging 250 showed a high intensity of compressive residual stress. The microstructure of different welding regions was analysed and compared.

Structure and properties of 17G1S-U low-carbon pipe steel microalloyed by boron

The results of analysis of the influence of boron microalloying on structure and properties of 17G1S-U pipe steel are given in the paper. Studies of metal structure were performed by electron microscopy and local X-ray spectral analysis. It has been established that metal containing 0.006 % of boron is characterized by an increased volume concentration to 0.029 % of oxide (OS) and oxysulfide (OSB) inclusions, whose content in metal without boron reaches 0.006 %. Separate sulphide inclusions (CB), whose concentration does not exceed 0.004 % against 0.029 % in a metal without boron, containing 0.01 % S is practically absent in the metal with boron containing 0.003 % S. The microalloying of pipe steel by boron has ensured the preferential formation of small nonmetallic inclusions, evenly distributed in the volume of metal. The proportion of nonmetallic inclusions with size less than 2 (rm is 76.1 %, whereas in steel without boron it is only 58.5 %. In this case, large nonmetallic inclusions of more than 10 rm are practically absent in the sample with boron. Their share does not exceed 0.6 %, which is 22 times less than their amount in the sample without boron. The structure of the sample without boron consists mainly of ferrite and a small amount of perlite, and the sample with boron is represented by a dispersed ferritic-bainitic structure. Increasing the microhardness of both ferrite and pearlite 80 and 100 HV10, respectively, is observed by adding boron to steel. The mechanical properties of 10 mm hot rolled metal from boron-containing 17G1S-U pipe steel are characterized by increased strength properties with preservation of plastic characteristics, due to the formation of predominantly small nonmetallic inclusions and a finely dispersed ferritic-bainitic structure. The absolute values of the yield stress and the time resistance of pipe steel containing in mass %: 0.006 B and 0.003 S are achieved without heat treatment at 585 and 685 MPa, respectively, and meet the X80 strength class, while retaining sufficiently high plastic characteristics. The pipe steel without boron containing 0.01 % of S belongs to the X70 strength class and is characterized by tensile strength lowered to 540 and 610 MPa and a temporary resistance, respectively.

М/А-Constituent in Bainitic Low Carbon High Strength Steel Structure. Part 1

Results are provided for experimental studies of conditions for the formation of various types of M/A-constituent (structural component consisting of martensite and austenite) in the microstructure of low-carbon pipe steel specimens produced by rolling with thermomechanical treatment (controlled rolling and accelerated cooling). As a result of experiments different types of M/A constituent are obtained and the temperature-time conditions for their formation are determined. A research procedure is developed making it possible with maximum confidence to determine the type, size and volume fraction of M/A-constituent in the microstructure. Depending on cooling conditions and exposure temperature, two critical states of the M/A-constituent are identified: at high exposure temperature, predominantly twinned martensite is formed, and austenite is formed at a low temperature. At intermediate temperatures, various combinations of these phases are observed, while the fraction of martensite in the composition of M/A “islands” decreases with decreasing exposure temperature, but the fraction of austenite increases.

Comparative Study on Polyvinyl and Polyamide (Polymers) Resins as Corrosion Resistance Coating on Low Carbon Steel

Two commonly applied corrosion resistance coatings (Polyvinyl and Epoxy Polyamide resins) in Rivers and Bayelsa areas of Nigeria, have been compared on performance properties. The coatings were applied on low Carbon Steel samples that were cut to specific sizes. These prepared samples were subjected to varying conditions of pH, temperatures and exposure to definite time periods. The corrosion rates in ML per year (MPY) were then analyzed. The results of the corresponding corrosion rate in MPY obtained at PH 2,3,4,5, and 6, for epoxy polyamid resin, were 0.566, 0.553, 0.379, 0.354 and 0.322 respectively, and that for polyvinyl resin were 0.334, 0.326, 0.314, 0.288 and 0.277 respectively. The effect of temperature at 30° C, 4 ° C, 50° C, 60° C and 70°C were compared and corresponding corrosion rate in MP obtained for epoxy polyamide were 0.158, 0.288, 0.477, .655 and 0.810 respectively, while that for polyvinyl resin gave values of 0.122, 0.21 ,0.411, 0.552 and 0.651 respectively. The time exposure in hours of 692, 1008, 1344, 1680 and 2016 for the test steel samples applied with epoxy polyamide resin coating gave a corresponding corrosion values in MPY of 0.012, 0.016, 0.030, 0.043 and 0.055 respectively, and that for polyvinyl resin coating were 0.002, 0.009, 0.020, 0.034 and 0.044 respectively. The results obtained showed that polyvinyl resin coating have better performance properties over epoxy polyamide resin. Therefore polyvinyl resin coating can be recommended as a good corrosion resistance coating on low carbon steel pipes used in crude oil exploration in Petroleum industries

Study of Low-Carbon Pipe Steel Strain Ageing

Strain aging of pipe steels 06G2FB and 07G2MFB with ferrite-pearlite and ferrite-bainite structures is investigated. It is established that a ferrite-bainite structure is more inclined towards strain aging than a ferrite-pearlite structure. The tendency towards strain aging of steel with a ferrite-bainite structure increases with increasing austenitizing temperature. During hot plastic deformation there is development of recrystallization and the tendency towards strain aging decreases.

Modification of the Structure of Low-Carbon Pipe Steel by Helical Rolling, and the Increase in Its Strength and Cold Resistance

The paper reports the investigation results on the microstructure and mechanical properties of low-carbon pipe steel after helical rolling. The processing of the steel leads to the refinement of ferritic grains from 12 (for the coarse-grained state) to 5 μm, to the strengthening of ferrite by carbide particles, a decrease in the total fraction of perlite grains, a more uniform alternation of ferrite and perlite, and the formation of regions with bainitic structure. The mechanical properties of the steel have been determined in the conditions of static and dynamic loading in the range of test temperatures from +20 to–70°С. As a result of processing, the ultimate tensile strength increases (from 650 to 770 MPa at a rolling temperature from 920°С) and the viscoplastic properties at negative temperatures are improved significantly. The ductile–brittle transition temperature of the rolled steel decreases from–32 to–55°С and the impact toughness at the test temperature–40°С increases eight times compared to the initial state of the steel.

Material expenditures in deep desulfurization of steel in the ladle–furnace unit

The desulfurization of steel in a 160-t casting ladle is investigated. On that basis, a technology for reducing the sulfur content of low-carbon and low-alloy pipe steel to 0.001–0.003% is developed. The material expenditures in deep desulfurization of steel in a 160-t ladle–furnace unit are assessed.

High temperature EMAT design for scanning or fixed point operation on magnetite coated steel

Bulk thickness measurements were performed at elevated temperatures on magnetite coated low carbon steel pipe and aluminium samples, using a permanent magnet electromagnetic acoustic transducer (EMAT). The design presented here exploits the non-contact nature of EMATs to allow continuous operation at elevated temperatures without physical coupling, sample preparation (in the form of oxide scale removal), or active cooling of the EMAT. A non-linear change in signal amplitude was recorded as the magnetite coated sample was heated in a furnace, whereas a steady decrease in amplitude was observed in aluminium. For a magnetite coated pipe sample, after a dwell time of 3h, a SNR of 33.4dB was measured at 450°C, whilst a SNR of 33.0dB was found at 25°C. No significant EMAT performance loss was observed after one month of continuous exposure to 450°C. EMAT-sample lift-off performance was investigated at elevated temperature on magnetite coated steel; a single-shot SNR of 31dB for 3.0mm lift-off was recorded at 450°C, highlighting the suitability of this design for scanning or continuous fixed point inspection at high temperature.

Influence of welding position and parameters in orbital tig welding applied to low-carbon steel pipes

The most notable characteristic of Orbital TIG welding is the constant geometric profile of the tubes. In the context of orbital TIG welding of tubes with a large diameter and thick walls, the relationship between the welding position, the use of constant or pulsed current and also the value of the average current on the geometric characteristics of the beads obtained was studied. We deposited welds on SAE 1020 carbon steel tubes, as well as taking macrographs of the cross-sections of the beads using optical microscopy. High-definition films were used to understand the behaviour of the weld pool in different welding positions. The geometric characteristics were quantified using macrographs and software, and the relationship between these characteristics and the above-mentioned variables were traced. In addition, an analysis of the microstructure of the samples was carried out, correlating with Vickers microhardness. It was concluded that the beads welded with pulsed current were more reinforced and wider, as well as being harder and having a finer microstructure. The vertical up position resulted in beads with a lower shape factor and more penetration, and the overhead position resulted in beads with a low shape factor.

Residual Stress, Microstructure and Hardness of Thin-Walled Low-Carbon Steel Pipes Welded Manually

The aim of this work is to evaluate the welding residual stress profile in ASTM A106 Gr. B steel pipes with 4 diameter and to correlate this profile with the microstructure and hardness of the joint. The results showed that the residual stresses are more uniform for a lower welding heat input. Higher welding heat input causes not only a non-uniformity of the stress profile but also promotes the maximum stress as high as the yield strength. The microstructure was composed of ferrite, perlite and possibly bainite; the presence of martensite was not verified. The hardness results indicated that none of the welding parameters used produced levels of hardness greater than 249 HV. Such a result is of fundamental importance because it suggests that low hardness does not necessarily mean low residual stress levels.

Influência da Vazão e Geometria da Região de Entrada Sobre a Eficiência Térmica Medida por um Calorímetro de Fluxo Contínuo de Água

Resumo: O principal objetivo do presente trabalho é analisar a influência da vazão de água e da geometria na entrada de um calorímetro de fluxo contínuo sobre a eficiência térmica do arco. O procedimento experimental consiste em testar diferentes vazões de água e três configurações geométricas na região de entrada de água no calorímetro: com rolha reta, com difusor cônico e com obstáculo. Os experimentos foram planejados e os resultados avaliados com base na análise de variância estatística de um único fator, no caso, a vazão de água na entrada do calorímetro. Os cordões de solda foram depositados através do processo Gas Metal Arc Welding – GMAW, sobre tubos de aço baixo carbono, usando os mesmos parâmetros e tempo de soldagem. A maior eficiência térmica média de 80,5% foi obtida para a vazão de 4 l/min, com baixo erro estatístico, utilizando rolha de entrada com geometria de difusor cônico, sendo que para vazões menores ou maiores ocorreu diminuição nos valores da eficiência medida. O modelo em que o fluxo entra diretamente no tubo apresentou todos os valores de eficiência térmica do arco com pequeno decréscimo numérico se comparados com o difusor cônico, enquanto a rolha com obstáculo apresentou elevado erro estatístico.

Development of the zinc coating pipe connection technology with arc soldering method using

The application of the arc brazing method for zinc-coated pipes joining with using the copper-based additives is suggested in this publication. This method is an alternative of the arc welding with minimal destruction of coating at the adjacent to the weld area, and it application has been analyzed and substantiated. The microstructure and microhardness research of the zinc-coated low-carbon steel pipes with the diameter of 150 mm and wall thickness of 3.2 mm was made and research results are presented. The research results have shown that joint formation takes place due to a diffusive layer at the alloy line, and the connection strength depends on its sizes. It is revealed that magnification of the intermetallic phases volume concentration in the weld metal increases its strength. It is found that the strength of the arc-welded pipe joints is affected by bevel edges. The connection with bevel edges has a greater strength with straight edges, as well as the contact area is increased with the base metal weld. The arc brazing method can be recommended for zinc-coated pipes joining with using the CuAl8 wire and the bevel edge has to be made before arc brazing via research results. This method will provide the sufficient joints strength without the considerable zinc cover damage.