Development and application of a complex polymer coating to ensure high corrosion resistance of the outer surface of steel pipes of urban heating networks

Study on mechanism of improving wear and corrosion properties of 20CrMnTi ring gear surface by laser carburizing

The study of the corrosion resistance of NiTi alloy surfaces with different wettabilities is important to achieve improvements in biocompatibility. In this study, a femtosecond laser was used to process different wettability surfaces on the NiTi alloy. The corrosion resistance of the surfaces was examined via potentiodynamic polarization and electrochemical impedance spectroscopy. Scanning electron microscopy and X‐ray photoelectron spectroscopy were used to analyze the morphology and chemical composition of the surfaces. The findings demonstrate that when an original oxide film is destroyed by femtosecond laser processing with a low laser fluence, hydrophilic or hydrophobic surfaces are more vulnerable to erosion. The corrosion resistance of superhydrophilic surfaces is improved to a certain extent, whereas superhydrophobic surfaces exhibit excellent corrosion resistance. Superhydrophilic surfaces are protected from further corrosion by the formation of a dense oxide film after corrosion, whereas superhydrophobic surfaces can inhibit corrosion because of their thicker oxide film and additional air film produced by air trapped in the micro/nanostructure.

Similar to the “lotus leaf effect”, super-hydrophobic surfaces have excellent self-cleaning characteristics and corrosion resistance. However, in the process of droplet condensation on a rough surface, the droplets on the surface can transform from the Wenzel-Cassie state to the Wenzel state, leading to failure of the superhydrophobic effect and greatly reduced corrosion resistance of the alloy surface. Aizenberg et al. first proposed the concept of a slippery liquid-infused porous surface (SLIPS), where lubricating oil is poured into the porous surface for preparation of super-slippery surfaces; a dynamic oil film forms on the surface, solving the problem of super-hydrophobic failure. Since then, research has been focused on mimicking nature and trying to fabricate such surfaces artificially. In this paper, double-layer zinc oxide was synthesized on an aluminum substrate by a sol-gel and hydrothermal method. The aluminum sheet coated with zinc oxide was infiltrated into the Dupon Krytox GPL104 lubricating oil for 2h to obtain an aluminum-based double-layer super-slippery surface. The surface has all the properties of a SLIPS, repelling all simple and complex liquids (including water, milk, coffee, juice, ink, and others); it also exhibits good anti-corrosion and antifouling properties. The corrosion resistance of the surface was tested by electrochemical impedance spectroscopy (EIS) in 3.5 wt% NaCl aqueous solution (simulated seawater test); the result was four orders of magnitude higher than that of an untreated aluminum sheet. It shows good corrosion resistance, and the corrosion resistance did not change significantly after three months. This provides potential application prospects for aluminum alloy corrosion protection.

Corrosion resistance of water repellent aluminum surfaces with various wetting morphologies

Purpose: of this paper was to examine the corrosion resistance of laser surface alloyed (LSA) stainless steels using electrochemical methods in 1M NaCl solution and 1M H2SO4 solution. The LSA conditions and alloying powder placement strategies on the material's corrosion resistance were evaluated. Design/methodology/approach: In the present work the sintered stainless steels of different microstructures (austenitic, ferritic and duplex) where laser surface alloyed (LSA) with elemental alloying powders (Cr, FeCr, Ni, FeNi) and hard powders (SiC, Si3N4) to obtain a complex steel microstructure of improved properties. Findings: The corrosion resistance of LSA stainless steels is related to process parameters, powder placing strategy, that determines dilution rate of alloying powders and resulting steel microstructure. The duplex stainless steel microstructure formed on the surface layer of austenitic stainless steel during LSA with Cr and FeCr reveal high corrosion resistance in 1M NaCl solution. The beneficial effect on corrosion resistance was also revealed for LSA with Si3N4 for studied steels in both NaCl and H2SO4 solutions. Ferritic stainless steel alloyed with Ni, FeNi result in a complex microstructure, composed of austenite, ferrite, martensite depending on the powder dilution rate, also can improve the corrosion resistance of the LSA layer. Research limitations/implications: The LSA process can be applied for single phase stainless steels as an easy method to improve surface properties, elimination of porosity and densification and corrosion resistance enhancement regarding as sintered material. Practical implications: The LSA of single phase austenitic stainless steel in order to form a duplex microstructure on the surface layers result in reasonably improved corrosion performance. Originality/value: The original LSA process of stainless steels (austenitic, ferritic and duplex) was studied regarding corrosion resistance of the alloyed layer in chloride and sulphate solutions.

IntroductionStainless steels are widely used as medical devices. Martensitic stainless steels can be hardened by quenching. Therefore, in the medical field, martensitic stainless steels are mainly used for knives and surgical instruments with cutting edges. However, carbon, a necessary additive for the hardenability of martensitic stainless steels, reduces their corrosion resistance. Therefore, it is theoretically difficult to achieve both high hardness and high corrosion resistance in stainless steels. To ensure the safety and longevity of devices made of martensitic stainless steels, improved corrosion resistance is required. In this study, an improved corrosion resistance of martensitic stainless steels was tried by laser thermal processing. Rapid heating and rapid cooling process by laser irradiation is expected to suppress the formation of corrosion-inducing (MnS) inclusions. The effects of the laser thermal processing on the corrosion resistance, microstructure, and hardness of the specimen surface and substrate layers were investigated.Materials and methodsThe specimens were commercially available type 420J2 stainless steel plates. Each plate was irradiated with a laser of 10 mm diameter at a rate of 100 cm min-1. The irradiation powers were 950 W, 1100 W, 1650 W, 2000 W, 2500 W, 3000 W, 3500 W, and 4000 W. The surface and cross-sectional metallography and inclusions of the laser-irradiated specimens were observed and analyzed using OM, SEM/EDS, and EBSD. Corrosion resistance was also evaluated by anodic polarization tests. A mixed aqueous solution of 0.1 M Na2SO4 and 0.585 M NaCl at 297 ± 3 K was used as the test solution. A Pt plate and a Ag/AgCl (saturated KCl aqueous solution) electrode were used as the counter and reference electrodes, respectively. The potential sweep rate was 20 mV min-1.Results and discussionThe specimens surface after the laser thermal process were observed. The surfaces of the specimens processed at 950 W or 1100 W were smooth, while those processed at 1650 W or higher had a wavy shape. The specimens with exposed cross sections were chemically etched. A light-colored area on the surface layer, and a dark-colored area around and inside the surface layer were formed. The light-colored area is the layer whose microstructure has been changed by laser irradiation. In addition, the light-colored area of the specimens processed at 1650W or higher were divided into two parts. Defined as phase A (upper part of light-colored area), phase B (lower part of light- colored area), and phase C (dark-colored area), in order from the surface. The main phase of the unprocessed specimen is ferrite with a small amount of residual austenite. EBSD and XRD results indicated that the main phase of phase A is martensite with some austenite phase. Additionally, Vickers hardness of phase A significantly increased compared to the unprocessed specimen. This result confirms that phase A is a martensitic phase, indicating that rapid heating and rapid cooling by laser irradiation caused the martensitic phase to form. Corrosion resistance of phase A layer was better than unprocessed specimen. The pitting potential of the phase A layer increased with irradiation power, with the highest value at 3500 W. Some cracks appeared on the surface of the specimen processed at 4000W. These cracks are the reason for the lower corrosion resistance. Inclusions consisting of spherical Si oxides smaller than 1 µm were observed in the microstructure of the phase A layer; no MnS inclusions were observed. The presence of fine spherical Si inclusions and the wavy surface suggest that phase A was formed by melting and then rapidly solidifying due to laser irradiation. MnS was solidly soluble in the matrix phase by melting, and its formation was inhibited by rapid solidification. As a result, MnS inclusions in phase A were reduced and the corrosion resistance of phase A was improved. On the other hand, phase C showed similar hardness and corrosion resistance to the unprocessed specimen, and there was no difference in corrosion resistance depending on irradiation power. Thus, although phase C was heated by the laser, no melting or microstructural transformation occurred. In other words, laser thermal processing does not degrade the properties of the inner layer. The corrosion resistance, hardness, and microstructure of phase B were intermediate between those of phases A and C.Conclusion420J2 stainless steel was subjected to laser thermal process at various power to evaluate microstructure and corrosion resistance. Laser thermal process suppressed the formation of corrosion-induced inclusions in the surface layer, and the surface layer transformed to martensitic structure. Laser thermal processing succeeded in modifying the surface to have both high corrosion resistance and hardness. Figure 1

Recently, the EDM finishing technique has progressed and very small surface roughness can be obtained by controlling machining conditions and/or using a metal-powder-mixed fluid. Also, hard layers such as TiC and WC can be formed on the surface. Therefore, instead of conventional surface finishing by hand in the die fabrication process, an application of EDM to the finishing process of the metal mold is expected in the near future. In this case, the lifetime of the metal mold depends on the surface characteristics of the EDMed surface. Therefore, the corrosion resistance of the EDMed surface is quantitatively evaluated by measuring the anodic polarization current in order to clarify the relationship with the EDM conditions. Also, the corrosion mechanism of the EDMed surface is discussed on the basis of experimental results. As a result, the corrosion resistance of the EDMed surface is higher than that of the ground one, because a white layer with fine structure and high resistance to corrosion covers the EDMed surface. The corrosion resistance of the EDMed surface does not depend on its surface roughness. When a silicon-power-mixed fluid is used as a dielectric in EDM, the corrosion resistance increases with the thickness of the white layer, since an EDMed surface without microcracks can be generated.

Purpose The purpose of this paper is to evaluate the effect of micro-nano mixed super-hydrophobic structure on corrosion resistance and mechanism of magnesium alloys. Design/methodology/approach A super-hydrophobic surface was fabricated on AZ91 and WE43 magnesium alloys by laser etching and micro-arc oxidation (MAO) with SiO2 nanoparticles coating and low surface energy material modification. The corrosion resistance properties of the prepared super-hydrophobic surfaces were studied based on polarization curves and immersion tests. Findings Compared with bare substrates, the corrosion resistance of super-hydrophobic surfaces was improved significantly. The corrosion resistance of super-hydrophobic surface is related to micro-nano composite structure, static contact angle and pretreatment method. The more uniform the microstructure and the larger the static contact angle, the better the corrosion resistance of the super-hydrophobic surface. The corrosion resistance of super-hydrophobic by MAO is better than that of laser machining. Corrosion of super-hydrophobic surface can be divided into air valley action, physical shielding, pretreatment layer action and substrate corrosion. Originality/value The super-hydrophobic coatings can reduce the contact of matrix with water so that a super-hydrophobic coating would be an effective way for magnesium alloy anti-corrosion. Therefore, the corrosion resistance properties and mechanism of the prepared super-hydrophobic magnesium alloys were investigated in detail.

The feasibility of Heavy Wall (HW) Seamless Line pipe application for high pressure/high temperature deep and ultra-deep field developments must be experimentally demonstrated to establish acceptable performance. Detailed mechanical, corrosion and fatigue qualification programs are required for validation of heavy wall line pipe and the associated girth welds for riser and flowline systems, especially those in fatigue-critical applications. Pipe manufacturers and Operators share a common interest in developing new technologies to economically and safely produce from challenging reservoirs. In OMAE 2013, Tenaris and ExxonMobil jointly presented the Phase 1 qualification effort performed on HW line pipe and associated girth weld via mechanical and full scale fatigue testing. The results confirmed the mechanical properties were acceptable and the fatigue performance of the associated girth welds was reasonable. As expected, most of the fatigue failures originated at the outer pipe surface. As such, the focus of the present work is to further examine the fatigue performance considering fatigue failure initiation at inner pipe surface. This would provide a better assessment of riser and flowline fatigue performance for applications where the inner pipe surface is subjected to degradation from potential aggressive components in produced fluids. To investigate the root girth weld fatigue performance, the adopted plan was to create an outer surface free of stress raisers/imperfections at weld cap toe which would help “push” the fatigue initiation to the root weld toe at the inner pipe surface. To achieve this, an enhanced grinding and flapping technique on the fatigue test specimen external surface was applied to remove the cap overfill and produce the desired flush profile. The same surface treatment technique was also applied on the pipe body in the proximity of the girth welds. This program utilized identical pipe and girth weld used for the Phase 1 qualification effort. The heavy wall pipe was an X65, 10 ¾″ OD × 46 mm WT. The welding procedure was a narrow-groove bevel, STT® process for the root pass and the GMAW process for hot, fill, and cap passes. Four full scale fatigue tests were conducted for this investigation, two girth welds per fatigue specimen. In the end, the enhanced surface treatment technique was successful in “pushing” the fatigue failure initiation to the inner pipe surface. This paper presents the fatigue performance results due to crack initiation at the inner pipe surface as well as post-mortem analyses of the failure surfaces.

This paper presents a novel and contactless water fraction (also known as water cut) measurement technique, which is independent of geometric distribution of oil and water inside the pipe. The sensor is based upon a modified dual helical stub resonators implemented directly on the pipe's outer surface and whose resonance frequency decreases by increasing the water content in oil. The E-fields have been made to rotate and distribute well inside the pipe, despite having narrow and curved ground plane. It makes the sensor's reading dependent only on the water fraction and not on the mixture distribution inside the pipe. That is why, the presented design does not require any flow conditioner to homogenize the oil/water mixture unlike many commercial WC sensors. The presented sensor has been realized by using extremely low cost methods of screen-printing and reusable 3D printed mask. Complete characterization of the proposed WC sensor, both in horizontal and vertical orientations, has been carried out in an industrial flow loop. Excellent repeatability of the sensor's response has been observed under different flow conditions. The measured performance results of the sensor show full range accuracy of ±2–3% while tested under random orientations and wide range of flow rates.

Measurement and simulation of residual stress in type 304 weld overlay stainless steel pipe

We investigate the possibility of using induction currents for improving the reliability of thermal power plants by increasing the corrosion resistance of internal surfaces of power-generating equipment, such as heating surfaces of boiler units. Corrosion resistance can be enhanced by improving the strength of an oxide film formed during passivation (oxidation). In this work, the oxide film strength was increased by electrochemical passivation of metal surfaces with induction currents. Using the method of multidimensional mathematical modeling of multi-parametric and multi-functional processes, we established that, for a continuous-loop economizer of a steam boiler comprising steel pipes with an inner diameter of 32 mm (24 coils operated simultaneously), an aqueous oxidant (oxygen) solution should be passed through the entire system of pipes for 4 h at an alternating current of 25 A. Under this treatment, oxygen should be added into the aqueous solution at a temperature of 130–450°C, an oxygen concentration of 1 g/kg, and a water flow rate of 0.5–5.0 m/s. Treatment intervals should be determined depending on the operating conditions of the equipment: reset, shutdown, or preservation. The efficiency of the method depends on the electric current passed over metal surface, treatment duration, oxidant concentration, as well as the type and size of the treated metal surface. The proposed passivation method can be used in both drum boilers and single-pass boilers. For example, it is recommended that passivation of water walls be carried out during boiler warm-up operation at 30–40% of boiler load, as well as passivation of superheat surfaces of boiler units and economizers. Therefore, the use of electrochemical passivation can increase the corrosion resistance of metal surfaces of power-generating equipment at thermal power plants.

The direct-current potential difference method (DC-PDM) is known as one of the promising non-destructive methods to evaluate the crack in the conductors. This method utilizes the change in the current path or the potential difference which is caused by the crack. In the previous study, a method of three-dimensional evaluation of semi-elliptical crack on the back surface of plate was proposed and its theoretical validity and practical utility were shown based on the results of numerical analyses and experiments. In this study, the method is extended to the identification of semi-elliptical crack on the inner surface of pipe and the related electric field analyses are carried out by the finite element method. The results show that the crack on the inner surface of pipe can be evaluated by the proposed method based on the distribution of potential difference measured on the outer surface of pipe. The present extension will be very useful for various practical cases which are often seen in the piping of power-generating and petrochemical plants.

Corrosion resistance of steel-based surface alloyed materials fabricated with Fe-based metamorphic powders by high-energy electron beam irradiation

This paper describes a novel method of inspecting the wall-thinning by means of the strain measurement on the outer surface of pipes. The strain on this surface increases under the same pressure when the wall thickness gets thinned due to the erosion or corrosion of the inner surface of pipes. This relationship between the strain and thinning is expressed in some simple equations in the case where the thinning occurs equally on the whole inner surface of pipes. From these equations, it is found that strain measurements on the outer surface enable the wall-thinning to be detected and quantified, and through FEM analyses, it is clarified that these simple equations can also be used in tapered pipes. In addition, through the experiment using the optical fiber strain sensor, it is confirmed that this sensor can be applied to the strain measurement at an elevated temperature.