Whenever large amounts of liquids or gases have to be transported over long distances, steel pipelines are used. They supply industry with raw materials, guarantee drinking water supplies to large cities, and convey energy sources around the globe. Despite the most stringent safety regulations, pipelines regularly suffer damage and leaks. Severe environmental pollution occurs when oil or gas pipelines, in particular, are damaged. In the case of both onshore and offshore pipelines, decontaminating the affected areas involves a great deal of time, effort, and cost. Moreover, in most cases the contamination cannot be eliminated completely. There are various reasons for damaged pipelines. Corrosion poses one of the greatest challenges here, and this can be influenced by the pipeline owners. There is a need for safe and reliable corrosion protection, and this is set to grow over the coming years. Based on current market data, between 13 and 18 million tons of line pipe were delivered in the years 2015 to 2020. This corresponds to a pipeline length of approx. 86,000 km per year. The objective of this paper is to illustrate why the corrosion protection currently used fails to work in some cases. It also aims to show how thermal coating can improve corrosion protection and what requirements its technical implementation must fulfil. To this end, line pipe is presented in the next chapter. Common standards and manufacturing processes are introduced. The third chapter outlines current corrosion protection measures. Moreover, weak points are analyzed by looking at damage that has already occurred. The requirements for thermal coating are determined based on this.

Surface treatments and coatings are widely used to protect components from wear and corrosion. Of all available methods, thermal spraying is arguably the most versatile with regard to coating material and morphology. Surface roughness and porosity can be adjusted in a wide range depending on the requirements. However, as-sprayed coating surfaces inevitably exhibit a certain roughness necessitating post-treatment if a smooth surface is required. The surface roughness of thermal spray coatings is usually determined by the used powder fraction and the particles’ melting degree. Using wires as feedstock material allows for a certain influence on the particle size distribution by adjusting process parameters. In this study, the influence of nozzle geometry and atomizing gas pressure on coating quality, surface roughness and cost-efficient post-treatments of wire-arc sprayed Fe-based alloys with a wide hardness-range is investigated. To allow for easy transfer to real components, the sample geometry is based on real world examples of coatings for new components and repair of worn parts. Using adapted process parameters and air-flow, the surface roughness could be decreased to allow for a less time-consuming post-treatment by grinding. Especially in repair coatings for large area applications requiring a smooth surface finish, significant runtime and cost reductions are feasible.

In addition to the proper functional properties, the adhesive strength represents one of the key criteria for industrial use of thermally sprayed coatings. Since conventional thermal spraying processes are almost carried out exclusively in air atmosphere, this leads to the oxidation of the particles and of interfaces within the coatings. As a result, conventional thermally sprayed metallic and metal-ceramic coatings are characterized by heterogeneous microstructures with interlamellar oxide fringes at the interfaces between individual splats and also between the coating and the substrate. This has a decisive influence on the bond strength and on the wear and corrosion protection properties of thermally sprayed coatings. The aim of this study is to present the potentials of thermal spraying processes carried out in a mixture of monosiliane and an inert gas at ambient pressure as an alternative to the known vacuum spraying process in order to prevent oxidation during the coating process. Using the example of arcsprayed coatings, it is demonstrated that the extremely low oxygen partial pressure in the silane-doped medium leads to coatings free of oxide seams with a reduced porosity and substantially enhanced properties.

Despite their light weight, 2.3 times lighter than Al, polymers are limited to application with low thermal, wear, and abrasion demands. The enhancement of the functional surfaces of the polymers using thermal spraying techniques is a challenging task due to the thermal degradation of polymers, the low wettability, and the disparate atomic properties. The twin-wire arc spraying (TWAS) process comprises two contradictory features. Almost all spraying particles are in a molten state on the one hand, and on the other hand, the spray plume has the lowest heat output among the different thermal spraying techniques. Therefore, it is a promising spraying technique for the required surface improvement. The surface of the 3D-printed parts was metalized using two successive layers. The first layer is a TWAS coating made of low-melting ZnAl 4 to avoid thermal degradation and provide a bond coat. The topcoat is also applied using a TWAS process and was made out of Ni-WC-Co as cored wires. The top hard coating has improved the wear resistance of the polymers by 14.6 times. The erosion of the coated and uncoated specimens was determined using a low-pressure cold gas spray gun. Ni-WC-Co coating led to more than five times higher erosion resistance.

In the current work, a typical NiCrAlY alloy and, moreover, amorphous Fe-based alloys are arc-sprayed for the desired application in cryogenic environments. Nitrogen is used as process gas, while the stand-off distance and number of passes were varied. The results demonstrate coatings with low, but varying porosity and oxide content and mostly high electrical conductivity. Especially the amorphous Fe-based coatings reveal homogeneous coating structures and promising properties. Further investigations regarded the deposition efficiency, tensile adhesive strength, hardness, durability under cryogenic conditions and the thermal diffusivity.

The production of light metal matrix composites (MMCs) using coated fiber prepregs processed by thixoforging offers several advantages over well-established technologies like squeeze casting and diffusion bonding. In order to obtain the required globular microstructure prior to thixoforging, reinforcement fibers are coated with the matrix material by twin wire arc spraying. Damage to the sensitive fibers is avoided by reducing the thermal load via optimized cooling. This study analyzes the influence of spraying parameters on the microstructure and mechanical properties of MMCs. An innovative method for automated the coating of reinforcement fibers is presented.

Twin wire arc sprayed aluminum coatings are used extensively in semiconductor processing equipment. In certain applications, such as metal reclamation, rough coating textures are desirable as the added surface area facilitates the collection of metals and lowers manufacturing costs. There are many factors that affect the surface roughness of twin wire arc sprayed coatings. This study investigates coating conditions that produce rough textures and the influence of surface roughness on bond strength. Traditional theory of arc spraying has been that to obtain a rough coating, particle velocity should be reduced by decreasing the atomizing air pressure of the system. Decreasing air pressure, however, may have a negative impact on bond strength, the extent of which is assessed in this study.

The aim of this investigation is to show that it is possible to inject powder into a wire arc spray process as an alternative to using cored wire to produce particle-reinforced coatings. The equipment, materials, and procedures used are described in the paper along with the microstructure and properties of the coatings obtained. By changing the feedrate of CrC particles injected into a stream of chromium steel droplets, particle-reinforced graded layers were produced by wire arc spraying on the fly without having to stop the process.

The intent of this study is to gain a better understanding of the twin wire arc spray process, particularly the correlation between spray path or gun movement and coating quality. Coatings were deposited on steel substrates using solid nickel and cored WC-Cr wire while moving the gun in various directions relative to the orientation of the electrodes. The coatings obtained are evaluated based on porosity, hardness, thickness, adhesion strength, and microstructure. It is observed that gun movements cause inhomogeneities in the spray cone that affect different coating properties in different ways depending on the direction of the movement and gas pressure.

The replacement of cast iron sleeves through thermal spray coatings is an interesting alternative to improve the inter bore reliability, to reduce weight and to reduce the inter bore distance for automotive engines. Most of the actual production and pilot equipments use the ROTAPLASMA process to provide such functional coatings. However, the wire-arc spray process may often present different advantages like a higher deposition rate and a lower cost of the produced coatings. The LDS (Lichtbogendrahtspritzen) technology developed by DaimlerChrysler is a wire-arc process working with two wires whereas the PTWA (Plasma Transferred Wire Arc) process designed by Flame Spray Industries and the Ford Motor Company use a single wire. The present paper shows that the wire-arc technology may replace efficiently the APS (Atmospheric Plasma Spray) for the generation of thermally sprayed coatings applied on engine cylinder bores. A first rotating wire-arc spray system was previously designed and tested a few years ago. The present paper shows how computational fluid dynamic (CFD) may help in solving industrial problems: the FLUENT CFD code was used in order to perform improvements of the initial gun design.

The precondition of a cost efficient wire arc spraying process is an ideal process setup according to the wire material. Modern power supplies are equipped with electronic control circuits to ensure stable arc conditions at the wire tips. This is necessary for high quality wire arc sprayed coatings. The key factors to achieve this are the arc energy and fluid mechanics as well. By the use of a PID controller to maintain set spray parameters, it is possible to reduce the spray voltage down to 15 V for zinc as feedstock material. Furthermore temperature dependent parameter fluctuations can be compensated with the electronic controller, while working at maximum capacity with one hundred percent duty cycle. The paper discusses the influence of a new power supply with regard to the process stability and the enhancement of former power supply based process limitation as well as the operator guidance.

A method for the production of particle reinforced coatings by wire arc spraying will be presented in this paper. This technology is based on twin-wire electric arc spraying (TWEA) process. Here, additional particles were injected into the atomizing gas stream and sprayed in a non molten state along with wire feedstock material onto the substrate. According to the reinforcing particles, the process can be applied to produce coatings with a high wear resistance as well as a high surface roughness. In a wide range of applications, these coating characteristics are required. Due to economic constraints, coatings of large surfaces have to be done in short times at low costs. Based on wire arc spraying, the thermal spray process with the highest deposition performance, the mentioned industry requirements can be fulfilled.

The effect of nano and microstructured powders in cored wires on formation and properties of Fe-TiB 2 composite coatings by high velocity arc spraying (HVAS) was investigated. Six cored wires filled with different average ceramic particle sizes (20-40 nm, 2 µm, and 420 µm) and fine powder contents (0, 8, 16, 20, 24, 32wt.%) were sprayed. The flattening behavior of sprayed particles was characterized and compared by using optical microscopy (OM) and 3D Surface Profiler. The microstructure of the coatings and phase compositions were characterized by means of Laser Confocal Scan Microscopy, SEM, EDAX and XRD. Hardness and wear properties were evaluated. The results showed that the splat shape of the cermets has a transitional tendency to change from a distorted heavy splash to a disk with little splash with (i) increasing the percentage of fine ceramic particles and (ii) decreasing coatings porosity. Fe –2 µm 32% TiB 2 coatings reveals a dispersion of fine ceramic particles and less scattering of hardness, which improved the wear resistance and changed the abrasion mode.