Korrosionsbeständigkeit von Verbindungen von Rohren aus nichtrostenden Stählen in Wässern

Corrosion of joints for stainless steel tubes in water The most important commonly used joining techniques for stainless steel tubes which are used for the transport of water and gases are welding and brazing. With corrosion attack by dry gases, both connections are resistant against corrosion. However, in water and aqueous condensates limits of application exist with regard to the corrosion resistance. The corrosion resistance of weld connections with stainless steel tubes is diminished by

• – annealing colours (oxide films) and scale layers in the weld area;
• – changes in the microstructure adjacent to the welds (sensitization of the stainless steel material);
• – surface finish of weld seams after welding;
• – welding faults resulting from bad handling and workmanship.

Type and extent of corrosion damage occurring on weld connections with decreased corrosion resistance depend on the composition of the water and condensates, mainly on their chloride content. Typical examples for the causes of degraded corrosion resistance of weld connections, and possible types of corrosion attack, namely pitting, crevice corrosion, and stress corrosion cracking and their mechanisms are described. Furthermore, measures are shown by which the corrosion resistance of weld connections with stainless steel tubes can be increased. Joints of stainless steel tubes by hard soldering with capillary fittings are endangered by knife line attack at the phase boundary between the stainless steel and solder (interfacial corrosion). Knife line attack means in this context the loss of adhesion between steel and hard solder. The severity of the corrosion risk, in particular the incubation time until the occurrence of the corrosion damage, depends on the water quality, mainly on chloride concentration, and pH. The press fitting with non-metallic gasket is a relatively new joining system, and it is used in the cold and warm water domestic installation. This joining technique is described. For domestic water distribution, an installation system with tubes and press fittings made of steel grade AISI 316 SS has been developed. This system is resistant to corrosion attack in potable water of usual composition, and it is already applied in-service in a considerable extent. Other joining systems are stainless steel weld fittings, threaded screw fittings, and compression couplings with cutting or clamping rings. They are used mainly in industrial installations.     

Zum Korrosionsverhalten nichtrostender austenitischer Chrom-Nickel-(Molybdän,Kupfer)-Stähle in nahezu wasserfreier Essigsäure

Corrosion of stainless austenitic steels in almost anhydrous acetic acid As-welded samples and looped specimens from 5 differently alloyed stainless steels were tested for up to 246 days in 99,5% to 99,95% acetic acid at 118°C (boiling temperature/normal pressure) and at 150°C; the chloride content was varied between < 1 and 100 ppm. Pitting corrosion – of shallow depth, however (approx. 0,1 mm) – was already observed at surprisingly low chloride concentrations. Only the following were found to be resistant to pitting corrosion:

• – stainless steels 1.4439 and 1.4539, containing approx. 4,5% molybdenum, in 99,5% acetic with < 1 ppm chloride at 118 and 150°C,
• – stainless steels 1.4439 and 1.4539 in 99,9% acetic acid with < 1 ppm chloride at 118°C, and
• – special stainless steel X 2 CrNiMoCuN 20 18 6, containing approx. 6% molybdenum, in 99,5% acetic acid with > 3, < 10 ppm chloride at 118 and 150°C.

Looped specimens and ground as-welded samples showed no sensitivity to transcrystalline, chloride-induced stress corrosion cracking at any of the concentration ranges. High surface-removal rates can be expected if air has access to the specimens; under this condition pitting corrosion and general corrosion may overlap. Contamination of acetic acid with chlorides must be prevented under all circumstances.     

Die Korrosionsbeständigkeit metallischer Werkstoffe für Automobilbremsleitungen

Corrosion resistance of metallic materials in automobile brake lines A statistical evaluation of the data compiled by the Swedish Automobile Inspection Authority and covering corrosion effects in brake fluid lines enables the following recommendation to be made:

• (a) Copper-brazed steel tubes, though very common, have no sufficient corrosion resistance; the same applies to welded or seamless drawn steel tubing.
• (b) The best suited materials are phosphorus deoxidized copper and stainless steels (about X 5 CrNiMo 18 12). The lower fatigue strength of copper must be compensated by suitable design; as compared to the stainless steel, copper is advantageous from the cost side.
• (c) Copper as well as stainless steel tubing can be corroded at fittings and fastening points; these problems must be eliminated by suitable design to be decided uon in each particular case.

     

Surface analysis in corrosion inhibition mechanisms

The importance of modern surface analytical techniques in understanding the mechanisms of corrosion inhibition is discussed. The discussion is conducted in terms of the following metals and inhibitors which inhibit them:

• copper and alloys – mercaptobenzothiazole, benzotriazole, and benzimidazole
• iron and nickel – acetyl acetone
• mild steel – 8-hydroxyquinoline and chromate
• tool steel – perfluoroalkyl ether containing perfluoroalkyl ether aryl phosphine
• mild steel – molybdate, tungstate, chromate, phosphate, nitrite, oxalate, arsenate, EDTA
• aluminium – silicate, molybdate, tungstate, phosphate and chromate.

     

Örtliche Korrosion von Komponenten aus Messing MS 58 in der Trinkwasser-Installation

Localized corrosion of yellow brass 58 in tap water installation Yellow brass material with 58 wt.-% Cu is subjected to dezincation and cracking in tap water. Both kinds of corrosion are enhanced by tensile stresses and by anodic polarisation resp. oxygen content of the water. Furthermore, the water type has an effect, where - according to this investigation – the chloride content is of interest. The presence of critical components for SCC (such as NH₃) are not necessary. In the case of mixed installation with tubing of inert material (such as stainless steel or plastics) the corrosion likelihood is increased in comparison to galvanised steel or copper because of oxygen consumption by corrosion of the latter materials. Bimetallic corrosion in mixed installation with stainless steel does not take place. Failures of components of domestic installations by corrosion should be prevented by using a material having a higher resistance to dezincation.     

Schwingungsrißkorrosion feuerverzinkter Schweißverbindungen im bauteilähnlichen Maßstab bei wechselnden Korrosionsbedingungen in chloridhaltigem Medium

Corrosion fatigue of hot-galvanized component-like welded joints in chloride medium at changing corrosion conditions The project was focussed on the investigation of the fatigue behaviour of welded specimens of hot-galvanized plate material of steel RSt 37-2, St 52-3 and St 70-2 as frequently used in steel constructions which were mended by thermal zinc-spraying in the fillet area and tested at changing corrosion conditions. In addition, the fatigue behaviour of welded specimens with additional PVC coating of both non-galvanized and galvanized types at changing corrosion reaction was also investigated. The established findings can be summarized as follows:

• – At constant amplitude loading, hot-galvanized precludes very markedly the drop in endurance which would occur under corrosion. By contrast, an increase of fatigue strength in the corrosive medium due to galvanizing is only conditionally discoverable at variable amplitude loading. In regard to the protection against corrosion, welding of hot-galvanized parts brings an improvement at variable amplitude loading only if a given thickness of the zinc coating depending on the material is not exceeded. Too thick coating results in the formation of pores at the subsequent welding and reduces the fatigue strength in spite of the later zinc-spraying.
• – The structural steels RSt 37-2 and St 52-3 in hot-galvanized state are better suitable for welding than the more notch- and corrosion-sensitive St 70-2.
• – Soldering brittleness could not be established as cause of the failure.
• – The application of PVC protective layers secures high rates of increase or the fatigue for the non-galvanized specimens.

     

Oberflächenbehandlungsverfahren und deren Einfluß auf die Korrosionsbeständigkeit nichtrostender Stähle

Surface treatments and their influence on the corrosion resistance of stainless steel The surface treatments pickling, grinding and glass beading were investigated on several stainless austenitic steels and one ferritic/austenitic steel. The different surface treatments were used on two different prepared types of samples:

• 1 high temperature oxidized samples
• 2 welded samples

The quality of the surface treatments has been examined by means of potentiodynamic, ferric chloride, dip and spray tests made in series. The corrosion resistance was highly depending on the used treatments. All in all the examination showed that a higher corrosion resistance was achieved by pickling than by grinding or glass beading.     

Applications and experience with a Superaustenitic 7Mo stainless steel in hostile environments

A new superaustenitic stainless steel is described in terms of chemical composition. mechanical properties and corrosion resistance. Results obtained by using this highly alloyed stainless steel, EN 1.4652, in a number of hostile environments are reported. Applications include neutral and acid chloride containing environments such as those existing in e.g. – pulp bleach plants, – ventilation systems of pharmaceutical plants, – equipment for flue gas cleaning in power plants and municipal waste incineration plants, – equipment for recovery of chlorinated hydrocarbons, – sea water piping, – nuclear power plant condenser tubes. The paper also contains laboratory corrosion test results positioning this steel in relation to other highly alloyed stainless steels and nickel base alloys, mainly in terms of its resistance to chloride induced localised corrosion.     

Erosionskorrosion - eine Folge lokaler Schädigungsvorgänge

Erosion corrosion - a consequence of local damage processes The aim of the present paper is to give an overview over results of investigations in erosion-corrosion. By means of four stages of erosive treatment of metal surfaces and the possibilities of interaction with a medium mechanisms of materials degradation are discussed including the behaviour of metals with reaction layers. The experimental devices used - rotating disc electrode, vibration cell, erosion-corrosion simulator - are described. The following topics are explained by experimental details:

相似文献   

Effect of carbon and silicon on the structure and corrosion resistance of 18cr-8ni cast steel in concentrated nitric acid solutions

The solutions of nitric acid can be divided into two concentration ranges: range I from 0 to 60–70% and range II from 80 to 100%. The 18Cr-8Ni cast steel with about 4% Si and up to 0.12% C exhibits very good corrosion resistance in concentrated nitric acid solutions (up to 98%); however, it is slightly inferior to a corresponding 18 Cr-13 Ni grade. The investigations were concentrated on the effect of the carbon and silicon contents on structure and corrosion resistance of an 18 Cr-8 Ni cast steel in cold nitric acid solutions. The following materials were used in these studies: a cast stainless steel of type 18Cr-8Ni with 0.48–6.75% Si and 0.021–0.220% C. A detailed analysis of the main result shows that

• 1. in cold HNO₃ solutions of concentrations above 80% the silicon content in a cast steel must not be lower than 2.5-3.0%;
• 2. the 18Cr-8Ni cast steel containing more than 4% Si and up to 0.12-0.13% carbon is practically not susceptible to corrosion in cold HNO₃ over the whole range of concentrations.

     

Counteraction of pitting in copper water pipes by bicarbonate dosing

Copper pipes are extensively used for tap water installations and generally perform well. Exceptionally, however, copper pipes are perforated due to pitting. Three main types of pitting (I, II and III) have been identified, but as for the causes and the mechanisms these have not yet been fully clarified. Through case studies, model experiments, thermodynamic calculations, and service tests, evidence has been obtained that waters having a pitting propensity for copper pipes can be made less corrosive by an increase of the HCO content. On water treatment the following water composition should be aimed at:

• – a pH value of at least 7
• – an HCO content of at least 70 mg/l, preferably 100 mg/l
• – as low SO content as possible, or at least lower than the HCO content (both in mg/l).

     

Joining steels with electrodeposited nickel or copper barrier layers using Cu–P brazes

Abstract

To prevent the formation of continuous brittle phosphides when steel is brazed with Cu–P–Sn alloy, barrier layers were deposited on the steel: nickel on stainless steel and copper for mild steel. Their effectiveness is demonstrated by the increase in the lap shear strength from <10 to 160 MPa for the mild steel joints and from 80 to 136 MPa for those with stainless steel. The microstructures of the brazements were investigated by optical and scanning electron microscopy (including microprobe analysis) to ascertain the reactions and mechanisms occurring at the intermediate layer interfaces – both with the basis metal and with the braze alloy. Interactions involving the barrier metal result in the formation of a solid solution with discrete particles of complex compositions in the interfacial region. These reactions are analysed and the resultant phases identified. Optimisation of brazing time and temperature and of the layer thickness resulted for both systems in (near) complete elimination of the phosphide particles in the joint zones adjacent to the parent metal. The suppression of the continuous brittle interfacial phosphide layer enhances the mechanical properties of the joints.     

Die Inhibition von Kühlkreisläufen

The inhibition of cooling systems The choice of an efficient corrosion inhibitor has to take in account the type of the cooling system, the materials used as well as the specific operating conditions, for instance

• – very low or very high velocities of the cooling water
• – heat transfer
• – the inhibitor may be asked to have some lubricating properties
• – vibrations, that can cause cavitation or fatigue corrosion
• – interaction between the corrosion inhibitor and other electrochemical systems of corrosion protection (cathodic protection).

In numerous applications it is necessary to improve the inhibition by an addition of other effective substances (like dispersants, hardness stabilizers, mixture of inhibitors with selective protection properties).     

Corrosion in solar heating systems. I. Copper behaviour in water/glycol solutions

A research programme has been developed in order to investigate the corrosion behaviour of metallic materials commonly used in solar heating systems. This paper presents the results of an experimental study on copper corrosion resistance in ethylene and propylene glycol/water solutions (1:1 by volume) constituting the most common bases of heat transfer fluids. Long time gravimetric tests were carried out on electrolytic copper at 80°C, even in glycol/water solutions previously degraded at their boiling temperature or polluted with 200 ppm chlorides. Chemical compositions, semiconducting properties and morphological characteristics of all surface products were investigated by X-ray diffraction analysis, pulse photopotential technique and SEM observations, respectively. Heat transfer effects on copper corrosion and copper/6351 aluminium alloy couple efficiency were evaluated by electrochemical tests. The following results were obtained:

• – Ethylene and propylene glycol/water solutions are low corrosive media. Nevertheless, chloride pollution and/or high temperature degradation of glycols markedly increase their aggressivity. Under all the experimental conditions, copper corrosion rates are higher in ethylene than propylene glycol solutions.
• – In chloride-free solutions, heat transfer stimulates the cathodic reaction of the copper corrosion process.
• – Galvanic contact between copper and aluminium alloy always causes pitting corrosion on aluminium electrodes. The severity of the pitting attack is enhanced by the presence of heat transfer conditions on copper and/or chloride ions in the solutions, particularly in ethylene glycol.

     

Determination of threshold stress intensity for chloride stress corrosion cracking of solution-annealed and sensitized austenitic stainless steel by circumferential notch tensile technique

This paper discusses a new approach to determination of threshold stress intensity factor for stress corrosion cracking (K_ISCC) of stainless steel in 42% MgCl₂ environment at 154 °C. K_ISCC of solution-annealed and sensitized AISI 304 stainless steel in chloride environment has been determined using circumferential notch tensile (CNT) technique. K_ISCC data generated using CNT technique have been compared with those generated using traditional techniques such as compact tension and double cantilever beam (reported in the literature). The results presented here validate the ability of CNT technique for determination of K_ISCC of sensitized as well as solution-annealed austenitic stainless steel. This paper also discusses the mechanistic aspects of the difference in fractographic features of the sensitized and solution-annealed stainless steel.     

Cover Picture: Materials and Corrosion. 06/2021

Cover: The effect of the presence of redox active molecules during a mild anodic polarization of AISI 304 stainless steels was studied with a focus on corrosion and microbially influenced corrosion (MIC) processes. The two-part publication demonstrates that the presence of minute amounts of flavins in the preconditioning medium is capable of altering the pit nucleation processes (Part I) and promotes subsequent biofilm formation (Part II). Unexpectedly, biofilms formed on surfaces preconditioned in the presence of flavins led to corrosion inhibition. More detailed information can be found in: Nina Wurzler, Oded Sobol, Korinna Altmann, Jörg Radnik, Ozlem Ozcan, Preconditioning of AISI 304 stainless steel surfaces in the presence of flavins – Part I: Effect on surface chemistry and corrosion behavior, Materials and Corrosion 2021 , 72, 974. and Nina Wurzler, Jan D. Schutter, Ralph Wagner, Matthias Dimper, Vasile-Dan Hodoroaba, Dirk Lützenkirchen-Hecht, Ozlem Ozcan, Preconditioning of AISI 304 stainless steel surfaces in the presence of flavins – Part II: Effect on biofilm formation and microbially influenced corrosion processes, Materials and Corrosion 2021 , 72, 983.     

Corrosion behaviour of micro-plasma arc welded stainless steels in H3PO4 under flowing conditions at different temperatures

This paper studies the general corrosion behaviour of the micro-plasma arc welded AISI 316L stainless steel in phosphoric acid at different temperatures (25–60 °C) and at a Reynolds number of 1456. Galvanic corrosion has been studied using zero-resistance ammeter (ZRA) measurements and polarization curves (by the mixed potential theory). Results show that the microstructure of the stainless steel is modified due to the micro-plasma arc welding procedure. Coupled current density values obtained from polarization curves increase with temperature. ZRA tests present the highest i_G values at 60 °C; however, the values are very close to zero for all the temperatures studied. This is in agreement with the low value of the compatibility limit and of the parameter which evaluates the importance of the galvanic phenomenon. Both techniques present the most positive potentials at the highest temperature. This study reveals that micro-plasma arc welded AISI 316L stainless steels are appropriated working in the studied H₃PO₄ media from a corrosion point of view for all the temperatures analysed.     

Double-loop electrochemical potentiokinetic reactivation behaviour of continuously cooled SUS329J4L duplex stainless steel

ABSTRACT

Sigma phase generally precipitates in duplex stainless steel during slow cooling, which usually causes loss in both corrosion resistance and fracture toughness. To develop a non-destructive method to detect the sigma phase in duplex stainless steel for in situ use in the quality management of large structures, the double-loop electrochemical potentiokinetic reactivation behaviour of continuously cooled duplex stainless steel SUS329J4L at different cooling rates was investigated under different conditions. The polarisation condition with the solution of 0.5?M H₂SO₄?+?0.01?M KSCN?+?0.5?M NaCl and the potential scanning rate of 0.83?mV?s^?1 were determined as suitable and sensitive.

This paper is part of a supplementary issue from the 17th Asia-Pacific Corrosion Control Conference (APCCC-17).     

Constitutive modeling of hot deformation behavior of X20Cr13 martensitic stainless steel with strain effect

Hot deformation behavior of X20Cr13 martensitic stainless steel was investigated by conducting hot compression tests on Gleeble–1500D thermo-mechanical simulator at the temperature ranging from 1173 to 1423 K and the strain rate ranging from 0.001 to 10 s^?1. The material constants of α and n, activation energy Q and A were calculated as a function of strain by a fifth-order polynomial fit. Constitutive models incorporating deformation temperature, strain rate and strain were developed to model the hot deformation behavior of X20Cr13 martensitic stainless steel based on the Arrhenius equation. The predictable efficiency of the developed constitutive models of X20Cr13 martensitic stainless steel was analyzed by correlation coefficient and average absolute relative error which are 0.996 and 3.22%, respectively.     

Improvement in Oxidation Resistance of Stainless Steel by Molten-Salt Electrodeposition of La

Improvement in the oxidation resistance of SUS304 stainless steel was accomplished by electrodeposition of La in a molten salt. The electrolysis of La was conducted using a potentiostatic-polarization method in an equimolar NaCl–KCl melt containing 3.5 mol. LaF ₃ at 1023 K. Observation of the specimen surface after polarization at –1.8 V (vs. Ag/Ag⁺ (0.1)) for 0.18 ks showed that La particles were uniformly dispersed on the surface. The oxidation resistance of the electrodeposited stainless steel was significantly improved as compared with the untreated stainless steel. The scale formed on the untreated stainless steel after oxidation was thick and consisted of Fe₂O₃ and Fe₃O₄, whereas the scale formed on the elecrodeposited stainless steel was extremely thin, and mainly consisted of Cr₂O₃.