Pitting Attack Research Articles

Surface analysis studies on the corrosion resistance of Mo implanted Al alloys

The effect on corrosion resistance by Mo additions into Al alloys is examined. Two different doses of Mo are implanted into alloy surfaces by ion beam mixing. The unimplanted and implanted alloys are subjected to general and localized corrosion testing using sulfate and sulfate plus chloride solutions. Electrochemical properties obtained from potentiostatic polarization curves are correlated to the Mo content and the surface chemistry as measured by Auger Electron Spectroscopy. The results show that Mo implantation forms a complex oxide within the top 1000 Å of the Al surface and inhibits pitting attack of these alloys.

Surface analysis studies on the corrosion resistance of Mo implanted Al alloys

The effect on corrosion resistance by Mo additions into Al alloys is examined. Two different doses of Mo are implanted into alloy surfaces by ion beam mixing. The unimplanted and implanted alloys are subjected to general and localized corrosion testing using sulfate and sulfate plus chloride solutions. Electrochemical properties obtained from potentiostatic polarization curves are correlated to the Mo content and the surface chemistry as measured by Auger Electron Spectroscopy. The results show that Mo implantation forms a complex oxide within the top 1000 Å of the Al surface and inhibits pitting attack of these alloys.

The measurement of corrosion using electrochemical [formula omitted] noise

Amplitude spectra of low frequency electrochemical noise are presented which show a correlation between the rate and mode of corrosion attack and fluctuations of the corrosion potential. The results indicate the possibility of a non-perturbative electrochemical corrosion monitoring technique capable of detection of pitting and crevice attack.

Corrosion of Alloy 600 by Cationic Resin Beads

Several instances of corrosion and stress corrosion cracking in light water reactor coolants have been attributed to the incidental presence of ion exchange resin in the coolant. Tests performed in high temperature water slurries of cation exchange resins have shown preferential pitting and general attack of Alloy 600. Continuous ac impedance measurements were performed to monitor the corrosion during the test. The frequency dependence of the ac impedance allows separation of the resistance of the corroding interface from the resistance of the slurry. The results have been shown that attack commences at relatively low temperatures near 80°C, increases with increasing temperature up to 289°C, and slows with decomposition of the resin held at 289°C. Postmortem analysis showed hemispherical pitting under partially decomposed beads, surrounded by a scale enriched in chromium and sulfur.

The passive state of stainless steels

With the advent of surface-sensitive techniques it has become possible to determine the surface composition of alloys. Analyses using electron spectroscopy for chemical analysis of CrNiMo alloyed steels exposed in acids and neutral solutions show that the reaction products formed on the surface consist mainly of chromium oxide and hydroxide. Nickel is not present in the passive films. The molybdenum content in the oxide is of the same order of magnitude as in the alloy. It is suggested that the beneficial effect of molybdenum is not related to the molybdenum content in the oxide. It is shown that the alloy elements nickel, molybdenum and chromium are accumulated in the metal phase underneath the oxide and that the enrichment of chromium seems to be dependent on the molybdenum content of the alloy. The enrichment of these elements is explained by selective dissolution of iron during the active phase preceding passivation. It is postulated that increased surface concentrations of chromium and molybdenum in the metal synergistically lower the dissolution rate in the active phase and provoke the formation of passive films of high chromium content both at first passivation and during repassivation in conditions of pitting and crevice attack.

Corrosion behavior of cast and forged cobalt-based alloys for double-alloy joint endoprostheses.

An ideal combination of mechanical and corrosion properties of long-term implants such as joint endoprostheses has yet to be found. Besides being resistant to pitting and crevice attack, which can lead to corrosion fatigue and stress corrosion cracking failures, the implant material must be highly resistant to wear and abrasion. Two cobalt-based alloys, wrought CoNiMoTi and air-cast CoCrMo, were subjected to a number of selected in vitro electrochemically and chemically accelerated corrosion tests in chloride-containing solutions with wrought AISI-316L used as a reference alloy. A limited number of immersion tests in FeCl3 and acidified FeCl3 solutions were also conducted. It is found that the mechanical properties of wrought CoNiCrMoTi alloy qualify it as a substitute for cast CoCrMo alloy and wrought AISI-316L in anchorage shaft production for all types of joint endoprostheses. Wrought CoNiCrMoTi has a higher resistance to fatigue cracking compared with cast CoCrMo and is as resistant to selective corrosion phenomena such as stress corrosion cracking.

ALLEGHENY LUDLUM AL 6X

Abstract ALLEGHENY LUDLUM AL-6X is an austenitic chromium-nickel-molybdenum stainless steel specifically designed for outstanding resistance to pitting and crevice attack in chloride-containing solutions. It possesses good ductility, high impact values and good weldability. It is an ideal material for condenser tubing. This datasheet provides information on composition, physical properties, elasticity, and tensile properties as well as fracture toughness. It also includes information on corrosion resistance as well as forming, heat treating, machining, and joining. Filing Code: SS-349. Producer or source: Allegheny Ludlum Corporation.

Development of Ferritic Stainless Steels for Use in Desalination Plants

Abstract This paper describes a research program aimed at optimizing the composition, heat treatment, and structure of ferritic stainless steels for use as condenser tube material in desalination plants. The results of corrosion tests carried out in a desalination plant are reported and discussed in relation to laboratory tests performed on the same alloy compositions. The corrosion measurements are used to outline general methods for maximizing the resistance of ferritic stainless steels to pitting and crevice crack attack in hot saline environments.

Stability of the anodic film on aluminium in relation to the nature of some anions

AbstractUsing a galvanostatic method of investigation the influence has been studied of various anions on the formation of anodic layers during anodization in borate solution. According to the results obtained sodium carbonate, phosphate, succinate and oxalate enhance the formation of the anodic oxide layer. Sulfite, sulfate, thiosulfate and nitrate lower the anode potential to a constant value which depends from the type of anion and may be extremely low in the case of halogen ions (chloride, bromide, iodide). This phenomenon is attributed in the case of the halides to a pitting type attack, while a duplex layer formation is assumed to take place with the other members of this group. The effect of the halides may be suppressed by the addition of phosphate ions, but rather high phosphate:halide ratios are required in order to achieve healing of the pits. The pores in the duplex layer may be sealed by a second anodization in borate, phosphate, benzoate or succinate solution.

Oxidation of Austenitic Stainless Steel Boiler Tubing in Carbon Dioxide

The long-term oxidation characteristics of austenitic stainless steel boiler tubing in CO2− vol.-% CO at up to 600 psig and at 650° and 700° have been studied. Weight gams, metallography and microprobe analysis indicated that heavily cold-worked material showed the best oxidation resistance owing to the formatiOn of a Cr2O3. protective scale. Oxidation of material heat-treated in nitrogen at the lower temperatures. resulted in the formation of a rather less resistant ‘spinel’ type oxide, while the material heat-treated in nitrogen at the higher temperature suffered severe pitting attack. Heat treatment in air at all temperatures provided a fairly resistant oxide film during subsequent oxidation in CO2. Hence heat treatment in air is preferable to heat treatment in nitrogen, and leaving the heat-treatment scale on surfaces which are subsequently to be exposed to CO2-based environment is recommended. Type 316 stamless steel showed rather better oxidation resistance than Type 347 stainless steel.

The effects of polarization on the failure in acids of cold-worked 18Cr [sbnd]10Ni steels

The fracture of tensile specimens of heavily cold-worked 18Cr 10Ni austenitic stainless steels subjected to a low strain-rate at room temperature has been examined by optical microscopy. Experiments were performed in air and in both H 2SO 4 and HCl + NaCl (a) under open circuit conditions and (b) polarized galvanostatically, cathodic and anodic at c.ds. up to 100mA/cm 2. Two types of fracture were induced by the environment: (i) s.c.c. occurred in HCl + NaCl under conditions of anodic polarization (this was associated with the prior occurrence of pitting and crevice attack and fracture did not always occur across the narrowest section of a specimen), (ii) embrittlement under conditions of cathodic polarization in both solutions (this was associated with blister formation which occurred more readily in H 2SO 4 and appeared to be promoted by plastic deformation). Experiments on pre-pitted specimens indicated that the effect of pitting was chemical rather than metallurgical.

Stress Corrosion of Beryllium in Synthetic Sea Water

Abstract Continuous total immersion testing of pickled beryllium sheet material in synthetic sea water revealed mat corrosion rate decreases asymptotically from about 21.5 to 2.0 mpy as exposure period increased from 5 to 150 days. Beryllium was observed to be susceptible to severe pitting attack. Testing established that beryllium is susceptible to stress-corrosion when exposed to synthetic sea water. Time-to-failure decreased from about 2340 to 40 hours as applied tensile stress was increased from 1220 to 40,000 psi. Electron fractography studies suggested that stress-corrosion failure occurred transgranularly.

Corrosion of Mild Steel In 40 Percent Sodium Hydroxide Solution at 316 C

Abstract Measurements of corrosion rate of mild steel in 40 percent sodium hydroxide solution at 316 C were correlated with microscopic examinations. Thick films of adherent magnetite were formed. Severe pitting attack occurred beneath the magnetite, perforating a 0.030 inch steel wall within 130 hours. Topography of the pits was similar to that described as typical of pitting in high pressure boilers. Mechanism of this attack is discussed. 6.2.3, 4.3.3, 3.2.2