ASTM G48 Research Articles

Influence of nitrogen and manganese on localized Corrosion behaviour of stainless steels in chloride environments

AbstractElectrochemical localized corrosion tests in substitute ocean water at 40°C and 70°C and ASTM G48 tests in 6% FeCl3 solution were performed on three classes of stainless steels: Ni‐austenitic (both traditional and with high nitrogen content ones), high nitrogen Mn‐austenitic nickel free and duplex (both traditional and with high nitrogen content ones).The Pitting Resistance Equivalent formula, PREMn = % Cr + 3.3% Mo + 30% N – 1% Mn, proposed to consider the presence of noticeable amount of manganese in some of the new high nitrogen stainless steels yields good linear correlation with experimental results. The existence of a threshold value of PREMn (≥ 45) to attain excellent localized corrosion resistance has been recognized. According to this observation the high nitrogen Ni‐austenitic 21Cr24Ni6MoO.24N, 24Crl8Ni4MoO.48N, 24Cr22Ni7MoO.52N and the duplex 25Cr8Ni4MoO.26N “super” stainless steels are immune to localized attack also in the most severe electrochemical test conditions. This superiority is maintained also in ASTM G48 tests. Due to their values of Critical Crevice Temperature (CCTASTM G48 ≥ 35°C) these steels seem suitable for practical service in seawater environments up to about 30 °C.

The evaluation of HCl and Na-EDTA additions for ferric chloride testing using auger electron spectroscopy

Two different additions to the ASTM G48 ferric chloride solution: HCl and Na-EDTA, that prevent the precipitation of hydrous iron oxide at temperatures above 45 °C are discussed. Adding Na-EDTA gave surfaces with characteristics similar to those of the normal ferric chloride solution, whereas the HC1 addition caused an increase in passive layer thickness at higher temperatures. Critical pitting temperatures (CPTs) determined in the different solutions were identical well above 45 °C, but the Na-EDTA addition gave a clearer indication once the CPT was passed. Close to the precipitation temperature, either addition gave a lower CPT than the normal solution, but they proved equally efficient in retaining the solution chemistry. Changes in the redox potential caused by the Na-EDTA addition did not affect the CPT.

Exfoliation corrosion testing of aluminium alloys

Abstract The exfoliation corrosion behaviour of sheet and plate materials of various conventional aluminium and Al–Li alloys has been evaluated using accelerated tests. Results are .compared with atmospheric exposure data published in the literature to assess the applicability of the testing techniques employed. For damage tolerant Al–Li based sheet and plate, the cyclic acidified salt fog (Mastmaasis) test according to ASTM G85, Annex A2 indicated susceptibility to exfoliation corrosion, reproducing the limited outdoor corrosion data for the Al–Li alloys 8090–T81 and 2091–T84 as well as marine exposure results reported for the conventional alloys 2024–T351 and 7075–T7351. Therefore, it appears to be a promising testing technique for predicting the service performance of high strength aluminium alloys. Compared with the ratings determined following the cyclic acidified saltfog tests, the standard Exco test according to ASTM G34 indicated better exfoliation corrosion behaviour of the alloys investigated, e...

Quantitative measurements of the degree of exfoliation on aluminium alloys

The paper deals with quantitative measurements of the degree of exfoliation on three aluminium-lithium alloys (Al-Li-Cu, 8090 and 2091) in under-aged and over-aged conditions and on 7075-T7351, 7175-T6511 and 2024-T351. A special device was used in this work to measure the forces developed by the corrosion products during exfoliation in Exco-solution. Potentiokinetic curves were obtained on these alloys in Exco-solution and sodium chloride solutions (0.6, 1, 2 and 4 M Cl −) at a sweep rate of 1000 mV min −1, to determine the pitting potential, E p , of each alloy. The curve obtained by plotting the forces developed by the exfoliation process as a function of time could be divided into two stages; an incubation period, t 1 , was followed by an increase in the forces to a level corresponding to a time of exfoliation equal to 240 h ( F 240h ). The results obtained were compared to those observed in the conventional Exco-test (ASTM G34). Finally, stress-corrosion cracking tests using the slow strain-rate tensile technique were carried out on the aluminium-lithium alloys, either in Exco-solution or in the sodium chloride solutions containing various chloride concentrations. The results obtained show that, when the time of incubation, t 1 , increases, the force of exfoliation, F 240h , decreases and the resistance to stress-corrosion cracking, R SCC , increases. This resistance is sensitive to the copper content, i.e. R SCC decreases also when the copper content increases. It is concluded that t 1 may be taken as an exfoliation criterion.

Three dimensional AE source location in metals : Kim, K.H.; Kishi, T. Nondestructive Testing Communications, Vol. 3, No. 3, pp. 75–88 (1987)

The paper deals with quantitative measurements of the degree of exfoliation on three aluminium-lithium alloys (Al-Li-Cu, 8090 and 2091) in under-aged and over-aged conditions and on 7075-T7351, 7175-T6511 and 2024-T351. A special device was used in this work to measure the forces developed by the corrosion products during exfoliation in Exco-solution. Potentiokinetic curves were obtained on these alloys in Exco-solution and sodium chloride solutions (0.6, 1, 2 and 4 M Cl−) at a sweep rate of 1000 mV min−1, to determine the pitting potential,Ep, of each alloy. The curve obtained by plotting the forces developed by the exfoliation process as a function of time could be divided into two stages; an incubation period,t1, was followed by an increase in the forces to a level corresponding to a time of exfoliation equal to 240 h (F240h). The results obtained were compared to those observed in the conventional Exco-test (ASTM G34). Finally, stress-corrosion cracking tests using the slow strain-rate tensile technique were carried out on the aluminium-lithium alloys, either in Exco-solution or in the sodium chloride solutions containing various chloride concentrations. The results obtained show that, when the time of incubation,t1, increases, the force of exfoliation,F240h, decreases and the resistance to stress-corrosion cracking,RSCC, increases. This resistance is sensitive to the copper content, i.e.RSCC decreases also when the copper content increases. It is concluded thatt1 may be taken as an exfoliation criterion.