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- High-alloyed metallic tank materials (5)
- NMR spectroscopy (3)
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- Infrared spectroscopy (2)
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Use of Corrosion Resistant High-Alloyed Metallic Materials for Transport Tanks of Dangerous Goods
(2005)
In Germany the BAM-List Requirements for Tanks for the Transport of Dangerous
Goods is the basis for substance-related prototype approvals for tank containers designed for
the carriage of dangerous goods. Such approval is undertaken by the Federal Institute for
Materials Research and Testing (BAM). Compatibility evaluations of selected metallic
material groups as well as of polymeric gasket and lining materials under the influence of
dangerous goods and water-polluting substances are published in section 5 of the BAM-List.
According to the relevant regulations for rail, road and sea transportation a compulsory
internal inspection after certain intervals is required. The required corrosion resistance
depends on the length of the inspection interval.
There is a large number of dangerous goods with a high corrosivity to metals, where the standard
steels are not corrosion resistant. Chemical companies, transportation providers and tank
producers need tanks made of corrosion-resistant materials in order to protect the tank shell
and prevent contamination of high-value cargo as well as the environment. One solution is to
line the tank with a polymeric material, an alternative solution to corrosion problems is the
application of high-alloyed materials.
Only a narrow limited number of corrosion test results of these high-alloyed materials under
the influence of corrosive dangerous goods are available. In order to change this situation and
include the superaustenitic steels X1NiCrMoCuN25-20-7 (Alloy 926), X1NiCrMoCu32-28-7
(Alloy 31) and the nickel-based alloy NiCr23Mo16Al (Alloy 59) in the BAM-List, BAM,
IKS Dresden and ThyssenKrupp VDM started an comprehensive test program with welded
specimens made. The program comprises corrosion resistance evaluations of the high-alloyed
materials in substances representing 12 major groups of corrosive dangerous goods (e.g.
inorganic halogenides, organic acidic halogenides, halogenic carbonic acids, chlorosilanes,
chlorates, perchlorates, chlorites, hypochlorites and hydrogen sulphates).
The test results, presented in this paper, will be included in the upcoming 8th edition of the
BAM-List and therefore available for the costumer.
To explore the impact of ambient and structural water on static fatigue, the initiation and growth of 3279 Vickers induced median radial cracks were automatically recorded and analyzed. We find that humidity is more efficient in initiating cracks and promoting their growth than water, which is dissolved in the glass structure. In particular for slow crack growth (< 3x10-6 m s-1), tests in dry nitrogen showed a considerable decrease in the crack growth exponent with increasing water content of the glasses. On the other hand, if tests were performed in humid air, the crack growth exponent was independent of the water content of the hydrous glasses, while stress intensity decreased slightly. These observations indicate that water promotes the processes at the crack-tip regardless of its origin. However, ambient water is more efficient.
Dissolved water has major impact on the physical and chemical properties of phosphate glasses. In the present study we have investigated the structural response to water incorporation for glasses in the system Li2O–MgO–Al2O3–P2O5.
Glasses containing 0–8 wt% H2O were synthesised at 500 MPa confining pressure in internally heated gas pressure vessels at 1323 K (LMP, Al-poor glass) and 1423 K (LMAP, Al-enriched glass). Water contents of glasses were determined by pyrolysis and subsequent Karl-Fischer titration (KFT) and/or by infrared spectroscopy. Density varies nonlinearly with water content implying large structural changes when adding up to 2 wt% H2O to the dry glass. Glass Transition temperatures measured by differential thermal analysis (DTA) continuously decrease with water content. The trend can be explained by depolymerisation of the phosphate network. Near-infrared spectroscopy shows that even in Al poor glasses only a minority of dissolved water is present as H2O molecules, but the largest amount is present as OH Groups formed by hydrolysis of P–O–P bonds. The network is stabilised by aluminium which is predominantly six-coordinated in these glasses as shown by 27Al MAS NMR spectroscopy. With increase of Al in the glasses, breaking up of the Phosphate network through hydrolysis is depressed, i.e. much lower OH Contents are formed at same total water content.
Network depolymerisation upon addition of H2O is evident also from 31P MAS NMR spectroscopy. While Phosphate tetraheda are crosslinked by two to three bridging oxygen in dry glasses, diphosphate Groups are dominant in glasses containing 8 wt% H2O.
To understand the influence of water and alkalis on aluminosilicate glasses, three polymerized glasses with varying ratios of Na/K were synthesized [(22. 5-x)Na2O-xK2O-22.5 Al2O3-55 SiO2 with x = 0, 7.5, and 11.25]. Subsequently, these glasses were hydrated (up to 8 wt% H2O) in an internally heated gas pressure vessel. The density of hydrous glasses linearly decreased with water content above 1 wt%, consistent with the partial molar volume of H2O of 12 cm3/mol. Near-infrared spectroscopy revealed that hydroxyl groups are the dominant species at water content of <4 wt%, and molecular water becomes dominating at water content of >5 wt%. The fraction of OH is particularly high in the pure Na-bearing glass compared to the mixed alkali glasses. 27Al magic angle spinning-NMR spectroscopy shows that aluminum is exclusively fourfold coordinated with some variations in the local geometry. It appears that the local structure around Al becomes more ordered with increasing K/Na ratio. The incorporation of H2O reinforces this effect. The differential thermal analysis of hydrous glasses shows a significant mass loss in the range of glass transition already during the first upscan, implying the high mobility of water in the glasses. This observation can be explained by the open structure of the aluminosilicate network and by the low dissociation enthalpy of H2O in the glasses (≈ 8 kJ/mol). The effect of the dissolved H2O on the glass transition temperature is less pronounced than for other aluminosilicate glasses, probably because of the large fraction of Al in the glasses.