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- Eisenbahnkesselwagen (2)
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- Polyethylen (1)
More than 400 Mt of dangerous materials are transported in Germany every year, of which 150 Mt are by road. Tank containers, tank vehicles and rail tank cars are used for the carriage of dangerous goods in large quantities. Data on the operating life of tanks are only available, in practice, to a minor degree. They are only partly published, mainly after accidents.
The BAM-List - Requirements for Tanks for the Carriage of Dangerous Goods, which has compatibility evaluations of metallic and polymeric materials, has been the basis for substance-related prototype approvals for tank containers and portable tanks designed for the carriage of dangerous goods by the BAM since publication of the first edition in 1989. These data are also used for the approval of rail tank cars and road tank cars and are used as a source of knowledge not only in Germany but also worldwide.
Tank leakages caused by tanks or rail tank cars being made of tank and sealing materials which are not resistant to the fill goods are avoided by using the material resistance data of the BAM.
Corrosion damage is among the main causes of damage. Uniform and non-uniform area corrosion without mechanical stress in aqueous substances is one of the most frequent types of corrosion during the transport of chemicals in tanks. Much damage by pitting corrosion occurs during the transport of substances containing chlorides or substances which separate chloride ions in the presence of moisture.
Operational stresses are caused by the effects of both the road and the dangerous goods being transported. Mechanical damage often results from long-term overstressing and occurs after longer operating times.
Operational failures cause damage which may appear during the service of tank containers, road tank cars or rail tank cars. The damage results from the inattention of employees when opening and closing the valves. Traffic accidents also cause damage to tanks and frames.
Many cases of damage are due to weld area cracks resulting from four basic errors in construction, material, manufacturing and operation. Manufacturing errors can be undetected and the starting point of cracks which only grow under service conditions.
Manufacturing errors result from variations in measurement and design, fittings, state of surface (hardness, abrasiveness) and mechanical surface damage (scratches, cracks). Incorrectly welded joints and errors during mechanical deformation are typical mistakes when installing the component parts. Variations in the wall thickness or combinations of different materials lead to manufacturing errors too. A lot of tanks are not used for the transport of dangerous goods before the end of their service life as they do not fulfil the revised technical safety requirements in the Dangerous Goods Regulations.
Predictions in the BAM-List based on literature data and corrosion test results are reflected in the service (operating) life. Rail tank cars made of carbon steel, for example, which are mainly used for the transport of petroleum products, can achieve a service life of 40 – 50 y.
Rail tank cars produced of austenitic CrNi- or CrNiMo-steel can reach an operating life of at least 30 y, whereby the corrosiveness of the transport substances plays an important role.
Daten über Schadensursachen und die tatsächliche Nutzungsdauer der Tanks zum Transport von Gefahrgütern liegen nur in begrenztem Maße vor. Auf der Basis der Daten von Tankbaufirmen, Speditionen und Eisenbahnkesselwagen-Vermietgesellschaften wurde die durchschnittliche Lebensdauer von Tankcontainern, Tankfahrzeugen und Kesselwagen zur Beförderung von Gefahrgütern in der Praxis ermittelt und die Hauptschadensursachen analysiert. Korrosion, Risse an Schweißnähten, Gestaltungs- und Dimensionierungsfehler sowie fertigungs- und betriebsbedingte Fehler zählen zu den Hauptschadensursachen. Viele Tanks werden vor Ablauf ihrer Nutzungsdauer nicht mehr für den Transport von Gefahrgütern eingesetzt, da sie nicht mehr den geänderten gesetzlichen Anforderungen in den Gefahrgutvorschriften entsprechen. Die Voraussagen durch Literaturangaben und Ergebnisse von Korrosionsversuchen in der BAM-Liste – Anforderungen an Tanks zur Beförderung gefährlicher Güter – spiegeln sich in der Nutzungsdauer/Lebensdauer der Tanks wider.
Seitens der Industrie besteht großes Interesse, Polyethylenterephthalat (PET) als Werkstoff für Verpackungen zum Transport von Gefahrgütern einzusetzen, da aufgrund der hohen Fes-tigkeit und Steifigkeit von PET die Wanddicken und somit die Kosten der Verpackungen reduziert werden können. Die Prüfung der Spannungsrissbeständigkeit von Polyethylenformstoffen als Werkstoffe von Verpackungen erfolgt mit Labormethoden unter Verwendung einer Standardflüssigkeit als Prüfmedium für die Spannungsrisse auslösende Wirkung auf Polyethylen (PE), wodurch Zeit und Kosten der Prüfungen reduziert werden.
Ziel dieser Arbeit war es, eine Laborprüfmethode zum Vergleich der Spannungsrissbeständigkeit von PE und PET auf ihre Anwendbarkeit zu prüfen, wie z.B. den Full Notch Creep Test (FNCT). Es wurde untersucht, ob die Prüfkörper aus PE und PET mit umlaufender Kerbe in dieser durch die chemische Industrie entwickelten und von der BAM konzipierten Apparatur auf der Basis des FNCT zu messbaren Ergebnissen unter Einfluss eines Ölsäureamidethoxylates als Netzmittel bei 50 °C führen.
Die Testergebnisse bestätigten die Eignung des Prüfverfahrens für die acht eingesetzten Formstoffe aus PE. Dieses Prüfverfahren konnte nicht für PET angewandt werden, da die Prüfkörper aufgrund der hohen Festigkeit und Steifigkeit des PET beim Kerbvorgang zerbrachen. Die gleiche Aussage konnte für den Nachweis der der Spannungsrissbeständigkeit von Verpackungen, der in der BAM Gefahrgutregel BAM-GGR 015 beschrieben wird, getroffen werden. Die einzige Möglichkeit zum Nachweis der Spannungsrissbeständigkeit von PET besteht in der Durchführung von Stapeldruckprüfungen.
Polyethylene terephthalate (PET) is used as material for packagings for the transport of dangerous goods due to its high strength and stiffness. For this reason, the wall thickness and weight of the packagings can be reduced.
According to the European dangerous goods regulations RID and ADR, samples of PET design types of packagings for dangerous goods must be pre-stored with the original filling good for six months at 23 °C, before the design type tests can be carried out. For packagings made of polyethylene (PE) tests to prove the stress cracking resistance by using laboratory methods are possible to reduce time and costs. Therefore, standard liquids, simulating the different types of damaging effects on PE are defined in RID and ADR. However, there is no information and research available about the damaging mechanisms on PET, especially regarding to stress cracking resistance and test methods.
One laboratory test method is the Full Notch Creep Test (FNCT), which was developed for polyethylene (PE) and is described in the standards EN ISO 13274 and EN 15507. It was investigated whether testing specimens made of PET with a full coplanar notch around the middle of the specimens show weakening after the impact of a tensile force in the standard liquid (5 % wetting solution) at 50 °C. The tests showed that this method couldn’t be used for PET because the specimens broke during notching due to the high brittleness of PET. Another disadvantage is the very time-consuming temper process for twelve hours after molding of the sheets.
Another test method is described in BAM’s Dangerous Goods Rule BAM-GGR 015. This test was carried out with 1l PET bottles, which were filled with a 5% wetting solution and mounted with a clamping tool for 28 days at 40°C. Tensile test specimens were cut out afterwards from the middle of the bottles in the deformed areas. The tensile properties of the PET specimens couldn’t be determined due to the hardness of the material.
The only test method to provide information about the stress cracking resistance of PET was to perform stacking tests with PET design types of packagings. 1l bottles made of PET were filled with the standard liquid (5 % wetting solution) and stored with a stacking load for 28 days at 40°C according to EN ISO 16495. The test bottles of PET passed the stacking tests.
In conclusion, samples of PET design types of packagings for dangerous goods must be pre-stored with the original filling good for six months at 23 °C, before the design type tests can be carried out.