Products and solutions, 2006-08-10, 03:50 PM
Mineral oil, caustic soda, sulfur, CO2: a huge variety of liquid media are transported by rail, safely enclosed in tank wagons. So that their valuable contents maintain their temperature as well as possible and neither solidify or vaporize on their journey, tank cars come wrapped in a layer of heat or cold insulation. The design of this insulation, which can take any of countless different forms, is always specially tailored to the product being transported and the route and restricts temperature change during the trip to a precisely defined range.
ThyssenKrupp Xervon is one of the few companies in Europe capable of designing and installing insulation in tank cars. The industrial service provider insulated 350 tank cars last year alone, working on the sites of car makers in Germany, France, Romania and Slovakia. It has been operating a separate department precisely for this task for years now. An insulation strategy is drawn up for each tank car and the associated product. Decisive factors are the type of transported goods, the length of journey and the geographical situation - a tank car for Norway has to be insulated differently from a Spanish one. Project manager Dirk Meyer, in charge of tank car insulation business, explains the complexity of the issue: "In a so-called temperature drop calculation, various conceivable scenarios are considered and calculated. The starting point is the temperature of the medium when it enters the tank car. Then we have to consider how many days the car will be traveling, the ambient temperatures that can be expected and the temperature range that the goods must remain within before arrival." This narrows down the parameters for the possible forms of insulation.
For the customer - tank car manufacturers and leasing companies that lease such tank cars to industry - it is ultimately the weight, price and efficiency of the insulation that are the crucial factors for the choice of system. If, for instance, a particularly effective insulation is required, the decision will probably go in favor of a more expensive insulating material. On the other hand, the weight of the insulation can also be important: the lower the overall weight of the tank car, the higher its possible payload. To meet the technical specifications, Xervon therefore always uses lightweight insulating materials and extra-thin sheet metal jackets.
Relatively insensitive substances like mineral oil or glue are perfectly happy with a layer of standard insulation. This consists of a 100 mm thick lagging of mineral wool and a metal jacket (inclusive of spacer construction) as protection from the weather and mechanical damage. However, the more aggressive the product is, the more resistant the metal jacket has to be. If concentrated lyes or acids have to be transported, the protective metal jacket is therefore usually made of stainless steel. This is because mishaps occasionally occur in the filling bays of chemical and petrochemical plants, allowing liquids to spill down the outside of the jacket. This and the aggressive air in such installations would attack the outer shell of the cars in the long run and prematurely curtail tank car service - otherwise an average of 25 years.
Polyurethane for extra-hot and -cold substances
Tank cars for exceptionally cold media, e.g. liquefied CO2 which enters the tank at as low as minus 45°C, are given an extra-thick lagging of polyurethane instead of mineral wool. First of all the supporting structure and the metal jacket are attached to the tank car. The cavity thus created is then carefully foamed with polyurethane. Even for hot media, the particularly effective insulating properties of polyurethane are exploited. Hot liquid sulfur at 145°C is sometimes transported in cars insulated with a combination of mineral wool and foam. Because polyurethane is stable only up to 100°C, the tank car is given an initial 100 mm thick insulation layer of mineral wool. Only then does the insulation layer of polyurethane follow.
The principle of tank car insulation comes from classical pipeline insulation. The materials, machines and work processes are identical. However, for the protective metal jacket on tank cars, larger, 1250 mm wide sheets are worked. This reduces the number of seams, looks better and limits the potential for flaws. The sheets are joined together mechanically. A rubber underlay profile breaks the contact between the overlapping metal seams and prevents them rubbing against each other. At the same time, the profile has lip seals on both sides into which a 57 mm wide stainless steel strip is slotted. This is inserted into the profile all the way around and tightened with turnbuckles, thus creating a firm joint that can be subsequently tightened.
However, although tank car insulation is similar to standard pipe insulation, it is precisely Xervon's specialized knowledge in this business niche that has brought success. Dirk Meyer is convinced of this: "From years of experience we know what really counts. This includes many little details. For instance, we equip the cars with drainage channels, insulate the bottom outlet and fit easily dismantled insulation at the various bolted connecting strips where the tank and underframe are joined." The insulation specialists are a smooth-running team with many years of experience and knowledge of these finer points. Basically, any trained insulator can carry out tank car insulation. "But he takes two to three times as long," says Meyer, speaking from experience. "Our six- to eight-strong teams manage a car per day." The car is then not only in excellent technical condition but also leaves nothing to be desired in terms of smart appearance. "The customer not only expects a tank car to be functional, but also to have the looks to match. After all, these cars travel right across Europe, advertising their owners en route."