|Infobox on Steel profiles|
|Example of Steel profiles|
|Origin||Trade in steel and steel products primarily flows:|
|Stowage factor (in m3/t)||Highly variable, depending upon packaging, dimensions and weight, e.g.: 0.83 m³/t (concrete reinforcement steel in bundles with metal strapping|
|Humidity / moisture||Relative humidity: <40 - 50%|
|Ventilation||(See text also) Steel profiles require particular humidity/moisture and possibly ventilation conditions. Steel corrosion accelerates rapidly at relative humidity > 60%. If possible, relative humidity should be reduced to below 60% by appropriate ventilation measures.|
|Risk factors||(See text also) Seawater damage, contamination and mechanical damage|
Description Steel profiles are steel products which have been rolled, drawn or pressed into a shape which is of the same cross-section over its entire length. Steel profiles are classed as follows:
• Concrete reinforcement steel is the name for smooth, profiled and ribbed round steel bars (structural steel bars/concrete reinforcement bars) which have elevated tensile strength and are used for strengthening reinforced concrete structures or components or for producing steel mesh for reinforced concrete structures (welded wire mesh).
• Prestressed concrete reinforcement steel (smooth, ribbed, profiled round steel bars) is used for prestressed concrete structures and is far stronger than concrete reinforcement steel.
• Large profiles (steel shapes): • I profiles (double T beams) • H profiles (wide flange beams) • U profiles • T profiles
• Angle steel (equal or unequal)
• Special profiles (nonstandard shapes)
• Round and rectangular bars or profiles (e.g. rectangular steel rod profiles, flat steel)
Applications Steel profiles are used, for example, as structural steel for bridges, construction and civil engineering or for fabricating handrails, ladders, struts etc..
Storage/Transport Steel products are particularly susceptible to deterioration due to corrosion or may often require elaborate treatment before being used or further processed.
One particularly frequent cause of damage is rust due to seawater, rain, condensation water in the means of transport, cargo sweat or condensation inside the packaging. Unsuitable means of transport, ships with poor hatch covers or without ventilation facilities, damaged containers, uncovered railroad freight cars and trucks, incorrect storage in the open, use of unsuitable tarpaulins, exposed loading in wet weather conditions, and variations in temperature and climatic conditions during long voyages may result in rust damage.
If a solid bond (adhesion) between concrete and reinforcement steel is to be achieved, relatively clean steel from which loose rust has been removed should be used, i.e. slight surface rust may even be advantageous. Care must, however, be taken to ensure that the diameter of the concrete reinforcement steel still fulfills the requirements of the statics calculations once it has been pickled or sandblasted. Prestressed concrete reinforcement steel, in contrast, must be rejected if it exhibits even the slightest corrosion.
The oxidation layer (scale) which is formed on the surface of steel during hot-rolling or annealing provides limited corrosion protection. This layer does, however, complicate application of anti-rust coatings or galvanization.
Some special, large and angle profiles have a hot-dip galvanized or zinc sprayed finish and are thus protected from corrosion.
The degree of rusting of steel consignments should be recorded in the shipping documents before acceptance of the consignment, possibly using the following definitions:
• Wet before shipment • Partly rust stained to rusty • Gear marked • Contaminated by foreign substance • Contaminated by saltwater • Chafed in places • Packing torn exposing contents
The AMERICAN RUST STANDARD GUIDES are mainly used to describe the condition of hot-rolled steel.
Steel profiles of all kinds are transported in bundles held together by steel strapping, for the most part without any further packaging.
Special steels should be protected from corrosion and mechanical stresses (e.g. scratching and buckling) and are generally packaged using corrosion protection (e.g. oiled paper or appropriately lined boxes or wood/corrugated board structures.
Steel profiles may be transported using the standard container.
Due to their very high density, steel profiles occupy only a small percentage of the container's volume. Loads must be very carefully secured inside the container, since the cargo must on no account be able to move. The container walls cannot withstand the heavy weight if it is concentrated in a small area.
Cargo handling should be carried out in dry weather or under cover, since the product is highly susceptible to corrosion.
Careless handling may result in damage to protective layers (e.g. zinc), which consequently lose their protective function, so causing corrosion.
Steel profiles must be handled carefully owing to their sensitivity to mechanical damage. Damage to flanges is frequently caused by improper handling and the use of incorrect cargo handling equipment. Edges and corners are damaged or entire profiles buckle.
The permissible loading capacity of the slinging and handling equipment and the lifting capacity of the load suspension equipment must also be taken into account.
Due to its weight, this cargo is generally stowed in the lower hold. The loading capacity of the decks must be taken into account when drawing up the stowage plan. Due to the risk of corrosion, this cargo should always be stowed in holds which are protected from the weather and seawater.
Comply with the consignor's/manufacturer's loading instructions in order to avoid damage due to mechanical stresses.
Truck: Profiles must be transported in vehicles having a headboard and side walls (stanchions) with sufficient strength and loading capacity. Nonslip material must also be placed under the load and between layers. Gaps between the load and the headboard and side walls should be avoided. Gaps in the longitudinal direction in particular may result in slippage of the profiles on hard braking. If gaps in the load are unavoidable for reasons of proper load distribution, the load must be secured in accordance with anticipated accelerations by direct securing (e.g. tight fit, loop lashing) and/or by frictional securing (e.g. tie-down lashing).
Ship: The following principles apply:
• Select stowage spaces in accordance with the sensitivity of the cargo and anticipated accelerations • Where possible, load cargo closely against parts of the vessel or other cargo having sufficient loading capacity, but ... • ... stow and secure in such a way that no excessive loads are applied to the hull or other parts of the vessel • Where possible, friction-enhancing materials should be laid beneath the cargo and between layers • Fill in any gaps between individual items of cargo • Protect cargo from chafing, scratching and similar mechanical damage • Protect cargo from harm caused by lashings and other securing materials • Heavy goods in particular, such as steel products, should where possible be stowed without gaps in a level layer from ship's side to ship's side
Railroad: Profiles must be transported in freight cars having a headboard and side walls (stanchions) with sufficient strength and loading capacity. Nonslip material must also be placed under the load and between layers. Gaps between the load and the headboard and side walls should be avoided. Gaps in the longitudinal direction in particular may result in slippage of the profiles on switching impact. If gaps in the load are unavoidable for reasons of proper load distribution, the load must be secured in accordance with anticipated accelerations by direct securing (e.g. tight fit, loop lashing) and/or by frictional securing (e.g. tie-down lashing).
Temperature Steel profiles do not have any particular ambient temperature requirements for transportation and storage. It should however be noted that the temperature of the steel determines whether the cargo sweats.
Humidity/Moisture Steel profiles require particular humidity/moisture and possibly ventilation conditions.
Designation Humidity/water content Relative humidity <40 - 50%
Steel is a cargo which is at risk of corrosion. Corrosion losses are in particular caused by
Seawater and seasalt aerosols, during maritime transport due to leaky containers or hatches during storage at sea ports near water Rain water, when containers are damaged uncovered railroad freight cars and trucks incorrect storage in the open use of unsuitable tarpaulins exposed loading in wet weather conditions Condensation water, on the means of transport on the cargo/load within the packaging Accompanying chemical cargo, Residues of chemicals from previous cargoes, possibly combined with moisture, Hygroscopic accompanying cargo (e.g. fresh lumber) and Relative humidities > 40%.
Steel corrosion begins at a relative humidity of 40% and rapidly accelerates at relative humidities > 60%:
A distinction may be drawn between various Types of corrosion.
There are two main causes of corrosion:
• Pure oxidation and • electrochemical decomposition of the metal due to the presence of an electrolyte (e.g. salts, acids, bases).
Pure oxidation means combination of the ferrous metal with atmospheric oxygen. Oxidation is assisted by electrochemical (electrolytic) processes. The extent of electrolytic decomposition is determined by the conductivity of the electrolyte present. For example, salt water is more conductive than fresh water and therefore has a greater corrosive effect. The effect of sulfurous acid is even more extreme.
If corrosion damage is suspected, testing is performed using the silver nitrate method, to find out whether chloride solutions or fresh water are the cause. When determining the origin of the sea salt on the cargo surface (corrosion resulting from contact with seawater or spray deposition by the hold/container air), the damaged surface is assessed with a magnifying glass (30x magnification): cubic sodium chloride (NaCl) crystals of an edge length of approx. 1/5 mm indicate contact with seawater. In the case of spray deposition, no crystal structures may be observed, since the crystals are too small (1/100 mm).
The load-carrying capacity of steel reinforced concrete structures is determined by the interaction between concrete and steel, adhesion between the concrete and the steel inserts creating a composite structure in which the two materials are virtually immovable. Due to the risk of corrosion, the steel inserts must be well embedded in the concrete, it being essential for the entire surface of the steel to provide a keying surface to ensure proper formation of the composite. The reinforcing action of the steel in reinforced concrete may be disrupted if steel products contaminated with salt are used for reinforcement. The salt remaining on structural steel after contact with seawater or salty, moist sea air (spray deposition) has negative effects on the quality of the steel reinforced concrete not only immediately but also over the extreme long term due to the chemical reactions which occur at the interface between the cement or cement-bound compositions and the structural steel. The hygroscopic salts continuously absorb water vapor from the air causing considerable corrosion damage and possibly significant long-term damage, such as progressive decline in strength, deficient setting, which may ultimately necessitate renovation of the outer walls of a building when rust stains appear on the outside years later.
In the case of hot-rolled steel, it is usual these days to store it in the open and to transport it without protection, such that no protection is provided against rain etc.. Such grades of steel therefore generally exhibit a layer of surface rust (rust film). Since the rust is removed from the steel (by pickling) prior to further processing, the quality of the steel is not impaired. However, corrosion must remain within reasonable bounds, since pickling cannot remove uneven local corrosion or pitting corrosion. Especially in the case of damage by salt water, the sheets should be rinsed off with fresh water as soon as possible after arrival with the receiver and then pickled because significant delay prior to pickling may have the above-stated consequences. For reasons of quality maintenance, the aim should always be to store, handle and transport the sheets in the dry.
To prevent corrosion, steel profiles may be provided with a protective coating. Prior to application of this coating, however, the thin, hard mill scale, which is formed during annealing or rolling has to be removed. Since this layer is very brittle, it is very easily damaged and may flake off. A protective layer applied on top of it would then also flake off and become ineffective, with the consequence that it could no longer provide sufficiently active corrosion protection.
Cold-rolled steel is more sensitive to corrosion than hot-rolled steel, such that cold-rolled steel is additionally packed, for example, in fiber-reinforced packing or plastic-coated kraft paper (montan paper) and plastic films. It is therefore important to keep moisture away at all times; storage in the open or cargo handling in wet weather must be avoided.
Galvanized profiles should likewise not be handled in rain and not stowed together with moisture-releasing goods. Moisture may give rise to a white bloom on the zinc coating. If rain or condensation water penetrates between the closely adjacent profiles, the thin, protective zinc oxide layer does not form, but rather a thicker layer of pure zinc oxide. At the contact points between the profiles, this layer has the appearance of scurf.
Ventilation Steel profiles require particular humidity/moisture and possibly ventilation conditions.
Steel corrosion accelerates rapidly at relative humidity > 60%. If possible, relative humidity should be reduced to below 60% by appropriate ventilation measures.
However, the following should be noted:
1. Steel exhibits a lower temperature than the external temperature anticipated during transit:
If the temperature of the ambient air outside the ship rises, this has only a minimal effect on the temperature of the cargo. Ventilation with "warm" external air may result in cargo sweat on the "cold" steel, if the temperature of the latter is below the dew point of the ambient air. In such a case, ventilation may encourage corrosion.
2. The steel is warmer than the external temperatures anticipated in transit:
Ventilation may be performed without any risk of cargo sweat formation. However, cooling of the ship's sides may cause their temperature to drop below the dew point of the hold air, resulting in ship sweat inside the hold. In this case, the temperature of the hold air should be adjusted by ventilation to match that of the external air.
Gases Sulfur dioxides (exhaust gases from e.g. cargo handling equipment) have an extremely corrosion-promoting action on steel. It is therefore essential to prevent any contact with sulfur and its gases. Holds should accordingly be cleaned prior to loading.
Risk factors Contamination Active behavior Steel profiles do not normally cause contamination. Rust dust resulting from corrosion may possibly cause contamination of other goods.
Passive behavior Dust from coal, ores, salts and especially fertilizers and other bulk materials has a corrosive effect. For this reason, holds/containers have accordingly to be washed clean, to remove any residues from previous cargoes. When washing out ship holds with seawater, it must be borne in mind that seawater also contains salts which would encourage corrosion later in the voyage. It is therefore best to use fresh water for cleaning purposes.
The product should also be protected from acids, aggressive gases (sulfur dioxide) and readily decomposing chemicals, as these also accelerate corrosion.
Oil contamination of concrete reinforcement steel gives rise to objections.
Mechanical influences In order to avoid damage to profiles or their packaging by mechanical stresses, it is essential that stowing, cushioning, bracing, lashing and securing on the means of transport are performed carefully and in accordance with regulations. Suitable slinging and cargo handling equipment and lifting gear must be selected and used on the basis of the cargo's weight and slinging points.
If the strapping is damaged or broken, the bundle loosens, as a result of which individual parts may protrude from the bundle and suffer damage. Strapping may also cause chafing on the surfaces and edges, so damaging them. Severe damage may make the products unusable for their intended use.
Careless use of handling equipment may result in buckling of the profiles or damage to the edges etc..
Note: (Source including Transport Information Service of the GDV)