A journey through the production of chains

In the deep sea of the maritime world, ship chains play a crucial role in the safety and reliability of ships. From careful material selection to meticulous rolling production and precise chain formation, each stage contributes to robust, durable, and reliable chains.

Step 1: material selection for maritime chains

The core of every ship chain is determined by the type of steel used, with three common types: carbon steel, alloyed steel, and stainless steel. These variations exhibit unique properties that directly impact the chain’s performance under various conditions.

Due to the corrosive nature of seawater, it is crucial to set specific requirements for the steel used. Stainless steel, with its high chromium content, is often preferred for its excellent corrosion resistance. This allows the steel to withstand prolonged exposure to saltwater, effectively protecting the ship chain from undesired rust formation.

In addition to corrosion resistance, ship chains are subjected to significant forces throughout their lifespan. The chosen steel must, therefore, have high tensile strength to ensure the structural integrity of the chain. High-strength carbon steel is commonly used, providing the required strength without compromising the structural stability of the chain.

Ship chains can wear out due to interactions with anchor chain wheels and contact with the seabed. Therefore, it’s crucial to select durable and wear-resistant steel. Choosing materials that resist wear helps extend the lifespan of the ship chain, reducing the frequency of replacements.

Step 2: roll production

A crucial phase in the formation of steel bars is hot rolling. Here, steel coils undergo heating to high temperatures, making them more pliable without breaking. This essential step allows the steel bars to take on the desired contours.

As the steel coils pass through a series of rollers during the hot rolling process, the initial links are formed. The selection of rollers and their configuration is crucial to obtain the correct dimensions and shapes of the maritime chains.

Precision in terms of dimensions and tolerances is pursued during hot rolling. Advanced measuring instruments are employed to regularly check the steel bars and adjust them to the specifications of the maritime chains, ensuring consistency in the production process.

After the formation of links, the steel bars undergo a cooling process to stabilise the microstructure of the steel. This cooling is crucial to maintain the desired mechanical properties and prevent undesirable changes in the material.

Step 3: chain formation

Before the actual forming process begins, detailed design drawings and specifications are prepared. These include information about the required dimensions, geometric shapes, tolerances, and other technical details necessary for producing high-quality maritime chains.

A special machine, designed specifically for making maritime chains, is used. This machine comes with different rollers, bending mechanisms, and precise instruments tailored to the design specifications.

Steel bars produced in the rolling production process are fed into the chain forming machine. These bars need to meet the required quality, dimensions, and mechanical properties.

The machine starts bending the steel bars into the desired shapes according to the design. This involves using various rollers and bending mechanisms to shape the bars into links of the maritime chain. The machine must be accurately adjusted to ensure the correct shape and dimensions.

Throughout the forming process, the created links are regularly checked for tolerances. This includes measuring the distance between links, the angles of bends, and other geometric properties to make sure the chain meets the specifications.

After formation, the links go through visual inspection and, if necessary, more advanced quality controls such as ultrasonic testing. This ensures that each link meets the high standards required for maritime chains.

Overview of chains

Step 4: welding

After the steel bars have been formed into links by the chain forming machine, the links are prepared for the welding process. This may involve cleaning the welding surfaces and removing any impurities.

For the welding of maritime chains, automated welding machines or qualified welders are employed. The choice between automated machines and manual welding depends on the design specifications, production scale, and desired accuracy.

Regardless of the method used, the weld joint must be strong and uniform. This means the weld penetrates deeply and has a consistent structure. The strength of the weld joint is crucial as maritime chains are subjected to significant tensile forces and other loads. After welding, the weld joints undergo non-destructive tests (NDT) such as ultrasonic tests or X-ray examinations. These tests detect potential imperfections, welding defects, or cracks that could compromise the structural integrity of the chain.

In addition to strength, the uniformity of the weld joint is important. A uniformly welded chain not only ensures structural stability but also contributes to the aesthetic aspect of the final product. Uniformity also reduces stress concentrations and enhances overall durability.

The welding of maritime chains must comply with international standards and certifications established by classification agencies and organisations such as the International Maritime Organization (IMO). Welders must be qualified according to applicable standards.

During welding, a heat-affected zone (HAZ) forms around the weld joint. Managing this zone is important to minimise undesired changes in material properties. This can be achieved through precise control of the welding process and possibly the use of cooled fixtures.

Step 5: heat treatment

After welding and forming the maritime chains, the steel links undergo a controlled heat treatment process to optimise their mechanical properties. Various heat treatment methods can be applied, such as normalisation, quenching and tempering, or a combination of both, depending on the desired properties of the maritime chains.

Normalisation is a process where the steel links are heated to a critical temperature, followed by air cooling. This helps reduce unwanted internal stresses and refine the crystal structure of the steel. Normalisation enhances toughness and reduces the risk of brittleness in the maritime chains.

Quenching and tempering involve heating the steel links to a high temperature (quenching) and then rapidly cooling them, followed by a tempering or annealing phase. This process provides a combination of high hardness and toughness in the steel, which is beneficial for maritime chains subjected to heavy loads.

During the heat treatment process, strict controls must be maintained over parameters such as temperature, dwell time at temperature, and the cooling process. This ensures precise control of material properties and prevents unwanted variations.

The goal of heat treatment is to induce favourable microstructural changes in the steel. This allows the crystals in the steel to assume an optimal arrangement, resulting in improved mechanical properties such as tensile strength, toughness, and fatigue resistance.

After completing the heat treatment process, the maritime chains undergo thorough quality controls. This may include hardness measurements, inspections of microstructure, and other tests to ensure that the intended properties are achieved and that the chains meet the specified standards.

Step 6: calibration

Before we start adjusting, we need to figure out the right dimensions and tolerances for each link in the maritime chain. These specifications are based on what the shipping industry needs and the design requirements.

Adjusting involves using precise tools like gauges, callipers, micrometres, and sometimes three-dimensional measuring equipment. These tools are designed to measure each link’s different dimensions super accurately.

We carefully check each link of the maritime chain to make sure it’s the right size according to the specifications. This includes checking the length, width, thickness, and other important dimensions that affect how well the chain works and how safe it is.

Adjusting is super important to make sure the whole maritime chain is consistent. Having uniform dimensions and tolerances is crucial so that the chain is evenly loaded and doesn’t have weak spots.

While adjusting, we also look closely at critical points of each link. This includes checking weld seams, transition areas between different parts of the chain, and other spots that might affect how strong and reliable the chain is.

We keep detailed records of all the measurements, adjustments, and inspection results during the adjusting process. This documentation is really important for traceability and quality assurance. It lets us identify and trace back each maritime chain to where it came from.

Adjusting isn’t a one-time thing; we might do it regularly to make sure the production machines and measuring tools still give accurate results. Doing this regularly, called recalibrating, is especially important in places where small differences can have big consequences.

Step 7: surface treatment

Maritime chains are exposed to harsh conditions at sea, where corrosion is a constant concern. The purpose of surface treatment is to provide effective protection against corrosion, especially when the chains are exposed to saltwater.

A common method for surface treatment of maritime chains is hot-dip galvanising. In this process, the chains are immersed in molten zinc at high temperatures. The zinc adheres to the steel surface, forming a protective layer that resists corrosion.

In addition to hot-dip galvanising, other corrosion-resistant treatments can be applied, such as applying special paint coatings, metallizing (applying a metal coating), or using corrosion-resistant alloys. The choice of treatment depends on the specific environmental conditions and the requirements of the shipping industry.

The protective coating applied during surface treatment significantly contributes to extending the lifespan of maritime chains. It reduces the frequency of maintenance intervals and increases the reliability of the chains, which is essential for the safety and performance of maritime applications.

Step 8: quality control

Destructive tests are performed on samples of the maritime chain to evaluate the material properties. For instance, tensile tests involve pulling the chain under load until it reaches failure. These tests aid in determining the tensile strength, elongation, and fracture strength of the material.

Non-destructive tests play a crucial role in assessing the chain’s integrity without causing damage to the material structure.

Key Non-Destructive Testing (NDT) methods applied to maritime chains include:

• Ultrasonic testing: This method is employed to identify internal imperfections, such as cracks, by transmitting ultrasonic sound waves through the material. Changes in the sound waves can reveal defects.
• Magnetic particle testing: Magnetic particles are applied to the chain’s surface, and if there are cracks or imperfections, the particles will gather at these locations, making defects visible.
• Visual inspection: This is significant and is often used as an initial screening. It involves closely examining each link for visible defects, such as cracks, deformations, or irregularities.
• Impact tests: These tests assess the resistance of the maritime chain to sudden loads, which is especially relevant as ships are subject to dynamic forces, and the chain must withstand shock loads without breaking.
• Fatigue resistance tests: These tests expose the chain to repeated loads typical of maritime environments, simulating the cyclic loads a chain may experience during use at sea.
• Analysis of the chemical composition of the steel: This is conducted to ensure it complies with the specifications and standards established for maritime chains. Material research may also be carried out to assess the microstructure of the steel.

Step 9: Marking and Certification

Each individual link of the maritime chain is marked with crucial information, including:

• Production Number: A unique identification number assigned to each chain link. This number is vital for traceability and identification.
• Tensile Strength: The maximum tensile force the chain link can withstand without breaking. This information is essential for correctly designing and using the chain in maritime applications.
• Production Date: The date on which the chain link is manufactured. This helps track the chain’s lifespan and can be useful in planning maintenance intervals.
  
• Certifications: Symbols or markings indicating that the chain link complies with specific international standards and certification requirements.
• The marking of maritime chains must adhere to international standards such as ISO 1704 and EN 818. These standards establish guidelines for marking the chains with information relevant to both manufacturers and end-users.

Step 10: Storage and Distribution

Ideally, finished ship chains should be stored in covered facilities to protect them from direct exposure to weather conditions. Indoor storage prevents corrosion and minimises the impact of atmospheric elements.

If the ship chains have not received a direct protective coating during the production process, it may be beneficial to apply a temporary, non-corrosive coating before storage. This provides additional protection during the storage period.

From raw material to certification: building reliable ship chains

From material selection to the meticulous rolling production process and then the precise chain formation, each stage in the production process of ship chains contributes to creating robust, durable, and reliable chains. The interplay of properties, precision, and quality controls ensures that these chains not only meet but often exceed the high demands of the maritime industry. Thus, essential links in the safety and performance of ships worldwide are not just produced; they are created.