Aluminium Pressure Vessel

Novelty Steel provides Aluminium Pressure Vessel and Heat Exchanger Fabrication services from its manufacturing facilities in Turkey


Table of Contents

1. Properties of Aluminium

Aluminium alloys offer a combination of properties that make them highly desirable for various industrial applications.

  • Corrosion Resistance: Aluminium alloys exhibit high resistance to corrosion in various environments, including atmospheres, water, and many chemicals. This makes them suitable for a wide range of applications.
  • Non-Toxicity: Aluminium alloys are non-toxic, making them safe for use in applications involving foods, beverages, and pharmaceuticals.
  • Colourless: Aluminium alloys are colourless, allowing them to be used with chemicals and other materials without causing discoloration.
  • Eco-Friendly: The corrosion products of aluminium alloys are not harmful to the environment, making them environmentally friendly.
  • Ease of Fabrication and Joining: Aluminium alloys can be readily fabricated and joined using most metal-joining processes, providing versatility in manufacturing.
  • Cryogenic Properties: Aluminium alloys exhibit higher ultimate and yield strengths at cryogenic temperatures (−350°F to −450°F or −212°C to −268°C) compared to room temperature, making them suitable for cryogenic applications.
  • Other Properties: Aluminium alloys also possess high electrical conductivity, high reflectivity, and are nonmagnetic, which ensures arc stability in certain applications.

2. Aluminium for Pressure Vessel and Heat Exchanger Applications

Aluminium is a frequently used material for Pressure Vessel and Heat Exchanger manufacturing due to the below benefits:

  • Lightweight and High Specific Strength: Aluminium alloys offer a combination of lightweight and high specific strength, making them suitable for compact and cost-effective heat exchangers compared to traditional copper and brass materials.
  • High Thermal Conductivity: While not as high as pure copper, aluminium alloys still possess high thermal conductivity, making them efficient for heat transfer applications.
  • High Corrosion Resistance: Aluminium alloys exhibit high resistance to atmospheric corrosion as well as various environments including freshwater, saltwater, and many chemicals.
  • Formability: Aluminium alloys can be formed, either hot or cold, into various shapes, tubes, and fin patterns, providing versatility in design.
  • Joining Capability: Aluminium alloys can be joined using welding, brazing, and soldering methods.
  • Corrosion Protection: Aluminium clad products can protect against pitting corrosion of the core alloys.
  • Cryogenic Properties: Aluminium maintains strength, ductility, and high thermal conductivity even at sub-zero temperatures, making it suitable for cryogenic applications such as heat exchangers.
  • Hygienic and Non-Toxic: Aluminium alloys possess hygienic and non-toxic qualities, making them suitable for applications involving food and beverages.
  • Nonmagnetic and Non-sparking: Aluminium alloys are nonmagnetic and non-sparking, offering safety benefits in certain applications.
  • Availability and Moderate Cost: Aluminium alloys are available in various product shapes and offer a moderate cost compared to some other materials.

On the other hand, Aluminium and its alloys experience a rapid decline in strength when exposed to temperatures exceeding 100°C. Furthermore, aluminium does not provide the same level of fire resistance as some other materials. As a result, it is typically avoided for Process Fluid Heat Exchanger (PFHE) applications operating at temperatures above 150°C, especially in high-pressure service.

Additionally, aluminium is vulnerable to damage from rough handling, excessive vibration, and localized unrelieved stresses. These factors can compromise the structural integrity of aluminium components and lead to premature failure or reduced performance.

3. Fabrication of Aluminium Pressure Vessel and Heat Exchangers

Aluminium alloys can be joined using a variety of fusion and solid-state welding processes, as well as brazing and soldering methods. Fusion welding is typically performed using processes such as Gas Metal Arc Welding (GMAW), Gas Tungsten Arc Welding (GTAW), Flux-Cored Arc Welding (FCAW), Shielded Metal Arc Welding (SMAW), resistance spot welding, and resistance seam welding. For specialized applications, Plasma and Electron Beam welding methods may also be utilized.

Oxyfuel gas welding is an option for applications where high strength and top-quality welds are not critical for the intended service. However, it’s worth noting that flux shielding is unsuitable for aluminium welding, as flux tends to corrode the metal and produce spatter, which can compromise the integrity of the weld.

3.1 Surface Preparation

The following methods can be employed to clean aluminium surfaces effectively:

  • Solvent Degreasing: This involves wiping, spraying, or dipping the aluminium surfaces in solvents to remove oil, grease, dirt, and loose particles. Vapour degreasing is also an effective method for removing contaminants.
  • Mechanical Cleaning: Oxide removal can be achieved through mechanical means such as stainless steel wire brushing, filing, milling, rubbing with steel wool, sanding, or rotary planning. These methods help remove surface oxides and other impurities.
  • Chemical Cleaning: Chemical cleaning processes can also be used to remove contaminants from aluminium surfaces. These methods typically involve the use of specific chemical solutions or cleaners tailored to dissolve and remove the particular contaminants present on the surface.

3.2 Cutting and Bending

Aluminium can be cut to size and shape and its edges prepared using a variety of metalworking tools and methods. However, oxygas cutting is not suitable for aluminium. When bending aluminium and its alloys, caution must be exercised to prevent scoring and mechanical damage due to their softness.

It is crucial to avoid introducing iron and other foreign metallic inclusions into aluminium surfaces. To achieve this, plates can be covered with plastic or sheets of paper, and paper can be pasted over rolls or a sheet of hardboard can be inserted between the plate and the rolls. When handling large sheets or plates, vacuum lifters can be used to lift them safely without causing damage.

3.3 Welding

Preheating: Preheating is usually avoided, because the properties and metallurgy of aluminium almost always suffer from high heat.

Travel Speed: Unlike steel, aluminium possesses high thermal conductivity, which mandates the use of higher amperage and voltage settings, as well as faster weld travel speeds. If the travel speed is too slow, it can lead to excessive burn-through, particularly when working with thin gauge aluminium sheet. Aluminium welding requires a “hot and fast” approach

Welding Wire: Select an aluminium filler wire that has a melting temperature similar to the base metal.

Welding Filler Metals: Aluminium welding rods and electrodes are commonly utilized in gas tungsten arc, gas metal arc, and oxyfuel gas welding methods. When deciding on aluminium filler material, consider aspects such as ease of welding, corrosion resistance, high-temperature durability, response to anodic treatments, improved strength or ductility, and reduced risk of hot cracking. Opt for a filler with a higher alloy content compared to the base metal. To achieve the desired weld metal properties, ensure that the filler materials are devoid of gas, non-metallic inclusions, and surface impurities. Store the welding wire in a dry location at consistent temperatures and keep it covered to maintain its quality.

Welding Methods:

  • GTAW: The gas tungsten arc welding (GTAW) process effectively addresses two key challenges associated with aluminium welding: its high heat conductivity and the presence of an aluminium oxide surface film. By concentrating substantial heat, GTAW efficiently removes the refractory oxide layer and rapidly melts the base metal, resulting in smooth, high-quality welds free from spatter. Due to aluminium’s high thermal conductivity, it tends to draw heat away from the arc. Therefore, before adding filler metal to the molten pool, the welder should pause to allow the arc to clean the base metal and ensure it reaches the required temperature.
  • GMAW: Gas metal arc welding (GMAW) is likely the preferred method for welding aluminium in heavier sections compared to gas tungsten arc welding (GTAW). It offers significantly higher production rates than GTAW. The combination of higher current density and effective heat transfer in the arc enables deep penetration, fast welding speeds, minimal distortion of the base metal, and excellent mechanical strength.

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