Materials and Pipe Supports for Cryogenic Services

Cryogenic piping refers to the piping network that operates below -290°C. This temperature represents the demarcation of embrittlement for carbon steel materials. However, various literature considers the piping systems operating below -196°C (-321°F) as true cryogenic piping systems. Industrial processes and transportation of propane, butane (LPG), methane (LNG), ethylene, nitrogen, ammonia, oxygen, etc., require extensive use of cryogenic piping. These piping systems must be designed with special care to work at such low temperatures. In this article, we will delve deeper into the details surrounding cryogenic piping.

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Properties of Common Cryogenic Materials

Cryogenic materials are typically odorless, tasteless, and colorless when vaporized. It is crucial to handle cryogenic liquids with care, as they may cause skin burns and frostbite. The temperatures and expansion ratios of several common cryogenic materials are provided below:

Oxygen: -860
Nitrogen: -196
Methane: -162
Helium: -269
Argon: -186
Hydrogen: -253
Fluorine: -188

Why is Cryogenic Piping Challenging?

At extremely low operational temperatures, the materials used for pipes can experience a variety of corrosion and deterioration issues, as their chemical and physical properties change significantly. Standard piping systems are unable to contain gases in liquid form; as depicted in the table, cryogenic liquids generate a substantial volume of gas upon vaporization. If vaporization occurs within a sealed container, the resulting pressure buildup could lead to catastrophic failures. Consequently, the design of cryogenic piping systems requires specialized materials, supports, and valves, distinct from those of traditional piping systems. Key requirements for cryogenic piping systems include:

• Flexibility to accommodate large thermal stresses from material contraction.
• Insulation to prevent heat gain from the environment, which can increase rigidity.
• Use of specially designed cryogenic valves to maintain effective operations.
• High-quality materials to reduce overall project costs.

Cryogenic Piping Materials

As temperatures drop, materials may become brittle, necessitating impact testing as mandated by relevant codes. When selecting cryogenic piping materials, various factors must be considered, including:

• Suitability for various fabrication techniques
• Corrosion resistance
• Resistance to oxidation and sulfidation
• Strength and ductility
• Compatibility with cleaning processes
• Toughness and resistance to abrasion and erosion
• Physical property characteristics
• Rigidity
• Impact resistance

The following are materials commonly recognized as suitable for cryogenic piping:

SA-333 Grade 1: -46°C
SA-333 Grade 7: -73°C
SA-333 Grade 3: -101°C
SA-333 Grade 8: -196°C
Austenitic Stainless Steel (Grade 304, 304L, 321, 347): -254°C
Austenitic Stainless Steel (Grade 316, 316L, 316 Ti, 316 Nb): -196°C

Aluminum Alloy: -254°C
Copper Alloy: -198°C
Monel 400: -198°C

Additionally, non-metallic materials such as Grafoil, Mineral wool, Fiberglass, Polyurethane, Styrofoam, Perlite, Viton, and glass reinforced Teflon, etc., are utilized across various components in cryogenic piping applications.

Cryogenic Piping Standards and Design Guidelines

ASME B31.3 serves as the primary governing standard for the design of cryogenic piping systems. Common design considerations include:

• Pipes are sized based on normal pressure drop criteria, accounting for potential phase changes.
• Heat leaks from ambient temperatures into cryogenic pipelines must be addressed in the design.
• Extended stem valves help maintain operator safety by keeping operators at ambient temperature.

Cryogenic Piping Insulation

Most cryogenic piping systems are insulated using one of the following insulation types:

• Expanded foams (e.g., foam glass, polyurethane)
• Powder insulation (e.g., perlite)
• Vacuum insulation
• Evacuated powder and fibrous insulation
• Opacified powder insulation

The primary goal of cryogenic piping insulation is to create a vapor barrier to prevent atmospheric moisture from permeating the insulation space, which could lead to increased corrosion and reduced performance. If insulation integrity is compromised, thermal efficiency will decrease, subsequently elevating energy consumption. Thus, utilizing appropriate insulation materials is crucial for maximizing efficiency and preventing moisture infiltration.

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Whenever a cold system is needed, comprehensive insulation shall be employed, encompassing all piping components, instruments, drains, equipment nozzles, and supports. Cryogenic insulation is typically applied in multiple layers.

Cryogenic Piping Supports

Due to their extremely low temperatures, cryogenic pipe supports must boast superior insulation properties, durability, and stable functionality. When designing cryogenic supports, structural characteristics, design loads, and economic factors must be considered for each shoe, guide, stop, and trunnion. It is vital to understand how cryogenic piping behaves throughout normal operations, including warm-up and cool-down conditions. This also addresses challenges such as higher displacements resulting from thermal expansion and contraction, material embrittlement, icing, and rapid phase changes linked to substantial heat flux variations.

Cryogenic pipe supports should fulfill the following requirements:

• Reduced weight
• Exceptional reliability in wet conditions, demonstrating resistance to oil and corrosion
• High weatherproof qualities
• Robust physical strength against compression, bending, and shearing
• Manufacturability for mass production
• Low water absorption
• Resistance to heat and flames
• Incorporation of a molded heavy-density layer bonded with stainless steel

Common materials used for cold insulation supports include:

• High-density polyurethane foam
• Phenolic foam insulation
• Polyisocyanurate (PIR)

Supports must meet design specifications related to compressive strength, thermal conductivity, friction coefficients, service temperatures, and flammability. Despite unexpected thermal bowing and flow rate fluctuations, the support span for cryogenic pipelines should be significantly shorter than for hot insulated piping, with supports placed immediately adjacent to any directional changes in piping.

Typical cryogenic supports come equipped with cutting-edge temperature-resistant technology to protect pipes under extreme cold conditions. In frigid environments, supports must manage both the challenges of fragile pipes and the detrimental effects of ice formation. Designs should ensure that they can support pipes in temperatures dipping as low as -320°F, encompassing the fragile insulation used in these systems.

To mitigate thermal transfer between the interior of the pipes and surrounding structures, the supports should be non-conductive. Some shoe designs feature foam-insulated cores, allowing for natural temperature regulation and energy conservation while also preventing ice formation. A cold shoe is an essential support for cryogenic applications where heat transfer is non-critical, operating effectively in conditions as low as -300°F.

Cryogenic Piping Stress Analysis

Cryogenic pipelines present unique challenges due to the significant temperature differences between their operational settings and installed ambient temperatures. Thorough flexibility analysis is critical for ensuring operational safety and hazard prevention, necessitating careful management of thermal forces, stresses, and displacements. Notable cryogenic piping stress analysis considerations include:

LNG and cold box piping systems serve as key examples of cryogenic piping.

Why use a cryogenic support for a cold pipeline?

Insulation types are classified according to their temperature ranges. Typically, high-temperature supports utilize distinct insulation types compared to low-temperature supports. Cryogenic systems require specific support designed for cold pipelines.

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