Cryogenic Piping: What is it?
Cryogenic piping is the system of piping networks that operate below -290C, representing the embrittlement point for carbon steel materials. Its use is widespread in the industrial processing and transportation of propane, butane (LPG), methane (LNG), ethylene, nitrogen, ammonia, oxygen, and other liquids.
Materials and Pipe Supports for Cryogenic Services
When handling cryogenic liquids, they must be treated with care to avoid skin burns and frostbite. Table-1 below lists the liquid temperatures and the liquid-to-gas expansion ratio of some of the common cryogenic materials. It is important to select the appropriate materials and pipe supports for cryogenic services in order to ensure the safety and efficiency of the system.
| Cryogenic Material | Liquid Temperature (°C) | Liquid-to-gas Volume Expansion Ratio |
|---|---|---|
| Oxygen | -183 | 1: 860 |
| Nitrogen | -196 | 1: 696 |
| Methane | -162 | 1: 579 |
| Helium | -269 | 1: 757 |
| Argon | -186 | 1: 847 |
| Hydrogen | -253 | 1: 851 |
| Fluorine | -187 | 1: 888 |
Cryogenic Materials
Cryogenic materials are substances that exist in a liquid state at extremely low temperatures. These materials are used in a variety of applications, including cryogenic cooling, cryogenic storage, and cryogenic processing.Liquid Temperatures and Volume Expansion Ratios
The table above lists the liquid temperature and liquid-to-gas volume expansion ratio of several different cryogenic materials. Oxygen has a liquid temperature of -183°C and an expansion ratio of 1:860. Nitrogen has a liquid temperature of -196°C and an expansion ratio of 1:696. Methane has a liquid temperature of -162°C and an expansion ratio of 1:579. Helium has a liquid temperature of -269°C and an expansion ratio of 1:757. Argon has a liquid temperature of -186°C and an expansion ratio of 1:847. Hydrogen has a liquid temperature of -253°C and an expansion ratio of 1:851. Fluorine has a liquid temperature of -187°C and an expansion ratio of 1:888.Challenges of Cryogenic Piping
Cryogenic piping presents a unique set of challenges due to the extremely low temperatures it operates at. The material of the pipe is subject to different types of corrosion and deterioration due to the changes in the chemical and physical properties of the material. In addition, cryogenic liquids generate a large volume of gases when vaporized which can create an enormous pressure in a sealed container, potentially leading to bursting.
Flexibility Requirements
In order to compensate for the thermal stresses created by the contraction of the pipe material at lower temperatures, sufficient flexibility must be incorporated into the piping system. All cryogenic lines must also be insulated to avoid heat gain from the environment and for safety, which adds additional weight.
Specially Designed Valves
Specially designed, long-stem, extended bonnet valves are used as Cryogenic Valves to ensure proper operation of the cryogenic piping system. The use of costly materials increases the overall project cost, so every chance of optimization must be taken to minimize the project cost.
Selecting Cryogenic Piping Materials: Considerations and Parameters
When selecting cryogenic piping materials, a number of factors need to be taken into account. These include suitability for different fabrication techniques, corrosion resistance, resistance to oxidation and sulfidation, strength and ductility, suitable for the cleaning process, toughness, resistance to abrasion, erosion, galling, and sizing, physical property characteristics, rigidity, and impact resistance.
Materials for Cryogenic Piping: Table of Suitable Options
Table 2 below provides a list of materials that have established themselves as suitable for cryogenic piping. Table-2: Common Cryogenic piping materials
| Ferrous Materials |
| Cryogenic Piping Material | Lowest Temperature (0C) for Application |
|---|---|
| SA-333 Grade 1 | -46 |
| SA-333 Grade 7 | -73 |
| SA-333 Grade 3 | -101 |
| SA-333 Grade 8 | -196 |
| Austenitic Stainless Steel (Grade 304, 304L, 321, 347) | -254 |
| Austenitic Stainless Steel (Grade 316, 316L, 316 Ti, 316 Nb) | -196 |
| Non-Ferrous Cryogenic Pipe Materials |
| Cryogenic Piping Material | Lowest Temperature (0C) for Application |
|---|---|
| Aluminum Alloy (1100, 3003, 5052, 5083, 6061, 5086) | -254 |
| Copper Alloy (C10200/C12200), Copper Nickel Alloy (70600, C71500) | -198 |
| Monel 400 | -198 |
Cryogenic Piping Standards and Design Guide
The ASME B31.3 is the primary governing standard for designing cryogenic piping systems. When designing a cryogenic pipeline and piping system, it is important to consider pipe sizing, heat leakage, and the use of extended stem valves.
Pipe Sizing for Cryogenic Piping
Pipe sizing is done according to normal pressure drop criteria. A drop in pressure can create flashing of part of the liquid which may result in a two-phase flow. In such cases, two-phase flow must be taken into account for sizing. However, for oxygen gas piping, the fluid velocity is also considered.
Heat Leakage Considerations
As the ambient temperature is higher than the cryogenic liquid temperature, there will be a continuous heat leak to the cryogenic pipeline and piping system. This heat leakage must be taken into account during the design.
Use of Extended Stem Valves
Extended stem valves are used to keep the operator at an ambient temperature. This is an important part of designing a cryogenic piping system.
Cryogenic Piping Insulation: Key Benefits
Cryogenic piping insulation provides a number of key benefits, including creating a vapor barrier to keep atmospheric moisture from leaking into the insulation space, preventing the build-up of water or ice, and reducing energy consumption. This insulation system helps maintain the thermal efficiency of the system, ultimately reducing energy costs.
Types of Cryogenic Insulation
When it comes to cryogenic insulation, there are a variety of materials used to effectively insulate piping and pipelines. These include expanded foams, such as foam glass and polyurethane, powder insulation, vacuum insulation, evacuated powder and fibrous insulation, and opacified powder insulation. The insulation must create a vapor barrier to keep atmospheric moisture from entering the insulation space and freezing against the cryogenic lines.
Insulating Entire Systems
When a cold system is needed, the entire system should be fully insulated, including any piping components, tubing and instruments, drains, equipment nozzles, and supports. Cryogenic insulation is applied in multiple layers in order to create an effective barrier. This helps to maintain the thermal efficiency of the system, ultimately reducing energy costs.
What are Cryogenic Piping Supports?
Cryogenic piping supports are designed to meet the requirements of extremely low temperatures, superior insulation properties, durability, and a stable function. When designing cryogenic supports, structural characteristics, design loads, other requirements, and economical aspects must all be taken into consideration for each shoe, guide, stop, and trunnion. The pipe supports must also be able to withstand warm-up and cool-down conditions.
What are the Challenges of Cryogenic Piping Supports?
Cryogenic piping supports must be able to withstand a variety of challenges in order to function properly. These include higher displacement due to thermal expansion and contraction, pipe insulation, embrittlement of materials, and rapid changes of phase due to large heat fluxes. Additionally, icing can form around or between the supports.
What Requirements Must Cryogenic Pipe Supports Meet?
Cryogenic pipe supports must meet a variety of requirements in order to be effective. These requirements include being lightweight, high reliability in water and resistance to oil and corrosion, high weather tightness, and physical strength against compression, bending, and shearing. It is also important that the supports are suitable for mass production, have a low water absorption, and are heat and flame resistant.
What Materials are Used for Cold Insulation Supports?
Cold insulation supports are usually made from high-density polyurethane foam, phenolic foam insulation, and polyisocyanurate or PIR. It is important that the supports meet the design requirements in respect of compressive strength under sustained load, thermal conductivity, coefficient of friction, service temperature, and flammability.
What are Cold Shoes?
Cold shoes are a type of support specifically designed for cryogenic applications. They must be able to withstand temperatures as low as -320°F and incorporate a molded heavy-density layer bonded with stainless steel in order to stop the thermal transfer from the interior of the pipes to the surrounding structures. Additionally, foam-insulated cores may be used to keep pipes from sudden temperature changes of heat transfer.
Cryogenic Piping Stress Analysis
When it comes to analyzing the stress of cryogenic piping systems, there are special considerations that need to be taken into account. These include the thermal-bowing effect of the pipes, the connection between pipes with different displacements, the use of Finite Element Analysis to qualify equipment nozzle loads, and the different behavior of cryogenic piping systems compared to high-temperature piping systems.
Thermal-Bowing Effect
The thermal-bowing effect of cryogenic piping must be taken into account when analyzing the stress of these systems. This effect occurs when pipes are exposed to a large temperature difference, with the pipe at cryogenic temperature contracting and the jacketed pipe usually at a temperature higher than ambient expanding.
Connecting Pipes with Different Displacements
When connecting two pipes with different displacements, the main pipe which is at cryogenic temperature contracts and the jacketed pipe usually at a temperature bit above ambient expands. This must be taken into consideration when analyzing the stress of cryogenic piping systems.
Finite Element Analysis for Equipment Nozzle Loads
Equipment nozzle loads are usually qualified using Finite Element Analysis or FEA. This method of analysis allows for the most accurate stress analysis of cryogenic piping systems.
Using Expansion Bellows and Flexible Hoses
In order to analyze the stress of cryogenic piping systems, expansion bellows and flexible hoses may be required. This will help to reduce the stress placed on the pipes and ensure that the system is functioning safely and efficiently.
Behavior of Cryogenic Piping Systems
Cryogenic pipe systems behave in a completely different way to high-temperature piping systems. Due to the contraction of the cryogenic piping system, the supports that are usually lifted off in high-temperature piping carry the load in cryogenic-temperature piping.
Examples of Cryogenic Piping Systems
LNG Piping and Cold Box Piping systems are typical examples of cryogenic piping systems. These systems require careful analysis to ensure the safety and efficiency of their operations.