Cryogenic Piping
- Apr 14, 2018 -

What are the scopes of design for cryogenic piping?

A: (1) Low-temperature pipelines have applications in all walks of life, especially in petrochemical enterprises. The carbon steel pipe is ductile in the range of +5°C to -19°C and can be used normally. If the service temperature is lower than or equal to -20°C, the carbon steel pipe gradually becomes brittle and the use is limited by certain conditions. Therefore, pipes below or equal to -20°C belong to cryogenic pipes.


(2) The cold pipe layout mainly considers two issues. The first is “low-temperature brittleness”, which requires designers to reasonably select steel plates with “impact toughness” and prevent brittle fractures and brittle fractures from piping design and piping production. The second is the design of the cold insulation structure of the pipeline and the design requirements for cold insulation. It is directly related to the operation, construction, and overhaul of energy consumption and equipment pipelines.


55 What are the requirements for cryogenic piping arrangements?


Answer: (1) The layout of cryogenic piping should consider that the entire pipeline is flexible enough to make full use of the natural compensation of the pipeline. When the design temperature is low and it cannot be compensated naturally, the compensator should be set.


(2) Pipeline vibration should be avoided during low-temperature pipeline layout, especially for pumps, compressors and exhaust pipes. Vibration of the entire pipeline must be prevented. If there is a mechanical vibration source, vibration-reducing facilities should be adopted to approach the source of vibration. The pipeline should be equipped with elastic elements such as corrugated compensators to isolate vibration sources.


(3) In the low-temperature pipelines of carbon steel and low-alloy steel, the branch pipes equipped with safety valves, exhaust pipes or drain valves shall pay attention to whether or not the cryogenic liquid medium is vaporized immediately after discharge. If the gasification requires a large amount of heat absorption, , It is necessary to dew condensation until the ice is formed, so that the temperature of the pipeline is reduced to very low, so this kind of branch pipe should be made of austenitic stainless steel in the range of easy freezing, and then use a flange to connect the branch pipes of different materials.


(4) The stress at the elbow of the low-temperature pipe is the largest, so the elbow is most likely to be brittle and should not be welded.


(5) On low temperature pipelines, close to the elbow or tee, welding flanges are generally not allowed. In order to remove the bolt without destroying the cooling layer on the main pipe, it is necessary to extend the length (with a short pipe) and then weld the flange. In the mating flange, it is only necessary to ensure the spacing of the loading and unloading bolts at one end of the flange. The piping of the valve group should consider that any one of the valves can be smoothly removed without affecting the cold insulation structure of the pipeline.


(6) Cold-temperature and cold-maintaining pipe supports must have measures to prevent the occurrence of "cold bridges";


1) When the low-temperature pipeline is laid horizontally, generally blocks of wood or hard insulation material are placed on the bottom of the pipeline to avoid loss of coldness in the pipeline.


2) When the low-temperature pipeline is laid vertically, when the bracket is rooted on the cryogenic equipment, blocks of wood or hard insulation should be placed on the equipment and pipeline.


56 pipeline sampling pipe layout principle is what?


Answer: (1) The sampling takeover should not be based on equipment and pipelines with vibration, such as pumps, compressors, etc. It should also be avoided on the pipeline directly connected to the vibration equipment. If it is difficult to avoid, vibration reduction measures should be taken;


(2) Sampling tube settings should meet the process requirements, and should avoid dead ends or "pockets." The sampling valve should be placed in a place convenient for operation; otherwise, a platform should be set up, and the pipe length between the equipment or piping and the sampling valve should be as short as possible.


(3) Leading position of gas sampling tube:


1) When sampling from a horizontal pipe, the sampling pipe should be located at the top of the pipe;


2) When sampling from the riser, when the gas flows from bottom to top, the sampling port shall be led out from the riser at an angle of 45° upward; when the gas contains solid particles, the sampling tube shall extend to the center of the tube; when the gas is from above The sample tube should be opened horizontally when flowing down

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