Development of a Cryogenic Test Device for Cryogenic Valves

Abstract: This paper presents a cryogenic test device for valves, comprising a cryogenic test tank, a support frame, and a spray system. The device serves dual purposes: cryogenic treatment of components and low-temperature performance testing of valves. The cryogenic test tank features an open, double-layer stainless steel structure with an insulated cover and polyurethane foam filling. The test tank incorporates a spray system, enabling low-temperature testing through both immersion and spraying. An internal support frame securely holds the test valve and facilitates height adjustment. The device has proven to be reliable and stable in practical applications.

1. Introduction

As industries like air separation, liquefied natural gas, and ethylene petrochemicals advance, the demand for cryogenic valves has grown steadily, with applications expanding significantly. Ensuring the safe and reliable operation of cryogenic valves at low temperatures requires designers to balance mechanical strength with heat transfer considerations.

The physical and mechanical properties of materials at low temperatures differ significantly from those at room temperature. As temperatures decrease, the tensile strength and hardness of steel typically increase, while its plasticity and toughness decrease sharply. This ductile-to-brittle transition compromises material strength and service life, potentially causing brittle fractures and critical failures.

Austenitic stainless steel is the material most commonly used for low-temperature valves. Thanks to its face-centered cubic lattice structure, austenitic stainless steel lacks a critical temperature for the ductile-to-brittle transition and maintains high toughness at low temperatures. While austenite is metastable at room temperature, it undergoes martensitic transformation at low temperatures, causing partial volume expansion and part deformation, which can lead to cryogenic valve leakage.

Conventional heat treatment processes struggle to enhance both the strength and toughness of metals simultaneously, often requiring a trade-off between these properties. Cryogenic treatment is a specialized process that simultaneously enhances the strength and toughness of metals, improves wear resistance, and reduces residual stress to minimize part deformation. Consequently, designing a cryogenic test device for valves, treating key components cryogenically before final processing, and conducting low-temperature performance tests are critical for ensuring reliability.

2. Design Requirements

The key design parameters of the cryogenic valve test device are as follows:
a) The test tank dimensions are 2200 mm (length), 1300 mm (width), and 1700 mm (height).

b) The height of the test valve is adjustable to meet specific test conditions.
c) The device supports two cooling methods: immersion cooling and spray cooling.
d) The surface of the test tank must remain free from condensation during testing.

3. System Structure Design

As illustrated in Figure 1, the cryogenic valve test device consists of a deep-cold test tank, a spray system, and a support frame. The device uses liquid nitrogen as the cooling medium to perform cryogenic treatment on critical valve components and conduct low-temperature performance tests on the entire valve. The deep-cold test tank primarily functions as a reservoir for liquid nitrogen and provides thermal insulation. It features two liquid inlets: one at the bottom for tests at 77K and another connected to the internal spray system for tests ranging from 77K to 300K. The support frame secures the valve, adjusts its height, and compensates for the torque generated during valve operation.

Figure 1 The structure of cryogenic testing devise for cryogenic valve

4. Main Component Design

4.1 Cryogenic Test Tank

The test tank consists of three main components: the tank cover, tank body, and base. The tank cover consists of two halves, with a circular coupling hole at the center. During testing, the valve stem extends outside the tank. The tank cover is lined with polyurethane foam for insulation. The tank body features a frame structure. The dimensions of the inner tank are 2200 mm × 1300 mm × 1700 mm. The space between the inner and outer liners is filled with polyurethane foam. The outer liner features a multi-door structure, reinforced with channel steel to minimize deformation caused by the expansion of the foaming agent during the insulation process, and is designed for easy maintenance.

The base consists of a square, load-bearing frame structure. The base, inner liner, and outer liner are designed separately (as shown in Figure 2). During testing, the inner liner is filled with liquid nitrogen, maintaining a temperature of 77 K, while the outer liner stays near room temperature. This temperature difference causes asynchronous contraction, resulting in deformation of the tank body. To reduce deformation, the inner and outer liners and the base are designed separately. The inner and outer liners rest on the bottom plate, supported by multiple epoxy mounts that provide stability and minimize movement. An L-shaped fixing block is mounted on the bottom plate, while a grooved recess is machined into the side plate. The side plate of the outer liner is fastened to the fixing block using bolts. Asynchronous shrinkage of the inner and outer liners during testing enables the bolts to slide vertically, reducing overall deformation of the tank. Additionally, this design provides cushioning to absorb impacts during hoisting.

Figure 2 The Separated Design Structure of the Inner and Outer Liners

4.2 Spray Device

As shown in Figure 3, the spray device consists of a vertical liquid inlet pipe and a spray pipe. The vertical liquid inlet pipe is connected to the spray pipe at the bottom of the tank using a slip-on ball joint, allowing for easy disassembly when the device is not in use. The spray pipe includes a stainless steel pipe, a ferrule joint, a copper pipe, and a nozzle. The valve on the liquid inlet pipe is opened to permit liquid nitrogen flow into the spray device, allowing for a test temperature range from 77 K to room temperature. The gas-liquid mixture is discharged through the brass nozzle to cool the test valve. The temperature of the test valve is controlled by adjusting the solenoid valve on the inlet pipeline.

Figure 3 The Design of the Spray Device

4.3 Support Frames

As shown in Figure 4, the support frame comprises a bottom plate, a height adjustment mechanism, a clamping mechanism, and a balancing device. The support frame secures the test valve, adjusts its height, and balances the torque generated during operation. Prior to testing, the bottom plate is adjusted to the required height using the height adjustment mechanism, and the test valve is then secured in place using two clamping mechanisms. The bolts at both ends of the balancing mechanism are adjusted to apply pressure to the inner wall of the enclosure, preventing the test valve from twisting during operation.

5. Conclusion

The cryogenic test device described in this paper uses liquid nitrogen as the cooling medium and supports both immersion and spray testing methods for cryogenic valve testing. The device operates within a test temperature range from 77 K to room temperature. The test tank features a separated inner and outer tank structure, effectively minimizing deformation of the tank body during testing. Additionally, the support frame includes adjustable fixing and lifting mechanisms, enabling height adjustment of the test valve and preventing twisting during operation. The device demonstrates reliable performance in practical applications and provides reliable cryogenic valve testing.