Pressure Anomalies & Safety Design |

Pressure Anomalies & Safety Design
Post-shutdown pressure spikes, high-point flashing, reactor bulging - four types of pressure anomaly scenarios with diagnosis and safety design essentials, plus real case analysis.

4 Pressure Anomaly Types
4 Real Cases
4 Safety Design Steps

Pressure Anomalies & Safety Design

Post-shutdown pressure spikes, high-point flashing, reactor bulging - four types of pressure anomaly scenarios with diagnosis and safety design essentials, plus real case analysis.

4 Pressure Anomaly Types4 Real Cases4 Safety Design Steps

Pressure AnomaliesFour Scenarios

Abnormal Pressure Rise After Shutdown

Scenario: LM-8 operating at -35C, pressure rose from 3 bar to 8 bar after shutdown. Root cause: Thermal expansion causes pressure increase; system lacks pressure relief devices. Solution: Add pressurized make-up water device or expansion tank to absorb volume changes from temperature variations.

High-Point Gas Flashing

Scenario: System pressure near critical point, coolant flashing at high points. Root cause: Insufficient system pressure, approaching saturation vapor pressure at current temperature. Solution: Increase nitrogen pressurization (e.g., from 50 kPa to 80 kPa) to ensure minimum pressure point exceeds saturation vapor pressure.

Reactor Bulging and Deformation

Scenario: LM-11C reactor bulged and deformed after closing valves. Root cause: After closing reactor inlet/outlet valves, temperature changes cause medium volume changes, generating enormous pressure. Solution: Do not fully close outlet valve; maintain tank connection. Or install safety pressure relief device.

Boiling and Overflow During Heating

Scenario: LM-15B boiled and overflowed when heated to 106C. Root cause: High water content in system; water boils at boiling point and carries coolant out. Solution: Let coolant stand to separate water first, then proceed with heating. Ensure system water content is within reasonable range.

Pressure AnomaliesReal Cases

2025.03.30LM-8

Aerospace Yisenlin · -

LM-8 operating at -35°C; pressure rises from 3bar to 8bar after shutdown

Thermal expansion without pressure relief device; recommended adding pressure-maintaining makeup device

2025.04.27LM-15B

Chongqing Changyu Electromechanical · Chongqing

LM-15B boils and overflows when heated to 106°C

High water content in system; boiling carries coolant out. Recommended separating water first before heating

2025.10.06LM-11D/LM-4

- · Taizhou

LM-11D replaced LM-4; temperature cannot decrease

11D specific heat and thermal conductivity both lower than LM-4; heat exchange capacity insufficient. Customer considering reverting to LM-4

2025.10.16LM-4

- · Zhejiang

LM-4 pressurization; system pressure near critical point

Recommended increasing nitrogen pressurization from 50kPa to 80kPa to prevent high-point flash vaporization

Pressure SafetyDesign Essentials

Install Expansion Tank / Make-Up Water Device

All coolant systems should be equipped with an expansion tank or pressurized make-up water device to absorb medium volume expansion caused by temperature changes. Tank volume should be calculated based on total coolant volume and temperature differential.

Safety Relief Devices Are Essential

Install safety valves or relief valves at key system positions. Reactors and other sealed vessels especially need pressure relief protection. Outlet valves should not be fully closed - maintain connection to tank or expansion tank.

Adequate Nitrogen Pressurization

When pressurizing the system with nitrogen, ensure the pressure at the system's highest point (weakest point) exceeds the medium's saturation vapor pressure at that temperature. Recommend leaving margin in pressurization, e.g., increase from 50 kPa to 80 kPa.

Control Water Content in High-Temp Systems

For high-temperature heat transfer oil systems like LM-15B, excessive water content causes boiling and coolant carryover during heating. Water must be separated before heating to ensure water content is within safe range.

Safety Red Lines

Reactor valve operation: For water-free coolant systems like LM-11C, reactor inlet/outlet valves must not be fully closed. Temperature changes cause medium volume changes in sealed spaces, generating enormous pressure that can cause bulging, deformation, or even rupture. Maintain tank connection or install safety relief devices.
Shutdown protection: Temperature rise during shutdown causes thermal expansion. Systems without relief devices may see pressure spike from 3 bar to 8 bar after shutdown. Expansion tanks must be installed to absorb volume changes.

PressureFAQ

System pressure abnormally rises after shutdown

Cause: Thermal expansion causes pressure increase; system lacks pressure relief device

Solution: Recommend adding pressure-maintaining water makeup device or expansion tank to absorb volume changes from temperature variations

System high-point flash vaporization

Cause: Insufficient system pressure, approaching saturation vapor pressure of medium at current temperature

Solution: Recommend increasing nitrogen pressurization (e.g., from 50kPa to 80kPa), ensuring system minimum pressure point exceeds saturation vapor pressure

Reactor bulges and deforms after valve closure

Cause: Closing reactor inlet/outlet valves with temperature changes causes medium volume change, generating enormous pressure

Solution: Do not fully close outlet valve; maintain connection to water tank. Or add safety pressure relief device

LM-15B boils and overflows when heated to 106°C

Cause: High water content in system; water boils at boiling point, carrying coolant out

Solution: First let coolant stand and separate water, then proceed with heating. Ensure water content is within reasonable range

Pressure Anomalies & Safety Design