What are the common faults of high temperature and high pressure gate valves?

2025-04-18 09:39:34

High temperature and high-pressure Gate valves, due to long-term operation in harsh working conditions (temperature ≥ 343 ℃, pressure ≥ 10MPa), often experience failures related to material performance degradation, seal failure, structural stress, and medium corrosion. The following are common fault classifications and cause analysis:

1、 Sealing failure fault

1. Sealing surface leakage (internal leakage)

reason:

Wear/scratch of sealing surface: High pressure medium erosion or particle impurities embedding can cause grooves on the sealing surface (such as Stellite alloy layer welding); The hardness of the material decreases and the wear resistance weakens at high temperatures.

Thermal deformation misalignment: Inconsistent thermal expansion coefficients between the valve body and the gate plate (such as carbon steel valve body with stainless steel gate plate), resulting in failure of sealing surface adhesion at high temperatures.

Sealing surface corrosion: The medium contains corrosive components such as sulfides and chloride ions, which can cause intergranular corrosion or stress corrosion cracking (SCC).

Typical manifestation: Even after the valve is completely closed, there is still medium flow in the downstream pipeline (insufficient pressure drop).

2. Leakage of stuffing box (external leakage)

reason:

Aging and failure of fillers: graphite fillers lose weight due to oxidation at high temperatures, PTFE fillers carbonize and lose elasticity; High pressure causes the packing gland bolts to loosen.

Valve stem wear/corrosion: Long term friction between the packing and the valve stem results in scratches on the surface; Under high temperature and high pressure, the protective layer (such as chrome plating) on the surface of the valve stem falls off, causing medium corrosion.

Thermal expansion gap variation: The fitting gap between the valve stem and the packing box changes due to temperature fluctuations, resulting in insufficient sealing pressure.

Typical manifestation: Medium leakage (such as steam, high-temperature oil droplets) occurs at the contact between the valve stem and the packing box.

3. Flange/gasket leakage

reason:

Improper selection of gaskets: Failure to use high-temperature and high-pressure specialized gaskets (such as metal wrap gaskets, toothed gaskets), or incompatible gasket materials with the medium (such as ordinary asbestos gaskets used for acidic media).

Bolt stress relaxation: under high temperature, the bolt undergoes creep and the pre tightening force decays; The bolt material (such as ordinary carbon steel) has insufficient strength at high temperatures, leading to fracture.

2、 Material and structural failure and malfunction

1. Cracks in valve body/valve cover

reason:

Thermal fatigue cracking: Frequent start stop or sudden temperature changes (such as rapid cooling and heating) can cause cracks in stress concentration areas of the valve body (such as corners and welds).

Creep deformation: After long-term operation at temperatures close to the creep temperature of the material (such as carbon steel>427 ℃), the material undergoes slow plastic deformation and the wall thickness decreases.

Welding defects: There are slag inclusions and porosity during the casting or welding process of the valve body, and the defects propagate into cracks under high temperature and high pressure.

2. Gate/stem fracture

reason:

Stress Corrosion Cracking (SCC): The valve stem material (such as martensitic stainless steel) undergoes intergranular fracture due to the synergistic effect of tensile stress and corrosion in media containing H ₂ S and Cl ⁻.

Fatigue fracture: Frequent switching causes stress concentration on the valve stem thread or gate connection, resulting in the formation and propagation of microcracks on the surface.

Material deterioration: At high temperatures, the material undergoes pearlite spheroidization (in carbon steel) and precipitation of σ phase (in stainless steel), resulting in a decrease in strength and toughness.

3. The valve stem is jammed/stuck

reason:

Lubrication failure: Lubricating grease carbonizes and dries under high temperature, or the gap between the valve stem and the guide sleeve is blocked by impurities due to high pressure.

Thermal expansion blockage: The valve stem and guide sleeve are made of different materials (such as steel+copper alloy), resulting in inconsistent expansion at high temperatures and loss of clearance.

3、 Transmission and operation faults

1. Difficulty in operating handwheel/gearbox

reason:

Component deformation: High temperature causes deformation of the gearbox housing and changes in gear mesh clearance; The keyway of the handwheel shaft is stuck due to thermal expansion.

Lubrication failure: Lubricating oil loses viscosity at high temperatures, or solidifies due to increased viscosity at low temperatures (if heat tracing fails).

2. Electric actuator malfunction

reason:

Motor overheating: Poor heat dissipation of the motor in high temperature environments, aging and short circuiting of the insulation layer;

Torque sensor misoperation: The valve stem is stuck, causing torque overload, or the sensor is triggered incorrectly due to high temperature drift.

4、 Other typical faults

1. Unqualified pressure test

Reason: The high temperature pressure test was not conducted in accordance with ASME B16.34. Valves that were qualified at room temperature had insufficient sealing pressure due to material softening at high temperatures.

2. Anti scalding/insulation layer failure

Indirect impact: Damage to the insulation layer can cause abnormal valve body temperature (such as local low temperature), leading to medium condensation corrosion or accelerated packing failure.

Key points of fault prevention and maintenance

Material adaptation:

Choose chromium molybdenum vanadium steel (such as F91) or nickel based alloys for high temperatures above 540 ℃ to avoid using carbon steel at excessive temperatures;

The sulfur-containing medium adopts SCC resistant materials (such as duplex stainless steel 2205).

Sealing optimization:

Hard sealing surface is welded with cobalt based alloy (such as Stellite 6) to improve wear resistance;

The filling material adopts a flexible graphite+metal wire reinforced structure, and the filling cover bolts are regularly tightened in a hot state.

Structural design:

Adopting an extended valve cover (heat dissipation type) to reduce the temperature of the packing box, and surface hardening treatment of the valve stem (such as nitriding);

Perform 100% radiographic testing (RT) on the welded valve body to eliminate potential crack hazards.

Operation and maintenance strategy:

Establish a temperature pressure monitoring ledger to avoid operating beyond normal conditions;

Periodic disassembly inspection of sealing surface wear (recommended once a year), replacement of aging packing and gaskets.

summarize

The core fault of high-temperature and high-pressure gate valves is material degradation and sealing failure caused by the coupling effect of "thermal mechanical corrosion". Prevention requires full process control from material selection, structural design, installation and commissioning to periodic maintenance, with particular attention to the sealing surface condition, valve stem lubrication, and bolt pre tightening force, to ensure long-term reliable operation under harsh working conditions.