Reasons and solutions for getting stuck when stainless steel gear pumps transport high-temperature liquids

The sudden jamming of stainless steel gear pumps during the transportation of high-temperature liquids is a complex multifactor problem. The following is a systematic analysis of the causes and solutions:

1、 Main cause analysis

1.  Abnormal gap caused by thermal expansion

 Problem : The difference in thermal expansion coefficient between the gear and the pump body material causes the gap to shrink or even disappear at high temperatures, leading to friction jamming.

 Typical scenario : The difference in expansion between stainless steel gears and cast iron pump bodies at 200 ℃ is significant, resulting in meshing.

2. Lubrication failure

Problem: High temperature reduces the viscosity, oxidizes or carbonizes the lubricating oil, ruptures the lubricating film, and causes direct metal contact.

 Case : Mineral oil is prone to failure above 150 ℃, resulting in dry friction of bearings or gear shafts.

3. Insufficient high-temperature performance of the material

 Problem : Stainless steel (such as 304) softens (tensile strength decreases) at sustained high temperatures, causing gear deformation or surface hardening layer failure.

 Data reference : The strength of 304 stainless steel decreases by about 30% at 400 ℃ and more than 50% at 600 ℃.

4.  Changes in dielectric properties

 Problem : High temperature liquids precipitate coking materials (such as carbonization of heat transfer oil) or carry hard particles, causing channel blockage or abrasive wear.

 Case : Thermal oil decomposes above 300 ℃ to generate carbon slag, which accumulates in the gear meshing area.

5.  Cavitation and cavitation

 Problem : When the saturated vapor pressure of high-temperature liquids increases and the suction pressure is insufficient, bubbles are generated. When they collapse, they impact the metal surface and form pitting corrosion.

Data: The saturated vapor pressure of water reaches 4.76 bar at 150 ℃, which is significantly higher than that at room temperature (0.03 bar at 25 ℃).

2、 Systematic solution

1.  Material and Design Optimization

Upgrading material selection

The gear/pump body is made of materials with a matching coefficient of thermal expansion (such as 316L stainless steel gear+duplex stainless steel pump body).

Use heat-resistant alloys (such as Inconel 625) or surface sprayed ceramic coatings (such as Al ₂ O3) at extreme high temperatures (>400 ℃).

Gap compensation design

Adopting a thermal compensation structure (such as a floating side plate), the dynamic clearance under high temperature conditions is preset (usually increased by 0.02-0.05mm compared to normal temperature design).

2.  Lubrication system enhancement

Selection of High Temperature Lubricants

Use synthetic high-temperature grease (such as polyurea based grease, with a temperature resistance of up to 260 ℃) or solid lubrication (molybdenum disulfide coating).

For forced lubrication systems, use silicate ester high-temperature circulating oil (flash point>300 ℃) instead.

Cooling assistance

Install a circulating water-cooled jacket (control pump body temperature ≤ 150 ℃) or air-cooled heat dissipation fins. Reduce the thermal expansion and contraction of stainless steel gear pumps.

3.  Media management

 Filter system upgrade

Install a dual filter (accuracy ≤ 25 μ m) at the entrance, set a pressure difference alarm, and replace the filter element in a timely manner.

For media that are prone to coking, add an online flushing interface (regularly inject solvent for cleaning).

 Cavitation protection**

Increase NPSHa (such as lowering installation height, increasing inlet pipe diameter), ensuring that NPSHr margin is ≥ 1.3 times.

4.  Improvement of operation and maintenance strategy

Temperature monitoring**

Install PT100 temperature sensors at the pump body and bearings, and set two-level alarms (first level warning 80% of the design temperature, second level shutdown protection).

Preventive maintenance

Check the wear of the gear meshing surface every 500 hours (maximum allowable reduction in tooth thickness ≤ 3%), and regularly replace the shaft seal (such as graphite filled PTFE seal).

3、 Typical troubleshooting process

1. Check after emergency shutdown

Measure the temperature distribution of the pump body and confirm the local overheating area.

Observe the wear mode after disassembly:

 Uniform scratches → Lubrication failure or insufficient clearance.

Local pitting corrosion → cavitation damage.

Adhesive tearing → Insufficient high-temperature strength of the material.

2.  Laboratory analysis

Perform metallographic examination on the failed gear to confirm whether intergranular corrosion or high-temperature tempering softening has occurred.

Lubricating oil sampling and testing for viscosity, acid value, and particle contamination (ISO 4406 standard).

4、 Recommended economical solution (taking 200 ℃ heat transfer oil pump as an example)

Low cost transformation: Use molybdenum containing stainless steel (316L) gears, with graphite lubricated bearings, and install a 40 mesh Y-shaped filter.

 Long term solution * *: Customized fully hardened gears (surface hardness HRC60+), integrated thermocouple temperature monitoring, reducing annual maintenance costs by more than 40%.

Through multi-dimensional optimization design, material upgrades, and intelligent operation and maintenance, the reliability of stainless steel gear pumps under high temperature conditions can be significantly improved, avoiding unplanned shutdowns.