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.