Reasons for piston rod fracture in reciprocating compressors
Thread Content
The unit’s reciprocating compressor is manufactured by Sichuan Huaxi, model 4M40-314/25. It took about 3 months to replace the piston rod. During operation, a fracture occurred at the connection point between the crosshead and the piston rod (the crosshead and piston rod are connected using a hydraulic tensioner, and the fracture occurred at the location of the locking nut). Please identify the possible causes of this fracture.
Simply put, fatigue fracture or manufacturing defects!
The possibility of fatigue fracture is low, as it has only been in use for three months
Based on the characteristics of the fracture, a preliminary assessment can be made, and metal analysis can be conducted to determine the cause of the fracture
Piston rod fracture is rare; usually, it is due to wear or bending. It is speculated that this might be intended to create problems, in order to check whether there are any defects in the fracture surface.
Could the original poster please upload a picture of the broken area so we can take a look? 1. When using a ultra-high pressure oil pump to generate pressure, is the operating pressure achieved in strict accordance with the specified requirements? 2. The crosshead lock nut fractured at its location; after installation, it is worth recording whether there was any variation in the piston rod’s movement, and comparing this with previous installation data to see if there are any differences 3. Were the piston rings and support rings not installed properly during installation? 4. During the installation of the new piston rod, was it checked whether there were any differences in its diameter, and whether the pressure element used for connecting it to the crosshead was suitable? 5. After installation, is the clearance between the front and rear dead centers of the piston too large, resulting in slight cylinder collision? 6. Manufacturing defects (the least desirable cause)
1. Were the installation specifications followed – regarding gaps, levelness, and alignment? 2. Issues related to the quality of the accessories. 3. If the above possibilities can be ruled out, then it’s likely that the cylinder contains liquid
Material quality, mechanical properties, operating conditions, design structure, manufacturing and installation accuracy
Port metallurgical analysis can be conducted under certain conditions to determine the cause of the fracture and prevent similar incidents from occurring again. It can also be analyzed from the following aspects: 1. Whether the installation was carried out in accordance with standards, regarding gaps, levelness, and alignment; 2. Issues related to the quality of the accessories, such as defects in the threads. 3 Stress changes at the screw shaft 4 Changes in operating conditions, such as liquid present in the cylinder
It is also possible that the inside of the cylinder is too dirty, resulting in increased load, or that the inlet and outlet pipelines are not unobstructed, which leads to an increased load; over time this can cause the piston rod to suffer from metal fatigue and break. The piston rod of the cylinder on the compressor side in my company (with a diameter of 50 mm) also broke at the locknut connecting it to the crosshead.