Failure causes and prevention methods of the hotte

2022-10-22
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Failure causes and prevention methods of pipe threads

there are two common connection methods for well water supply pipelines: one is the connection of adhesive ring sealing flange, and the other is the connection of pipe threads. Among them, the pipe thread connection has the advantages of simple installation process and easy pipe laying, which can be widely used when opening the oil nozzle at the left bottom of the dynamometer when draining oil

during the use of pipe thread, due to the influence of itself and external factors, various faults often occur, affecting the normal work. Through the investigation and analysis of failure management, it is found that most of the failure parts occur at the pipe thread connection, and the failure forms mainly include the following types: thread adhesion (thread sticking), thread leakage, thread fracture and pipe body crack at the connection

I. failure original 5 experimental steps because

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1. Thread adhesion

thread adhesion refers to a failure form in which the thread at the pipe coupling is worn and damaged, changing the shape and size of the thread

wear is the main and direct cause of thread sticking. The wear of pipe threads mainly includes abrasive wear and composite wear

during the screw in and screw out process of connection and disassembly of well pipe threads, various sundries will inevitably fall into the thread surface and groove. These hard granular sundries have the effect of cutting and scraping the thread teeth, resulting in the falling off of the material on the connection surface and the formation of abrasive wear

the load on the pipe thread includes the dead weight of the pipe, the additional load generated by the preload after tightening the coupling, the axial static load formed by the internal pressure of the fluid medium in the pipe, etc. These loads produce large contact stress on the thread surface of the pipe thread, causing the large load-bearing hump on the thread surface to adhere. The change of contact stress makes the adhesion point cut and form abrasive debris. The abrasive debris becomes abrasive between the contact surfaces of thread teeth, and then abrasive wear occurs. The result of this cycle is the formation of new composite wear

2. Thread leakage

the main cause of thread leakage failure is corrosive wear. The thread material has a chemical reaction or electrochemical reaction with some chemical components in the fluid in the pipe, and the generated corrosive substances are not firmly adhered to the surface of the thread and are easy to fall off. The surface of the new thread continues to react with the fluid medium, so the repetition of this process forms corrosive wear

after corrosion and wear on the side surface and crown of thread teeth, the tooth shape changes, and new progress has been made in the research of polyurethane elastomer materials for self-healing of internal and external threads. The radial gap outside the thread thread engagement increases, resulting in leakage

3. Thread breakage

the weight of the pipe itself, the axial load generated by the action of the fluid medium in the pipe and the pre tightening force of thread anti loosening all act on the thread of the pipe thread. Corrosive wear will reduce the thickness and strength of the thread. When the load is greater than the strength limit of the thread, the thread breakage will occur

II. Preventive measures for failure

1. Measures to prevent thread adhesion

wear is the main and direct cause of thread adhesion, so the following preventive measures can be taken:

(1) spray plating technology (such as brush copper plating) is used to coat the surface of pipe thread to improve its wear resistance

(2) carry out surface induction hardening on the thread surface to increase the strength and hardness of the thread. This method has good applicability. Generally, as long as the sufficient hardness of the screw thread can be guaranteed, the screw thread will not have the failure of sticking. The actual hardness of the screw thread can be obtained through its strength calculation

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