Pump Body Pre-Compression via Displacement Plugs
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Solution Overview
Problem
Multiplex pumps used for fracturing fluids experience fatigue failure due to stress cycles, which can lead to crack initiation and failure at the fluid end, despite autofrettage processes, indicating a need for improved methods to inhibit fatigue cracks and extend operational life.
Innovation Solution
Applying pre-compressive forces in pump bodies through expanded displacement plugs and raised surfaces, which are connected and tightened between end plates to distribute stress and inhibit fatigue crack initiation, combined with autofrettaging for enhanced residual stress management.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If autofrettage process is applied to induce residual compressive stress in fluid end cylinders, then fatigue crack initiation is inhibited, but the operational life is still limited due to cumulative stress cycles from pumping operations
Solution Approach 1:
The pump body is pre-compressed during manufacturing by expanding displacement plugs within cavities to induce residual compressive stresses in critical areas before the pump enters service. This preliminary action creates a stress state that counteracts the cyclic stresses encountered during operation, thereby extending operational life by inhibiting fatigue crack initiation and propagation
Solution Approach 2:
The residual stress parameters in the pump body are modified by controlled plastic deformation through displacement plug expansion. By changing the stress state parameters (inducing compressive residual stresses) in critical regions, the pump body's resistance to fatigue failure is enhanced, allowing it to withstand more stress cycles before failure
2Ease of manufacture
If a monoblock fluid end design is used to simplify structure, then manufacturing and assembly are easier, but maintenance and replacement of individual components become more difficult
Solution Approach 1:
The pump body is divided into separate modular sections (fluid end, power end, etc.) that can be independently manufactured, assembled, and replaced. This segmentation allows the fluid end to be produced as a separate module with pre-applied compressive forces, maintaining manufacturing simplicity while enabling easy replacement of individual modules during maintenance without replacing the entire pump
3Reliability
If pre-compressive forces are applied through expanded displacement plugs in cavities, then stress concentrations are reduced and fatigue crack initiation is inhibited, but the device complexity increases
Solution Approach 1:
The displacement plugs are expanded in situ within the pump body cavities, allowing the pump body itself to generate and distribute the pre-compressive forces without requiring external autofrettage equipment. This self-service approach integrates the stress application mechanism into the manufacturing process, reducing the need for complex external equipment while achieving the desired residual stress distribution
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The pre-compressive forces effectively reduce stress concentrations and extend the operational life of the pump by preventing fatigue crack initiation, allowing for easier maintenance and replacement of individual pump bodies, thus enhancing efficiency, flexibility, and reliability.
Implementation Method 1
The pressure during autofrettage causes plastic yielding of the inner surfaces of the cylinder walls. Since the stress level decays across the wall thickness, the deformation of the outer surfaces of the walls is still elastic.
Implementation Method 2
When the hydrostatic pressure is removed, the outer surfaces of the walls tend to revert to their original configuration. However, the plastically deformed inner surfaces of the same walls constrain this deformation.
Implementation Method 3
Typically, this is done through an autofrettage process, which involves a mechanical pre-treatment of the fluid end in order to induce residual stresses at the internal free surfaces
Data Source
AI summary
A pump body is pre-compressed by expanding a displacement plug in a cavity to pre-compress a portion of a pump body comprising a piston bore, an inlet bore and an outlet bore spaced from said cavity, and connected in a pump assembly. A fluid pump assembly is made up of a plurality of pump bodies connected side by side between opposing end plates with a plurality of fasteners tightened to compress the pump bodies between the end plates, wherein each pump body comprises a piston bore, an inlet bore, an outlet bore and an expanded displacement plug in a cavity; and wherein the expanded displacement plug applies a pre-compressive force at the cavity on each of the pump bodies.