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Slip joint
Slip joint
Slip joint
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A slip joint is a mechanical construction allowing extension and compression in a linear structure of slip joint.

General forms

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Slip joints can be designed to allow continuous relative motion of two components or it can allow an adjustment, by unclamping from one fixed position, and re-clamping to another. Examples of the latter are tripods, hiking poles, or similar telescoping device. The clamping mechanism is based on a cam, a set screw, or a similar locking mechanism. Slip joints can also be non-telescoping, such as the joints on some older wooden surveyor's levelling rods. These use a joint that keeps the sections offset from each other but able to be slid together for transport.

Examples of continuous slip joints are given below.

Special purpose slip joints

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Civil engineering

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Slip joints in large structures are used to allow the independent motion of large components while enabling them to be joined in some way. For example, if two tall buildings are to be joined with a pedestrian skyway at some high level, there are two options in structural engineering. If the buildings are identical in mass and elasticity they will tend to respond similarly to ground motion induced by earthquakes. In this case, it may be appropriate to construct a rigid connection between the buildings, although this may require additional supporting members within the structures. On the other hand, a lower cost connection may be made by using a lightweight structure that is not coupled rigidly but instead is allowed to slide or "float" relative to one or both structures. This is especially suitable where the two structures may respond differently to ground motion. The structure will not be completely free to move but rather may use elastic materials to locate it near the center of its range of motion and viscous shock absorbers to absorb energy and to restrict the speed of relative motion. When a sliding connection is used it is extremely important that there be sufficient range of motion without failure to accommodate the maximum credible relative motion of the structures. Additional "fail-safe" flexible connections may be added to ensure that the structure does not fall, although it may be damaged to a point of being unserviceable or unrepairable.

Slip joints are common under conditions where temperature changes can cause expansion and contraction that may overstress a structure. These are generally referred to as expansion joints. Bridges and overpasses frequently have sliding joints that allow a deck to move relative to piers or abutments. The joints can be constructed with elastomeric pads that permit motion or can use rollers on flat surfaces to allow the ends to move smoothly. The exact details are limited by the imagination of the designer.

Mechanical engineering

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Slip joints are sometimes found in tubular structures such as piping but are generally avoided for this application due to requirements for sealing against leakage, instead of using either a large loop that is allowed to flex or a semi-rigid bellow. Slip joints are used when the main problem is a large axial movement.[1] Pipe supports often are slip joints to allow for the thermal expansion or contraction of the pipe relative to the support.

Wastewater plumbing

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Slip joint connections are also commonly used in wastewater plumbing, most commonly under kitchen sinks. Here, the slip joint provides a water-tight seal for non-pressurized drainage, with adjustability to aid installation. The slip joint includes a gasket that fits snugly on a pipe end, with a threaded nut behind the gasket, but with gasket position adjustable as needed. This pipe end fits loosely into another with a flange for the gasket to seal against, and threads for the nut to clamp the gasket to the flange.

See also

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References

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Revisions and contributorsEdit on WikipediaRead on Wikipedia

Slip joint

View on Grokipedia
from Grokipedia
A slip joint is a mechanical connection that permits limited relative sliding or telescoping movement between two components, allowing for axial extension, compression, or rotation while maintaining structural integrity. This design accommodates displacements caused by , pressure changes, , or settling, preventing stress accumulation and potential in connected elements. In mechanical and , slip joints function through a sliding interface, often incorporating seals or packing materials to ensure fluid-tightness during movement. They are classified into types such as axial slip joints for and rotational slip joints for angular adjustments, with the mechanism relying on or low-restraint sliding to dissipate energy. In civil and building systems, slip joints—also known as expansion joints—relieve stresses in walls, ceilings, and bridges by enabling horizontal and vertical movements, thereby minimizing cracking in materials like or . In applications, slip joints provide a compressible washer-based seal, commonly used in drain traps to connect pipes without rigid fixation. No rewrite necessary — no critical errors detected.

Overview

Definition and Purpose

A slip joint is a mechanical construction designed to permit linear extension and compression between connected components, allowing relative axial movement while maintaining overall structural or system integrity. This functionality is achieved through mechanisms such as telescoping or sliding interfaces that accommodate displacements caused by , contraction, pressure variations, or external forces. The primary purposes of slip joints include absorbing axial displacements in pipelines, structural assemblies, and linear systems to prevent stress accumulation from environmental factors like changes or seismic activity. By enabling controlled movement, these joints help avoid damage to connected elements, such as or cracking, and support adjustability in applications requiring flexibility, including support systems and drainage setups. In distinction to rigid joints, which constrain all to transmit forces and moments without relative motion, or hinged joints that allow but limit , slip joints prioritize in linear sliding to isolate and manage directional movement effectively. Slip joints are broadly employed in linear structures to sustain operational functionality amid dynamic loads and varying conditions.

Historical Context

Early forms of slip joints, known as open joints in , date back to at least the era of Tutankhamen around 1323 BCE, where they allowed for adjustable or sliding connections in furniture and structural elements. Basic telescoping structures, resembling primitive slip mechanisms, also appeared in ancient constructions for poles and supports, enabling limited linear movement. The marked the widespread adoption of slip joints during the , particularly in piping systems and bridges to accommodate amid the rise of steam engines and iron construction. In bridge engineering, sliding bearings emerged as a key innovation; for instance, Ralph Dodd introduced grooved sliding mechanisms on the Chelmer Bridge in 1820, while John Rennie proposed moveable sectors for the Leeds Bridge in the same year to permit independent span expansion. These developments coincided with early railroad bridges in the 1800s, where roller and knuckle bearings further refined slip-type allowances for thermal and load-induced movements. In the , slip joints underwent significant refinements for enhanced resilience in civil structures. Events like the spurred the evolution of building codes emphasizing dynamic response and movement accommodation. Packed slip types, suitable for high-pressure piping, advanced in the mid-1900s with innovations such as self-lubricated injectable packing introduced in 1968, enabling reliable sealing under demanding conditions. Standards from organizations like ASME began evolving in the 1950s through codes such as B31 for piping, providing guidelines for expansion joint design and integration. As of 2025, modern applications include slip joints in offshore wind turbines, where conical overlap designs facilitate installation and movement absorption; the first such foundation was installed by in 2020 as an alternative to grouted connections.

Design Principles

Operating Mechanisms

Slip joints operate through a core mechanism involving a sliding interface between inner and outer components, typically a pipe or rod telescoping within a or , which permits axial displacement while restricting radial or angular motion. This configuration allows the joint to accommodate longitudinal movements without compromising structural integrity, as the inner element slides relative to the outer one under applied forces. Friction and sealing dynamics are managed through the use of packing materials, such as flexible or elastomers, compressed within a or to form a barrier against leakage and ingress. These packing materials, often made from or PTFE, conform to surface irregularities and handle dynamic pressures during sliding. Lubricants may be injected to reduce frictional resistance between the sliding surfaces, enabling smoother operation under compressive or tensile loads while maintaining pressure containment. Movement accommodation primarily addresses thermal expansion, calculated using the linear expansion formula: ΔL=αLΔT\Delta L = \alpha L \Delta T where ΔL\Delta L is the change in length, α\alpha is the coefficient of thermal expansion of the material, LL is the original length, and ΔT\Delta T is the temperature change. Joint design incorporates this to predict and provide sufficient stroke length for cyclic expansions and contractions, ensuring the system remains aligned and functional across operating temperature ranges. Operational limitations include potential wear from repeated sliding cycles, which can degrade sealing materials and increase over time, necessitating periodic . Misalignment or lateral offsets may cause binding, leading to uneven stress distribution and premature , thus requiring precise installation with guiding supports. Additionally, these joints are constrained to axial movements and perform poorly under high lateral or torsional loads.

Components and Materials

Slip joints in and mechanical systems primarily comprise an inner or that slides within an outer to accommodate axial movement. The inner component, often a splined in high-pressure applications, transmits while allowing extension and compression, typically with a length of up to 5 feet per joint. The outer serves as the stationary . In certain high-pressure downhole applications, it encloses pressure-balanced chambers to minimize sensitivity to internal pressures. Retaining mechanisms, such as flanges, collars, or limit stops, secure the assembly and prevent excessive displacement. Sealing elements are critical for maintaining integrity during sliding action, commonly including braided packing in stuffing boxes or O-rings for low-friction containment. Braided packing, often made from graphite or PTFE yarns, compresses via packing glands to form a leak-tight barrier without impeding movement. These seals are housed in integral guides within the stuffing box to ensure alignment. Material selection prioritizes durability, corrosion resistance, and compatibility with operating conditions. The primary structural components, such as the inner sleeve and outer housing, are typically fabricated from or (e.g., grades 304 or 316) to withstand high pressures and temperatures in process environments. For sealing, elastomers like are used in applications requiring chemical resistance and operation up to 150°C, while braided packing employs synthetic fibers for enhanced wear resistance. Assembly involves threaded or welded connections for adjustability and to systems. Welded sleeve joints, for instance, use seal welds to join components, with packing glands enabling compression of seals during installation. Flanged ends facilitate alignment and integration into larger systems. Slip joints must comply with relevant standards to ensure safety and performance. The ASME B31.3 Process Code governs design and application of slip-type expansion joints in industrial settings, specifying requirements for metallic and leak tightness. Material testing adheres to ASTM standards, such as A105 for forgings and F1007 for packed slip-type joints in marine and applications.

Types

General Forms

Slip joints in their general forms encompass basic configurations that facilitate linear adjustment or movement between components without complex sealing or high-load capabilities. The most prevalent is the telescoping form, where inner sections nest within outer tubes or pipes, enabling extension and retraction for variable lengths. This design is commonly secured using friction grips, set screws, or cam locks to maintain position once adjusted. A representative application of the telescoping form appears in photographic tripods, where leg sections slide concentrically to achieve height adjustments from compact storage to full extension, often spanning several feet. Similarly, poles employ this mechanism with multiple nested aluminum segments that lock via twist or mechanisms, allowing users to adapt for variations. In contrast, the non-telescoping form involves offset or parallel sections that slide alongside each other without nesting, prioritizing compactness for transport over deep overlap. This configuration is typical in older tools, such as Chicago-style leveling rods, where wooden or sections connect via slip joints to form extended rods up to 13 feet while folding flat for portability. Both forms share simple, low-friction designs suited to light-duty scenarios, such as manual adjustments rather than automated or high-stress operations, and can accommodate substantial changes—up to 50% or more in telescoping variants—facilitated by principles of in compatible materials. Everyday implementations include antenna masts, where slip-fit sections assemble into extendable poles for signal elevation, and adjustable furniture legs, which use sliding tubes with locking pins for customization in tables or chairs.

Specialized Forms

Packed slip joints represent an advanced variant of slip joints, utilizing compressed packing materials such as or (PTFE) to achieve reliable sealing under high- conditions in systems. These joints are particularly suited for applications requiring substantial axial accommodation, with designs capable of handling compressions up to 48 inches (1.22 meters) in concentrated pipe movement while maintaining pressure ratings up to 300 psi at elevated temperatures. The packing allows for field repacking under full line , enhancing efficiency without system shutdown. Guided slip joints incorporate external guiding mechanisms, such as rails or keys, to constrain lateral and angular movements while permitting controlled axial expansion. This design ensures precise alignment in piping systems where misalignment could compromise integrity, with movement capacities reaching up to 48 inches in specialized configurations. The guides, often integrated as structural supports, distribute loads evenly and prevent binding, making these joints ideal for high-precision installations in industrial pipelines. Slip-type expansion joints feature a sleeve-over-pipe configuration that facilitates axial sliding for large linear movements—typically up to 12 inches per unit—while maintaining a seal, primarily for pure axial motion in layouts. Rotational slip joints, also known as ball-and-socket joints, allow for angular adjustments and limited rotation between components, often used in applications requiring flexibility in direction such as or structural connections. These differ from axial types by permitting multi-axis movement through a spherical interface. Recent innovations in slip joint designs for offshore structures include polygonal and conical overlap configurations, which enhance resistance compared to traditional circular profiles. These geometries, applied in monopile-to-tower connections for wind turbines, improve frictional grip and load transfer under rotational forces, with polygonal sections demonstrating superior torsional capacity in finite element analyses. Conical variations with unequal angles further optimize settlement and contact during installation, addressing challenges in marine environments.

Applications

In Civil Engineering

In , slip joints function as a type of in bridges to accommodate thermal contraction and expansion, allowing structural elements to slide relative to one another without inducing excessive stress. These joints are essential for long-span bridges, where variations can produce significant movements, such as up to 1 meter in spans exceeding several kilometers, preventing cracking or in the . In buildings and skyways, slip joints connect separate structural sections, such as in high-rise towers or elevated walkways, enabling independent lateral sway during seismic events to minimize damage from differential movements. These connections often incorporate elastomeric pads for friction reduction and , alongside dampers to control oscillations and protect adjacent components like curtain walls or floor slabs. Design of slip joints in these applications requires accommodating at least twice the predicted movement range to account for uncertainties in , seismic, or settlement loads, ensuring and . They are typically integrated with shock absorbers, such as friction-based elements, to dissipate seismic energy through controlled slipping, enhancing overall structural resilience without compromising load transfer. Following the , retrofits in infrastructure, including bridges and elevated structures, extensively incorporated slip joints as part of upgrades to address vulnerabilities exposed by the event, such as joint failures leading to span collapses. These enhancements, applied to over 2,000 state bridges, focused on increasing movement capacity and adding seismic restrainers, significantly improving performance in subsequent events like the .

In Mechanical Engineering

In mechanical engineering, slip joints facilitate axial adjustments in machinery and industrial systems, enabling components to accommodate operational loads such as without compromising system integrity. These joints typically consist of overlapping tubular sections that slide relative to one another, often sealed with packing materials to prevent leakage while allowing controlled movement. They are particularly valued in dynamic environments where precise alignment and moderate flexibility are required under varying pressures and temperatures. In systems, slip joints compensate for thermal growth in process lines, functioning as robust alternatives to expansion joints by permitting straight axial movements of up to 500 mm. This design is ideal for high-temperature applications in power plants and facilities, where pipes expand and contract due to heat cycles; the sliding mechanism absorbs these displacements while maintaining a leak-tight seal through annular packing. Unlike more complex , slip joints offer simpler installation and lower for pure axial motions, though they require proper guiding to prevent misalignment. For tubular structures in equipment such as heat exchangers and conveyor supports, slip joints enable alignment adjustments during assembly and operation, historically providing a reliable means to handle minor shifts from or mechanical loads. In heat exchangers, they allow tubes to slide within shells to mitigate differential expansion stresses, while in conveyor supports, they facilitate telescoping adjustments for leveling and load distribution. These applications have been common since the mid-20th century in industrial machinery, but they are increasingly supplemented by flexible loops to enhance adaptability in modern designs. The sliding mechanisms, as detailed in operating principles elsewhere, underpin their ability to permit controlled extension and compression without binding. Performance metrics for slip joints in these contexts include the capacity to handle pressures up to 100 bar, depending on material and design, making them suitable for moderate- to high-pressure . They exhibit moderate rigidity against bending, resisting lateral deflections while allowing axial compliance, which helps maintain under operational loads like or uneven forces. This balance of stiffness and flexibility is critical in preventing excessive deformation in tubular assemblies.

In Plumbing and Piping

In and systems, slip joints are primarily utilized in drainage and applications to create adjustable, leak-proof connections, particularly in low-pressure environments such as residential fixtures. These joints are commonly employed in fixture trap assemblies under sinks, bathtubs, or floor drains, where a threaded nut compresses an elastomeric —typically made of rubber or —to form a watertight seal between tubular components. This design facilitates easy assembly and disassembly for , such as clearing clogs, without requiring specialized tools beyond a . The adjustability of slip joints is a key feature, allowing linear movement to accommodate variations in fixture positioning during installation. For instance, in a standard P-trap setup, the slip connection between the tailpiece and trap arm enables precise alignment with the wall drain outlet, reducing the risk of leaks from improper fit. This is especially beneficial in tight spaces under vanities or cabinets, where exact measurements may be challenging. Sealing materials like rubber washers, as referenced in broader component discussions, ensure reliability in these humid, wastewater-exposed environments. In systems, slip joints are widely used with PVC or ABS materials due to their compatibility with solvent-weld connections and ease of handling in confined areas. These plastic-based joints prevent backups caused by misalignment by permitting on-site adjustments that maintain proper for drainage—typically 1/4 inch per foot as per code standards. Common in both new and retrofits, they support efficient flow from fixtures to main drains without the rigidity of fully glued systems, minimizing installation errors in residential and commercial settings. Slip joints must comply with the International Plumbing Code (IPC), which specifies their use only on the trap outlet, inlet, or within the trap seal, employing approved friction-type elastomeric washers to prevent escape. This code adherence ensures safe, durable performance, with factors like and usage frequency influencing longevity. Variations include compression-style slip joints for solvent-weld PVC pipes in DWV (drain, waste, vent) applications, providing adjustable seals while maintaining code-compliant integrity.

References

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