Snubber - Shock Absorber
Introduction
In industrial piping systems, snubbers, also known as shock absorbers, play a critical role in preventing excessive movement caused by dynamic forces like seismic activity and operational vibrations.
This post explores snubbers' purpose, types, and application in industrial piping systems.
1. Purpose of Snubbers
The primary function of a snubber in a piping system is to absorb and mitigate dynamic forces, preventing damage to pipes, supports, and connected equipment. Unlike traditional supports, snubbers allow for free movement during normal operating conditions (such as thermal expansion or contraction) but instantly restrict movement during abnormal events, such as:
Seismic events or earthquakes
Sudden pressure surges or fluid hammer
Vibration from pumps, compressors, and other equipment
Without snubbers, piping systems are vulnerable to stress-related failures, including cracking, fatigue, or misalignment. The proper placement of snubbers is critical to the integrity of piping systems, particularly in areas exposed to dynamic forces.
2. Types of Snubbers
There are two main categories of snubbers used in industrial piping systems: mechanical and hydraulic snubbers.
Mechanical Snubbers
Mechanical snubbers utilize a gear or friction mechanism to restrict pipe movement. They engage when the speed of the pipe movement exceeds a certain threshold. Mechanical snubbers offer the advantages of being relatively simple in design and low maintenance, making them suitable for less critical areas.
Key features include:
Effective at limiting both shock and vibration
Low maintenance requirements
Durability and long service life
Hydraulic Snubbers
Hydraulic snubbers function using a piston-cylinder mechanism filled with a hydraulic fluid. The fluid allows the piston to move slowly in normal operation, accommodating thermal expansion. However, the fluid flow is restricted during a sudden dynamic load, rapidly stiffening the system and preventing excessive movement.
Advantages of hydraulic snubbers include:
Smooth operation and ability to handle large dynamic loads
High energy absorption capacity
Suitability for high-pressure and high-temperature environments
Hydraulic snubbers are widely used in critical areas, such as near large rotating equipment, and in regions where seismic activity is a concern.
SNUBBER TYPES
3. Application of Snubbers in Industrial Piping Systems
Snubbers are strategically placed in piping systems based on dynamic load analysis and the nature of the potential forces acting on the pipe. Common applications include:
Seismic Protection
In seismic zones, piping systems are designed to withstand significant movement caused by ground shaking. Snubbers are placed to absorb seismic forces, preventing piping and associated equipment damage.
Vibration Control Near Rotating Equipment
Pumps, compressors, and turbines generate vibrations that can resonate through piping systems. Snubbers installed near these machines reduce vibrations and protect the pipe from fatigue and failure.
Control of Fluid Hammer
A fluid hammer occurs when a fluid in motion is suddenly forced to stop or change direction, causing a pressure surge. Snubbers absorb the resulting shock, minimizing the risk of pipe rupture or valve damage.
High-Energy Piping Systems
In high-pressure steam or gas piping systems, snubbers prevent excessive movement due to transient loads and temperature variations. These snubbers help maintain system stability and operational safety.
4. Maintenance and Inspection
Regular inspection and maintenance of snubbers are crucial to ensure their reliability. Key maintenance activities include:
Visual inspections for leaks (in hydraulic snubbers) or wear (in mechanical snubbers)
Functional testing to verify proper movement during normal conditions and restriction during dynamic events
Replacement of worn-out parts or hydraulic fluid, if necessary
Following manufacturer guidelines for routine checks is essential, as snubbers are often installed in critical piping systems where failure could lead to significant safety hazards.
5. Standards and Guidelines
Several codes and standards govern the use of snubbers in piping systems, particularly in industries such as oil and gas, power generation, and chemical processing. Relevant standards include:
ASME B31.1 (Power Piping)
ASME B31.3 (Process Piping)
NRC Regulatory Guide 1.61 (For seismic snubbers in nuclear facilities)
Compliance with these standards ensures the correct design, installation, and maintenance of snubbers in high-stakes environments.
Disadvantages of Using Snubbers
1. Maintenance Requirements
Frequent Inspection: Snubbers, especially hydraulic ones, require regular inspection and maintenance to ensure they function correctly. Leaks, degradation of hydraulic fluid, and mechanical wear can lead to performance issues.
Replacement Costs: Snubbers can wear out or fail over time, leading to costly replacements or repairs. Their lifespan depends on operating conditions, making maintenance planning more complex.
2. Complexity in Installation
Complicated Installation: Installing snubbers can be more complex than rigid supports or spring hangers. They require careful positioning, alignment, and calibration to ensure effective operation.
Space Constraints: Snubbers can take up more space than other supports, which may complicate layout designs in confined or congested piping areas.
3. Limited Response to Thermal Expansion
Limited Flexibility in Slow Movements: Although snubbers are designed to allow slow movements like thermal expansion, their response is sometimes less effective than flexible supports (e.g., expansion loops or bellows). They can occasionally impede free thermal movement if not designed or adjusted correctly.
4. Cost
Higher Cost: Snubbers are generally more expensive than pipe supports, such as spring hangers or rigid supports. This includes the initial purchase and the long-term maintenance and replacement costs.
Operational Costs: Hydraulic snubbers, in particular, can have higher operational costs due to the need for hydraulic fluid replenishment and periodic recalibration.
5. Potential for Failure
Mechanical Failure: Snubbers are mechanical devices, meaning they can fail under extreme conditions or due to wear and tear, primarily if not appropriately maintained. Sometimes, a failed snubber might cause more harm than not having one.
Leakage in Hydraulic Snubbers: Fluid leakage in hydraulic snubbers can lead to reduced effectiveness and the need for repairs.
Snubber Sizing and Load Capacity
1. Importance of Proper Sizing The effectiveness of a snubber depends mainly on its proper sizing and load capacity. Undersized snubbers may fail to protect the piping system from dynamic loads adequately. In contrast, oversized snubbers could result in unnecessary restrictions during regular operation, potentially affecting the pipe's natural thermal movements.
Properly sizing a snubber involves considering several key factors:
The piping system's dynamic loads will be exposed to (e.g., seismic forces, fluid hammer, vibration from rotating machinery).
The thermal expansion of the piping system during regular operation.
The weight and length of the pipe section are supported.
The snubber's location is relative to the source of dynamic forces (e.g., near a pump or a valve subject to a water hammer).
2. Snubber Load Capacity
Snubbers must be selected based on their load capacity, which refers to the maximum force they can absorb or restrict during dynamic events. The manufacturer specifies load capacities, which are usually classified into ranges to accommodate different applications. A snubber's load capacity typically varies depending on its design (mechanical or hydraulic) and the specific dynamic forces it is expected to counteract.
Mechanical Snubbers
Mechanical snubbers' load capacities are typically lower than hydraulic ones, often ranging from a few hundred kilograms to several tons. These are generally sufficient for low to moderate shock loads, such as machinery vibrations or minor pressure surges.
Hydraulic Snubbers
Hydraulic snubbers are designed to handle higher loads, with load capacities ranging from several tons to hundreds of tons. They are particularly suited for heavy-duty applications, such as seismic protection or large rotating equipment that induces high dynamic forces. Manufacturers typically provide hydraulic snubbers in different sizes and load ratings to match specific piping stress requirements.
3. Factors Influencing Snubber Sizing and Load Capacity
Dynamic Load Characteristics
The type and magnitude of dynamic loads the snubber will experience are key to determining the appropriate load capacity. For example, in seismic applications, snubbers must be sized based on the expected ground acceleration forces and the mass of the piping and equipment.
Pipe Size and Weight
Larger pipes or those carrying heavier fluids will require snubbers with higher load capacities. The weight of the piping section and any supported equipment (valves, pumps, etc.) must be considered when calculating the load the snubber will need to absorb.
Thermal Movements
Another critical consideration is the snubber's ability to allow for thermal expansion and contraction. A snubber should be sized to allow the pipe to move freely during thermal expansion but must immediately restrict movement during abnormal conditions.
Stroke Length
The stroke length of a snubber refers to the distance over which the snubber can operate. In other words, it defines how much movement the snubber will allow before it engages to restrict dynamic forces. Longer stroke lengths are required for more significant thermal movements, while shorter strokes may be adequate for applications with minimal thermal expansion.
4. Manufacturer Guidelines
Most snubber manufacturers provide detailed technical specifications to assist engineers in selecting the appropriate snubber size and load capacity. These specifications include:
Load ratings in terms of force (usually in kN or tons).
Stroke length (how far the snubber can move before locking).
Temperature ratings to ensure the snubber functions correctly under varying operating conditions.
Reaction time of the snubber, especially critical for hydraulic models where the speed at which the snubber locks up is a major performance factor.
5. Sizing Calculation Example
Engineers typically perform a load analysis to determine the appropriate snubber size for a specific application. It involves calculating the forces generated by dynamic events (seismic forces, water hammer, etc.) and comparing them against the available snubber capacities.
For example:
A seismic load might result in a lateral force of 50 kN on a pipe section. If the piping system is in a high-seismic zone, the snubber must be able to absorb at least this force to protect the system.
For vibration control near a pump, the snubber must be sized to handle the combined weight of the piping and equipment while restricting excessive movement caused by the pump's vibration.
After calculating the required load capacity, engineers select a snubber with a slightly higher rating to account for safety factors and ensure reliability under all conditions.
Please keep in mind the following text:
When choosing snubbers for an industrial piping system, it is essential to consider the specific dynamic forces, the weight of the supported piping, and the thermal expansion characteristics. Snubbers that are appropriately sized and have sufficient load capacity safeguard the piping system from dynamic events while maintaining operational flexibility. Refer to manufacturer data and conduct a comprehensive load analysis to ascertain each application's appropriate snubber size and capacity.
The Snubber Manufacturers
Several reputable manufacturers specialize in producing snubbers (shock absorbers) for industrial piping systems. These companies offer a range of snubber types, including mechanical and hydraulic snubbers, each designed for different load capacities and dynamic conditions. Below are some well-known manufacturers:
1. Lisega
Type: Mechanical and Hydraulic Snubbers
Industry: Power generation, oil and gas, chemical, and petrochemical industries.
Features: Lisega offers mechanical and hydraulic snubbers for seismic, thermal, and dynamic load applications. It also provides high-energy damping devices suitable for heavy-duty industrial use.
Website: Lisega
2. Anvil International (Gruvlok)
Type: Hydraulic Snubbers
Industry: Oil and gas, HVAC, and industrial piping systems.
Features: Anvil offers a wide range of hydraulic snubbers for large dynamic loads in industrial piping applications. They specialize in supporting seismic and vibration-related issues.
Website: Anvil International
3. Bergen-Power Pipe Supports
Type: Mechanical and Hydraulic Snubbers
Industry: Power plants, nuclear, and industrial sectors.
Features: Bergen-Power is known for its high-performance snubbers, particularly in nuclear and power generation applications. It provides custom-engineered solutions to meet specific project requirements.
Website: Bergen-Power
4. Piping Technology & Products (PT&P)
Type: Mechanical and Hydraulic Snubbers
Industry: Power plants, chemical plants, and refineries.
Features: PT&P offers both mechanical and hydraulic snubbers for vibration control and seismic protection in piping systems. Their snubbers are known for reliability and performance under extreme conditions.
Website: PT&P
5. Viking Corporation
Type: Hydraulic Snubbers
Industry: Industrial, oil and gas, and water supply systems.
Features: Viking Corporation produces hydraulic snubbers for dynamic force absorption, specializing in custom designs for high-pressure environments.
Website: Viking Corporation
6. ITT Enidine
Type: Hydraulic Snubbers
Industry: Power generation, aerospace, and industrial sectors.
Features: Enidine is known for high-quality hydraulic snubbers, particularly in applications where critical damping and shock absorption are required, including seismic and vibration control.
Website: ITT Enidine
7. Eaton
Type: Hydraulic and Mechanical Snubbers
Industry: Energy, aerospace, oil and gas.
Features: Eaton provides advanced hydraulic snubbers with excellent load-bearing capacities and custom designs for seismic, thermal, and mechanical shock applications.
Website: Eaton
Conclusion
Snubbers play a vital role in ensuring industrial piping systems' structural integrity and safety. They absorb shock and control vibration, protecting piping, equipment, and personnel from the detrimental effects of dynamic forces. Proper selection, installation, and maintenance of snubbers are critical to maximizing their effectiveness and extending the life of the piping system.
For engineers and maintenance teams, understanding the types of snubbers available and their applications is essential for creating a safe and reliable piping infrastructure.
This blog is intended as a guide to determining the minimum safe spacing of plants and equipment in Oil Refineries, Petrochemical Complexes, and similar installations.
The spacing recommendations will apply in the absence of Clients' standards or supplement such standards where necessary. They are based on current industry practice.
The spacing recommendations aim to ensure that available plot areas are used economically without affecting personnel safety or plant vulnerability.