Why Clamps Damage Pipes – The Role of Rubber Inserts and Their Selection
At first glance, a clamp seems to be the simplest element of the entire installation. A screw, a steel clamp, a bolt – what could possibly go wrong? In practice, it's different. After years in the industry, I know that pipe damage caused by incorrect clamps is far more common than you might expect. The plastic pipe jacket ground into dust. A copper pipe with a visible groove around the entire circumference where the metal edge sat. A stainless steel pipe with corrosion exactly where the steel clamp contacted the surface without any insulation. And in all cases, the same answer from the installer: "Well, I put in the clamp I had."
This article focuses on what is actually happening at the contact point between the clamp and the pipe, why the rubber insert is a much more important element than it looks, and how to correctly choose it for a specific type of installation. If you're also interested in selecting the type and material of the clamp itself, I recommend looking at the related article How to Choose the Right Clamp for the Pipe – Material, Type, and Use, or Steel Clamps with Rubber vs. Plastic Clamps – When to Use Which.
What Actually Happens at the Contact Point Between the Clamp and the Pipe
When you fasten a metal element around the pipe and tighten the bolt, several concurrent physical processes occur at the contact point, each of which can cause damage on its own. In combination – and this is the reality of every large heating system – these processes accelerate the degradation of the pipe exponentially.
Stress Concentration and Point Loading
A steel edge without a rubber insert acts on the pipe like a knife. Not immediately, but over months. The pipe expands, contracts, and slightly vibrates – and each of these movements is a micro-movement, during which the metal edge cuts deeper into the material of the jacket. With plastic pipes (PP-R, PE, PEX), you see this as a white groove or crack on the surface. With copper pipes, mechanical scratches appear, where corrosion later begins. With composite (PEX-Al-PEX) pipes, the aluminum layer may be disturbed, which threatens the static strength of the entire pipe.
A rubber insert distributes this stress over a larger area. Instead of a linear contact (edge–surface), you get an area contact, where the pressure is evenly distributed over the entire clamp seat. It sounds simple, but the effect is crucial.
Micro-vibrations and Material Fatigue
Every circulation pump, every section with increased flow speed, every sudden closure of a valve generates vibrations in the pipe system. These vibrations are small – in the range of hundredths of a millimeter – but they are constant and repetitive. A metal clamp without a damping element not only transmits but amplifies these vibrations: a rigid connection "metal–pipe–metal" creates resonance, which accelerates material fatigue. Rubber works as a damper – it absorbs the energy of vibrations before it reaches the pipe wall.
In practice, you recognize this by the noise: an installation with improperly mounted pipes "humms" or "clicks," while a properly mounted installation with rubber inserts is almost silent. If you want to know more about the correct spacing of clamps in terms of damping, see the article Installation of Pipe Clamps – Correct Spacing and Mounting Procedure.
Electrochemical Corrosion at the Contact Point
This is the most dangerous damage mechanism, because it proceeds unnoticed under the surface. When two metals with different electrochemical potentials come into direct contact – for example, a steel clamp and a copper pipe, or a steel clamp and a galvanized pipe – a galvanic cell is created. The moisture, which is practically always present in boiler rooms and technical rooms, serves as an electrolyte. The result is accelerated corrosion – typically on the "cheaper" metal, but not always.
A rubber insert electrically isolates these metal surfaces. No metal contact, no galvanic cell, no electrolytic corrosion. For the long-term reliability of the installation, this is perhaps the most important function of the rubber insert – and yet it is talked about the least.
Rubber Insert – Not All Rubber is the Same
Here we come to the core of the problem. Most people think that a rubber insert is just some elastic black rubber piece that is pressed into the clamp to make it not look so hard. The reality is much more complicated. There are several types of elastomers from which rubber inserts are made, and each has different properties – thermal resistance, chemical resistance, hardness, compressibility, and resistance to aging.
Types of Elastomers and Their Properties
EPDM (ethylene-propylene-diene rubber) is the most common material for rubber inserts in water and heating installations today. It has excellent resistance to hot water, steam, and UV radiation, and works reliably in the temperature range from –40 °C to +150 °C. It is not suitable for contact with oil products and some oils. For most installations of hot and cold water, heating, and solar collectors, EPDM is the first choice.
NBR (nitrile rubber, also Buna-N) is more resistant to oils and oil products, but has lower thermal resistance (typically up to +120 °C) and weaker resistance to ozone and UV. It is used in industrial installations where contact with oil or fuel may occur.
Silicone offers the widest temperature range (–60 °C to +200 °C and more), is inert, and does not repel food approval, but is mechanically less resistant – it is easily cut and torn. For standard construction installations, it is an unnecessarily expensive solution, but for special applications (steam, high temperatures), it is justified.
Neoprene (polychloroprene) is a universal rubber with good resistance to weathering, mild chemicals, and temperatures up to +120 °C. It was popular in older installations, but today it is mostly replaced by EPDM in new projects.
Rubber Hardness – Shore A and Why It Matters
Along with chemical composition, the key parameter is the hardness of the elastomer, measured in Shore A. Too soft rubber (lower Shore A, for example 40–50) deforms too much under the pressure of the clamp – the pipe is not damaged, but the clamp loses the ability to firmly fix the position and the pipe can move. Too hard rubber (Shore A 80 and above) on the other hand stops fulfilling its damping and distribution function – it behaves almost like a rigid plastic and does not provide sufficient protection to the pipe.
For standard heating and water installations, the optimal range of Shore A is 55–70. Quality clamp manufacturers usually list this number in the technical documentation, and if they don't, it is a warning sign of the product's quality.
Aging of the Rubber Insert – an Underestimated Problem in Long-Term Installations
Rubber ages. It is a fact that is easily forgotten during installation, when the material looks perfect. After years of exposure to heat, pressure, and cyclic loading, the elastomer undergoes a process of oxidation and heat-induced degradation – it hardens, cracks, and loses elasticity. The result is that a clamp that perfectly protected the pipe ten years ago now behaves almost like a metal edge.
Quality EPDM under normal operating conditions (temperature up to 90 °C, without aggressive chemicals) will last 15–25 years without significant degradation. Cheaper rubbers of unknown origin begin to break down much sooner – in practice, I have seen clamps where the rubber cracked after 5–7 years at the operating temperatures of a low-temperature heating system. For more on when and how to replace rubber inserts, see the article Maintenance and Replacement of Pipe Clamps – When and How.
Aging is accelerated by:
- high operating temperatures (every +10 °C above the rated temperature roughly doubles the aging rate – Arrhenius law)
- temperature cycling (heating turns on and off – each cycle mechanically stresses the rubber)
- presence of ozone (in some industrial spaces)
- contact with oils or chemicals unsuitable for the given elastomer
- excessive compression of the rubber insert during installation (over-tightened clamp)
Examples of Damage from Practice – What I Have Seen on Jobs
Allow me to present a few real cases, in which I was personally involved or which my colleagues described to me. These examples are not exceptional – if you talk for a while with anyone who does inspections of older installations, they can tell you several similar ones.
Case 1: PP-R Pipe in an Apartment Building, Installation Year 2006
During the renovation of an apartment installation, the installer discovered a series of PP-R distribution lines in the riser, where steel clamps without any rubber insert were used – apparently someone bought a cheaper variant in the store or omitted the rubber during installation. After 17 years of operation, each PP-R pipe had a visible groove 0.8–1.2 mm deep at the clamp location. PP-R usually has a wall thickness of 3.5–5 mm (depending on the pressure class), so the groove represented 20–35 % of the wall thickness. The system had not yet reached a critical condition, but during pressure testing, two elbows cracked right where the wall was weakened and the stress concentration was highest.
Case 2: Copper Installation with Galvanic Corrosion
A boiler room in a family house, copper pipes of the central heating system fixed with common cheap steel clamps, without rubber, without anti-corrosion treatment. After 12 years – during the boiler replacement – installers discovered characteristic greenish spots on the pipes exactly at the clamp locations. Under the spots, the copper material was peeled off – galvanic corrosion had turned the pipe wall into a "cheese" in the contact area. One location was problematic enough that the pipe cracked during handling. The cost of a new installation of the entire boiler room was several times higher than the cost of those correct clamps with rubber would have been twelve years ago.
Case 3: PEX-Al-PEX and Poorly Chosen Rubber Hardness
This is a less common case, but interesting. A customer used clamps with very hard rubber (Shore A 85) on PEX-Al-PEX pipes. The hard rubber did not absorb the vibrations from the pump. The pipes vibrated, the clamp with the hard rubber functioned as a rigid support point – and the aluminum layer was disturbed after two years of operation. The installation had to be partially remade.
Correct Selection of Rubber Insert According to Application
Based on the above-described mechanisms and practical experience, we can summarize the selection of a rubber insert into a few simple rules:
For Installations of Hot Domestic Water and Heating (up to 90 °C)
A standard EPDM insert with a hardness of Shore A 60–70 is ideal. It covers the entire spectrum of standard installations in single-family homes, apartment buildings, and commercial buildings. The correct thickness of the insert for standard clamps is 3–5 mm – thinner will not sufficiently dampen and distribute the pressure, thicker may cause instability of the clamp.
For standard lines in this temperature range, for example, Steel Clamp with One Hole and Rubber 1/2" for smaller diameters or Steel Clamp with One Hole and Rubber 1" for inch-sized lines, where the rubber insert is part of the clamp construction, are ideal.
For Heating with Higher Temperatures or Solar Installations (up to 150 °C)
EPDM is still usable here, but the certification of the specific manufacturer for the given temperature must be checked. An alternative is a silicone insert with a confirmed temperature range. Do not buy clamps with rubber inserts without stating the temperature range – in solar systems with pipes near collectors, temperatures can briefly exceed 130 °C in summer months.
For Larger Diameters and Main Lines
With larger diameters, the contact area is larger, but the weight of the pipe (including content) is significantly higher. The rubber insert here must handle greater static loading. For pipes of 2" and larger, for example, Steel Clamp with One Hole and Rubber 2" or Steel Clamp with One Hole and Rubber 2 1/2", or Steel Clamp with One Hole and Rubber 3" for the largest dimensions – in these diameters, the correct rubber is even more important, because the total weight of the occupied pipe can be dozens of kilograms and each unevenly distributed pressure is more pronounced.
If you are unsure which diameter of clamp you need for your pipe, I recommend reading the article What Diameter Clamp Do I Need – Inch vs. Metric Pipe Dimensions and also How to Convert Inch Clamp Dimensions to Millimeters – Practical Overview.
For Cold Lines and Condensate Pipes
Here, the specific risk is condensation of moisture on the outer wall of the pipe. A wet environment combined with a metal clamp without a rubber insert is a recipe for rapid galvanic corrosion. An EPDM insert also serves as an insulator here. In addition – for cold pipes, the risk of temperature movement is smaller, but vibrations are just as present.
Wall Thickness of the Pipe vs. Clamp Contact Pressure – What the Numbers Say
For technically knowledgeable customers and installers, I provide a more specific look at why the thickness and quality of the rubber insert matter for different types of pipes.
PP-R pipe PN20, DN32 (the most common size in apartment installations) has an outer diameter of 32 mm and a wall thickness of 5.4 mm. If a steel edge (edge width typically 0.5–1 mm) creates a point contact with a pressure corresponding to the weight of the pipe + content (can be 3–5 kg/m for larger diameters), the local specific pressure at the contact point can reach 2–8 MPa. The strength of PP-R in pressure is 25 MPa, but remember we are talking about static loading at room temperature. At 70 °C, the strength of PP-R drops to about 50–60 % of the value at 23 °C, which means that the long-term allowable pressure at the edge can be close to the limit of permanent deformation.
A rubber insert of 4 mm thickness with a contact area covering at least 120° of the pipe circumference reduces this specific pressure 8- to 12-fold – to values at which no plastic deformation occurs even at temperatures of 70–80 °C.
For copper pipes Cu 28×1 (wall thickness 1 mm at an outer diameter of 28 mm), the situation is even more sensitive – the wall is thin and mechanical scratches will appear on it much sooner. The copper's conductivity also predisposes the pipe to galvanic corrosion in contact with steel.
Installation and Tightening of the Clamp – Mistakes the Rubber Won't Forgive
Even if you use the correct rubber insert, improper installation can cause the rubber not to function or to be damaged prematurely. A few rules from practice:
- Do not over-tighten. The rubber insert needs a certain degree of compression to sit on the pipe, but if you compress it to less than 50 % of its original thickness, the material suffers permanent deformation and quickly loses elasticity. Correct tightening = the clamp holds firmly, the rubber visibly contacts the pipe, but is not visibly squeezed to the sides.
- Do not combine different rubber materials. If you replace one clamp in a series, use the same type of rubber insert. Different hardness in one series of clamps causes uneven load distribution along the route.
- Before installation, check the surface of the pipe. No dirt, rough scratches, or sharp edges at the clamp location – every irregularity is a concentration of stress, which even rubber may not compensate for.
- Make sure the rubber insert fully surrounds the pipe. If the insert is smaller than the pipe circumference (for example, you mistakenly used a smaller clamp), the uncovered area will be in direct metal contact with the pipe.
Other installation errors and their consequences are discussed in more detail in the article Common Installation Errors of Clamps and How to Avoid Them.
Special Environments – Boiler Rooms and Technical Rooms
In boiler rooms and technical rooms, rubber inserts in clamps are subject to increased demands: temperature fluctuations are greater (the boiler cycles on and off), humidity is higher, and more aggressive atmospheres may be present (in pellet or wood-fired boiler rooms, there may be higher levels of sulfur dioxide or other combustion products). For these conditions, I always recommend EPDM with proven temperature certification and preferably clamps made of galvanized or stainless steel, where the corrosion of the clamp's base material is also protected. More about the specific requirements for these spaces is discussed in the article Clamps for Pipes in Boiler Rooms and Technical Rooms – Specific Requirements.
Most Frequently Asked Questions (FAQ)
Can I use a clamp without a rubber insert on a steel pipe?
Technically, it is not forbidden, but it is not correct either. Steel on steel may look durable, but galvanic corrosion is a real threat, especially with different types of steel (e.g., galvanized pipe and black steel clamp). In addition, without a rubber insert, vibrations are transmitted directly into the structure and the pipes are noisy. For steel pipes, a rubber insert is just as desirable as for plastic or copper.
How do I know that the rubber insert in an old clamp is worn out and needs to be replaced?
Visual signs include: cracking or breaking of the rubber (cracks on the surface), hardness – the rubber cannot be pressed with a finger even slightly, a visible gap between the rubber and the pipe, a popped out or shifted rubber. If you have doubts during an inspection, replace the insert – the cost of the rubber insert is negligible compared to the cost of pipe repair after damage.
Is there a difference between a rubber insert in a cheap and expensive clamp?
Yes, and sometimes it is crucial. Cheaper products use recycled or mixed elastomers without precisely defined chemical composition and certified temperature range. Quality clamps (such as the steel clamps with one hole available at atria.sk) have a defined material of the insert, its hardness, and temperature range. This is why it pays to not buy clamps only by price when selecting.
Can I retrofit a rubber insert into old clamps without rubber?
Theoretically yes – you can buy EPDM strips or profiles and adapt them to the shape of the clamp. In practice, it is time-consuming and the result is not reliable, because the improvised insert may not have the correct thickness, fit properly into the clamp's profile, or last long-term. Much smarter is to replace the entire clamps with new ones with an integrated certified insert.
Does the rubber insert affect the maximum pull of the clamp (pipe load)?
Yes, slightly. The rubber insert reduces the stiffness of the connection – the pipe can slightly slip in the clamp during extreme thermal expansion, which is often desirable (it allows controlled movement without destabilizing the route). For fixed points, where the pipe must be absolutely fixed, special fixed point constructions exist. A standard clamp with rubber is a sliding point, and that is its correct function for most routes.
What is the lifespan of a rubber insert in a solar installation?
Solar installations are the most demanding application for rubber inserts: temperatures in summer can briefly reach 120–150 °C (collector stagnation), and the cyclic loading is intense. With the use of quality EPDM with certification for these temperatures, you can expect a lifespan of 10–15 years. With low-quality elastomers, hardening and cracking can occur after 3–5 years. Therefore, it is especially important in solar installations to select clamps with a proven specification of the insert material.
Conclusion – the Rubber Insert is Not an Accessory, It is a Functional Element
This entire article revolves around one key message: the rubber insert in the clamp is not an aesthetic detail or a cheap substitute for something better. It is a functional element that simultaneously fulfills three essential roles – distributing contact pressure, damping vibrations, and electrically insulating the pipe material from the metal body of the clamp. Without it, these three protective functions are zero and the pipe is vulnerable to damage in the long-term horizon.
The selection of the correct rubber insert follows relatively simple rules: for most heating and water installations, EPDM with Shore A 60–70 and a thickness of 3–5 mm is the optimal solution. It is just important to make sure that the temperature range of the elastomer corresponds to the application, that the insert is not over-compressed, and that it is regularly inspected during the life of the installation. An installation designed in this way with well-chosen clamps will last for decades without problems – in contrast to one where the savings were made in the wrong place.