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"Wall thickness matters" – facts and myths about copper lines in brake system

Brake lines are one of brake system's elements responsible for our safety on the road. Brakes pads, discs or ABS and EPS systems will not work properly, unless we have functioning brake lines. Despite the fact they play such an important role in the brake system, there are only few publications about technical aspects of using copper pipes as rigid brake lines. As a result we face myths related to their use that we shall disprove.

Each rigid brake line is just the same, only the manufacturer is different - FALSE

As opposed to other elements of the brake system (e.g. discs or brake pads), brake line are not a subject to homologation. Because of that, when buying these elements we should pay attention on their manufacturer. Buying lines from unknown source or unknown manufacturer may result in purchasing a product which does not meet recommended standards, and thus - negatively affects our safety.

Only steel lines can be used in brake systems - FALSE

Copper brake lines are an standard value replacement of steel lines, so there is no reason not to use them in brake systems.

Despite lack of homologation requirement, there are documents which regulate the issue of brake line properties and effective standards applying to them. One of such documents is the Polish standard PN-EN 12449. "Copper lines and tubes of WP Company present all mechanical properties mentioned in that standard. Tensile strength and yield strength are significant parameters.” – says Witold Pniewski, Chairman of the "WP" Company. Another standard (PN-ISO 4038) regulates the dimensions of flares and provides specification of connecting elements, such as fittings. Specification of guidelines can be found in the latest industry standard BN-90 3617-09, which defines that low-carbon steel can be replaced by copper or copper-nickel alloys (so-called cupronickel) with specified parameters.

Wall thickness in copper brake lines does not affect durability - FALSE

Brake lines, in order to maintain appropriate parameters during operation under pressure, should withstand pressure exceeding 1000 bar. Achieving such durability is affected by adequate process of tube cleaning and annealing. The tubes must have appropriate internal structure and constant peripheral cross-section over entire length, and also keep specified dimensions. The parameter of wall thickness is easy to verify in order to determine whether particular line meets effective standards. With the external diameter of 4.75 mm (standard brake line dimensions), the thickness of copper tube wall should be 0.90 mm. With such parameters of the properly prepared material, the brake line withstands applied pressures.

Decreasing the wall thickness, by as little as 0.10 mm or to thickness of 0.80 mm, results in durability decrease of even 200 – 250 bar. You should bear that in mind, as such brake lines with thinner walls are offered in the market. Some manufacturers, while willing to reduce the price of their products, decide to apply these solutions, saving on materials. Because of that unaware customer who bought the lines (nearly 25% less durable) might have problems with the brake system, and particularly when having ABS or ESP, where that durability has extremely great importance.

There is the standard EN 12735-1 that says tubes with external diameter of 4.80 mm and wall thickness of 0.80 mm can be used in cooling systems only. That’s why manufacturers should not refer to this standard while producing brake lines. "You should be aware of that and check wall parameters of the brake line you are going to buy for your brake system" – warns Rafał Lanczyk, Manager of "WP" Company's National Sales Department.

Installation of copper brake lines changes vehicle construction - FALSE

Journal of Laws of the Republic of Poland provides a discussion of the matters related to car inspection, and thus also regulations regarding brake system. In the section referring to that it is not mentioned about excluding, nor prohibiting the use of copper as a replacement of steel. There is only a warning provided in point 5.1.1 related to incompleteness of this system, lack of closed operating circuit or use of parts non-compliant with technical conditions.

Copper lines of correct parameters meet technical conditions, then they completely do not change nor affect the vehicle construction. "Sometimes manufacturers of original parts unjustifiably threaten with those warnings. You should not believe this propaganda, because while following that you would not be able to use any car replacement parts apart from the original ones, even if they met technical requirements" - Witold Pniewski explains.

Copper brake lines are more prone to electrochemical corrosion than steel ones - FALSE

Doubts when using copper in brake system appear when mentioning of electrochemical corrosion. This is a phenomenon which occurs between two different metals. It happens when water particles are found between e.g. aluminum and a different metal, initiating current flow between cathode and anode, eventually resulting in corrosion. Such effect is very unnoticeable in case of combining copper with e.g. an aluminum element. The circuit of such combination is a closed one, oxygen-free (brake system should not contain air nor water). Brake fluid in the system is hygroscopic and has anti-corrosive properties, which limits the electrochemical corrosion. Even if water appears in the system through air fumes, it is absorbed by the fluid, and its negligible amount does not significantly affect occurrence of the aforementioned phenomenon. It is, among other things, the reason why manufacturers schedule obligatory replacement of brake fluid.

To sum up, this phenomenon, even when it occurs to a low extent, goes the same way for copper, carbon steel or stainless steel, and even galvanized steel ("Informator – metale nieżelazne" - "Guide - non-ferrous metals", 2007, 7th edition, page 53). Having considered the above, if steel lines meet technical requirements, then it is safe to assume that copper lines do not cause significant changes in this case, presenting similar behavior with this combination.

Copper brake lines are more resistant to atmospheric conditions than steel ones - TRUE

When affected by atmospheric conditions (e.g. moisture) and other unfavorable conditions (e.g. effect of road salt), the surface of copper lines oxidizes. The coating formed in such way creates a protective layer against further corrosion.

Copper brake lines are easier to install – TRUE

Mechanics who use copper lines when repairing or replacing brake systems underline that these are easier to install than steel lines. It is caused by higher plasticity of copper, thanks to which lines made of this material can be shaped many times to provide better fitting and be installed in a vehicle.

Steel brake lines can be replaced with copper ones – TRUE

After disproving myths related to brake lines, we would like to show that copper lines can be used in brake systems. They are the standard value replacement of steel lines if they meet all the aspects listed above and the technical requirements. Because of that, you should remember not to underestimate the described issues and pay attention what you buy.

Issues to focus on when buying brake lines:
• external diameter of copper brake line should be 4.75 mm,
• line's wall cannot be thinner than 0.90 mm,
• you should check if a manufacturer has certificates proving product quality,
• you should check if lines are correctly marked (e.g. computer marking over the entire length with a company name, manufacturer's batch number, etc.).

"All products such as lines, tubes and fittings offered by "WP" Company are manufactured following the standards and requirements applicable to these elements. We use our best efforts so that our products would present the highest quality and meet the required standards. Then we encourage you to use original "WP" Company's products, what will ensure safety of yours and your relatives while using brakes in your vehicle” – says Witold Pniewski, Founder and Director of "WP" Company.

Prepared by: Damian Sołtysiak, Sales Specialist at "WP" Company