Applications: Automotive - Brake Hose Hydraulics (2023)

  • Abstract
  • Introduction
  • Trailer Corrosion Tests
  • Test Results
  • Additional testing
  • bibliographical references


For many years the pipes in car brake systems have been made of low carbon steel. One or more surface coatings are applied after welding to protect the steel substrate from corrosion because steel has no inherent resistance to corrosion in the road environment. Although the coating composition has changed since the original hot lead-tin coatings were used, coating defects remain a problem. The addition of zinc-rich paints slightly improved the protection of the pipe. Current aluminum-zinc coatings and added polyvinyl fluoride coatings are still insufficient to fully protect steel pipe.

In a recent series of tests, copper-nickel 90-10 (UNS C70600) pipe was fabricated into standard brake system "shapes," which were then attached to a test trailer and transported through various corrosive and mechanically abusive test track environments. The tests involved holding the tubes in a high humidity chamber for a portion of each 24-hour test cycle. After 40 cycles and every 10 cycles thereafter, individual tubes were required to pass a pressure test of 20,684 kPa (3,000 psi). Candidate pipe materials had to complete 60 cycles to meet the minimum requirement.

Current production steel tubes passed the 60 cycle requirement but failed well before 120 cycles. The 90-10 copper-nickel tubes completed 200 cycles with virtually no reduction in their original burst strength.

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The brake pipes are in a highly corrosive area. Although many other automotive components operate in the same hostile environment, few are less forgiving in the event of a breakdown. Thus, one of the main considerations in the design of an automotive hydraulic brake system is the integrity of the brake line that distributes the system pressure.

In 1965, an annual safety check of motor vehicles was introduced in Sweden and subsequently in other European countries. This process included inspecting the hydraulic brake lines for rust. At the same time, the Swedish Motor Vehicle Inspection Society began publishing annual reports on the results of these tests.1

In 1969, laboratory tests were reported comparing some inherently corrosion resistant copper alloy pipe materials with then current production materials.2

In the early 1970s, the Swedish Corrosion Institute approached the problem of brake pipe corrosion from the point of view of using a corrosion-resistant material instead of trying to protect the surface.1

(Video) How do hydraulic brakes in cars and light vehicles work 3D animation

The European car industry's initial response to brake pipe corrosion problems was to end the use of the then existing hot-dip ternet metal coating over steel pipe. Laboratory testing in a 6% neutral vapor salt spray test showed that corrosion resistance could be achieved with a 25 micron zinc coating in place of the ternet coating. In the years that followed, it became apparent that the laboratory tests did not accurately reflect the conditions that exist in the real operating environment. Various plastic coatings were then applied over the zinc and some are still used today.1

Applications: Automotive - Brake Hose Hydraulics (1) Figure 1.Copper-nickel brake lines run from 1990 Volvo master cylinder.

Efforts to achieve a metallurgical solution to the corrosion problem continued. Volvo began using copper-nickel 90-10 ("Cunifer Alloy") tubing in its 1976 vehicle models and has used it ever since.Figure 1shows the installation on the master cylinder in a 1990 Volvo model. Audi started using this material in 1990. The other European cars that use this material are Porsche and Aston Martin.2

The bar graph shown inFigure 2illustrates the percentage of vehicles that fail safety inspections due to defects in the brake systems of eight-year-old Volvo passenger cars. 1970 model cars had terne coated steel pipes. The pipes on the 1971 models were zinc coated. Defects other than rusted pipes are included in these values, but their effect on the data is minimal. The reduction in defects associated with the introduction of 90-10 copper-nickel tube in 1976 is dramatic.

Applications: Automotive - Brake Hose Hydraulics (2) Figure 2. Annual Swedish Vehicle Safety Inspection Results. Bars indicate the percentage of 8-year-old Vovlo passenger cars inspected in the indicated year with brake lines that did not meet inspection requirements. 1976 was the year Volvo introduced 90-10 copper-nickel ("Cunifer Alloy") pipes to its vehicles.

The paper2presented at the SAE Annual Meeting in January 1970, which dealt with the then "state of the art" in pipe coatings. the data presented in this paper are still relevant. Voids, poor adhesion, discontinuities and physical damage in the surface coatings used today can lead to accelerated, localized corrosion attack that renders any intact coating elsewhere in the pipe useless.

An incident reflecting the latter situation was recorded in an SAE paper presented in 1991.3A brake line that should have burst when tested at 1 1 5 832 to 158 579 kPa (1 6 800 - 23 000 psi) actually burst at 4 825 kPa (700 psi). The document states, "This particular section of pipe was at the end, above and behind the rear axle, and had extensive corrosion, perhaps due to impact with gravel."

(Video) Start Up: The hydraulic brake system

Based on the background summarized above, a test program was undertaken by the Copper Development Association Inc., in cooperation with an automobile manufacturer, to thoroughly evaluate the applicability of Copper Alloy C70600, 90-10 copper-nickel pipe, for the line car brake application. The pipe material is described inTable 1.

Table 1. Material requirements for copper alloy C70600 for use in automotive brake line
Composition, maximum percentage, unless shown as a range
9,0 - 11,0
1,0 - 1,8
Rest of
Mechanical properties
Output power, min. (0.2% offset)
Tensile strength, min
Extend to 50.8mm (2.0)
110.316 kPa (16.000 psi)
310.179 kPa (45.000 psi)
Pressure proof test
Unless otherwise specified, the finished tubing shall withstand a hydrostatic profile test, without evidence of failure, at a pressure p which will subject the material to a fiber stress of 110,316 kPa (16,000 psi). The test pressure is determined by Barlow's equation for thin hollow cylinders under tension:
Applications: Automotive - Brake Hose Hydraulics (3)
Piis internal pressure, psi
tis pipe wall thickness, in.
smallis allowable pipe wall tensile strength, psi
Heyis pipe O.D., in.

No pipe shall be tested in excess of 34,473 kPa (5,000 psi) hydrostatic pressure unless otherwise specified.

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Trailer Corrosion Test

The design test procedure generally used today to evaluate the corrosion resistance and integrity of motor vehicle body and chassis components consists of 100 cycles of moisture-controlled soaking and drying, salt spray and mileage accumulation on various road surfaces with test specimens mounted on a trailer. The sequence of events of the test cycle is listed inTable 2.

Table 2. Test Cycle Sequence for the Evaluation of Car Body and Frame Components
1)Salt bath
20 km/h (12 mph)
2)Dirt road
70 km/h (45 mph)
Test cycle
3)Salt spray chamber
15 minutes
10)Vehicle ramp closure controls
4)Salt bath11)Salt bath
20 km/h (12 mph)
5)Washboard Salt Highway
65 km/h (40 mph)
12)Washboard Salt Highway
65 km/h (40 mph)
6)Dirt Road (Car/Lt Trk)
Gravel (Hvy Trk)
70 km/h (45 mph)
13)Dirt road
70 km/h (45 mph)
7)Washboard Salt Highway
65 km/h (40 mph)
14)Washboard Salt Highway
65 km/h (40 mph)
8)Dirt road
70 km/h (45 mph)
15)Dirt road
70 km/h (45 mph)
9)Humidity Chamber
@ 50C (120°F)
85-92% R.H. 6 hours
16)Humidity Chamber
@ 50C (120°F)
85-92% R.H. 7 hours

Applications: Automotive - Brake Hose Hydraulics (4) Figure 3. Brake line samples attached to test trailer.

Applications: Automotive - Brake Hose Hydraulics (5) Figure 4. Equipment used to test brake pipe hydrostatic pressure.

The trailer is exposed to salt, dust and stone pecks as well as temperature and humidity fluctuations. The total moisture soaking time is approximately 2,600 +/-25 hours. The total soaking time of the drying chamber is 375 +/-25 hours. The test trailer accumulates approximately 13,800 km (8,600 miles) during the full test cycle. The total trial time is approximately 26 weeks.Figure 3shows test samples attached to a standard test trailer. The tube size used for testing was 4.76 mm (0.1875 in.) outside diameter, 0.7 mm (0.028 in.) wall thickness. It was built in standard brake system configurations with flares and pipe nuts. The ends were encapsulated to allow for subsequent pressure testing. These test pieces were then attached to various areas of the test trailer to ensure exposure to all test items at varying degrees of intensity.

Beginning with the 40th cycle and at 10 cycle intervals thereafter, each tube is subjected to an internal pressure test of 20,684 kPa (3000 psi). Candidate materials must complete 60 cycles to meet the minimum requirement.Figure 4shows the test equipment on which the hydrostatic pressure tests were performed.

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This performance would have been expected even if a measured surface friction had been induced on the pipe as a prerequisite for evaluating the pipe surface.

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Test Results

The data inTable 3 4reveal that after 200 test cycles, which exceeds three times the minimum benchmark of 60 cycles, the copper-nickel material retained more than 89% of its original average burst strength.

Table 3. Trailer Corrosion Test Results4
Sample No.Hydrostatic compression pressure
Before the test report
After 200 Test Cycles

Also notable is the close difference in burst pressure after the test. This confirms the uniformity of strength and physical properties of copper-nickel, a feature not present in the currently used carbon-coated steel tube.

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Additional testing

Applications: Automotive - Brake Hose Hydraulics (6) Figure 5. The 1976 Volvo engine bay features uncorroded copper-nickel brake lines.

Figure 5shows the engine bay of a 1976 Volvo four-door sedan. The vehicle was in a used auto parts dealer's warehouse. The engine had already been removed and the actual mileage is unknown. However, using corrosion in the engine bay as a criterion, it can be concluded that the uncorroded copper-nickel brake pipes seen coming out of the master cylinder had, indeed, survived a hostile, corrosive environment.

The brake pipes were removed from this vehicle and hydrostatic break-in was tested with the following results:

Tube No. 1 111.694,95 kPa (1 6.200 psi)
Tube No. 2 106.868,62 kPa (1 5.500 psi)

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This real-world data is a welcome confirmation of the trailer test results.

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The automotive industry faces many challenges in the market and on its test tracks. It must produce vehicles that will compete in a global market based on quality, safety, reliability, durability and cost. The test results presented above demonstrate that 90-10 nickel copper pipe is a significantly better choice for automotive brake lines than low carbon steel because:

  1. Using an inherently corrosion-resistant material is the best protection against long-term brake pipe corrosion. This has been proven by Volvo, which has been using 90-10 copper-nickel tubes in cars it has produced for the past 15 years.
  2. Trailer corrosion test results indicate that copper-nickel 90-10 (UNS 70600) pipe is a superior product compared to the coated steel pipe used for brake lines in today's US-built vehicles.
  3. Current double-wrapped, brazed and coated steel pipes are susceptible to weld gaps, coating gaps, poor coating adhesion and discontinuities. These vulnerabilities, combined with accidental service damage, mean that the actual life of brake line materials currently used in US-built vehicles should be considered unacceptable.

It must be recognized that all underbody components, including the brake pipes, will be struck by objects thrown from the tires. Such accidental damage should be considered the most vulnerable link in the chain.

The pipe designer generally specifies the addition of a metal or plastic sleeve to the areas of the pipe believed to be most vulnerable to rock damage. However, an inherently corrosion-resistant copper-nickel tube provides the surest protection against such accidental damage, especially when compared to a coated steel tube.

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bibliographical references

  1. Svenson, G.E., Swedish Motor Vehicle Inspection Company, Brake Pipe Corrosion - the Situation 1986, In addition to document ISO 150/22/2WG 8N 82, February, 1986.
  2. Ingram, A.G. and Miner, D.K., Hydraulic Brake Line Corrosion; An Initial Investigation of the Problem, SAE Technical Paper 690530; presented at the SAE Annual Meeting, Detroit, Mich., May 1969.
  3. Bologna, D.J., Accelerated Corrosion Tests and the Evaluation of New Automotive Brake Line Coatings, SAE Technical Paper 912292, Conference, Dearborn, Michigan, Οκτώβριος 1991.
  4. Brantigan, J., Control Power Company, Hydrostatic Burst Test Results, September 11, 1992.


What are the applications of hydraulic braking system? ›

A hydraulic brake circuit has fluid-filled master and slave cylinders connected by pipes. Many other vehicles use hydraulic brakes such as cranes, lifts, elevators, aeroplanes, and mining vehicles. The uses and applications for hydraulic brakes are endless, and all use similar systems and components.

Where are flexible hydraulic brake hoses used and why? ›

Flexible hoses are used in the brake system to transmit hydraulic fluid pressure between the master cylinder and the calliper or cylinder, and in the clutch system between the clutch pump and the clutch slave cylinder.

What does a brake hydraulic hose do? ›

Brake hoses create a flexible connection between brake pipes and wheel brakes. They transmit the hydraulic pressure to the wheel cylinders and brake callipers. Brake hoses are usually made form a special inner and outer rubber with a multi-layer fabric insert in between.

Can you use hydraulic hose for air brake line? ›

We find it surprising that some mechanics use hydraulic hose for air brake applications. Perhaps they figure that since hydraulic hose is rated at a much higher pressure than air brake hose it is safe to use.

What are the application of hydraulic system in automotive industries? ›

Power steering, shock absorbers, windshields, and brake are the common applications of hydraulics in vehicles. Two-post lifts and four-post lifts are used in the automobile industry to lift vehicles for servicing and inspecting.

Where can I use a hydraulic hose? ›

It is normally used to transfer mineral and hydraulic oils or emulsions of water and oil, which makes it particularly useful for constructions and civil engineering, mining and quarrying, oil industries and agriculture – among others.

What are advantages of flexible hydraulic hoses? ›

The primary advantage of flexible metal hoses is their flexibility. They can bend and twist without breaking, which makes them ideal for applications where rigid piping would not work. This flexibility also allows for easier installation in tight spaces and around obstacles.

What do braided brake hoses do? ›

The main benefit of braided brake lines is that they help improve performance by reducing the issue of swelling, most commonly associated with the standard rubber brake lines. Over time and extensive use, rubber lines can swell under the pressure caused by applying the brakes.

What is an example for hydraulic brake? ›

An example of a hydraulic brake system

Hydraulic brakes transfer energy to stop an object, normally a rotating axle. In a very simple brake system, with just two cylinders and a disc brake, the cylinders could be connected via tubes, with a piston inside the cylinders.

What are the applications of anti braking system? ›

Anti-lock braking systems (ABS) help you steer in emergencies by restoring traction to your tires. What It Does: Helps prevent wheels from locking up – possibly allowing the driver to steer to safety. What It Does Not Do: May not shorten stopping distance; pedal may vibrate or push back – that's normal.

What are the application of hydraulic components? ›

Hydraulic System Components
  • Reservoir. The purpose of the hydraulic reservoir is to hold a volume of fluid, transfer heat from the system, allow solid contaminants to settle and facilitate the release of air and moisture from the fluid.
  • Pump. ...
  • Valves. ...
  • Actuators. ...
  • Vane Pumps. ...
  • Piston Pumps. ...
  • Gear Pumps. ...
  • Hydraulic Fluids.

What are the applications of mechanical braking system? ›

The mechanical braking system powers the hand brake or emergency brake. It is the type of braking system in which the brake force applied on the brake pedal is carried to the final brake drum or disc rotor by the various mechanical linkages like cylindrical rods, fulcrums, springs etc. In order to stop the vehicle.


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