ISO 7628:2010

Road vehicles - Thermoplastics tubing for air braking systems

ISO 7628:2010 specifies the minimum requirements for mono wall and multilayer tubing used in air braking systems on road vehicles. The conformity of production is the responsibility of the tubing manufacturer. The marking of the tubing does not automatically imply that the tube assembly (i.e. tube with end fittings) is appropriate for its use on a vehicle.

Véhicules routiers — Tuyauteries thermoplastiques de dispositifs de freinage pneumatique

General Information

• Status: Published
• Publication Date: 25-Jan-2010
• ICS: 43.040.40 - Braking systems
• ICS: 83.140.30 - Plastics pipes and fittings for non fluid use
• Technical Committee: ISO/TC 22/SC 33 - Vehicle dynamics and chassis components
• Drafting Committee: ISO/TC 22/SC 33 - Vehicle dynamics and chassis components
• Current Stage: 9093 - International Standard confirmed
• Start Date: 17-Jun-2021
• Completion Date: 13-Dec-2025

Relations

• Revises: ISO 7628-2:1998 - Road vehicles - Thermoplastics tubing for air braking systems - Part 2: Mounting on vehicle and test methods
• Effective Date: 15-Apr-2008
• Revises: ISO 7628-1:1998 - Road vehicles - Thermoplastics tubing for air braking systems - Part 1: Dimensions and marking
• Effective Date: 15-Apr-2008

Overview - ISO 7628:2010 (Thermoplastics tubing for air braking systems)

ISO 7628:2010 sets minimum requirements and test methods for thermoplastics tubing (mono‑wall and multilayer) used in road‑vehicle air braking systems. The standard covers materials, construction, dimensions, marking, installation guidance and extensive performance testing. Conformity of production is the responsibility of the tubing manufacturer, and tube marking alone does not guarantee that a tube assembly (tube + end fittings) is suitable for vehicle use - tube assemblies must be tested (Annex B).

Key topics and technical requirements

• Scope & categories: Tubing is classified into four categories with specified maximum working pressures and temperature ranges (e.g., categories for 1 000 kPa and 1 250 kPa with temperature limits up to 125 °C for engine‑compartment use).
• Dimensions and sizes: The standard defines nominal sizes and minimum wall thicknesses for common tubing diameters (examples: 4×1 mm through 19×2 mm).
• Materials & manufacture: Tubing shall be extruded from 100% virgin material (own reworked material allowed up to 20% of new feedstock); reinforcement is permitted when suitable for the application.
• Marking requirements: Tubing must be indelibly marked along a generating line (minimum 2 mm letter height), repeated at least every 350 mm, with seven items separated by slashes (ISO 7628, tubing category, outside diameter × wall thickness, material symbol per ISO 1043‑1, manufacturer designation, date code, etc.).
• Performance testing: A comprehensive test matrix includes:
  • Burst tests (at ambient and specified elevated temperatures)
  • Deformation under pressure
  • Cold impact and impact after ageing
  • Layer adhesion (for multilayer tubing)
  • Chemical resistance tests (ethanol, battery acid, oil, urea)
  • Stress cracking, moisture absorption, low‑temperature flex, heat ageing, artificial weathering and ozone exposure
  • Tube‑assembly tests (pull‑out strength, leak testing, pulsating pressure fatigue, vibration, salt spray)
• Acceptance criteria: The standard specifies pass/fail thresholds (e.g., minimum burst factors at ambient and elevated temperatures) and sample sizes for each test.

Practical applications and users

• Who uses ISO 7628: tubing manufacturers, automotive OEMs, tube assemblers, quality and testing laboratories, component suppliers, aftermarket manufacturers and compliance engineers.
• Practical value:
  • Ensures tubing safety and reliability in pneumatic braking systems
  • Provides harmonized dimensions and marking for traceability
  • Defines repeatable test methods for chemical, thermal and mechanical durability
  • Helps OEMs and suppliers select compatible tubing and fittings and validate tube assemblies for vehicle integration
• Installation guidance: routing, support and storage recommendations to avoid chafing, kinking, excessive sag and fatigue.

Related standards

• ISO 7375‑1, ISO 7375‑2 - coiled tube assemblies for pneumatic systems
• ISO 1043‑1 - plastic material symbols
• Referenced test standards (e.g., ISO 179‑1, ISO 4892 series, ASTM B117) are used for specific test procedures.

Keywords: ISO 7628:2010, thermoplastics tubing, air braking systems, road vehicles, tube assemblies, burst test, tubing categories, multilayer tubing, marking, automotive standards.

Standards Content (Sample)

INTERNATIONAL ISO
STANDARD 7628
First edition
2010-02-01
Road vehicles — Thermoplastics tubing
for air braking systems
Véhicules routiers — Tuyauteries thermoplastiques de dispositifs de
freinage pneumatique
Reference number
©
ISO 2010
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ii © ISO 2010 – All rights reserved

Contents Page
Foreword .iv
1 Scope.1
2 Normative references.1
3 Terms and definitions .2
4 Marking and identification.2
5 Dimensions .3
6 Manufacture .4
6.1 Materials .4
6.2 Tubing.4
7 Installation on the vehicle.4
7.1 Use of tube assemblies on the vehicle .4
7.2 Installation precautions .4
8 Testing and requirements.5
9 Test procedures and requirements .7
9.1 Burst test.7
9.2 Deformation under pressure .9
9.3 Cold impact test.9
9.4 Impact test after heat ageing.10
9.5 Layer adhesion test multilayer pipes .10
9.6 Moisture absorption .10
9.7 Low temperature flexural test .10
9.8 Stress cracking test .11
9.9 Resistance to ethanol .12
9.10 Resistance to battery acid.12
9.11 Resistance to oil .13
9.12 Resistance to urea solution.13
9.13 Heat ageing .14
9.14 Artificial weathering test.14
9.15 Ozone test .14
9.16 Tube assemblies.15
Annex A (normative) Cold impact apparatus.16
Annex B (normative) Tests on tube assemblies (tube with end fittings).19
Annex C (informative) Method for leak detection in leak-proof testing .22
Annex D (informative) Synopsis of test and corresponding samples.25
Bibliography.26

Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies
(ISO member bodies). The work of preparing International Standards is normally carried out through
ISO technical committees. Each member body interested in a subject for which a technical committee has
been established has the right to be represented on that committee. International organizations, governmental
and non-governmental, in liaison with ISO, also take Part in the work. ISO collaborates closely with the
International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. Draft International Standards
adopted by the technical committees are circulated to the member bodies for voting. Publication as an
International Standard requires approval by at least 75 % of the member bodies casting a vote.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. ISO shall not be held responsible for identifying any or all such patent rights.
ISO 7628 was prepared by Technical Committee ISO/TC 22, Road vehicles, Subcommittee SC 2, Braking
systems and equipment.
This first edition cancels and replaces the second edition of ISO 7628-1:1998, the first edition of
ISO 7628-2:1998 and ISO 7628-2/Cor.1:1999, which have been technically revised.

iv © ISO 2010 – All rights reserved

INTERNATIONAL STANDARD ISO 7628:2010(E)

Road vehicles — Thermoplastics tubing for air braking systems
WARNING — The use of this International Standard may involve hazardous materials, operations, and
equipment. This International Standard does not purport to address all of the safety concerns, if any,
associated with its use. It is the responsibility of the user of this International Standard to establish
appropriate safety and health practices and determine the applicability of regulatory limitations prior
to use.
1 Scope
This International Standard specifies the minimum requirements for mono wall and multilayer tubing used in
air braking systems on road vehicles. The conformity of production is the responsibility of the tubing
manufacturer.
The marking of the tubing does not automatically imply that the tube assembly (i.e. tube with end fittings) is
appropriate for its use on a vehicle.
It is the responsibility of the tube assembler and/or the vehicle manufacturers to ensure that the tests
described in Annex B, relating to the tube assembly itself, are successfully performed.
For the requirements on coiled tube assemblies refer to ISO 7375-1 and ISO 7375-2.
2 Normative references
The following referenced documents are indispensable for the application of this document. For dated
references, only the edition cited applies. For undated references, the latest edition of the referenced
document (including any amendments) applies.
ISO 179-1, Plastics — Determination of Charpy impact properties — Part 1: Non-instrumented impact test
ISO 1043-1, Plastics — Symbols and abbreviated terms — Part 1: Basic polymers and their special
characteristics
ISO 1183-1, Plastics — Methods for determining the density of non-cellular plastics — Part 1: Immersion
method, liquid pyknometer method and titration method
ISO 4892-2:2006, Plastics — Methods of exposure to laboratory light sources — Part 2: Xenon-arc lamps
ISO 4892-4:2004, Plastics — Methods of exposure to laboratory light sources — Part 4: Open-flame carbon-
arc lamps
ASTM B117, Standard Practice for Operating Salt Spray (Fog) Apparatus
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
tube
tubing which has been cut to its appropriate length
3.2
tube assembly
tube which has been equipped with suitable end fittings
3.3
tubing without fittings
tubing of unspecified length without end fittings
3.4
tubing with fittings
tubing of a specified length with end fittings
3.5
impact energy
energy determined by means of an impact bending test
4 Marking and identification
Tubings shall be indelibly marked along a generating line with letters of a minimum height of 2 mm and
repeated at least every 350 mm as follows:
⎯ ISO 7628;
⎯ tubing category, i.e. either 1 000 kPa or 1 250 kPa for the temperature range −40 °C to 100 °C;
⎯ tubing category, 1 250 kPa; for the temperature range −40 °C to 125 °C;
⎯ outside diameter times wall thickness;
⎯ symbol for the material type, in accordance with ISO 1043-1;
⎯ manufacturer designation;
⎯ date code of manufacture.
These seven indications shall be separated from each other by slashes.
2 © ISO 2010 – All rights reserved

5 Dimensions
The tubing defined in this International Standard belongs to four possible categories, as defined in Table 1.
Table 1 — Tubing categories for air braking systems
Maximum working pressure Minimum temperature Maximum temperature
Category
kPa °C °C
0 1 000 −40 80
1 1 000 −40 100
2 1 250 −40 100
a
3 1 250 −40 125
a
For use in the engine compartment.
Tubing shall have the dimensions given in Table 2.
Table 2 — Dimensions
Nominal tubing size Tubing basic Outside diameter Inside diameter Inside diameter Minimum wall
outside diameter outside diameter tolerances basic tolerances thickness,
mm mm mm e mm
4 × 1 4 ±0,1 2 ±0,1 0,9
6 × 1 6 ±0,1 4 ±0,1 0,9
8 × 1 8 ±0,1 6 ±0,1 0,9
9 × 1,5 9 ±0,1 6 ±0,1 1,4
10 × 1 10 ±0,1 8 ±0,1 0,9
10 × 1,25 10 ±0,1 7,5 ±0,1 1,15
11 × 1,5 11 ±0,15 8 ±0,15 1,35
12 × 1,5 12 ±0,15 9 ±0,15 1,35
14 × 2 14 ±0,15 10 ±0,15 1,85
15 × 1,5 15 ±0,15 12 ±0,15 1,35
16 × 2 16 ±0,15 12 ±0,15 1,85
18 × 2 18 ±0,15 14 ±0,15 1,85
19 × 2 19 ±0,15 15 ±0,15 1,85
6 Manufacture
6.1 Materials
The tubing shall be extruded from 100 % virgin material (not reground). The use of recycled material is not
permitted, but own reworked material may be used as grinding stock, as long as it does not make up more
than 20 % of the new material, is of the same material type and is from the manufacturer's own production,
and the tubing meets all other requirements of this International Standard. If reinforcement is used, then the
user must be satisfied that the reinforced tubing is suitable for the application. The materials used may have
additives to enhance material performance provided the tubing produced complies with the requirements of
this International Standard.
6.2 Tubing
6.2.1 Quality and appearance
The tubing shall comply with the requirements of this International Standard. The tube shall show no
manufacturing faults, voids, scratches, cracks or lack of homogeneity which could affect service use. Additives
shall be evenly distributed throughout the material.
6.2.2 Construction
6.2.2.1 General
Tubing shall consist of an extrudate of one or more layers.
6.2.2.2 Inner layer
The materials used in the inner layer should be able to withstand contact with chemicals found in a system
environment. The inner layer of the tubing can be exposed to such an environment at the “ends” that are
attached to the various connection points in a system.
6.2.2.3 Colour
The outermost layer may be of a different colour to the subsequent layers but must be the colour designated
by the end user.
7 Installation on the vehicle
7.1 Use of tube assemblies on the vehicle
The choice of appropriate fittings and tube shall be approved by the vehicle manufacturer.
In order to allow its mounting on the vehicle, the tube assembly shall have been tested in accordance with
Annex B.
7.2 Installation precautions
When installed on a vehicle, the tube shall be routed and supported so as to
⎯ eliminate chafing, abrasion, kinking or other mechanical damage,
⎯ minimize fatigue conditions and
⎯ avoid excessive sag.
The tube should be stored inside a dry environment not exceeding a temperature of 40 °C.
4 © ISO 2010 – All rights reserved

8 Testing and requirements
For the purpose of these tests, the tube samples shall be at least two weeks (336 h) old. Unless otherwise
stated, the tests shall be performed at an ambient temperature of (23 ± 2) °C, at a relative humidity between
45 % and 75 %, and unpressurized. All burst tests shall be conducted using the same type of fitting.
The list of appropriate tests to be performed on the tubing is given in Table 3. All the tests listed in Tables 3
and 4 shall be successfully completed before the marking of the tube.
Table 3 — List of tests
Test Subclause Tube size to test
Surface appearance 6.2.1 Every
Burst at 23 °C 9.1.2 Every
Burst at 100 °C 9.1.3 Every
Burst at 125 °C 9.1.4 Every
Deformation under pressure 9.2 Every
Cold impact 9.3 Every
Impact after ageing 9.4 Every
Layer adhesion 9.5 Sample
Moisture absorption 9.6 Sample
Low temperature flexural 9.7 Sample
Stress cracking 9.8 Sample
Resistance to ethanol 9.9 Sample
Resistance to battery acid 9.10 Sample
Resistance to oil 9.11 Sample
Resistance to urea 9.12 Sample
Heat ageing 9.13 Sample
Artificial weathering 9.14 Sample
Ozone 9.15 Sample
Tube assemblies 9.16 Every
Table 4 — Requirements
Test Requirement Subclause
No manufacturing faults, voids, scratches, cracks or lack of homogeneity which
Surface appearance 6.2.1
could affect service use. Additives evenly distributed throughout the material.
Burst All five samples:
9.1.2
1 000 kPa (10 bar) tubes; > 4 000 kPa (40 bar)
at 23 °C
1 250 kPa (12,5 bar) tubes; > 5 000 kPa (50 bar)
at 80 °C 1 000 kPa (10 bar) tubes; > 2 500 kPa (25 bar) 9.1.3
1 000 kPa (10 bar) tubes; > 2 500 kPa (25 bar)
at 100 °C 9.1.3
1 250 kPa (12,5 bar) tubes; > 3 130 kPa (31,3 bar)
at 125 °C 1 250 kPa (12,5 bar) tubes; > 2 500 kPa (25 bar) 9.1.4
All three samples
Deformation under
Deviation between datum lines u 3 % 9.2
pressure
Deviation outer diameter u 10 % initial mean diameter
All five samples
Cold impact No cracks or breaks 9.3
One sample: cracks or breaks, further ten samples to be tested and pass.
Impact after ageing All ten samples no cracks or breaks 9.4
Layer adhesion All five samples no cracks or breaks 9.5
Moisture absorption As agreed between customer and supplier 9.6
All three samples
Low temperature
9.7
No damage
flexural
Rewound area; pass burst test at 23 °C
All six samples
No cracks or breaks
Stress cracking 9.8
Burst pressure at 23 °C > 80 % of the reference value measured on samples from
the same batch
Resistance to ethanol All three samples no evidence of cracking 9.9
All three samples
No dimensional change exceeding ±2%
Resistance to battery Change in weight u 2%
9.10
acid
No evidence of cracking
Tensile force > 80 % of the minimum applied tensile force in accordance with
Annex B
Resistance to oil Average volume change of three samples < 5 % 9.11
Resistance to urea All three samples no evidence of cracking 9.12
Heat ageing To be specified by the end user 9.13
All three samples
Burst test at 23 °C
Artificial weathering 9.14
Burst pressure at 23 °C > 80 % initially measured on samples from the same batch
All three samples ductile burst area
The samples shall show no evidence of cracks when visually inspected under seven-
Ozone 9.15
power magnification
Pull out strength; no loosening or pull off shall occur. Neither the tube nor the fittings
shall fail
Leak test; no leakage
Vibration test; end user's specification
Tube assemblies Pulsating pressure fatigue test 9.16
No sign of failure or leakage
Burst test requirements mentioned above and at least 80 % of the reference value
measured on samples from the same batch
Salt spray test; no evidence of cracking
6 © ISO 2010 – All rights reserved

9 Test procedures and requirements
9.1 Burst test
9.1.1 Test procedure
The burst test shall be carried out on five tube assemblies for each temperature. The tube length between the
end fittings shall be approximately 150 mm. The test procedure comprises the steps given in 9.1.2, 9.1.3
and 9.1.4.
9.1.2 Burst at 23 °C
Soak the tube assemblies in water at 23 °C for 10 min to 15 min. Before testing, keep the tube assemblies for
the following times at 23 °C and (50 ± 10) % relative humidity:
a) 1 h minimum for tubes with a nominal wall thickness e u 1,25 mm (see Table 2);
b) 2 h minimum for tubes with a nominal wall thickness e > 1,25 mm (see Table 2).
Apply hydrostatic pressure at a constant rate by means of a hydraulic pump or accumulator system with a
calibrated pressure gauge at such a speed that the tube will burst between 30 s and 60 s after starting to
pressurize the tube.
The burst pressure at 23 °C is the maximum pressure obtained during the test.
NOTE Fittings can be specified in agreement with the customer.
9.1.3 Burst at 80 °C and 100 °C
This test shall be performed with an inert internal pressurizing medium and air outside.
Place the assemblies in an oven at (80 ± 2) °C or (100 ± 2) °C respectively and allow to condition for 1 h.
Apply pressure at a constant rate by means of a pump or accumulator system with a calibrated pressure
gauge at such a speed that the tube will burst between 30 s and 60 s after starting to pressurize the tube.
The burst pressure at 80 °C or 100 °C is the maximum pressure obtained during the test.
NOTE Fittings can be specified in agreement with the customer.
9.1.4 Burst at 125 °C
This test shall be performed with an inert internal pressurizing medium and heated air, water or silicon oil
outside the tube.
Place the assemblies in an appropriate autoclave. The autoclave shall be equipped with a suitable coupling
unit for fitting the tubes and connecting to the pressurizing equipment (Figure 1). Heat the medium, preferably
water, in the autoclave to the required temperature and keep the temperature constant for 10 min. Apply
pressure at a constant rate by means of a pump or accumulator system with a calibrated pressure gauge at
such a speed that the tube will burst between 30 s and 60 s after starting to pressurize the tube.
The burst pressure at 125 °C is the maximum pressure obtained during the test.
NOTE 1 The autoclave should preferably be suitable for the different tube sizes specified in Table 2.
NOTE 2 Fittings can be specified in agreement with the customer.
Key
1 heating mantel 4 thermometer heating medium
2 autoclave 5 pressure gauge
a
3 pipe assembly Gas inlet.
Figure 1 — Burst test at 125 °C — Schematic figure
9.1.5 Requirements
The burst criterion is the burst of the tube itself.
All five samples shall have a burst pressure as specified in Table 5.
Table 5 — Burst pressure
Test temperature Tube class Burst pressure
1 000 kPa (10 bar) > 4 000 kPa (40 bar)
23 °C
1 250 kPa (12,5 bar) > 5 000 kPa (50 bar)
80 °C 1 000 kPa (10 bar) > 2 500 kPa (25 bar)
1 000 kPa (10 bar) > 2 500 kPa (25 bar)
100 °C
1 250 kPa (12,5 bar) > 3 150 kPa (31,5 bar)
125 °C 1 250 kPa (10 bar) > 2 500 kPa (25 bar)
8 © ISO 2010 – All rights reserved

9.2 Deformation under pressure
9.2.1 Test procedure
This test shall be carried out on three tube assemblies. The tube length shall be approximately 300 mm
between the end fittings.
Condition the tube assemblies for 24 h at 23 °C.
Mark the tube with two datum lines at approximately 50 mm from the end fittings. Measure the initial length
between these datum lines and the initial outer diameter of the tube. Fix one end of each sample.
At t = 0 min expose the samples for 1 h at (80 ± 2) °C for category 0, (100 ± 2) °C for categories 1 and 2 and
(125 ± 2) °C for category 3. At t = 55 min the pressure shall be gradually increased to reach a pressure of
125 % of the maximum working pressure after 30 s to 60 s (see Figure 2) and hold until t = 60 min.
Stabilize the tube at 23 °C for one hour and measure the length between the datum lines and the outer
diameter of the tube.
Figure 2 — Deformation under pressure; time line
9.2.2 Requirement
The length between the datum lines shall not deviate by more than 3 % from the initial measured length and
the outer diameter shall not deviate by more than 10 % from the mean value of the initial measured diameter.
9.3 Cold impact test
9.3.1 Test procedure
This test shall be carried out on five tube samples 150 mm minimum in length with a test apparatus in
accordance with Annex A.
Condition the tube samples for 2 h at (−40 ± 2) °C. Within 5 s of removal from the cold cabinet, subject the
samples to a cold impact test at 23 °C.
9.3.2 Requirements
The five tube samples shall exhibit neither cracks nor breaks. Samples that are only deformed are considered
to have passed the test.
If only one sample exhibits cracks or breaks, a further ten samples shall be tested. If more than one of these
ten samples exhibits failur
...