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
Current Stage
9093 - International Standard confirmed
Start Date
17-Jun-2021
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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 7628:2010(E)
ISO 2010
---------------------- Page: 1 ----------------------
ISO 7628:2010(E)
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ii © ISO 2010 – All rights reserved
---------------------- Page: 2 ----------------------
ISO 7628:2010(E)
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

© ISO 2010 – All rights reserved iii
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ISO 7628:2010(E)
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
---------------------- Page: 4 ----------------------
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
© ISO 2010 – All rights reserved 1
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ISO 7628:2010(E)
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
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ISO 7628:2010(E)
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
3 1 250 −40 125
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
© ISO 2010 – All rights reserved 3
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ISO 7628:2010(E)
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
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ISO 7628:2010(E)
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
© ISO 2010 – All rights reserved 5
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ISO 7628:2010(E)
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
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ISO 7628:2010(E)
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.
© ISO 2010 – All rights reserved 7
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ISO 7628:2010(E)
Key
1 heating mantel 4 thermometer heating medium
2 autoclave 5 pressure gauge
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
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ISO 7628:2010(E)
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 failure, then the tube is considered to have failed the test.

© ISO 2010 – All rights reserved 9
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ISO 7628:2010(E)
9.4 Impact test after heat ageing
9.4.1 Procedure

The impact test shall be carried out on three tube samples about 150 mm in length, with a test apparatus in

accordance with Annex A.

Expose the samples in a circulating air oven to a temperature of (150 ± 2) °C for 72 h, then cool them down to

23 °C over a period of 4 h. Subject each sample to an impact test at 23 °C.
9.4.2 Requirement
The samples shall show no evidence of cracks or breaks.
9.5 Layer adhesion test multilayer pipes
9.5.1 Procedure

This test shall be carried out on five tube samples 150 mm minimum in length and consists of the cold impact

test (see 9.3) followed by a burst test at 23 °C (see 9.1.2).
9.5.2 Requirement
The samples shall show no delamination at the fractured surface.
NOTE 1 Fittings can be specified in agreement with the customer.

NOTE 2 The layer adhesion test can be combined with the cold impact test (see 9.3).

9.6 Moisture absorption
9.6.1 Procedure

This test shall be carried out on three tube samples approximately 40 mm in length.

Expose the samples for 24 h in a circulating air oven to a temperature of (100 ± 2) °C. Remove the samples

from the oven, weigh immediately and expose the samples for 100 h at 100 % relative humidity at 23 °C. After

5 min, remove surface moisture from both the interior and exterior surfaces of the tube and reweigh. The

moisture absorption is determined by the mass variation.
9.6.2 Requirement
The requirement shall be agreed between customer and supplier.
9.7 Low temperature flexural test
9.7.1 Procedure

The test shall be carried out on three straight tube or tube assembly samples 300 mm minimum in length.

Condition the samples in a cold chamber for 2 h at (−40 ± 2) °C. Include the mandrel with a diameter 10 × the

outer diameter of the tubing. After conditioning and within 60 s, bend the samples W 180° around the mandrel.

After a 4 h stabilization period at an ambient temperature of 23 °C, subject each sample to the burst test at

23 °C described in 9.1.2. The length necessary for the burst test shall include the rewound area.

10 © ISO 2010 – All rights reserved
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ISO 7628:2010(E)
9.7.2 Requirements
The samples shall show no evidence of damage (e.g. cracks, crazing, kinking).
All three samples shall pass the burst test at 23 °C (see 9.1.2).
9.8 Stress cracking test
9.8.1 Test principle

The tube assembly samples shall be exposed for a certain period of time to a high level of humidity at 60 °C,

with intermittent short immersions in a corrosive solution at ambient temperature. The tube assemblies shall

be bent in accordance with Figure 3.
l = (11πD /2) + 4 D
1 1 1
l = 5 ± mm
2 0
where:
l is the length of the free tube/fitting contact area;
l is the distance between the tube and the solution surface;
D is the outer diameter of the tube.
Key
1 level of the solution
Figure 3 — Stress cracking test
© ISO 2010 – All rights reserved 11
---------------------- Page: 15 ----------------------
ISO 7628:2010(E)
9.8.2 Specification of the corrosive solution
⎯ 50 % water;
⎯ 50 % mixture of:
⎯ 30 % copper chloride,
⎯ 20 % sodium chloride,
⎯ 20 % potassium chloride,
⎯ 30 % zinc chloride.
9.8.3 Test procedure

The test shall be carried out on six tube assemblies. Immerse the samples in the bath at ambient temperature

(avoiding contact between the fittings and the solution, see Figure 1) for (5 ± 0,5) minutes. Place the tube

assembly samples in a chamber at 60 °C with relative humidity greater than 85 % but avoiding condensation

on the tube.

Repeat this immersion seven more times with an interval of 24 h between each immersion. One of the

intervals may be of 72 h. Stop the test 24 h after the eighth immersion. Inspect the tubes for cracks and breaks.

Carry out the burst test at 23 °C in accordance with 9.1.2.
9.8.4 Requirements

At the end of the procedure described in 9.8.3 the samples shall show no cracks or breaks and the burst

pressure shall be greater than 80 % of the reference value measured at 23 °C on samples from the same

batch.
9.9 Resistance to ethanol
9.9.1 Test procedure

The test shall be carried out on three tube samples 300 mm minimum in length. Bend each sample W 180°

over a mandrel with a diameter 10 × the outer diameter of the tubing. Immerse the bent tube still on the

mandrel in 95 % ethanol for 200 h at an ambient temperature of 23 °C. Remove the tube and straighten.

9.9.2 Requirement
The samples shall show no evidence of cracking.
9.10 Resistance to battery acid
9.10.1 Procedure

The test shall be carried out on three tube samples 300 mm minimum in length, sealed at each end. Weigh

the samples and measure their length, inner and outer diameter.
Bend each sample W 180° to a
...

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