DBL 4040 – Tubes for Brake and Fuel Systems -Mercedes-Benz Company Standard – Double-walled wrapped tubes made of steel


This DBL refers to the characteristics and requirements for tubes for brake and fuel lines as well as aluminum tubes for regeneration and breather lines. Tubing for other applications such as hydraulic lines are not covered by this DBL.
This edition supersedes the previous edition of this Standard dated 2013-12.

Application note:
In line with the scope of application, the application of the present version of this Company Standard shall be checked for new vehicle projects or components for which no concept/basic specifications or component requirement specifications have been approved yet at the issue date of this version.
The respective contract documents regulate the mandatory application of the present version of this Company Standard by the supplier.

1 Scope of application

The product versions of the tube types for brake, fuel, regeneration and breather lines are listed in Table 1. The product version defines the base material as well as the coating type and coat thicknesses of the inside and outside surfaces of coated tubes.

Table 1: Product versions, overview

Product versionOutside surface coating
4040.31Electrolytically zinc coated≥ 25 µmPA 11≥ 120 µm
4040.32Al hot-dip coated≥ 120 µmPA 11≥ 100 µm
4040.33Electrolytically zinc coated≥ 25 µmPA 11≥ 80 µm
4040.40Electrolytically zinc coated≥ 25 µmPVF≥ 8 µm
4040.41Al hot-dip coated≥ 25 µmPA 12≥ 120 µm
4040.42ZnAl hot-dip coated≥ 100 µmPA 12≥ 100 µm
4040.43Al hot-dip coated≥ 12 µmPVF≥ 8 µm
4040.45Electrolytically zinc coated≥ 100 µmPA612≥ 40 µm
4040.46Al hot-dip coated≥ 25 µmPA612≥ 120 µm
4040.47Electrolytically zinc coated≥ 100 µmPA612≥ 100 µm
4040.48Electrolytically zinc coated≥ 25 µmPA12≥ 80 µm
4040.49Electrolytically zinc coated≥ 25 µmPA612≥ 80 µm

Double-walled wrapped tubes made of steel (PVs.10-.49) are preferably used where there are very high demands on pressure resistance, for example with brake line tubes. Single-walled welded tubes made of steel (PVs.51-.57) are preferably used where there are less stringent demands on pressure resistance, such as with fuel lines. For secondary requirements for temperature and pressure resistance, with regeneration and breather lines for example, aluminum tubes can be used (PVs.60-.62). In cases of continuous temperature exposure above 130° C, welded tubes made of stainless steel (fuel lines, PVs.71-.74) or seamless drawn CuNiFer tubes (brake lines, PV.80) shall be used. The requirements for high-pressure fuel lines do not fall within the scope of this DBL.

The finishes/coatings shall be selected based on the requirements with regard to corrosion and thermal resistance. Maximum operating temperatures for surface coatings are listed in Table 2.

2 Normative references

The following referenced documents are required for the application of this document. For dated references, only the referenced edition applies. For undated references, the latest edition of the referenced document (including any changes) applies.

  • ASTM B 750 Aluminum-Mischmetal Alloy Made of Zinc and 5% Aluminum (UNS Z38510) in Ingot Form for Hot-Dip Coatings
  • DBL 8585 Negative Substance List for the Selection of Materials
  • DIN 74234 Hydraulic Braking Systems; Brake Pipes, Flares
  • DIN EN 10130 Cold Rolled Low Carbon Steel Flat Products for Cold Forming
  • DIN EN 10296-2 Welded Circular Steel Tubes for Mechanical and General Engineering Purposes – Part 2: Stainless Steel
  • DIN EN 12449 Copper and Copper Alloys – Seamless, Round Tubes for General Purposes
  • DIN EN 573-3 Aluminum and Aluminum Alloys – Chemical Composition and Form of Wrought Products – Part 3: Chemical Composition and Form of Products
  • DIN EN ISO 1463 Metallic and Oxide Coatings – Measurement of Coating Thickness – Microscopical Method
  • DIN EN ISO 6892-1 Metallic Materials – Tensile Testing – Part 1: Method of Test at Room Temperature
  • DIN EN ISO 8492 Metallic Materials – Tube – Flattening test
  • DIN EN ISO 8493 Metallic Materials – Tube – Drift-Expanding Test
  • DIN EN ISO 9227 Corrosion Tests in Artificial Atmospheres – Salt Spray Tests
  • MBN 10338 Fuel Systems – Hose Connections; Tube Ends – Design Standards
  • MBN 10375 Corrosion Test of Metallic Materials in Fuels
  • MBN 10494-6 Paint Test Methods
  • MBN 10517 Corrosion Test Preparation of Pipes for Brake and Fuel Systems
  • SAE J2044 Quick Connect Coupling Specification for Liquid Fuel and Vapor/Emissions Systems

3 Terms and definitions

A50Symbol for elongation at rupture for a specimen with 50 mm measuring length.
A10Symbol for elongation at rupture for a specimen with 10 mm measuring length.
PVAbbreviation of “product version”
CASSAbbreviation of “copper accelerated acetic acid salt spray test”
DBLAbbreviation of “Daimler-Benz-Liefervorschrift“ (“Supply Specification”).
DINAbbreviation of “Deutsches Institut für Normung“ (“German Institute for Standardization”).
ISIRAbbreviation of “initial sample inspection report”
ENAbbreviation of “Europäische Norm“ (“European Standard”)
ISOAbbreviation of “International Organization for Standardization“
AHTAbbreviation of “condensation climate with alternating humidity and air temperature“
CDCAbbreviation of “cathodic dip coat”
MIGAbbreviation of “metal inert gas”
MBAbbreviation of “Mercedes-Benz“
MBNAbbreviation of “Mercedes-Benz Norm“ (“Mercedes-Benz Standard”)
NfNNot for new designs
NSSAbbreviation of “neutral salt spray test“
PAAbbreviation of “polyamide”
PVFAbbreviation of “polyvinyl fluoride“
Symbol for tensile strength
Symbol for offset yield strength at 0,2 % permanent strain
Abbreviation of “Society of Automotive Engineers”
SALTabbreviation for “Source Approval Lab Tests”

4 General requirements

To guarantee product safety and product quality, and to meet homologation requirements, all relevant
statutory regulations and laws shall be complied with. In addition, the relevant requirements of the Daimler Group shall apply.
All materials, procedures, processes, components, and systems shall comply with all current statutory
requirements regarding regulated substances and recyclability.
DBL 8585 shall be observed.
The prerequisite for supplying to Daimler is an approval of procurement source for each product version and each production site made by the specialist materials department. Details on the manufacturing process and the raw materials used shall be provided here.

5 Abbreviated material designation for documentation

e.g. for a single-walled welded tube: steel DIN EN 10130 – 1.0330 (DC01) + DBL4040.50

6 General properties of materials and delivery condition

6.1 Materials, production and coating

6.1.1 Materials

The base tube material and standard regulations of the respective product versions are listed in Table 3.

Product VersionTube type and materialSpecification
.10 to .49Double-walled wrapped tube made of steelaccording to DIN EN 10130
.50 to .57Single-walled welded tube made of steelaccording to DIN EN 10130
.60 to .62Aluminum tubeEN AW 3103 according to DIN EN 573-3
.71 to .74Tubes made of stainless steel*according to DIN EN 10296-2
.80Seamless drawn CuNiferTubeCuNi10Fe1Mn according to DIN EN 12449

* In areas which are subject to heavy corrosive stress such as the underfloor area, materials 1.4404 and 1.4571 shall be used

6.1.2 Double-walled wrapped tube made of steel

Steel strip with electrodeposited copper or nickel coating on one or both sides is formed into a doublewalled tube in a roll drawing process and then brazed without additional filler material. The tubes are drawn and annealed as necessary. The steel strip coated on both sides shall be used for product version 4040.10.

6.1.3 Single-walled welded tube made of steel

Steel strip with electrodeposited nickel coating on one or both sides is formed into an initial tube (hollow billet) in a roll drawing process, welded by means of an inductive process or resistance welding and then cold formed to its final dimensions in an immediately following stretch reducing mill. The Ni layer on the inside of the tube flows over the weld seam during welding. Coat thicknesses of the Ni internal coating smaller than 3 μm are permissible in the seam area, at which a minimum value of 1 μm shall not be undercut.

6.1.4 Tubes made of stainless steel

The tubes are manufactured, at the discretion of the manufacturer, by fusion or pressure welding from appropriately formed strip or sheet. The welding seams can be smoothed by suitable methods such as hammering or rolling within the course of production.
Various stainless steels that differ in their corrosion resistance can be used as a material for the tubes, see also Chapter 8.1 Materials. The choice of steel grade depends on the corrosion load of the tubes on the vehicle and shall be clarified by the relevant specialist departments. In general, due consideration shall be given to the selection of the material and the careful assurance of the corrosion behavior for tube applications made of stainless steel.

6.1.5 Drawn aluminum tubes

The tubes are extruded with porthole tools made from solid material and then drawn to the required final dimension. The tubes are soft-annealed between the drawing processes if necessary.

6.1.6 ZnAl hot-dip coating

ZnAl hot-dip coating with PV.43 is carried out in accordance with ASTM B 750 (approx. 5% aluminum).

6.2 General properties of the tubes

The tubes shall have a smooth, clean surface on the inside and outside with a spotless, uniform appearance and shall be free of corrosion products. The zinc coating shall not be visible. Clamping marks on the surface are permissible if the tube diameter tolerances are complied with. In the case of welded tubes, slight defects are tolerated in the area of the welding seam on the inside of the tube

Irrespective of the total length of the tubes, the tubes shall roll automatically off a gage table with 10° inclination.
If tubes with laser-cut ends are supplied, the cut edges shall be clean and level. A protrusion as a result of cutting to length is not permissible (see Figure 1).

6.3 Limits for visible surface defects of PVF coated tubes

Product versions concerned: PV.40, PV.43, PV.50
This information is intended as an outline specification to facilitate understanding between the tube manufacturer and the supplier.
For the definition and limits for visible surface defects, refer to Annex A.

6.4 Deliveries

Ongoing deliveries shall correspond to the approved samples.

6.5 Marking

The tubes shall be marked with a company sign, date of manufacture and production line, which are permanent, wipe-proof and non-detachable. At least one complete imprint shall be present. UV marking is permissible. For tube diameter ≤ 3,4mm, the marking may be omitted.

6.6 Packaging

For tube diameters up to 4,75 mm and lengths up to 2000 mm, the tubes shall be supplied loose in the container, and for lengths over 2000 mm in bundles of 50 tubes. The ends of the tubes in the bundles of 50 tubes shall be protected against the ingress of dirt by means of a film bag. Tubes supplied “loose” in containers shall be protected against the ingress of dirt by means of a film. For all other tube diameters, the packaging rules shall be agreed upon according to the customer’s specifications.
Batches shall not be mixed in packaging. Containers containing more than one batch are subject to the agreement of Daimler, and this shall be marked accordingly on the container.

7 Tolerances

7.1 Fixed length tolerances

Table 4 provides the fixed length tolerances for all product versions.

7.2 Double-walled wrapped tube made of steel

Table 5 provides the tolerances of outside diameters (with and without surface protection) and wall thicknesses for the product versions of double-walled wrapped tubes.

Wrapped tubes and welded tubes shall not have any seam ditches or recesses ≥ 60 µm at the seam start. The depth of the seam recess shall be measured both on the outside of the plastic coating (top coat seam recess, Figure 2) and on the steel side without coating (seam recess, Figure 3). To measure the top coat seam recess, place a circle around the plastic coating and measure to this. To determine the seam recess, place the circle around the uncoated tube and measure to the base material.

7.3 Single-walled welded tube made of steel

Table 6 provides the tolerances for the product versions of single-walled welded tubes without surface protection. The roundness tolerances limit is max. 70 µm. Figure 4 provides a schematic diagram of the maximum permissible weld joint reinforcement and wall thickness reduction in the seam area.

7.4 Aluminum tubes

Table 7 provides the tolerances for the outside diameters and wall thicknesses of aluminum tubes with and without surface protection.

7.5 Tubes made of stainless steel

Table 8 provides the tolerances for tubes made of stainless steel. According to DIN 10296-2, Table A. 1 WCR, metallic bright. Welding seams shall be hardly noticeable.

7.6 Seamless drawn CuNifer tubes

For seamless drawn CuNiFer tubes the dimensions and tolerances in accordance with DIN 74234 D apply.

8 Tests

8.1 Coat thicknesses

The coat thicknesses are determined metallographically from at least 6 measurements, which are spread evenly across the circumference of the tube. The values in Table 1 for minimum coat thicknesses shall apply. The minimum and maximum coat thicknesses as well as the average coat thicknesses shall be determined. The maximum coat thicknesses are not explicitly defined, but the tolerances for the maximum outside diameter with surface protection in Tables 5-8 shall be complied with.

In cases of disputes, the coat thicknesses for metallic coatings and plastic coatings are determined in accordance with DIN EN ISO 1463. In the case of PA11/PA12/PA612-coated tubes, the plastic coating shall be removed before flaring. Subsequently, at least 15 µm zinc / 25 µm Al shall be present in this area.

8.2 Tensile test and drift expanding test

Table 9 provides the strength values to be achieved on the coated tube in as-supplied condition. The yield strength, tensile strength and elongation after fracture are determined in a tensile test in accordance with ISO 6892-1. The drift expanding test is carried out in accordance with DIN EN ISO 8493.

*PV.33, PV.48 and PV.49 to 430 MPa possible

8.3 Internal pressure test

The internal pressure test is only relevant to PVs .10 to .49 (double-walled wrapped tubes) and PV .80 (seamless drawn CuNifer tube). The burst pressure of the tubes shall be tested systematically and documented. The values in accordance with Table 10 shall apply.
Table 10: Permissible pressures in the internal pressure test

8.4 Flare suitability and bending test for all product versions

Flares shall be manufactured in accordance with MBN 10338, DIN 74 234, and SAE J2044.
The tubes shall be capable of being bent over the smallest bending radii according to Table 11. The maximum change in cross-section is shown in Figure 5.

8.5 Bending shear test

For wrapped tubes and coating systems

If a tube section is bent by hand into the shape of a hairpin and bent backwards and forwards until fracture, the individual layers of the coating shall not separate, and the brazing seam shall not split open. For tube diameters ≥ 8 mm of PVs .10 – .49, small tears of the brazing seam are permitted with the exception of the seam start provided that these do not affect the technological values and processability, e.g. flare sinkage. The applied coatings shall not crack.

Alternatively, a close flattening test in accordance with DIN EN ISO 8492 can be carried out in order to assess the brazing seam.

In addition, the following applies with regard to the close flattening test in accordance with DIN EN ISO 8492 and the bending shear test:
To assess the brazing at the outside start of the seam, the start of the seam shall lie in the 12 o’clock position.
After the close flattening test, no copper shall be visible at the outside start of the seam.

8.6 Corrosion tests

8.6.1 Corrosion resistance of the outside surface of the tube

Product versions .31 to .62, with coating of outside surface

The surface protection with regard to base metal corrosion and zinc corrosion according to Table 12 shall be tested on specimens bent (180 °) into hairpins. The bending radius shall be taken from Table 11 (shaping roller). Store hairpin-shaped tube sections suspended in the test chamber with the ends of the tubes pointing downwards.

To test the adhesion of the plastic, the plastic coating shall be initially damaged by applying a scratch. The scribed mark shall be made according to MBN 10517. The assessment is carried out according to MBN 10494-6 infiltration at the scribed mark, short description U/2. The assessment shall be carried out 24 hrs
after removal from the test chamber. The test angle of the scratched tubes shall be complied with in accordance with DIN EN 9227.

Product version .71 to .80, without coating of the outside surface

The corrosion resistance test regarding base metal corrosion is carried out on 300 mm long tube sections.
The assessment shall be carried out 24 hrs after removal from the test chamber.

8.6.2 Corrosion resistance of tube inside surface of fuel lines

The pipeline or component supplier shall provide evidence of the suitability of the inside surface for the fluids to be conveyed by means of corrosion tests. The fuel resistance is verified by testing according to MBN 10375. This is performed once per production site and fuel grade.

Note that the corrosion behavior of metallic materials is a system property (material/environment) and that therefore no conclusions can be drawn, for example, from the corrosion behavior of a material in diesel fuel to the corrosion behavior in gasoline. The same principle applies to the increasing use of synthetic or biogen fuel additives.

8.7 Adhesion following thermal exposure

For the product versions with plastic coating, PVs .30 to 62, the adhesion following thermal exposure shall be tested. The test shall be performed on straight unbent tubes with a length of some 300 mm.

8.8 Documentation of test results

The results of the specified tests shall be documented and kept by the supplier (min. requirement: material test certificate, leaktightness and strength and burst pressure). The results shall be available for submission on request at any time.

Annex A (normative): Limits for visible surface defects of PVFcoated tubes (product versions 40, 43, 50)

A.1 Definition of permissible surface defects

· Inclusions/chippings: surface defect caused by a foreign object embedded in the PVF layer, or uncoated location caused by the removal of the foreign object.
· Scratches: surface defects that constitute a small recess and an irregular shape in an undefined direction.
· Notch (deep scratch): surface defect with a noticeable line-shaped recess caused by contact with a foreign object.

A.2 Limits for visible surface defects

To facilitate the rapid determination of surface deviations, the criteria summarized in Table 13 shall apply. The following applies in principle: the zinc coating shall always be present. The zinc shall show a closed silvery gloss. No copper shall be visible. If copper is visible, then the lines are not ok.

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