Dast 021

HIGH-STRENGTH STRUCTURAL BOLTING ASSEMBLIES FOR PRELOADING
Part 4: System HV — Hexagon Bolt And Nut Assemblies

This document on structural bolting reflects the situation in Europe where two technical solutions exist to achieve the Necessary ductility of bolt/nut/washer assemblies. These solutions utilize different systems (HR and HV) of Bolt/nut/washer assemblies, see Table 1. Both systems are well proved and it is up to the experts responsible for Structuring bolting whether they use the one or the other system.
It is, however, important for the performance of the assembly to avoid mixing up the components of both systems. Therefore, the bolts and nuts for both systems are standardized in one single part of this European Standard each And the marking of the components of the same system is uniform.

Technical Conditions
  Bolt/nut/washer assembly System HR Bolt/nut/washer assembly System HV
General Requirements EN 14399-1
Bolt/nut assembly EN 14399-3 EN 14399-4
Marking HR HV
Property classes 8.8/8 10.9/10 10.9/10
Washer(s) EN 14399-5 or EN 14399-6 EN 14399-5 or EN 14399-6
Marking H H
Suitability test for preloading EN 14399-2 EN 14399-2

Preloaded bolted assemblies are very sensitive to differences in manufacture and lubrication. Therefore it is important that the assembly is supplied by one manufacturer who is always responsible for the function of the assembly. For the same reason it is important that coatings of the assembly is under the control of one manufacturer. Beside the mechanical properties of the components, the functionality of the assembly requires that the specified preload can be achieved if the assembly is tightened with a suitable procedure. For this purpose a test method for the suitability of the components for preloading was created which will demonstrate whether the function of the assembly is fulfilled.
It should be pointed out that compared to ISO 272 the widths across flats (large series) for M12 and M20 have been changed to 22 mm and 32 mm respectively. These changes are justified by the following reasons. Under the specific conditions of structural bolting the compressive stresses under the bolt head or nut for the sizes M12 may become too large with the width across flats of 21 mm, especially if the washer is fitted eccentrically to the bolt axis.
For the size M20, the width across flats of 34 mm is very difficult to be produced. The change to 32 mm is primarily motivated by economics but it should also be pointed out that the width across flats of 32 mm is already common practice in Europe.
For the time being, the product standards EN 14399-3 to EN 14399-6 are the only European Standards which have regard to the general requirements of EN 14399-1. However, further product standards on
- fit bolts,
- head bolts, and
- load indicating washers
for the use in high strength structural bolting for preloading are under preparation

Marking

Bolts shall be marked accordance with ISO 898-1 and shall additionally bear the symbol ‘HV’.

Important Note :

Preloaded bolted assemblies are very sensitive to differences in manufacture and lubrication. Therefore it is Important that the assembly is supplied by one manufacturer who is always responsible for the function of the assembly. For the same reason, it is important that the coating of the assembly is under the control of one manufacturer. Beside the mechanical properties of the components, the functionality of the assembly requires that the specific preload can be achieved if the assembly is tightened with a suitable procedure. For this purpose a test method for the suitability of the components for preloading was created, which will demonstrate whether the function of the assembly is fulfilled.

Characteristics Of The EN 14399-4 HV Bolts Include
•   Large under-head surface of the bolts, which reduces the surface pressure and setting
•   Large under-head radius of the bolts with an improved fatigue strength as well as a smaller notching effect
•   Defined friction properties which enables the preloading of these assemblies F
•   Batch marking on the product as required by the buyer in order to clear the inspection report or certificate.
•   Last but not least the CE mark or Conformity Europeans. The CE marking is a certification mark which indicates
•   That the product sold by either the manufacturers or supplier confirms to the health, safety, and environmental protection standards within the European Economic Area. In this case these assemblies need to be harmonized according to the European standard EN 14399-1.
Marking Of Bolts
a) Property class marking in accordance with EN ISO 898-1 and the letters HV.
Example 1 10.9 HV
  • Identification mark of the RFL. It is permissible for the marking to be either embossed or indented on the top surface of the head.
Example 2 bolt making
Specifications For Bolts And Reference Standards
Material Steel
General Requirement EN 14399-1
Thread Tolerance 6ga
International Standards ISO 261, ISO 965-2
Mechanical properties Property Class 10.9
European Standard EN ISO 898-1
Impact Strength Value K V, min = 27 J at – 20 °C
Test pieceb ISO 148
Test EN 10045-1
Tolerances Product grade C except:
dimensions c and r.
Tolerance for lengths ≥ 155 mm: +IT 17 -1/2 IT17
International Standard EN ISO 4759-1
Surface finishc Normal as processedd
hot dip galvanized EN ISO 10684
Others to be agreede
Surface discontinuities Limits for surface discontinuities as specified in EN 26157-1.
Acceptability For acceptance procedure, see EN ISO 3269.

a. The tolerance class specified applies before hot-dip galvanizing. Hot-dip galvanized bolts are intended for assembly With oversize tapped nuts.
b. The location of the charpy V-notch test pieces in the bolt shall be as specified in EN ISO 898-1.
c. Attention is drawn to the need to consider the risk of hydrogen embrittlement in the case of bolts of property class 10.9, when selecting an appropriate surface treatment process (e.g. cleaning and coating), see the relevant coating standards.
d. "As processed" means the normal finish resulting from manufacture with a light coating of oil.
e. Other coatings may be negotiated between the purchaser and the manufacturer provided they do not impair the Mechanical properties or the functional characteristics. Coatings of cadmium or cadmium alloys are not permitted.

Specifications For Nuts And Reference Standards
Material Steel
General Requirement EN 14399-1
Thread Tolerance 6H or 6AZ
International Standards ISO 261, ISO 965-2, ISO 965-5
Mechanical properties Property Class 10
European Standard EN 20898-2
Tolerances Product grade B
International Standard EN ISO 4759-1
Surface finish Normal as processeda
hot dip galvanized EN ISO 10684
Others to be agreedb
Surface discontinuities Limits for surface discontinuities as specified in EN 493.
Acceptability For acceptance procedure, see EN ISO 3269.

a. "As processed" means the normal finish resulting from KE with alight coating of oil.
b. Other coatings may be negotiated between the purchaser and the KE provided they do not impair the mechanical properties or the functional characteristics. Coatings of cadmium or cadmium alloys are not permitted.

Decarburization of the nut thread

The decarburization of the nut thread, when measured in analogy to external threads as given in EN ISO 898-1, Shall not exceed G = 0,015 mm.

Marking of Nuts

High-strength structural nuts according to this document shall be marked with:
a) Property class marking in accordance with EN 20898-2 and the letters HV.

Example 1 10 HV

b) The identification mark of the manufacturer of the KE.
The marking shall be indented on either bearing face.

Example 2 nut making