A: The use of HV or HR systems should be primarily guided by the mandatory design codes (e.g. European guidelines, referred to as standards) and local practices in the region where a project is located. HV systems are more prevalent in Germany and Central Europe while HR systems are more common in France, the United Kingdom and so on.
The fundamental difference between the two systems is in their overload failure modes because HR series bolts have longer thread length so when they're overloaded, the body would stretch a lot before breaking-and such failures are easily identifiable during visual examination. while HV systems would potentially break at the screwed interface and not being easy to notice. Therefore, HR systems can be recommended to applications with rigid safety surveillance.
The most severe limitation is that parts can never be used interchangeably. For the reasons explained, bolts nuts and washers must be sold as a full matching assembly because of differences in production processes and surface lubrications. The integration of parts from different systems or suppliers is not allowed, and can cause a loss of preload control and structural safety risks.
Lastly, the importance of checking bolt length must be emphasized; because the non-threaded shank portion on HR systems is shorter, you don't want to stack up a typical plate bundle thickness which exceeds the non-thread section length or no good clamping force will be developed. Preload locking methods such as the torque method or direct tension indicators can be used with both systems.
