EN 14399 preloaded fasteners larger than M36

[citizented]

Dear All

I have a number of large subsea bolted joints that are designed to BS EN 1993-8 that fall in the following categories:-

• Category C: Shear connection, Slip-resistant at ultimate limit state
• Category E: Tension connection, preloaded bolts

BS EN 1993-8 directs you to use high strength structural bolts in conformity with 'BS EN 14399 High Strength structural bolting assemblies for preloading', and to control tighten them using methods in 'BS EN 1090-2 Execution of Steel Structures'. In general we will use hydraulic tensioning equipment.

My connections use M42 and M48 fasteners, some use studs, others bolts. BS EN 14399 only covers bolts in the range of M12 to M36. In the wind industry there are high strength structural bolts available between M39 and M64 in the HV system designed using German guideline 'DASt guideline 021' but the HV system uses grade 10.9 material which is unsuitable subsea because of the risk of Hydrogen Induced Stress Cracking (HISC) from the Cathodic protection system. We must use grade 8.8 materials.

What type of bolts, studs, nuts and washers should I specify for these large fasteners to be sure they meet the preloading requirement of these connections.

Can I use the material requirements and design features incorporated in BS EN 14399 to specify/design the larger fastener?

Anyone's experience on this matter would be much appreciated.

Regards Ed

 

[RolMec]

Hello Ed,

EN 13499 and and its derivates are intended for common and standardized structural design, where M36 is the largest usually utilized size.

With M 42 + you are off out of this size, so your application cannot be designed to EN 13499, but only "following..." or "in analogy to EN 14399... ", and you are basically on your own.
Some additional info:
- If based on EN 14399 and its derivates, you can have 8.8 grade bolting only in the HR system, not in the HV system. Perhaps you can reconsider sizing of your bolted connections in order to get back within the range.
- Studs are special in themselves, there you may encounter need for to authorization, as this is not basically a threaded rod / nut design but a welded or blind hole joint which is out of standards for bolted connections.
- DASt 021 is valid for 10.9 hot dip galv. bolt connections only, but then (if purchased from a reputable supplier under high grade QA controlling) the design and manufacturing / processing of such bolt sets is such that HISC would not occur. You may want to approach such manufacturer to get to know more!

What I do for the EU market is to design / calculate the bolted connections based on VDI 2230, but for your large size threads, the (welded) studs & surely high safety requirements (submarine env.) you are imo in for a full scale design & approval procedure including testing and acceptance by an independant classification society as DNV or else.
Regards
R.

 

[CoryPad]

Consider NORSOK M-001 Materials selection for guidance on subsea applications.