Subsea Bolts
Subsea Bolts
(OP)
Have a client who has ask me to recommend subsea bolts for a 14", 20" 30" flat face flange. Could anyone please recommend bolting proper material that an standup to saltwater submergine. Flanges are critical as pipeline is used for oil.





RE: Subsea Bolts
Welding Units UK will be able to advise you on flanges and bolting.
Have a look at www.welding-units.co.uk
We have used them before and they do a good job.
Regards,
Quadswift
RE: Subsea Bolts
Also it is relatively cheap.
I would like to read also other people comments on silicon-bronze material
RE: Subsea Bolts
RE: Subsea Bolts
TaperLok Knows flanges but not enough about loaded bolts in salt water.
This is not an easy cook book solution.
RE: Subsea Bolts
RE: Subsea Bolts
A look through the Norsok standards will give good guidelines on bolt selection through: http://www.standard.no/imaker.exe?id=244
This will irrespective of the coating the bolt has. An expensive solution, if the system will not part of the cathodic protection system (with no associated hydrogen embrittlement concerns however), is to use a Inconel 718 type. Pricey, but will probably outlast the flanges they connect!
RE: Subsea Bolts
To add just a little, albeit late:
- Should stick to bolts of tensile strength less than 690 MPa if you are in an area covered under CP, so as to avoid hydrogen embrittlement. The same limit applies if the bolts may be covered in mud/sediment, as this condition can lead to the creation bacteria which can again lead to the production of hydrogen.
- If you can stay under 690MPa and are in a CP environment, suggest using B7M or L7M studs with 2HM nuts (all ASTM). Use uncoated, as long as you are sure you have a link to the CP system. If you use PTFE, removed some of it with a wire brush prior to installation, or ensure you have continuity with the CP system through measurements.
- If you can't stay under 690MPa, try using L7 or B7 (with 2H nuts) with a hardness less than 34HRC, but preferably 28HRC. Same coating comments as above.
- If all else fails, utilise MARINEL+ material, which is immune to hydrogen embrittlement, and sulphide stress corrosion cracking, but has a yield of 720MPa. No coating required.
- Outside of a CP system, use Inconel 625 to avoid issues (max 35HRC), against ASTM B446-93.
RE: Subsea Bolts
Regards
Andrew
RE: Subsea Bolts
Steve Jones
Materials & Corrosion Engineer
http://www.pdo.co.om/pdo/