Procedure for making V bolt chainplates?

What is the correct procedure for bending 316 round bar to make chain plate V bolts?

I'm renovating a 1974 Nicholson 48. These boats were built with V bolt chain plates that pass through the side deck and have a small aluminium backing pad underneath. The existing V bolts (12) all look original and at 40 years old have probably reached their replace by date.
Can new V bolts be cold bent using a press brake mandrel? Or is this creating the conditions for stress corrosion? I'm getting conflicting advice from local fabricators. What is the correct procedure to bend 316 bar to avoid long term cracking issues in a sailboat rig situation?
Nick

 

Why are you thinking that 40 years have made the original bolts unusable

 

You can cold bend the stock, no need to anneal, if the radius is reasonable.

 

Thanks for the replies.

Barry. I didn't say the bolts were 'unusable' just that they have probably reached their replace-by date just as you would replace any other rig part that can become fatigued, corroded etc. See this surveyors article on Westerly U bolts.. Decking U bolts | BMSE http://www.bmse.co.uk/articles/decking-u-bolts/ in which it is recommended to replace every ten years.

Par. Do you think I should get the parts annealed after bending? The clevis pin is 5/8 and the bar is 1/2 inch. The bolts also have a small (20 deg) bend where they pass through the deck.

Nick

 

If the part is highly loaded and/or will receive max cyclic loading, annealing will help make stainless, stainless again. It all really depends on the part. If it's a racer and the part is spec'd to a specific set of properties, with a small margin to save weight (for example) you're best off bringing the 316 back to these original spec's, which would include (likely) annealing. If this is a cruiser, where a fairly hefty safety margin is employed (after 30 years, quite probable), cold bending will do fine.

 

Thanks Par
The 48's are long keel heavily built old style cruising boats with relatively low stressed rigs and weight saving is not an issue.
Last summer we did a ring of Ireland up the west coast, a short cruise through the Scottish islands and back on the east coast. The weather was very variable with some severe gales including one of force ten while we sheltered in Tobermory. The west coast would be an unforgiving place to have a rig failure in those conditions.

 

Article: Stress relieving heat treatments for austenitic stainless steels http://www.bssa.org.uk/topics.php?article=76

an interesting read

 

Thanks Barry
Yes, I have seen it before but got the impression that if heat was used wrongly ie too much, too little, wrong cooling cycle etc then you could well do more harm. I asked local fabricators, one said that it was fine to do cold forming, no annealing or heat necessary and another said heat must be used on bent portions.
(Correction..The Westerly article said inspect every ten years, replace every twenty)