Extending Stainless Plate By Welding - Strength

[RunAgroundHard]

I have a 5mm thick stainless plate mounted at 45 degrees to a 5 mm thick stainless base plate, supported each side by welded gussets. The 45 degree plate is slightly undersized on length and the mounting holes for a foot block will be quite close to the edge. I can have my welder add two 20mm strips, one each side, full penetration welds, ground back flush to increase width by 40 mm. I can then mount the footblock, drill the 4 x M10 holes and fit washers and nylon nuts, all within the extended footprint of the 45 degree plate.

My concern is that the HAZ may cause the stainless to be more susceptible to cracks. The footblock sees a lot of force when hard on the wind, under full Genoa and staysail and if the sail flogs, can impart significant shock loads. Are there any other concerns? Should I just have a new pair of bases made to the correct dimensions?

Masthead rig, hence large overlapping genoa, 18mm sheets.

 

[rogerthebodger]

I would grind a 45 degree chamfer on the edges of the 20mm wide plate and the joining plate to ensure the weld filles up the chamfers to get full penetration.

If you welded without the chamfers the Gring back, you are in effect grinding away the weld and strength away.

What type of welding are you going to use stick, MIG of TIG. I generally us Argon gas for welding Stainless but CO2 could be used but I prefer Argon,

 

[RunAgroundHard]

Thanks for the advice.

I don't know the welding process, it is a professional welder that made the plates to my design. The design was for different footblocks.

 

[dunedin]

Would it be quicker and not much more expensive for the welder to make a new item - as very slightly more material, but less welds required?

 

[vyv_cox]

The HAZ of itself is not weaker than the main body, assuming a 300 series stainless steel. The HAZ becomes susceptible to cracking if chromium carbides form in it, reducing the chromium content of the alloy. This is avoided by using the low carbon version of the alloy, e.g.316L, both as the extra plates and as the filler metal. Even better is to use filler rods of one of the alloys containing preferential carbide formers, such as 347. Good technical article here Carbide Precipitation - Hobart Brothers and a less technical but informative one here 304 vs. 304L - An Answer to Carbide-Precipitation Issues - Kay & Associates Brazing Consultants

 

[RunAgroundHard]

Would it be quicker and not much more expensive for the welder to make a new item - as very slightly more material, but less welds required?

I did initially wonder about that. Far more expensive to make a new one: 5 welds v 2 welds and less cutting from stock.

 

[Lee Shaw]

In my opinion, the repeated loads you describe on footblock are more likely to cause fatigue cracking from surface imperfections rather than cracking in the heat affected zone. Making sure the additional welds are ground smooth is a good idea.

 

[RunAgroundHard]

Thanks everyone. I think from an aesthetic point and load distribution point, making a new fitting larger all round will be better in the long run.

It’s my own fault for thinking that new foot blocks (smaller), would be better than the originals (larger).

Thanks everyone for your input.