Reducing corrosion/ choosing rivets/anti corrosive compounds

C

Chainsaw

Brmmm Brmmm

To cut a common story short:

Mast broke yesterday at rivet in top section. Sail sleeve ripped. Skipper back-flipped into water. Broken top section to become new boom. New top section ordered. May look at replacing sleeve on sail and using sail for practice only (sleeve repair not legal) – seems a waste to chuck it.

I’ve been searching the threads here for info on what rivets to use to reduce corrosion when building new boom. General agreement is 18/8 stainless and 316 stainless for high load points. However, aluminium would be better than 18/8 – if you can find it in an alloy that is hard enough. So below is the galvanic table for anyone looking for options. The metal with the lower number on the table will corrode first.

The only other way to stop/reduce corrosion is to use a barrier/jointing compound. A short list follows the table.

Laser spars are, or are similar to, Al 6061-T6


The Galvanic Table (of dissimilar metals in seawater)

Active (Anodic)
  1. Magnesium
  2. Mg alloy AZ-31B
  3. Mg alloy HK-31A
  4. Zinc (hot-dip, die cast, or plated)
  5. Beryllium (hot pressed)
  6. Al 7072 clad on 7075
  7. Al 2014-T3
  8. Al 1160-H14
  9. Al 7079-T6
  10. Cadmium (plated)
  11. Uranium
  12. Al 218 (die cast)
  13. Al 5052-0
  14. Al 5052-H12
  15. Al 5456-0, H353
  16. Al 5052-H32
  17. Al 1100-0
  18. Al 3003-H25
  19. Al 6061-T6
  20. Al A360 (die cast)
  21. Al 7075-T6
  22. Al 6061-0
  23. Indium
  24. Al 2014-0
  25. Al 2024-T4
  26. Al 5052-H16
  27. Tin (plated)
  28. Stainless steel 430 (active)
  29. Lead
  30. Steel 1010
  31. Iron (cast)
  32. Stainless steel 410 (active)
  33. Copper (plated, cast, or wrought)
  34. Nickel (plated)
  35. Chromium (Plated)
  36. Tantalum
  37. AM350 (active)
  38. Stainless steel 310 (active)
  39. Stainless steel 301 (active)
  40. Stainless steel 304 (active)
  41. Stainless steel 430 (active)
  42. Stainless steel 410 (active)
  43. Stainless steel 17-7PH (active)
  44. Tungsten
  45. Niobium (columbium) 1% Zr
  46. Brass, Yellow, 268
  47. Uranium 8% Mo.
  48. Brass, Naval, 464
  49. Yellow Brass
  50. Muntz Metal 280
  51. Brass (plated)
  52. Nickel-silver (18% Ni)
  53. Stainless steel 316L (active)
  54. Bronze 220
  55. Copper 110
  56. Red Brass
  57. Stainless steel 347 (active)
  58. Molybdenum, Commercial pure
  59. Copper-nickel 715
  60. Admiralty brass
  61. Stainless steel 202 (active)
  62. Bronze, Phosphor 534 (B-1)
  63. Monel 400
  64. Stainless steel 201 (active)
  65. Carpenter 20 (active)
  66. Stainless steel 321 (active)
  67. Stainless steel 316 (active)
  68. Stainless steel 309 (active)
  69. Stainless steel 17-7PH (passive)
  70. Silicone Bronze 655
  71. Stainless steel 304 (passive)
  72. Stainless steel 301 (passive)
  73. Stainless steel 321 (passive)
  74. Stainless steel 201 (passive)
  75. Stainless steel 286 (passive)
  76. Stainless steel 316L (passive)
  77. AM355 (active)
  78. Stainless steel 202 (passive)
  79. Carpenter 20 (passive)
  80. AM355 (passive)
  81. A286 (passive)
  82. Titanium 5A1, 2.5 Sn
  83. Titanium 13V, 11Cr, 3Al (annealed)
  84. Titanium 6Al, 4V (solution treated and aged)
  85. Titanium 6Al, 4V (anneal)
  86. Titanium 8Mn
  87. Titanium 13V, 11Cr 3Al (solution heat treated and aged)
  88. Titanium 75A
  89. AM350 (passive)
  90. Silver
  91. Gold
  92. Graphite
End - Noble (Less Active, Cathodic)


Anti corrosive jointing compounds/barriers/anti-fret compounds:

Duralac Anti Sieze
Loctite marine grade anti-sieze
Loctite Zinc anti-sieze
Lanocote long term corrosion control


CRC Instant galvanise spray paint – zinc rich galvanise coating may also work as an inexpensive barrier. Anyone tried it?
 
You do realize you can repair the sleeve and the sail would still legal.

If you thru bolt the high load fittings (and use washers or large heads on the bolts), while you still get corrosion, it's not as catastrophic as it is with rivits pulling out because the hole enlarged due to corrosion.

I've yet to see a boom corrode enough to allow a large head bolt or one with a washer to pull thru the hole..
 
26a specifically allows for the repair of the sleeve -what they are trying to prevent with 26d is someone removing the complete sleeve and either putting it back on with different luff curve, or putting on a different sleeve, with different widths, again to change the luff curve...
 
Look for MONEL rivets (Think I spelt it right) - tougher than aluminium and don't set up electrolysis fastening SS fittings to aluminium spars.
 
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