Stainless Steel Tubing vs. Welded Aluminum Pipe

If you are considering a T-Top, it is important to understand the differences in quality, strength, finish, longevity and resistance to the elements that welded stainless steel tubing provides versus welded aluminum pipe, which most T-Tops are made of. If you'll notice, almost all boat railings are stainless steel, with little or no aluminum used at all. Aluminum is used on after market items since it is easier and cheaper to work with.

1. Ease of Manufacture - Aluminum pipe is relatively soft and easy to cut, bend, machine and drill. It is also easy to weld, and shops with minimal equipment investment can manufacturer after-market items that look very nice. Stainless, on the other hand, is very difficult to bend, drill and weld, and increases labor and costs significantly. The marine industry uses stainless steel on steering wheels, bow rails, side rails and windshield grab bar because it is strong and corrosion resistant. Boat manufacturers and RNR-Marine commit to this extra investment to insure quality: strength, safety, longevity and good looks.
   
   
2. RNR-Marine's Materials - Our tops are made from American Iron and Steel Institutue (AISI) type 304L ("L" = Low Carbon = no rust) thick wall (16 gauge = 0.065") tubing, which is Tungsten Inert Gas (TIG) welded to 0.125" thick wall AISI type 316 (surgical grade) polished, cast joint and end fittings using a Swaglok(r) orbital welder. The orbital welder (as used in Nuclear and chemical plants) provides quality, consistent welds exceeding human capabilities.
   
   
3. Aluminum T-Top Materials - Aluminum T-Tops are typically made from anodized "1.50 inch" schedule 40 (standard thickness) aluminum pipe. Pipe is specified by nominal inside diameter, and this pipe has about 1.60 inch ID and 1.90 inch OD. It is noteworthy that these tops are made FROM anodized tubing, but are not anodized after manufacturing when they are cut, drilled, welded, etc. Instead, the welded aluminum joint is simply painted over with shiny aluminum paint. Clearly, this aluminum paint is not the same as anodizing, and will not provide the same corrosion resistance or last as long.
   
   
4. Appearance - Highly polished 304L stainless steel tubing NC TIG welded to 316 polished cast fittings have a reflective shine that aluminum cannot achieve or retain. Aluminum attains some shine through anodizing (a surface oxidation method), but it can never match highly polished stainless. When welded, the anodized aluminum surface on aluminum is burned off, leaving the aluminum unprotected. RNR Marine orbital welds (Numerical Control) for perfect looking welds, then passivates (for longevity and chemical resistance) and electropolishes each weld to a high luster.
   
   
5. Strength - Stainless steel is 2-3 time stronger than aluminum pipe. The tensile strength of 304L stainless is 79,000psi (316 is 80,000psi), compared to 25-40,000psi for aluminum pipe (depending on grade used). The strength of aluminum welds is greatly decreased by welding over the anodization, which produces hydrogen cracking. By comparison, Numerical Controlled (NC) orbital welded (the process RNR uses) low-carbon (304L and 316) stainless welds are often stronger than the source material, and will last virtually forever.
   
   
6. Fatigue - Stainless steel has 5-10 times the fatigue strength (resistance to bending & vibration) of aluminum pipe. The fatigue strength of stainless is 25-75,000psi, compared to aluminum at 6-18,000psi.
   
   
7. Welding - RNR Marine uses Swagelok(r) Numerical Control (NC), Orbital, Tungsten Inert Gas (TIG) welding to join low carbon (304L and 316) stainless, producing welds that are as strong as or stronger than the tubing it joins. Used by NASA, nuclear power plants, food service, rocket manufacturers, chemical and chemical/food/beverage processing plants, orbital welded stainless tubing is the only option considered world-wide for high strength, high quality welds. By contrast, Aluminum does not weld very well, and the pipe is usually anodized prior to welding. When welded, Aluminum's hard anodized surface resists welding, and "pops" off, making the weld joint brittle, and removing all anodized surface protection/shine in the weld "heat affected zone". Longer term, these aluminum welds eventually succumb to hydrogen cracking. Aluminum T-Tops are rarely anodized after welding, due to the cost of the anodizing equipment and the size of the immersion tank that would be required to fit the entire T-Top in, so the welded aluminum areas are subject to corrosion and pitting.
   
   
8. Saltwater Resistance - 304L (low carbon) and 316 (low carbon with molybdenum) stainless steel maintains its luster, shine and strength over time. Passivation and electropolishing the stainless remove any surface carbon and iron molecules to provide a very saltwater resistant surface. Aluminum does not resist corrosion well, except by anodizing (building an oxide layer on the surface). Welding removes this oxidation at the most critical points, the joints, which will corrode (by pitting) over time, and fail due to fatigue.

   RNR Marine orbital welded 304L to 316 stainless ...

   

   Aluminum welds lose their luster quickly ...

   
   Note the corrosion where the anodization was burned off near the weld joints.

   ... aluminum welds crack ...

   
   Note how this "textbook" weld has cracked down the center.

   ... and in some cases, the aluminum pipe itself cracks ...

   
   Note how this top was painted to help protect the aluminum,
   but developed cracks anyway.

   Some comments from boat owners about aluminum T-Tops ...

   "Was out cleaning the Sea Pro and looked up at the TTop and noticed a crack in the horizontal tubing That ties the two vertical tubes together. The entire bottom of the tube is cracked. I tried to call the dealer but they haven't returned my call, yet. Will this be under warranty? The boat is 18 months old. Thanks" - bletort, Ocean Springs, MS
   
   ref: http://www.thehulltruth.com/boating-forum/117208-ttop-crack-aluminum.html

   "Does anybody know someone that can weld some cracked tubes on a T-top." "It is just a support brace from console to top in front of the windshield. Also that brace caused the main pole from floor to the top to shear. That pole is broke completely and has a crack right up top. 3 places to weld. The sheared pole might need more support after it is welded. I was told that the whole T-top will have to come out. Is that true or can it be avoided. Thanks Steve." - hydra2450, Charleston, SC
   

   "I had a stress crack on one leg of mine and we did not have to remove it to fix weld it but it takes a LOT of COVERING UP. Sea Pro 210cc" - tprice, Charleston, SC
   
   ref: http://www.charlestonfishing.com/forum/topic.asp?TOPIC_ID=66437

   "Noticed a crack in a joint weld in my aluminum T-Top while wrapping the boat up for the season. I would appreciate any info on marine welders in the Falmouth/Mashpee area to contact for a late winter, early spring fix. Thanks in advance." - garo 22, MA
   
   ref: http://www.thehulltruth.com/northeast/196583-welder-options.html

   "We have a 247 Advance and several of our welds on the T-top are breaking. Has anyone had this problem? We are in South Carolina and have to run the boat pretty hard to get to the gulf-stream. I would appreciate any feedback from people who have had a similar problem." - PalmettoGrady, SC
   
   ref: http://www.greatgrady.com/forum/viewtopic.php?p=51328

   "T-Top Aluminum repair. I noticed a crack in the weld and I was wondering if JB weld would do the trick for a while at least until the winter or if there is another option available. - boatowner1122, North Texas
   
   "I've got the same problem with mine, 04 boat. Naturally its where wiring leads to the electronics box. Wonder if anyone has had succuss repairing one with alumalloy or similar type products which work like solder? Brian" - big bass, Greensboro, NC
   
   "Ditto. Had the same problem. Thought I would "take it easy on her" and try to delay the repair. BAD IDEA. When the original crack gave way after hitting an unexpected wave, the stress created on the other welds caused two more to break, which effectively trippled the cost of repair. My repair bill was about $200, but I removed and reinstalled my canvas top and e-box myself which probably saved me $100. Get it fixed now unless you want to spend more $ than necessary. __________________ Mac Solo, 1985 25' Parker Sou'Wester---2005 F250 Yamaha" - originalsin, OIB NC
   
   ref: http://www.thehulltruth.com/boating-forum/56711-t-top-aluminum-repair.html

   "Anyone who deals with aluminum long enough has cracks. As good as it is for specific purposes, that is what aluminum does, it cracks. Particularly if it was anodized before it was welded. Aluminum has some great properties but fatigue strength is not necessarily one of them. Strip the paint from the suspected area and do, or have someone do it for you, a dye penetrant check. This will verify there is indeed a crack and determine the extent of it. Although the crack can be welded over, if it were mine I would have some reinforcing gussets welded in to support the welded over area and to minimize the likelyhood of future cracks. None of this should be difficult for an experienced welder." - jethro1
   
   ref: http://www.thehulltruth.com/boating-forum/80842-crack-armstrong-bracket.html

   "The fairy tale is that the crap doesnt corrode. The hull truthis you have to watch aluminum for pitting along with a few others : stress cracking corrosion,groove corrosion,galvanic corrosion....can be nasty stuff ..." - captct, Vancouver Island
   
   ref: http://www.thehulltruth.com/boating-forum/155242-pilothouse.html

   "Can anybody give me an idea how much it should cost to get an area on my T-top welded. It is a crack through one of the brackets that attach the T-top to the center console. About 3 inches long. Tried to post photos but can't figure it out. I can trailer to get the work done, but obviously don't want to have to drag the boat around to several different guys to compare prices. Hopefully I can get the photos to post. Also if anyone in the Wilmington, NC area can recommend a welder I would appreciate it. Thanks!" - gb, Wilmington, NC
   
   ref: http://www.thehulltruth.com/boating-forum/40611-t-top-welding.html

   Some comments from welders about welding aluminum ...

   "You are going to need a LOT of welder to burn the anodizing off as you go. And, then be ready for the towers to come back to you in a few years with cracks in them. My boat tower is aluminum, and the anodizing has pitted badly, and the tower cracks in a new spot every 2 years. Anodized aluminum kinda sucks, IMHO. I will rebuild it in stainless next year... we just got done repairing it all over the place for this season. So it's time to fish, and break my ugly pitted tower. I'd rather use mill spec aluminum TUBE, instead of pipe, and just paint it in the first place. My first tower was like that. No cracks in 7 years, no pitting. I got talked into the anodized by the boat shop. Never again. To typically get through the anodizing, you need to run about 210-230 amps, and set for a lot of cleaning with your sq. wave. The extra heat is to push that turd out of the way, and to compensate for the extra cleaning vs. penetraion. Then, you bump back your welds to push the anodizing turd to the outer edges. clean with acetone, and paint. I hate doing it. I'd rather tig weld rusted trailers all day, upside down. It can be made to look good with some practice and tuning your welder." - Rojodiablo, Moderator, www.WeldingWeb.com
   
   ref: http://weldingweb.com/showthread.php?t=1159

   Q. Why are the majority of T-Top fabricated from aluminum?
   
   A. Working with stainless is difficult to cut, form, weld and polish, requiring special draw-type tube benders, high tech TIG welding equipment and electropolishing gear. Working with aluminum is easier and cheaper ...
   
   The choice is yours ...