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SteveWag (Civil/Environmental) (OP)
16 Sep 08 15:37
I am looking at a design for a 50 foot diameter sewage digester cover (roof). It has 20ea 3x4 inch arched tubes 23-foot +/- long extending inward and upward from a 50-foot diameter tension ring and ending at a 2-foot diameter compression ring. The rings are either 3x3 tubes or 3-inch pipe. Welded to the underside of the radial beams (tubes) are 20ea pie shaped plates. This is a standard design and thousands have been made of mild steel/structural steel with a painted finish. As all of the shapes are available in 304SS, I am thinking of specifying SS for all members/plates. Could anyone hazard a guess as to the cost multiplier?

This project needs to be completed in a 90 day window (college campus) and is in an environmentally sensitive area. I am thinking that the additional cost could be justified by the elimination of blasting and painting on-site. Also, the steel plates need to be welded continuously at the bottom of the lap where SS plates need only to be welded at the top lap. I am thinking that elimination of the overhead weld would save some money.
Thanks in advance !!
Steve
 
MikeHalloran (Mechanical)
16 Sep 08 19:51
Get a quote from your steel supplier.  

Also check Syp before you get all worked up over stainless.

 

Mike Halloran
Pembroke Pines, FL, USA

stanweld (Materials)
17 Sep 08 13:01
Just an observation. While I have not been involved in the engineering/design phase of these units, I have been involved in their construction. I have never seen a roof from 304; all stainless roofs have been 316L; lap welds were made on both inside and outside surfaces to mitigate crevice corrosion.

JoeTank (Structural)
18 Sep 08 15:48
Cost-wise, I'd guess it would up the price by 2 to 3 times.

Joe Tank

mcguire (Materials)
18 Sep 08 17:32
Check with Contrarian Metal Resources. They have stainless roofing in many alloys and they can give rolled finishes which buys extra corrosion resistance. You may find that you can save money by buying a lighter gauge in higher strength, higher corrosion resistance duplex. This was just done in Qatar for their new airport. Made of alloy 2003 from Allegheny. It will last longer than their oil!

Michael McGuire
http://stainlesssteelforengineers.blogspot.com/

EdStainless (Materials)
19 Sep 08 8:23
I would also suggest that LDX2101 and AL2003 be considered.
They are stronger than 300 series alloys.  They are designed as step-up (in both strength and corrosion resistance) replacements for 304 and 316 respectively.
They are also less expensive than 316.

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