price impact estimate - Head THK.

[picasa]

I want to quickly find out the price impact of changing thickness of a vessel head without contacting the fabricator. Following are the details

Material SA516 Gr 70N
2:1 Elliptical Head with 2" SF.
Original thickness: 1.9375"
New thickness: 1.625"

Is there a way to do it on my own? Is there any website that has tools for doing these quick checks, calcs?

 

[JStephen]

Probably the best you'd come up with would just be a price per pound. Check back over past head quotes, and see how they average out.

The problem is, you don't know what's involved in making these until you contact the fabricators. One thickness might be out of the range of one machine, or it might be the difference between hot work and cold work, they might get rounded up differently, might match stock thicknesses, etc. And you'll probably find a fair range of price differences from fabrictor to fabricator.

 

[Weldmedic]

I echo JStephens advice. A good rule of thumb is the price per pound. Other things to consider are the current surcharges on steel. Perhaps the fabricator has it in stock and can give you a better price. If your changing horses here and have one on order and need to change, get up with the fabricator immediately. The cutting, handling and forming of these component takes valuable shop time and coordination of resources.

Steve

 

[JoeTank]

While price-per-pound is okay for budgeting, the real killer is sometimes schedule. For example, you want to change the design, but the fabricator has already bought the head. You may be too late in the schedule. Now you get to pay for both heads... the old one and the new one!

Steve Braune
Tank Industry Consultants

http://www.tankindustry.com

 

[jlcochran1]

As a fabricator of vessels, (but not heads), I would recommend contacting the fabricator. While you could price the head both ways from a head manufacturer to get a relative price difference there are several other variables. Depending on whether you have ordered the vessel the fabricators markup will be higher if this represents a post order change. He has to revise drawings and calculations. However if the shell is also thinner then there could be offsetting weld time, radiography and PWHT savings. It is rare that we fabricate a vessel without changes and it is always best IMO to work closely with the fabricator and communicate any design intent changes you might be considering.

 

[sitidor]

I agree entirely with jlcochran1.

I have purchased hundreds of vessels in the past and I strongley suggest that you openly communicate with your fabricator, otherwise you can just about gaurantee that the final product will not be what you want nor expected.

Although it sounds a simple change, the knock on affect (eg. nozzle reinforcement in heads, thickness transitions, weight etc....) may far outweight the head purchase cost.

Good Luck!