Vessel head manufacturing / Case: thickness "slimming" or "less than"

[Saver2008]

Hi!

I have the following situation:
-In the company where I am, It manufactures head vessels. I have a client that sent us a Purchase Order of manufacturing 30 tank heads (diameter of the head is 122.25 inches). The client supplied all material (plates of 1/2" thickness - 8ft x 40ft ASTM 572 Gr.50). In order to make the head form, we use a 1000 tons press cylinder. Before heating the plate and put it into the press cylinder , we measure thicnkess in some points of the plate, and we report values o 0.522 inches, 0.53 inches, 0.528 inches, 0.52 inches. Once we heat it and then put it into the press cylinder and make the form of the head, when we measure again we have the following measures in some points of the already formed head (0.489 in, 0.48 in, 0.47 in, 0.49 in and so on). As per experience, when we use carbon steel plates for diameter head higher than 1.5 mts and thickness of 0.5 inches, we buy 3/4" plate becuse of the "slimming" or "reduction of thickness). But, as we are not supplying the plates in this situation we are having thickness less than 0.5 inches. The client says that it is possible to have thickness at least of 0.5 inches and higher but we want to make an analysis to see the truth and we pretend to make a simple analysis on solidworks simulation putting a plate with the diameter of the cylinder of the press cylinder and just applying a static analysis -> force for compression in all the area of the modeled plate -> material as spec and taking into account the temperature of heated plate (1200°C) for youngs modulus.

The following question is:
1.- My assumption of modeling and simulate the process of forming head with solidworks and just applying a force perpendicular to whole area (face contact with face press cylinder) is correct?
2.- I was thinking that maybe if we heat less than 1200°C probably we could "meet" the final thickness required.

Hope you can help me

Thank you
Saver

 

[JStephen]

In general, I'd expect to see 1/16" to 1/8" allowable loss or so in thickness in forming, and wouldn't ever expect a head formed from 1/2" plate to hole 1/2" thickness.

Trying to accurately simulate that in finite element work seems like it would be an exceptionally difficult problem, and I would not expect the results to be too meaningful.

 

[r6155]

Is this hemispherical head in segments?
Head diam is 3111 mmm, plate is 2438 mm.

Regards
r6155

 

[Don56]

If you are forming hemispherical segments the thinning will be minimal. If you are forming a complete hemispherical head many variables come into play. How many hits to form? How much if any hold down pressure applied to the blank? Die clearance vs actual material thickness, etc.