Cap thk higher than starting plate

[ElCidCampeador]

Hi,

I've this stainelss steel ASME SA 403 WP 316 cap, 8" Sp.8.18mm, cold formed and acc. to B16.9.

Referring to this item, I've 2 certificate:

-Manufacturer's one, which says that material was cold formed+PFHT acc. to ASME SA 403 WP 316 and B16.9
-Starting plate's one, which is the material used by manufactuer to carry out the cap. Material is a plate acc. to SA 240 TP 316.

What I think it's odd is that thickness of the starting plate used is 8mm!

How is it possible? From a thk 8mm to obtain something thk 8,18?

What I suppose is that product is acceptable if thk is within under-tolerance.

Cap has 12,5% undertolerance, so minimum thk is 8,18mm*0,875 = 7,16mm.

Cold forming plate usually imply 15% of thickness reduction. So, if I use 8mm thk starting plate, min.thk of cap after forming is: 8*0,85 = 6,8mm

But 6,8mm is less than 7,16mm! It's not acceptable, isn't it?

I don't understand how manufacturers work. What do you think?

 

[meltedEng]

I'm sorry, I'm not entirely sure what you're trying to question and I'm having trouble reading your question.

You don't use any "implied" reduction. There is what is acceptable and what is not.

Is the finished item above your minimum thickness?
Do you have the proper PFHT to account for reduction in forming?
Is the cold forming reduction within allowed reduction?

 

[ElCidCampeador]

The thing that I find odd at least is that thickness of the starting plate is less than finished thickness of the final cap (8mm vs 8,18m)!

 

[KevinNZ]

If the plate is "pushed" rather 'stretched' into shape then it could be thicker than the stock plate.

Fittings to B16.9 do not have a wall thickness requirement. They only have to show that when welded to a pipe of the same nominal thickness. the pipe would fail first.

 

[Don56]

Where are you measuring the after forming thickness, on the straight flange? If so, it is normal for this area to be thicker than the starting material thickness as material gathers her as it is drawn through the die. You will find thinner areas in the dish portion of the head as this is where material stretches.