[PSUBS-MAILIST] (no subject)

Fri Jan 9 21:19:50 EST 2015

My take on this is that EE mostly deals with huge, thick pieces for pressure vessels in the oil and gas industry, and they probably don't typically manufacture to the tight tolerances required of vessels subject to external pressure. There is no question that forming in a single piece maintains shape better, but to accommodate the thinning you end up needing a thicker blank, which robs you of payload capacity because of the superfluous material. This is particularly true in small vessels, and I recall that during one of the Nuytco tours, Phil indicated that this is why they segment the DeepWorker hulls.  It requires three times the welding of a single circumferential weld, but manages hull thickness without extensive machining after welding. As with anything, you can get it near perfect when you throw time, money and effort at it, so you can probably make a jig to do segmented construction with high accuracy, but I would definitely do the math to see if it's necessary. With a large
enough hull, you might be able to live with the extra weight if the cost is significantly less than the alternative.

Sean

On January 9, 2015 6:12:47 PM MST, "swaters at waters-ks.com via Personal_Submersibles" <personal_submersibles at psubs.org> wrote:
>Sean,
>In the sales reps response he mentioned the disadvantage of segmented
>is the shape, but it is uniform thickness. Isn't the shape critical?
>Perhaps I interperted this wrong. I should be getting the hemi in
>segmented for this sub correct?
>Thanks,
>Scott Waters
>
>
>Sent from my U.S. Cellular® Smartphone
>
>
>-------- Original message --------
>From: "Sean T. Stevenson via Personal_Submersibles"
><personal_submersibles at psubs.org> 
>Date:01/09/2015  6:46 PM  (GMT-06:00) 
>To: Personal Submersibles General Discussion
><personal_submersibles at psubs.org> 
>Subject: Re: [PSUBS-MAILIST] (no subject) 
>
>The issue is really the extraneous weight that you would end up
>carrying if you used, for example, two formed hemispheres versus the
>segmented construction. To achieve the minimum required shell thickness
>at all points, the deviation from this with a smaller pressed segment
>is much less than that with a fully formed hemisphere. The extra weight
>would otherwise reduce your payload capacity significantly, and this is
>significant enough to justify doing three times the welding that would
>otherwise be required with a pair of full hemispheres. A while ago, I
>emailed a sales representative at Edmonton Exchanger for some
>background information on this, as I was curious how much deformation
>is actually expected during head forming. 
>(Bear in mind that they tend to work with SA 516-70 N steel plate, and
>also typically make much larger heads than the submarine hulls we're
>discussing here. )
>
>His reply is below.
>
>-Sean
>
>
>******
>
>Forming SE2:1 heads:
>
>There is no advantage to forming SE2:1 heads in segments if it can be
>hot formed using a press in one piece. We can form up to 4" thick SE2:1
>head with only 1/8" thinning and up to 8" with 1/4" thinning (based on
>ID being 48" ID or more). The thinning on a hot formed head occurs at
>the top of the head (middle of head). During the forming process the
>material moves toward the Straight Flange so the SF thickness of head
>after forming is usually 1/8" to 1/4" thicker depending on the
>thickness and size of head. It is true that forming a SE2:1 head in
>segments would give you a more uniform thickness..........but the
>disadvantage is the additional welding and the shape of the head. When
>you hot form a SE2:1 head the inside shape of the head is a perfect
>SE2:1 shape. When making the head in segments and putting it together
>the head will deviate from its true shape which is not desirable. If
>SE2:1 head is too big to form in a press we would have to cold dish and
>hot spin the head ma! nually with different equipment. During this
>process the head can thin up to 20% and the shape can deviate slightly.
>A segmented head may be a
>option in this case because of the material savings and the extra labor
>involved in dishing and spinning.
>
>Forming Hemispherical Heads:
>
>Because hemi heads are very deep they tend to thin more than the SE2:1
>head. The loose rule for hot forming a Hemi head is that it will thin
>1/8" for every inch of thickness. Based on this, if you form a 5" thick
>x 96" ID Hemi............it could thin as much as 5/8". Again, the head
>would thin on the top and material would move into the SF of Hemi
>making it approx 5% thicker. The advantage of hot forming is the ID
>shape of the Hemi is perfect. Also, in both the SE2:1 heads and Hemi
>heads - the labor involved in hot forming is minimal compared to
>segmented construction. Even with the extensive thinning on hemi
>heads it is usually more cost effective to hot form a Hemi head rather
>than
>form in pieces and weld together.
>
>******
>
>
>
>On January 9, 2015 10:56:24 AM MST, hank pronk via
>Personal_Submersibles <personal_submersibles at psubs.org> wrote:
>
>Scott,
>Okay sounds good.  You probably already know that the figures you were
>given are calculated on nominal thickness.  That means you will need to
>have segmented heads built to stay at your desired thickness.  If you
>get pressed heads or formed heads they will need to be much thicker to
>achieve 1in nominal.  The thicker material will effect your weight and
>net buoyancy. 
>Hank
>
>On Fri, 1/9/15, swaters at waters-ks.com via Personal_Submersibles
><personal_submersibles at psubs.org> wrote:
>
> Subject: Re: [PSUBS-MAILIST] (no subject)
>To: "Personal Submersibles General Discussion"
><personal_submersibles at psubs.org>
> Received: Friday, January 9, 2015, 11:21 AM
> 
> Hank,The
> way it looks, I think building from scratch unless I get a
> good deal is the way to go. I might be taking Katy on a
> surprise vacation to Honduras in just a bit and do a deep
> dive and a ton of pictures down t!
> here. I
>have sent a quote
> request for the two 1" thick 60" diameter heads of
> 516 gr 70. Thanks,Scott
> Waters
> 
> Sent
> from my U.S. Cellular® Smartphone
> 
> -------- Original message --------
> From: hank pronk via Personal_Submersibles  
> Date:01/09/2015  9:43 AM  (GMT-06:00) 
> To: personal_submersibles at psubs.org 
> Subject: [PSUBS-MAILIST] (no subject) 
> 
> Scott,
> The trail went cold on the Pisces sub in the UK.  I
> just spoke with the park people and the sub was on loan and
> the owners took it back 4 years ago or so.  We could
> press on and find the owner but I suspect if you could but
> it, it would be quite expensive.  
> Hank
>
> Personal_Submersibles mailing list
> Personal_Submersibles at psubs.org
> http://www.psubs.org/mailman/listinfo.cgi/personal_submersibles
> 
> 
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