[PSUBS-MAILIST] Specifications when ordering shell

[Stephen Fordyce via Personal_Submersibles]

Hi guys,
The material certificate thing is all about quality control and
traceability of exactly what is the composition of the elements in
it.  Ie. when the steel gets smelted and poured into a block (or whatever)
at the mill, that particular batch gets analysed for exact percentages
of all elements, and all parts poured from that batch are given the "heat
number" of the batch.  Since the certificate is meant to trace back to the
original steel mill, it's often called a "Mill Certificate".

Each time the steel goes through a process (ie. rolling into sheet, the
sheet formed into pipe or endcaps) there is a chance the traceabilty to the
original analysed composition could be lost, if the material gets mixed up
- and there are varying levels of quality control that make sure of this,
and these are reflected in different types of material certificates.

The EN 3.1 cert is pretty high end (ie. good enough for the SS304/316
cryogenic liquid ethane pressure vessels I'm currently involved with at
work) and typical for most industrial applications at least.  I've not come
across requirements for 3.2 (which is even more stringent), and we
frequently work with lesser requirements than 3.1.
Here's a good explanation of the difference:
http://www.classicfilters.com/blog/materialcertificates/

Tracing the material back to the mill is supposed to be important in case
there is a failure in another part in the same batch, so it can prevent
other failures.  I've always thought the whole certificate/traceability
thing was just a PITA and that so long as you get steel or parts from
reputable suppliers who's QC practises you trust, then that's just as
effective.  Especially when you're building a big system with hundreds of
welded parts.

Cheers,
Steve
(Among other things - mechanical engineer in Melbourne, Australia)

On Mon, Mar 23, 2015 at 10:55 PM, James Frankland via Personal_Submersibles
<personal_submersibles at psubs.org> wrote:

> Hi Andre,
>
> I was in this position some years ago.  Not knowing what to specify on the
> order.
>
> I believe the EN number is a certificate of the material quality.  Mine
> was done to EN10204.3.1.B but i never specified it.  I just asked for the
> material type.
>
> So just ask for your dimensions of shell, material, percentage of round,
> bevel, weld.
>
>
> Example.
>
> Shell.  P355 Steel.  10mm Thick.
>
> OD 1000mm x 2000mm length.
> Shell to be within +\- 3mm on diameter.
> Welded seam.
> 35 degree external bevel with 2mm nose.
>
>
> Something like that should do it.  They will send you a quote and should
> tell you what material grade it what code they will be working to.
>
>
> Make sure you specify clearly the tolerance of roundness you want and say
> your not paying for it if its not right.  They will probably need to
> re-roll the cylinder.
>
> Ideally go to the factory with a wooden template and measure the cylinder
> before you accept it.
>
> Get the bevel put on, it will save you pain.  But. don't bother with grit
> blasting, you need to paint it straight away after that or it will start to
> oxidise again.  By the time you've finished your hull, it will be all rusty
> again.  Grit blast when you've finished working on the hull.
>
> Someone else may have some other suggestions.  Comments.
>
> Hope this helps.
>
> Kind Regards
> James
>
>
>
> On 21 March 2015 at 22:30, André Eriksen <personal_submersibles at psubs.org>
> wrote:
>
>> Hi,
>>
>> I`m in the process of ordering the shell and tower for my submarine.
>> What specification should I ask for? (Europe)
>>
>>  I asked for EN10204 with 3.1 Sertificate (Not 100% sure of this, but
>> this is what I got when I ordered the endcaps from another company. 3.2
>> Sertificate was a bit too expensive)
>> Told them I had no special requirements for the plates and needed no edge
>> preperation.
>>
>> *They replied*: "this is not the normal enquiry type, but we will not
>> ask any longer" (?)
>> And said the plates was going to be EN10028-3 with certificate 3.2.
>>
>> I want to keep the cost down, but should I ask that they grit blast the
>> shell after rolling?
>> Also I didn`t ask for bevel on the edges. Again to keep cost down. But
>> maybe I should, to spare me the extra work?
>>
>> May I ask what you tell your supplier when ordrering?
>>
>>
>> -André
>>
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>>
>
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