[PSUBS-MAILIST] Heads Question

Wed Sep 20 08:17:51 EDT 2017

Fatigue issues in weldments typically arise as a result of the geometry of the weld, where fatigue sensitive details such as doubler plates, sharp interfaces, inherent "cracks" at the apexes of partial penetration welds, overlapping weld toes etc. cause local amplification of the service stress ranges. Pressure hulls are inherently resistant to fatigue as a result of the mandated geometries, CJP welds, and barring the high strength alloys, the generally tougher nature of e.g. ASTM A516 Gr. 70 steel. I might go as far as to say that a PSub is unlikely to see enough high stress cycles within its lifetime to justify worrying about fatigue at all. Indeed, ABS only requires a fatigue analysis under specific conditions:

>From the ABS rules (2017):
Section 6/9:

Fatigue  (2002) A  fatigue analysis  is  to  be submitted  when  it is  anticipated  that the life time  full range pressure  cycles  N will exceed  that obtained  from  the following  equation: 

N = [1160(3000  –  T)/(Kfτ  –  14500)]^2 

where

T = temperature  in  degrees  C  (degrees  F)  corresponding  to  application  of  the  cyclic  or repeated stress
K  =  5688 SI/MKS units (4  U.S.  units) 
fτ = range  of  cyclic stress  kg/mm2  (lb/in2) 

Pressure cycles  of  less  than  full  pressure are to  be included  in  N  in  the ratio  p/P  where  p  is  the  actual pressure of  the  cycle  under  consideration  and  P  is  the design  pressure. 

Sean

On September 19, 2017 12:39:42 PM MDT, River Dolfi via Personal_Submersibles <personal_submersibles at psubs.org> wrote:
>I'm sure Sean can also speak at length about this, but a single
>pressure
>test gives no information about fatigue life. The size of flaw in a
>weldment (and all welds have flaws) may not be constant over the
>service
>life of the vessel. Weld material with sufficiently low fracture
>toughness
>(aided by low temperatures) will have it's flaws elongate with each
>cycle,
>as predicted by the Paris Law of crack propogation, until eventually
>reaching a critical size and fracturing. This is compounded rather
>unpredictably by the corrosion typical of a marine environment.
>
>All I know is that I know nothing. But sometimes I think we should pool
>our
>money and buy an ultrasound machine...
>
>-River J. Dolfi
>
>412-997-2526
>rdolfi7 at gmail.com
>
>On Tue, Sep 19, 2017 at 1:29 PM, via Personal_Submersibles <
>personal_submersibles at psubs.org> wrote:
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>>    1. Re: Heads Question (hank pronk via Personal_Submersibles)
>>
>>
>>
>----------------------------------------------------------------------
>>
>> Message: 1
>> Date: Tue, 19 Sep 2017 17:23:42 +0000 (UTC)
>> From: hank pronk via Personal_Submersibles
>>         <personal_submersibles at psubs.org>
>> To: Rick Patton via Personal_Submersibles
>>         <personal_submersibles at psubs.org>
>> Subject: Re: [PSUBS-MAILIST] Heads Question
>> Message-ID: <674133299.2545129.1505841822312 at mail.yahoo.com>
>> Content-Type: text/plain; charset="utf-8"
>>
>>  Dan, Rick,I would argue that you guys are indeed experts. ?I am
>> not,,,but,, I am an expert experimenter and tester . ?My welder has a
>60%
>> duty cycle and I have welded and tried to destroy the weldments and
>> actually wrecked a jack trying . ?I test welded and bent and tortured
>> material and not once did a weld break. ?Again you guys are the
>experts but
>> Elementary 3000 had 392,500 lbs trying to push the hatch through the
>> opening with no issues at all. ?I can talk about my welding all day
>long
>> but it is the pressure test that says it all. ? I would have tested
>it a
>> lot higher but that was the limit of the chamber.How can you explain
>my
>> pretty welds holding ?6,500 lbs per inch? ?If my welder can only weld
>sheet
>> metal, why did it not fail? ? I am a pretty luck guy, maybe that is
>it
>> ;-)Hank
>>
>>     On Tuesday, September 19, 2017, 11:00:50 AM MDT, Rick Patton via
>> Personal_Submersibles <personal_submersibles at psubs.org> wrote:
>>
>>  Mig welds can be deceptive sometimes. I have seen very pretty
>factory
>> fellet mig welds come threw my doors in both aluminum and mild steel
>where
>> the weld had completely let go of one of the two sides due to lack of
>> penetration.? The prep or process wasn't done correctly but yet it
>still
>> looked good.?This is not the case with TIG or stick. There is a
>saying
>> amongst Welders that if a stick weld looks good, it probably is. If
>it is a
>> critical weld, you still want to X ray or UT it but you will always
>have
>> penetration on both sides unlike mig. Beginners and novice welders
>> sometimes gravitate towards Mig as it is easier than stick but a
>pressure
>> vessel that you are going to be in, then l would stick with stick
>"pun
>> intended " or if your insistent on Mig, have it done professionally
>or make
>> darn sure your using the correct equipment as Dan inferred.?Rick?
>> On Tue, Sep 19, 2017 at 9:08 AM Daniel Lance via
>Personal_Submersibles <
>> personal_submersibles at psubs.org> wrote:
>>
>> Hank,I do not in any manner consider myself an expert .? I am just
>relying
>> on what I learned during 36 years in the welding industry . My motto
>is if
>> a person keeps the right attitude he or she can learn something new
>> everyday ! ?:)Dan
>> On Tue, Sep 19, 2017 at 7:43 AM, hank pronk via Personal_Submersibles
><
>> personal_submersibles at psubs.org> wrote:
>>
>>  Dan,I could tell you all about the million tests I did after loading
>the
>> wire into my shiny welder and i could talk about the results, but,
>you are
>> the expert and we should take your advice.? No question about it, i
>would
>> not want to encourage anything else.Hank
>>     On Tuesday, September 19, 2017, 4:52:00 AM MDT, Daniel Lance via
>> Personal_Submersibles <personal_submersibles at psubs.org> wrote:
>>
>>  ?Since the topic has come up in this current thread I want to state
>for
>> the record that I would encourage anyone contemplating using the "
>Short
>> Arc MIG welding process " to weld their submarine's pressure hull to
>> consult a licensed qualified , experienced ?Welding Engineer before
>doing
>> so ( and NOT the Welding machine manufacturers sales rep) . MIG (
>short arc
>> ) should only be used on light gauge metals ( .1875" and below ) ,
>when
>> used on heavier thickness steel it produces welds brittle in nature
>and
>> ultimately prone to cracking . This process is ill suited for
>building
>> pressure vessels especially ones intended for PVHO . Steel has an
>inherent
>> tendency to become brittle at low ambient temperatures ( think a
>northern
>> latitude lake where the bottom temperature could possibly be in the
>upper
>> 30s , 40s or 50 degrees F range ) add to that a welding process well
>> documented to produce brittle welds and then factor in a bottom
>pressure of
>> hundreds maybe even thousands of pounds p!
>>  er square inch. Chances are very good that the hull won't fail on
>the
>> first dive or hydro test but basically what you have is the
>proverbial "
>> one bullet in the revolver " situation ?leading to a false sense of
>> security . ? ?Like I mentioned earlier consult a "Licensed" qualified
>,
>> experienced Welding Engineer and heed his advice before loading that
>spool
>> of wire in your shiny new welding machine or hiring the "expert
>welder from
>> down the street . Like the old saying goes " what you don't know can
>hurt
>> you " .Dan Lance
>> On Mon, Sep 18, 2017 at 2:57 PM, hank pronk via Personal_Submersibles
><
>> personal_submersibles at psubs.org> wrote:
>>
>>  Alec,Yup, I have heard it all from the stick welding only crowd.? I
>hear
>> all the time "I like to turn it up and burn it in" ?or ?" I like to
>crank
>> er up" ?LOL.The fact is, too much penetration is bad because you
>introduce
>> parent metal into the filler metal, and that is bad.? You need
>sufficient
>> penetration and I have no problem achieving that.? I mig welded
>Elementary
>> 3000 and it is 1 inch thick, with no problem, and it has been to
>1,250
>> psi.Hank
>>     On Monday, September 18, 2017, 10:13:50 AM MDT, Private via
>> Personal_Submersibles <personal_submersibles at psubs. org> wrote:
>>
>>  Yep, I think you're probably right! My only concern would be using
>mig on
>> a pressure vessel though. I'm not an expert, but what I've always
>heard
>> from those who are is that it's for high-productivity jobs but not
>for jobs
>> like full penetration where quality trumps speed.
>> On Sep 18, 2017, at 7:56 AM, hank pronk via Personal_Submersibles
>> <personal_submersibles at psubs. org> wrote:
>>
>>
>>  Alec,I like a bevel on both sides, and I also do a mig pass on the
>inside
>> then grind outside as you do.? When your welding such light material,
>the
>> external grind job is creating the same shape weld grove as if you
>started
>> with a bevel on both sides.? Same difference really.? The big
>difference is
>> guys like Rick and Dan can do this all at ounce because they are
>> professional welders.Hank
>>     On Sunday, September 17, 2017, 8:33:43 PM MDT, Alec Smyth via
>> Personal_Submersibles <personal_submersibles at psubs. org> wrote:
>>
>>  Here's the method I used. The starting point is a bevel with the
>sharp
>> end of course on the ID and the wide end of the wedge on the OD. An
>air gap
>> of about 1/8" is left between the two parts.
>> 1) TIG weld the root pass, from the inside of the hull, plugging the
>air
>> gap.?2) Grind with an angle grinder from the outside into the root
>pass.
>> Use a 1/4" wheel on the angle grinder. You need to get a clean shiny
>U
>> shaped channel, pure like-new metal, with no visible discontinuities
>> whatsoever.3) Stick weld from the outside building up layers until
>meeting
>> the plate thickness.
>> Perhaps a double bevel would be needed for very thick material. The
>method
>> I'm describing, I've used on material up to 1/2" with no problem.
>> Dan, if I'm talking rubbish please set me straight!
>>
>>
>> Best,
>> Alec?
>>
>> On Sun, Sep 17, 2017 at 9:52 PM, Rick Patton via
>Personal_Submersibles
>> <personal_submersibles at psubs. org> wrote:
>>
>> Definitely want to bevle both sides. If you don't, your
>wire/stick/Tig
>> will short out way too soon becoming molten and not reaching the ID
>of the
>> hull and you will have to do a lot of back gouging before reaching
>your
>> first pass.Rick?
>> On Sun, Sep 17, 2017 at 3:54 PM Brian Cox via Personal_Submersibles
>> <personal_submersibles at psubs. org> wrote:
>>
>> I have found that I get a better weld if both sides are beveled
>.?Brian
>>
>> --- personal_submersibles at psubs. org wrote:
>>
>> From: Private via Personal_Submersibles <personal_submersibles at psubs.
>org>
>> To: Personal Submersibles General Discussion
><personal_submersibles at psubs.
>> org>
>> Subject: Re: [PSUBS-MAILIST] Heads Question
>> Date: Sat, 16 Sep 2017 19:30:01 -0400
>>
>> Hi David,
>> Absolutely, you want it with the flange. Any impression otherwise was
>my
>> "mind typo" that I was trying to clarify in the second email. If you
>can
>> avoid beveling it yourself, however, it'll save quite a job. You only
>need
>> one of the two edges beveled, either the head flange or the end of
>the
>> cylinder it will mate to, and it doesn't matter which. Greg has a
>good
>> point, but I suppose a key factor is whether you'll be welding
>yourself or
>> contracting out. I learned to do my own, with an awful lot of help
>from Dan
>> Lance.
>> Best,
>> Alec
>> On Sep 16, 2017, at 12:50 PM, james cottrell via
>Personal_Submersibles
>> <personal_submersibles at psubs. org> wrote:
>>
>>
>> Hi David,
>> In my experience it was cheaper and faster to hire an ASME tank
>fabricator
>> to produce a steel cylinder with the head (or heads) welded on. Mine
>came
>> machine welded with an ASME code stamp.?If your design will feature
>> external frames, ask them for both heads welded on. If your design
>will
>> feature internal frames (done later) ask them to weld one end only.
>This
>> will be cheaper in the long run and better built. It's hard to beat
>> pressure vessel code machine welding. Specify NO backing strips.
>> Another tip- call it a "vacuum tank".
>> Greg Cottrell
>>
>>       From: David Colombo via Personal_Submersibles
>> <personal_submersibles at psubs. org>
>>  To: Personal Submersibles General Discussion
><personal_submersibles at psubs.
>> org>
>>  Sent: Saturday, September 16, 2017 12:20 PM
>>  Subject: Re: [PSUBS-MAILIST] Heads Question
>>
>> Hi Alec, I just spoke with the company that Roberto mentioned here in
>> California to place an order for dished head for the SeaQuestor. I
>will be
>> using the 36"OD x .375 A516-70 steel what they call Elliptical 2:1
>Ratio
>> ASME Code Type. It comes with a 2" flange which is really a 36" od
>ring
>> shape as part of the forming. This would mate up to the 36"OD first
>hull
>> section. I'm thinking that this would give me the best welding
>condition
>> with two matched surfaces that I would bevel for full pen welding.
>I'm
>> curious why not to have the flange? ? My cost here is $480.00 + $96
>to have
>> it shipped to northern California from southern California. even
>though its
>> only a nine hour drive one way, I think my time would be worth more
>than $5
>> hr to pick it up. LOL Unless of course its cheaper in Canada (Hank),
>I
>> might make the trip and could serve as support crew for the Gamma.
>Any
>> thoughts out there from fellow Psubers would be appreciated.
>>
>> Best Regards,
>> David Colombo
>>
>> 804 College Ave
>> Santa Rosa, CA. 95404
>> (707) 536-1424
>> www.SeaQuestor.com
>>
>>
>> On Fri, Sep 15, 2017 at 2:28 PM, Alec Smyth via Personal_Submersibles
>> <personal_submersibles at psubs. org> wrote:
>>
>> Ugh, mental typo. I meant "un-beveled" and "bevel them yourself", not
>> "un-flanged" and "flange them yourself".
>> !!!!!!!
>> On Fri, Sep 15, 2017 at 5:25 PM, Alec Smyth <alecsmyth at gmail.com>
>wrote:
>>
>> Hi Roberto,
>> I believe the short description for what you need is flanged,
>beveled, and
>> code. You could get them unflanged, but it takes quite a while to
>make a
>> flange with an angle grinder. The flanges if I recall are 2". Do set
>up a
>> project page or something so we can follow progress!
>>
>> Best,
>> Alec
>> On Fri, Sep 15, 2017 at 5:07 PM, roberto alvarez via
>Personal_Submersibles
>> <personal_submersibles at psubs.o rg> wrote:
>>
>> Hi, lost the plans cd for the k250, i am? interested in the? head
>> selection, i found a seler in california and have?flanged ,beveled
>,code,
>> non code,
>> Will apreciate your support in this ( until i found the plans cd )
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