March 7, 2019

Submarine Pressure Hull Steel (Tables) Especially Swedish

Pete Comment

All submarines have pressure hulls that are made of special steel alloys. In the past the Soviets/Russians bankrupted their economy by also using Titanium alloys. Essentially pressure hulls protect the crew, sensors and engines from excessive water pressure and provide the airtight conditions the crew rely on to breathe.

Pressure hulls need special high yield steel alloys that are flexible enough to:
-  contract as water pressure increases (during diving), 
-  is also strong enough to stop contracting (at maximum diving depth) and
-   can then expand as water pressure reduces on the way to the submarine surfacing.  

High proof or yield steel for submarines can be measure in pounds per square inch (psi), (eg. HY80 = 80,000psi) or Mega/million pascals (MPa) with this conversion
 https://www.unitconverters.net/pressure/megapascal-to-psi.htm.

A submarine can only go through a limited number of contraction-expansion cycles (especially if it has to deep dive) before it loses flexibility, putting it in danger of metal fatigue.

For a diesel-electric submarine with AIP (eg. a Swedish Gotland class ) on a typical short 12 day mission in the Baltic Sea it may dive and the operate on its Stirling AIP for 10-12 days. It then surface only once = 1 cycle. Perhaps its pressure hull is good for 200 cycles (?) - although its service life is more rapidly limited by hull rust and corrosion - all contributing to a 34 year service life. 

ANONYMOUS' TABLE 1.

Many thanks to Anonymous advising that the pressure hull details in Table 1. below apply to the:

-  Swedish (Gotlands, future A26s), 
Swedish designed Australian Collins, and
-  future SAAB-Damen entry for the Walrus Replacement competition 

In the [cylinder like] design of a submarine, the diameter of a pressure hull significantly effects on many other feature of a submarine [including space, propulsion choices and acoustics]. In terms of diameter (which may sometimes equal Beam) Gotland's are 6.2m, A26s 6.75m, Collins 7.8m and 8m for a SAAB-Damen Walrus replacement. Part outer hulls and sonars on hulls will effect the overall beam of a submarine.

Table 1 Similarity of pressure hull of Swedish and Australian submarines
Submarine
Pressure hull steel
[MPa]
Beam
[m]
Diameter of pressure hull
Estimation
Gotland
Weldox700EM
[1]
700
6.2
Same
In A26, sound absorption rubbers (thickness 100mm) are presumably attached on the surface of prssue hull. In A19, no sound absorption rubbers are attached, or very thin rubbers are used.
A26
700
Collins
700
7.8
Same
Difference in beam is due to difference in position or shape of flanl arry sonar.
SAAB-Damen
Walrus
Replace-ment
700
8
[1] Weldox is old brand name of Strenx.

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Below is a broader comparison of Chinese, Russian & Western Submarine Pressure Hull Steel Strengths originally published on July 20, 2015. Note the Swedish measure Weldox700 and Australian BIS 812 EMA in both Tables with both at 700MPa equivalent to HY100..

TABLE 2.



YS = Yield Strength or proof stress. HY = High Yield
YS US    UK FranceGermanyChinaRussia
and
India
JapanAustraliaSweden
550MPaHY80Q1N1.3964India
DMR-
292 #
* 1)
NS56
590MPa60HLES921A
TA5-A
AK-25
48-OT3
630MPa1.3974
690MPaHY100Q2NAB-2* 2)
NS70
700MPa80HLESBIS812
EMA
Weldox
700
785MPa980AK-29NS80
890MPaHY130100HLES*4)
Ti80
AB-3?NS90Weldox
900
980MPaAK-33
1075MPa

AK- ??
1178MPaHY156

* 3)
NS110

1) steel of 550MPa and NS56 is equivalent to HY80 grade steel.
* 2) steel of 690MPa and NS70 is equivalent to HY100 grade steel.
* 3) steel 1078MPa and NS110 is equivalent to the HY156 grade steel.
* 4) Ti80 Titanium alloy under development 880MPa equivalent to NS90 or HY128 steel - source.

The Table is from towards the end of Japanese Document "High-tensile steel Summary of national submarine" or Summary of High Tensile Steel for Submarines by Country 2013 http://seesaawiki.jp/w/doramarine/ .
---


COMMENTS FOR TABLE 2.

    The higher the yield (stronger) the steel alloy or Titanium alloy in a submarines pressure hull the deeper it can dive in operations. As well as alloy strength other factors also influence diving depth including:

    - supports for the the pressure hull

    - compartments or multiple pressure hulls, and

    - strength of the welds used to join sections of the pressure hull.

    It is not possible to verify the accuracy of most of the figures. Commenters who know more are invited to supply corrections.

    FURTHER READING

    See  Soryu Submarine Steel Details - Japan Offer to Australia, January 20, 2015

    Anonymous and Pete

    7 comments:

    Anonymous said...

    Hi Pete,

    It seems that the beam for the A26 is 6.75 m, see the fakta section in the link (in Swedish check for bredd).

    /Kjell

    Pete said...

    Thanks /Kjell

    For the 6.75m correction. I will change the text accordingly.

    And the FMV link http://fmv.se/sv/Projekt/Ubat-typ-A26/ you have identified is a very useful source in itself.

    Regards

    Pete

    Anonymous said...

    Hi Pete

    Beam of 6.75m for A26 is correct. This data is based on FMV (http://fmv.se/sv/Projekt/Ubat-typ-A26/A26-del-for-del/).

    Beam of 6.4 for A26 is based on (https://en.wikipedia.org/wiki/A26_submarine#cite_note-datasheet-3) referred to http://www.kockums.se/PageFiles/736/A26_Datasheet.pdf which is Kockums under TKMS.

    Then, pressure hull of A26 is different from Gotland.

    Regards

    Nicky said...

    Hi pete

    Check this out from India

    India signs $3 billion contract with Russia for lease of a nuclear submarin
    https://www.defensenews.com/global/asia-pacific/2019/03/08/india-signs-3-billion-contract-with-russia-for-lease-of-a-nuclear-submarine/

    Maybe Russia should start talking to India on selling them the Akula class SSN.

    Pete said...

    Hi Nicky

    1. I was writing my Akula lease article yesterday but decided to not be like the herd and to publish on Monday.

    2. I would guess non-proliferation conventions (the NPT?) argue against actual sale of nuclear submarines and nuclear weapons.

    So leasing a Russian submarine (by an already nuclear submarine building India) is more or less "legal"

    Regards

    Pete

    Anonymous said...

    Hi Pete,

    I found a document describing the Polish Orka replacement program PULASKI POLICY PAPER: Poland’s ‘Orka’ submarine programme. Part 3. The A26 submarines – Swedish Offer maybe it can be of interest, and of cource there is a part 1, HDW Class 212A/214 and a part 2, Scorpène.

    /Kjell

    Pete said...

    Thanks Kjell [at 9/3/19 10:19 PM]

    An excellent paper on the A26 entry in the Polish Orka competition.

    I'll use it in a few days for an article.

    Regards

    Pete