April 8, 2015

Submarine Steel Strength, China and Japan.

High-strength steel welding, monitoring and other functions are now highly automated including  computer dependent, particularly in well established assembly lines. (Photo courtesy Design News and Bosch Rexroth)

This present article continues discussions first raised in Soryu Submarine Steel Details - Japan Offer to Australia of January 20, 2015 and then raised in comments on previous articles over the last week.

Japan is particularly concerned that defence exports to customers/allies might increase the chances that Japan's submarine secrets (including its hull steel characteristics, cutting and welding techniques) might pass to potential enemies. A particular threat is passage of secrets to China. Particular concerns are China's ability to reverse engineer or develop counter-actions against allied weapons like the F-35.

Regarding the specific and sensitive issue of the operational depth of submarines. This depth is not soley dependent on the steel strength estimates discussed below. There are so many other determining factors including weld strength and hull structure.

Noone knows operational or crush depth except designers and naval officers who operate the submarines. Detailed computer simulation and materials testing is required to calculate pressure distribution on submarine hulls. 

Chinese submarines appear to be rapidly improving. Chinese submarines used to be clearly inferior to US or Japanese submarines, but now, the situation is changing. Ignorance of such rapid changes  makes people too optimistic. The latest Chinese subs may be superior to Collins subs at least in hull strength. Australian and Japanese hull strengths therefore need to be improved. 

Documentary Comparisons of Chinese and Japanese Submarine Steel Strengths

Chinese submarine hulls appear to made of "980 steel" with a yield strength of 800 MPa. China's "980" and Japans NS 80 are nearly the same. Their chemical components and mechanical strengths are very similar - see http://www.mod.go.jp/trdi/data/pdf/G/G3111C.pdf , page 3, table 3, chemical composition (NS80E) 4.2.1 left column.

See the following document: Shanghai Jiaotong University, School of Naval Architecture and Ocean Engineering's, "High Crack Propagation of Steel 980 Welded Joiont under Spectrum Load” (Chinese), http://image02w.seesaawiki.jp/d/e/doramarine/16dc6f08dbd1d96c.pdf
Page 5, “ 2.2 Fatigue Testing indicates:

“Test material for high-strength structural steel submarine 980 steel welded joints. 980 steel (VHD402), yield strength σs> = 800MPa, China developed high strength, high toughness, can be welded with a submarine pressure hull.” See Page 5, Table 1 Chemical component (Steel and Weld for upper and lower rows respectively), Table 2 Mechanical Property (ibid).

 Using conversion site http://www.convertunits.com/from/psi/to/MPa  800 MPa = 116,030 psi = "HY-116".

Returning to G3111C.pdf

Soryu Submarine Steel Details - Japan Offer to Australia of January 20, 2015 very briefly describes  http://www.mod.go.jp/trdi/data/pdf/G/G3111C.pdf ,  Within that document see page 4, table 4.2.1 left column, which seems to indicate the Soryu has Japanese naval steel measure NS80 = 80kgf/mm2 which converts to 113,760 lbf/in2 or HY-114.

So assuming the translations and conversions are correct China's use of HY-116 steel is very similar to the Soryu's HY-114.

Soryu Submarine Steel Details - Japan Offer to Australia also discusses NS110 which may also be used in the Soryu. NS110 means 110kgf/mm2 proof stress converting to 156,414 lbf/in2 or HY-156 . HY-156 using simple linear calculations allow the Soryu an operating depth of just over 600 metres.


It has to be pointed out, however, that operational depth is not soley dependent on steel strength. There are so many other determining factors including weld strength and hull structure.

Noone knows a submarine's operational or crush depth except designers and naval officers who operate the submarines. Detailed computer simulation and materials testing is also required to calculate pressure distribution on submarine hulls. 

Anonymous and Pete


Anonymous said...

Hi Pete

Welding is also one of decisive factors in hull constructing. As welder’s skill reflects his welding experience, we may consider number of built submarines as a measure of country’s hull welding ability, which suggests that China perhaps shows the better welding ability.


Peter Coates said...

A bit off topic. Americans tend to value economic relations with China more than relations with Japan. see http://thediplomat.com/2015/04/surprising-trends-in-u-s-views-of-china/

Anonymous said...

Sentiment behind economy is also important. I admit that America gets along better with China than Japan for following reasons:
1) America and China respect each other. American respects history and culture of China. Chinese respects America’s democracy and fairness, because Chinese is very democratic in his nature.
2) Their characters are very similar. They are frank, do not mind small things and sometimes show great kindness.
3) Historically, America has tried to be best friend of China. When China was invaded by western counties and Japan, only America was kind to China. I admit Japan was the one of worst invader of China. You may point out Korean War, but it was political, not invasive.

It’s rather unpleasant for us Japanese, but we must admit these facts to construct better relationship with China and America. I do not think that emotional reaction is productive.

Peter Coates said...

Hi Anonymous

Thank you for your comments.

I think the economic attraction of China is a bigger issue in American thinking than Japan's WWII record.

The US resents China's war record including:

- Chinese troops fighting US troops in the Korea War in the early 1950s, and

- Chinese military assistance to North Vietnam which fought the US (1965-75). This included Chinese made weapons shooting down US aircraft.



Anonymous said...

For many Americans, the economic attraction of China is no longer what it used to be. Sure there is always that dream of 1B consumers hanging out there, but that is now more distant than ever before. A decade of massive trade deficit with China at $200B-$300B/year changes our mindset. It is hard to find a country that does not have a negative trade deficit with China, one of the very few exceptions is Japan in fact. American businesses also see that their businesses with China, even those that have been localized in China, are usually not profitable. In contrast, American businesses see the Japanese market as one of the more profitable market in Asia. Bad revenues versus good profits. Sure, there are significant barriers for entry in Japan, but all markets have those.

Peter Coates said...

Hi Anonymouse (of April 10)

Thanks for that economic overview. The economic (including the balance of trade) relationship between Japan, US and China makes a deep and complex impact on their strategic relationship.

I assume slower growth in the Chinese economy is causing a slow down in Chinese purchases of US goods and services.