Seawater Resistant Stainless Steel


Seawater Resistant Stainless Steel
YST130N

Surprisingly high corrosion resistance to seawater and hot springs

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Metal corrosion by seawater is a serious problem, and countermeasures have been sought by related industries for years.
To solve this problem, YOKOTA has developed the material YST130N based on our many achievements and experience in this area. YST130N has excellent seawater resistance, and also excellent corrosion resistance to a wide range of corrosive liquids including corrosive hot water at geothermal generation plants and hot springs among others.

Features

Excellent crevice corrosion resistance and pitting corrosion resistance in seawater environments.

Excellent corrosion resistance to general chemical liquids.

Highly suitable for seawater containing sand and slurry due to its excellent wear resistance.

Remarkable mechanical strength, being nearly twice as strong as conventional stainless steel.

Heat and high temperature resistance.

Can be formed into any shape because it is made of casting.

Easily welded by covered arc or TIG welding without preheating or residual heating.

Being attracted to a magnet, it can be easily located or sorted using the magnet.

Due to the above, drastic reduction in equipment and maintenance costs is possible.


Note 1:
Most of the seawater pump parts are made of stainless steel casting and gray cast iron. As gray cast iron pumps require a lot of maintenance, the share of stainless steel pumps has been increasing. However, a lot of local corrosion in the form of crevice corrosion and pitting corrosion occurs in conventional stainless steel. Though crevice corrosion is similar to pitting corrosion, crevice corrosion occurs more often than pitting corrosion in systems with crevices.



Pitting corrosion resistance

5% ferric chloride 40 deg C, 50hr
Seawater Resistant Stainless Steel / Pitting corrosion resistance

This figure shows that YST130N has far superior corrosion resistance in comparison with JIS stainless steel.

Test piece after test
YST130N
YST130N
SUS329J1
SUS329J1
SUS316
SUS316

Crevice corrosion resistance

(1)

Field test with actual liquid (Seawater + hypochlorous acid (90-100ppm))

Test period: approx. 1 year and 9 months



Seawater Resistant Stainless Steel / Crevice corrosion resistance

Seawater Resistant Stainless Steel


Test piece after test
YST130N
YST130N
SUS316
SUS316


(2)

Field test of seawater intake pump

Operating period: approx. 5 years

 
YST130N
(YOKOTA duplex
stainless steel)
SCS14
(JIS austenite
stainless steel)
Suction flange
Seawater Resistant Stainless Steel / Field test of seawater intake pump
SCS14
Suction cover
Seawater Resistant Stainless Steel / Field test of seawater intake pump
SCS14


Corrosion resistance to liquids other than seawater

In addition to seawater, YST130N has excellent corrosion resistance to a wide range of corrosive liquids including hot springs water, corrosive hydrothermal liquids, chemicals and others.
The high corrosion resistance of YST130N has been proven consistently in a number of comparative corrosion resistance tests, detailed below, carried out throughout Japan.
Even when compared with materials such as Hastelloy C equivalents, currently the most corrosive resistant material known, YST130N proves to be equally efficient. Moreover, because it is comparatively more economic, YST130N has gained a widespread reputation for excellent cost performance.


Field test with actual liquids: Kusastsu Hot Springs


At the Kusastsu Hot Springs in Gunma Prefecture, well known for its acidic hot springs that contain hydrogen sulfide, pumps made of normal materials quickly become corroded.
Under these conditions, a comparative corrosion resistance test using various materials and a operational test of a pump made from YST130N were performed.

Kusatsu Hot Springs - Spring water composition

Water temp.

94.2 deg C

PH

l.7

Spring water composition

Acid chlorides, sulfates

Main elements
(mg/kg)

Positive ions

Sodium ions

149

Magnesium ions

57.9

Calcium ions

93.2

Negative ions

Chloride ions

901

Sulfate ions

826

Dissolved gas

Free hydrogen sulfide

0.3


(1) Test pieces immersed in hot springs reservoir (Test period: May 26 to Dec. 2, 1999)

Test conditions
Test results: Amount of damage due to corrosion

Seawater Resistant Stainless Steel / Test conditions
Seawater Resistant Stainless Steel / Test results
By comparing the corrosion rates of the different materials, it is clear that YST130N proves to have the highest level of corrosion resistance.

(2) Pump operation test: Hot springs pump room (Operating period: Mar. 6 to Sept. 6, 2000)

Test pump

Test pump external view

Type

YOKOTA Centrifugal Pump UEN-0420

Specs.

6m3/h x 55m x 3000rpm x 5.5kW

Material

YST130N

Shaft seal

Gland packing

Operation time

4,416 hours (Mar. 6 to Sept. 6, 2000)

Seawater Resistant Stainless Steel / Test pump external view

Inspection of opened test pump after operating period

Casing
Suction cover
Seawater Resistant Stainless Steel / Inspection of opened test pump
Seawater Resistant Stainless Steel / Inspection of opened test pump
Impeller front view
Impeller rear view
Seawater Resistant Stainless Steel / Inspection of opened test pump
Seawater Resistant Stainless Steel / Inspection of opened test pump

As seen in the photos, the pump constructed using YST130N exhibits no signs of corrosion, clearly demonstrating its perfect suitability for hot springs use.


Pump operation test: Kaike Hot Springs


At the Kaike Hot Springs in Tottori Prefecture, well known for its salt springs, pumps made of normal materials will quickly become corroded.
Under these conditions, a pump constructed using YST130N has been operating normally for a period of over ten years without signs of corrosion, proving once again, the perfect suitability of this material for use at these hot springs also.

Kaike Hot Springs - Spring water composition

Pump operation results

Water temp.

79.8 deg C

Spring water composition

Sodium and calcium chlorides

Main elements
(mg/kg)

Positive ions

Sodium ions

2156

Magnesium ions

40

Calcium ions

1658

Negative ions

Chloride ions

5846

Sulfate ions

669.8


Pump type

YOKOTA Self-Priming Centrifugal Pump UHN

Bore

40-100mm

Material

YST130N

Shaft seal

Gland packing

Pumps in operation

34 pumps (First put into operation in 1980)

Operation results

Over 10 years of operation with no corrosion



Field test with actual liquids: Waste incineration plant toxic gas removal unit


A "toxic gas removal unit" that sprays caustic soda (NaOH) on toxic gases to collect the toxic components is one example of devices used to remove toxic gases (such as hydrogen chloride, sulfur oxide, and nitrogen oxide) generated during waste incineration. The interior of this type of unit presents an especially harsh environment where corrosion easily occurs.
In order to compare their relative corrosion resistance, test pieces of various materials were suspended inside this type of unit and positioned so that they would be exposed to both the caustic soda sprayed from the nozzle and the gases that pass through the unit.

Test specs.

Test location

H City Environmental Affairs Bureau A Plant

Test equipment

Waste incineration toxic gas removal unit No. 2

Test conditions

Exhaust gas: 260 deg C, HCI, SO3
Liquid: 70 deg C, NaOH 8%, PH 7-8

Exposure time

9,288 hours (387 days)


Hanging test pieces
Test results: Amount of damage due to corrosion and wear

Seawater Resistant Stainless Steel / Hanging test pieces
Seawater Resistant Stainless Steel / Test results

The metallic surfaces of SCS10 and SUS316 are clouded due to corrosion.
However, the metallic sheen remains on YST130N and Hastelloy C equivalent material, proving their suitability for this type of equipment.
The performance of YST130N is especially outstanding.
The fact that the amount of wear includes that from the test pieces rubbing against each other gives further proof of YST130N's extremely strong durability.


Field test with actual liquids: Human-waste treatment plant deodorization unit (alkali cleaning tower)


One example of a deodorization system to remove the noxious fumes created when treating human waste consists of gas being passed through an acid-cleaning tower, an alkali-cleaning tower, and then an active carbon-absorption process tower. Within this system, the interior of the alkali-cleaning tower, which utilizes sodium hypochlorite (NaClO), presents an especially harsh environment where corrosion easily occurs.
Test pieces of various materials were placed inside of an alkali-cleaning tower to compare their relative corrosion resistance.

Test specs.

Test results: Amount of damage due to corrosion

Test location

H City Environmental Affairs Bureau D Treatment Plant

Test equipment

Human-waste treatment plant deodorization unit - Alkali cleaning tower

Test conditions

Liquid: 20 deg C, NaClO 12% + NaOH 25%, PH 8-9

Exposure time

6,660 hours (278 days)

Seawater Resistant Stainless Steel / Test results

The metallic surfaces of SUS316 are clouded and streaks of pitting have developed due to corrosion.
However, the metallic sheen remains on YST130N and Hastelloy C equivalent material, proving their suitability for this type of equipment.
The performance of YST130N is especially outstanding.

The above tests prove conclusively that YOKOTA's duplex stainless steel material, YST130N, has excellent corrosion resistance to, of course, seawater, but also hot springs water, corrosive hydrothermal liquids, chemical liquids, and corrosive gases.


Note 2:
Metallographic structure

Duplex stainless steel is a stainless steel that is composed of two types of compounds, austenite (white part) and ferrite (gray part).

Seawater Resistant Stainless Steel / Metallographic structure


For details on items such as chemical composition, mechanical properties, corrosion and wear resistance data, please refer to this page.


Supply record

Aquariums (

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"Current Topics: Aquarium" )

Central Fisheries Research Center (Ministry of Agriculture, Forestry and Fisheries of Japan), Fisheries research institutes

Fish farms, Fish markets (

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"Current Topics: Seawater Intake" )

Food processing plants, Salt manufacturing plants

Seawater desalination plants

Undersea tunnels (

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"Current Topics: Undersea Tunnel" )

Chemical plants (

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"Current Topics: Seawater Intake" )

Iron and steel works (

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"Current Topics: Steel Works" )

Atomic/thermal/geothermal power plants (

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"Current Topics: Slurry Self-Priming" )

Sewage treatment plants (

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"Current Topics: Sewage Treatment" )

Hot spring facilities

other



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