Wednesday, June 10, 2015

Corrosion-resistant material for Sulfuric acid

Ceramic internal of an absorbing tower, Chiba, Japan

At the beginning : 

Sulfuric acid facilities, is the fight against every day is corrosion and oxidation.
When you mistake the selection of material, it can not write leads to all stop of injury or equipment. Maximum attention is required.

Optimum recommended material at the current time of each device, " new facilities "and" equipment update in ", please refer Because it is stated for each device.

That want to keep in first remember corrosion by sulfuric acid,

For the metal material:

1. Corrosion by sulfuric acid, significantly different concentrations, temperature, dissolved components. 

In the metal material, generally, "the amount of corrosion temperature increases 10 ℃ is two-fold," It is said that. Since this is said to metal corrosion = chemical reaction of sulfuric acid and the metal, because the reaction rate is increased due to the rise of temperature.

There are no related at all relationship of concentration and the amount of corrosion. High concentration of sulfuric acid, it can not be said always to have strong corrosive.

Although strong lead = dilute sulfuric acid which are corroded rapidly to but no problem in practical use dilute sulfuric acid in carbon steel = room temperature in concentrated sulfuric acid resulting in soluble in concentrated sulfuric acid

In addition, it also varies in the dissolved components.
Sulfuric acid of sulfur combustion type, you may even those close to the dissolved impurities less purified sulfuric acid, but it is not said to be a "good because few impurities".
I, luxury nickel alloy circulating acid pump impeller, "even though not anything in the refining gas sulfuric acid plant, is severely corroded by sulfur burning sulfuric acid plant" was the experience of. That this is, during the refining gas is a very small amount, but that metals such as Cu, etc. have been dissolved NO2, these raw materials are beautiful too far sulfur to make a non-conductive coating, it could not be non-conductive coating but it has been estimated to cause.

So, "Examples of self-factory" will be greatly helpful, but "Examples of other plants" must not be to blindly reference.
If consult, let's strictly compared with the conditions of the factory conditions and their own factory.                                                                                                                                                                  

2. Note the turbulence. 

In particular, in the piping, you may site = elbow caused the flow of turbulence, cheese, corrosion downstream such as = valve seen violently. Especially often seen in stainless steel, these sites when a concern you should keep exchanged like Teflon lined.                                                                                                                                                                       
3. Note that even material itself is changing.

With the advancement of technology, the material itself is improved in the constant component is changing subtly. Once upon a time was not a problem material also might cause problems now.

We do not talk about details because belonging to the know-how, when you update the process equipment using a stainless steel alloy, even though such should have been using the material "the same as the original", severe corrosion accident occurred.
When you try to study, has become very small compared to the original C (carbon) content of the new material, this was the cause of the corrosion.
JIS provisions of the C content of stainless steel, because there is only an upper limit, manufacturers I had been reduced more and more To the amount of C is, the "improvement for the service."

So, it is really "the same as the old days" thing of? And you do not have to change? Let's leave well to check the material manufacturer.                                                                                               

          Inorganic materials (ceramics, glass, etc.) and organic synthetic resin:
These materials, when compared to metals, it is insensitive to changes in the concentration of sulfuric acid and temperature. If there is corrosion resistance in concentrated sulfuric acid, most things no problem even in dilute sulfuric acid.
However, for fuming sulfuric acid, Teflon and carbon it is not recommended.
For more details, it said in particulars.                                                                                         

References :

For documentation that summarizes the various corrosion-resistant material with sulfuric acid, it has settled well is old "sulfuric acid Handbook" is the best. (But it is out of print)
Other, there is also a book called "chemical equipment corrosion-resistant material table", which summarizes the corrosion-resistant material for various chemicals in addition to sulfuric acid. (This also has become out of print)

At present, materials such as corrosion curve of metal, probably most of the fastest way is to get the technical documentation is offered to manufacturers.
(Without permission, it had to publish anti-corrosion data to the net every manufacturers such as Mitsubishi Materials and Japan metallurgy, but no longer now. The reason is unknown.) * After this, we will continue to write the corrosion resistance and applications for each material.

Metal material:
"Metal material is corrosion with any time to varying degrees."

This also is true that I would like you to remember. It will not be long-lasting equipment to understand the "difference of degree."  

Carbon steel :

SS Toka SGP in JIS, is a material that is expressed, such as the STPG.
The least expensive as the metal material, will that easy to come by.

Is this,

1) concentrated sulfuric acid 2) Same as above oleum 3 at room temperature (room temperature)) molten sulfur

There is practically sufficient corrosion resistance.
However, since the corrosion of certain parts of the flow will be greater than the stationary state, the use of the pipe is avoided, it should be used in the product storage tank.
(Room temperature of the piping SUS304 or 316, would be sure Teflon lining in high temperature of piping)

Other, but it has been used for the following sites, in the case of new construction and remodeling Let's say right.
(If economically afford)

A) converter around duct → converter is the first layer outlet duct SUS304
B) gas heat exchanger → tube and channel cover SUS304
C) combustion furnace and towers of the casing → SUS304
D) sulfur tank → ceiling SUS304
                                                                                                                                   Stainless steel : 

There are very many kinds, but I will in time in roughly SUS304 and 316 for sulfuric acid.

This of most applications

1) at room temperature of concentrated sulfuric acid, piping fuming sulfuric acid, pump, valve 2) converter around gas butterfly valve                                                                                              3) molten sulfur valve It is. Other, there is also above A) ~ D) applications.

In addition 4) drying tower, absorption tower circulation acid piping

There is also in that factory used to, but since there is also a case that caused the trouble by being violently corrosion, as long as there is no past performance at the factory, is not recommended. Generally speaking, it is to have good when the low acid temperature.
Stainless steel, the temperature of the acid, the amount of impurities, the flow rate, can vary greatly, such as in the corrosion behavior presence or absence of flow of turbulence. In addition, it is also affected by the carbon content of the stainless steel itself. Performance of a factory, also necessarily fact that does not apply to other plants, it is a place well hear.

It is a special purpose, but the heat-resistant stainless steel such as SUS310S will be used in the boiler bypass gas valve in the sulfur burning.

High nickel alloys : 

There are a wide variety of alloys for each manufacturer, but what is often used in sulfuric acid

1) Hastelloy-C group 2) Carpenter-20 (Alloy20)
3) pump manufacturer that has developed (such as Pilomet)

Below, we'll explain.

1) Hastelloy-C group

It is developed corrosion-resistant alloy of the United States Haynes International Inc.. Although initially it was Tadano "C",
Then various kinds have been developed.

The is often used in concentrated sulfuric acid C276
It is two.
(In Haynes's home page is located that there is a corrosion resistance to "B3" because sulfuric acid, but this is the original as for anti-HCl)
Ni 57, Cr 14.5-16.5, Mo 15.0-17.0, W 3-4.5, Fe 4.0-7.0, Co≤2.5, Si≤0.08, Mn≤1.0, C≤0.01, V≤0.35

It is widely used in the plate cooler for the tower circulation acid.
According to our catalog Haynes "by preventing particle deposition in the weld heating section, and has a high degree of corrosion resistance without treatment after welding" "and localized corrosion, and there is an oxidizing, resistant to reducing substances." → Haynes catalog C276 → corrosion curve of C276

Just "metal material is corrosion with any time to varying degrees," he said. C276 is no exception. In the plate cooler, the entrance of San is corrosion most early (because the temperature is the highest).
Therefore, after you have used a few years, you need to check is opened. 

Also this time, also help to extend the life of the entire cooler to the entrance and exit of the acid in reverse. → " maintenance "," acid cooler "                                                                                  
Ni 56, Cr 22, Mo 13, W 35, Fe 3, Co≤2.5, Si≤0.08, Mn≤0.50, C≤0.010, V≤0.35

This also seems to be used to the plate cooler.
In the catalogs of Haynes, "especially" C276 has excellent corrosion resistance than "pitting, crevice corrosion, you have stated that there is strong resistance to stress corrosion cracking", concentration for sulfuric acid in the same catalog - temperature - corrosion amount Look at the graph and, but should not be seen as there is much difference in the 98% H2SO4. →  

2)Carpenter-20 (Alloy 20)

It has been developed by the United States Carpenter Technologies Corp., component Ni 34, Cr 20, Mo 2.5, Cu3.5, Fe balance, Nb≤1 (≥C * 8), Si≤1, Mn≤2, C≤ 0.06

Hastelloy-C22 as well as has been touted as "pitting, crevice corrosion, resistant to stress corrosion cracking" but it seems to the extent that is now being used in wire mesh demister of the tower exit.                                                                                                                                            

3) pump manufacturer that has developed (such as Pilomet) 
Ltd. Matsuda pump Works of Pilomet, such as Lewmet of rice Lewis is something that has been developed as a material for sulfuric acid pump.
However, even these, you must be careful because you may be subject to corrosion by the "impurities" of temperature, other than the sulfate concentration.

Tantalum : 

Tantalum, 100 ℃ almost completely in the following concentrated sulfuric acid (corrosion weight = 0) is shown a corrosion resistance, shows no practical problem corrosion resistance at 200 ℃ or less.
However, for very expensive, it has been used parts that are used special a small amount, for example, the diaphragm of the diaphragm type pressure liquid to a sulfuric acid plant.

Also by heating concentrated dilute sulfuric acid is used as a lining material in concentrated cans in equipment for the production of concentrated sulfuric acid.

However, the fuming sulfuric acid it must be careful because it is corrosion even at low temperatures. 

 Cast iron :
Selfish, cast iron had been widely used as piping material and material of acid pump for concentrated sulfuric acid.
(Fuming sulfuric acid, next to SiO2 is silicon content in the cast iron oxidation, this can not be used because that would divide the material itself swells)
The low temperature of concentrated sulfuric acid at a low cost and has in its own way, but in cast iron distinctive of "su" problem, one day you suddenly or cause a sulfuric acid leak accident.
Production of cast iron, so typical 3K is the work, has been migrated production from early to subcontract overseas, seems to have become the maintenance of quality it is also difficult.

As for the concentrated sulfuric acid, and high-silicon cast iron containing around 15% Si, there was a low chromium cast iron containing 1% less than the Cr, almost all stainless steels and high nickel alloys currently are alternative such as Teflon lining You.
High silicon cast iron, seems to the electrode of current even electrolysis equipment being used. 

Lead : 
Lead is also a material that has been widely used in the nitric acid-type era sulfuric acid.
The dilute sulfuric acid there is corrosion resistance, but it can not be used because it soluble in concentrated sulfuric acid.

Even in contact sulfuric acid, although in dilute sulfuric acid portion of gas purification equipment other than sulfur raw materials (such as the casing of mist Cottrell) was used, this was also replaced by the FRP and other organic material. Again and price, it seems that is a problem that the weight is increased.

By decreased demand, craftsman itself to work also declined. Lead, because there is a use as a shielding material of nuclear power plants in other than sulfuric acid plant, there in is like Some craftsman in its own way, under the influence of this accident, I will also decrease.

It had been also hard lead with increased hardness by the addition of 3-12% of antimony in the lead used in such dispersion tube of pump and cooling tower, which was also no longer mostly seen now.
Lead, the hardness lead both, it is now replaced by the plastics and ceramics such as Teflon and PP.  

Other metals:
In other metals, gold, platinum is about to have a sufficient corrosion resistance to concentrated sulfuric acid.
Platinum, seems to have been used as a spray of dilute sulfuric acid in the nitric acid-type equipment such as lead room selfishness. (It is sometimes so stolen)
Other metals, it can safely keep in stores almost all the "unavailable" for the concentrated sulfuric acid.
For the dilute sulfuric acid, titanium, zirconium seems there is also some of the corrosion resistance, etc., but does not have expensive late almost used.

Inorganic materials : 

Acid porcelain :
Acid porcelain, lining material and sites that is in direct contact with the sulfuric acid, such as towers and pump tank as brick, has been used to tower packings such as interface Rochus saddle.
The component basis, is what good be considered the same as porcelain for tableware (such as Arita). Come to think of it, is a leading manufacturer of acid porcelain Iwaojikikogyo Co., Ltd. is located in Arita. Originally, it seems to be a ceramics manufacturers such as tableware.
Concentrated sulfuric acid, there is a nearly complete corrosion resistance in dilute sulfuric acid. In my experience, acid brick that was used 50 Toshi-yo also, apparently no different at all new.
Recently, domestic to that of the quality of the clay has been reduced, it seems to have fallen somewhat from those quality-old. The color of the bricks, was a complete white things of long ago, those of recently has been tinged with pale reddish brown. I will be thought that due to the impurities.
Brick is possible semi-permanent use, but the joint material to be used during construction will be affected in the sulfuric acid. Around from the gap of the joint material in the back of the sulfuric acid is brick, the casing is damaged by corrosion of the carbon steel of the casing. To prevent this, in recent years it has been made to put a Teflon sheet between the bricks and the casing.
→ "equipment update," " drying tower, absorption tower "reference

As the standard of acid porcelain, following JIS, and Iwaojikikogyo Ltd. Please refer to the catalog.

JIS R1501 general General Rules of the chemical industry for the oxidation porcelain
JIS R1503 test methods for the chemical industry acid porcelain
JIS R1528 for the chemical industry acid porcelain fillings
JIS R1536 for the chemical industry acid heat-resistant bricks

The oxidation porcelain manufacturer, NGK Insulators, Ltd. is also available.

In addition, you heard that in recent years has been around also made in China acid brick, I have never used still.  

Glass :
Glass also, dilute sulfuric acid, there is a nearly complete corrosion resistance in both of concentrated sulfuric acid. (Especially in the case of hard glass = borosilicate glass)
However, since weak fragile to shock, it is rare to be used as such.
Those of the wall thickness is used for sight glass in the middle of the piping.

Also, heat-resistant glass which has improved thermal shock resistance by lowering the thermal expansion coefficient, is used for the absorption tower for purification of concentrated sulfuric acid production. This, Corning Pyrex is famous.
However, because it is expensive, recently it has been replaced by glass-lined below.

 Glass lining (GL):
Glass cast iron, by lining the inside of carbon steel or stainless steel, is what was to maintain the mechanical strength and corrosion resistance.
If the pipe is inserted into the metal pipe after heating the glass tube, to those brought into close contact by applying pressure from the inside, while others baked covered with a glaze vitreous inside of the metal tube.
Prepared by the course of the latter method in such a large container. This will things to be rather referred to as "enamel".

Concentrated sulfuric acid corrosion resistance, of course, since it helps to minimize pollution of sulfuric acid by the dissolution of the metal, which is used in the purification of concentrated sulfuric acid manufacturing equipment instead of quartz glass.

In the case of printing method, since it may rarely a pinhole, you must perform a sure pin hole test at the time of completion.
In addition, it said that the excellent mechanical strength, because there is a risk of peeling is give and blow lining glassy, ​​such blow is taboo.
And such as suddenly put the high temperature of the liquid, care must be taken because there is that glass is peeled off by thermal shock.

As those of similar applications, there is a Teflon lining, but more of the glass lining is excellent in heat resistance, it is used in higher temperature applications. It Would not it be okay to the boiling point.

For other chemicals sulfuric acid, weak alkali because it is glass, also violently it is affected because the phosphoric acid in the fluorine is difficult to use. It is also affected to a high temperature of steam.
Currently, for to alkali, so it seems there is also a special case, such as for a pair of steam please try to consult with the manufacturer.

As a manufacturer, there is a following.
Ltd. Kobelco Eco-Solutions
NGK Insulators Ltd.
Hakkosangyo Co., Ltd.
AGC Technology Solutions Co., Ltd. - insertable GL piping only Fire-stone :
This is a kind of pumice that lava was Deki solidified, those of Niijima production of Izu Islands have been conventionally used.
Lightly (specific gravity 1.2-1.4), because there are easy and acid resistance processing, it will be used in gas purification part in equipment other than sulfur combustion.
In applications other than sulfuric acid, since it also has excellent fire resistance, it is used as the acid lining material of the chimney. It is also used as a general of residential building materials.

As manufacturers and contractors, anti-fire stone Industry Co., Ltd., has Niijima Bussan Co., Ltd..

Organic material :

Teflon :

Originally with Teflon, it is that of PTFE that DuPont has developed in 1938.

PTFE = polytetrafluoroethylene (-CF2-CF2-) n

It has high chemical resistance, heat resistance, and is also has excellent properties such as low coefficient of friction, a part of the F in order to improve this because of the poor workability hydrogen, chlorine, other which was replaced by the olefin has been developed. Collectively, these are called "fluorine resin".

FEP = tetrafluoroethylene-hexafluoropropylene copolymer (-CF2-CF2-) n - (- CF2-C2F4-) m
ETFE = tetrafluoroethylene-ethylene copolymer (-CF2-CF2-) n - (- CH2-CH2-) m
PFA = tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (-CF2-CF2-) n - (- CF2-CF2OCF3-) m
PVDF = polyvinylidene fluoride (-CF2-CH2-) n

In DuPont, it will be referred to PTFE, PFA, FEP, the "Teflon", but other fluorine resin are wearing each different name, in Japan we practice called everyone "Teflon".

Although as a concentrated sulfuric acid and all organic materials in the best, without being corroded with time differences between the metal, without also contaminating the sulfuric acid by dissolution of the components, it is an ideal material.
However, other than PTFE and PFA has difficulty in heat resistance, and can not be used in oleum for transmitting the SO3.
As a lining material of many metal inner face, piping, it is used valve, such as a vessel.
As a lining material of the valve, NICHIAS Co., Ltd. is a PFA, Valqua Industries Co., Ltd. is I am using PTFE and PFA.
In addition, as a thin tube acid cooler it is used to.
When used as a gasket, the left but it will be used, flexible pinch cushioning material such as rubber in order to increase, also it has to not mix a filler of mineral in order to avoid cold flow.
Drying tower, absorption tower, and such as a pump tank for them, in towers and vessels lining the acid brick, the corrosion due to the fact that touch is across the sheet directly to the (seat lining) shell sulfuric acid between the brick and steel shell It has been made to prevent. However, Teflon because it does not adhere to brick in steel, you can paste it or use the process the surface or adhesive.

From the characteristic that it does not contaminate the product, purified sulfuric acid, has been often used for high-purity sulfuric acid.

The nature of the typical Teflon class I is shown below. 

Viton :

Viton is the same fluorine rubber DuPont has developed a Teflon.
Compared to teflon, flexible, on rich in elasticity, strong acids include concentrated sulfuric acid, withstand strong alkali, excellent heat resistance (~ 250 ℃), the nature of Teflon as oil resistance, excellent in solvent resistance It also features.
Structurally, the base is what is obtained by copolymerizing hexafluoropropylene in polyvinylidene fluoride.
(-CF2-CH2-) n - (- CF2-C2F4-) m
Currently, there are those obtained by copolymerizing other tetrafluoroethylene and perfluoroalkyl vinyl ether according to the application.

In the sulfuric acid plant, it is common as a gasket of concentrated sulfuric acid for the plate cooler.

FRP stands for Fiber Reinforced Plastics.
Because it is sometimes referred to as "fiber reinforced plastic", although it is considered that the combination of a wide variety, as being practical use,

Plastic = unsaturated polyester resins, epoxy resins, polyamides, polymethyl methacrylate fiber = glass fiber, carbon fiber, aramid fiber (Kevlar)

And so on.

Lighter than the metal, there also have strength and excellent corrosion resistance, but it will not be able to withstand it will be carbonized in concentrated sulfuric acid.
Only, it is intended to be used in an atmosphere of dilute sulfuric acid and wet SO2 gas. Washing tower, mist Cottrell of the casing, it will be used, such as the gas duct of the gas purification system.
Is it been put to practical use in sulfuric acid facilities,

Unsaturated polyester resin + glass fiber

It is a combination of.
There is a kind also in unsaturated polyester, isophthalic acid-based, bisphenol-based, there is a vinyl ester. 2 who has excellent corrosion resistance as compared to the isophthalic acid system later, it seems no problem in isophthalic acid system for the sulfuric acid plant.

If you want to use in gas purification system, in the conditions, including fluorine in the gas, because there is a danger that glass fiber is corroded, and synthetic resins such as PP as the fibers on the surface in contact with the gas, you can use the carbon fiber.

As a manufacturer, in the major
Showa Denko Co., Ltd.
Oriental Gas Kiko Co., Ltd.
Fuji Resin Industry Co., Ltd.
There is such, but since that can be anyone production if there is a resin and glass fiber, to say that small and medium-sized manufacturers is infinite number is not an exaggeration.

PVC (polyvinyl chloride):

It is one that is used in large quantities is referred to as a "PVC".
FRP Again, it can not be used will be carbonized in concentrated sulfuric acid. Is for the dilute sulfuric acid it is possible to use.
However, it is degraded by ultraviolet light, so easy to crack in the piping of the outdoors will require regular updates.

For reinforcement, which was inserted PVC in the carbon steel pipe (LP tube), while others that were plated FRP on the outside of the PVC pipe.

PVC, because it contains chlorine, from concern to generate dioxin when incinerated, seems to have been reduced use.

                                                                                                                                                              PE (polyethylene):

This also is what is used in large quantities as plastics.
There are HDPE and LDPE but, HDPE (high density polyethylene) made of tank and pipes are used in the sulfuric acid plant.
PE, although at high temperatures will be attacked by concentrated sulfuric acid, there is no problem in practical use at room temperature.
Therefore, the storage tank of purified sulfuric acid and, it has been used as a 20L plastic tank for the product sulfuric acid sales.
The polyethylene tank, Dairaito Ltd. is famous ones.

Those lining the PE to carbon steel piping, have been used to dilute sulfuric acid. Even for concentrated sulfuric acid, I think that it can be used as long as it is a low temperature. 

PP (polypropylene):

Also PP should say representative also of thermoplastic resin along with the PE, has been put to practical use as a piping material, it seems to have become the alternative of PVC pipe.
This is also used to dilute sulfuric acid is possible, concentrated sulfuric acid, it can not be especially used in high temperature.

Rubber :

Natural rubber even though the rubber, there are synthetic rubber various Although it is a wide variety, corrosion resistance is generally to sulfuric acid "It is attacked by concentrated sulfuric acid, withstand the dilute sulfuric acid."
It is. ( Viton I except = fluorine rubber)
Therefore, it is hardly used for the sulfuric acid plant of sulfur raw materials, and are used in gas purification equipment by other raw materials. Majority is used as a lining material of carbon steel.  

Carbon :

It is referred to as "carbon", but one that is improved is by impregnating synthetic resin in the synthetic graphite strength and air-tightness those used in the sulfuric acid plant, properly to be referred to as "impervious graphite" It is.
Phenol resin is common as a resin, but some impregnated with Teflon.

Heat transfer is very good, the dilute sulfuric acid there is a sufficient corrosion resistance, but it is attacked violently by generating CO2 in hot concentrated sulfuric acid. Therefore,
1) cooler 2 of sulfuric acid dilution equipment) and is used to dilute sulfuric acid cooler and gas cooler of gas purification equipment.

It used if concentrated sulfuric acid of 90 ℃ about the absorption tower outlet but should of possible, increased concentration of product sulfuric acid is abnormally in tourists operation mistake when it was used as a selfish product acid cooler, Become a fuming sulfuric acid Have closed, this time there was an accident that the entire cooler melts. Since there is such a thing, it is not recommended to concentrated sulfuric acid cooler.

As the heat exchanger for the sulfuric acid plant, it is often for shell / tube type that is easy to clean the scale, but as the heat exchanger will have this also in addition to the block type or plate type.

As a manufacturer, therefore expensive electricity rates, which account for large proportion of the cost, Japan independent manufacturers no longer. Both currently is a joint venture with overseas manufacturers.

Nippon Carbon Melthene (Ltd.) = Japan (Nippon Carbon) + France (Melthene)
Graphite Chemical Co., Ltd. = Japan (Tokai Carbon) + US (SGL)

And so on.

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