When you are thinking about buying a new water storage tank, there are several things you must consider. The important considerations for most people buying a storage tank are cost, location and size. However, another important thing that most people fail to consider when buying a water tank is the material used in its construction.

Water storage tanks are available in wide variety of materials including polyethylene, steel and concrete. Each has its own advantages. However, stainless steel water tanks are considered better than most other water storage tanks. Why?

Corrosion Protection

Stainless steel offers greater durability than concrete, plastic or carbon steel. This strong material resists oxidation by biocides and water, which is an extremely beneficial feature for businesses that need to store water in the tank or any other corrosive material. Moreover, exterior or internal coating isn’t required for these tanks.

Longevity and Durability

Stainless steel water tanks offer greater resistance to crevice corrosion, cavitation, and wear and tear in pure and contaminated waters. This material is also heat resistant and doesn’t get affected when exposed to harmful radiations. Moreover, stainless steel tanks are less likely to crack, rust or freeze.

Hygienic

Concrete water storage tanks are used by some people because they are less expensive than stainless steel storage tanks. However, what many users don’t realize is that concrete water storage tanks are unhygienic. They are highly susceptible to mold and bacterial growth as well as chemical leaking. Since concrete tanks are porous, they leach calcium that contaminates water.

On the other hand, stainless steel water storage tanks are hygienic. Due to the high passive-firm stability of stainless steel, this material is inert in water.

Recyclable

Water storage tanks manufactured using stainless steel are environment friendly. The advancements in the stainless steel production in the past many years have focused on the use of natural resources and energy. The majority of stainless steel storage tanks available now contain 60 to 70 percent recycled materials which makes them recyclable.

Mobility

We have seen that many concrete water storage tanks are installed in one place and they remain in their fixed spot until they are replaced. However, this isn’t suitable for everyone. A company may need to change the location of a water tank. It’ll be almost impossible to move a fixed concrete water storage tanks. Companies who use stainless steel water storage tanks can easily move their tank to another location with a forklift. This eliminates the efforts and stress associated with moving a tank.

Aesthetic Value

Storage tanks made using plastic or concrete aren’t appealing to the eye. They look dull after only a few years of use. In most cases stainless steel water storage tanks look like new even after years of service. Moreover, they can be painted to match the surroundings.
As you can see there are several advantages of stainless steel water storage tanks that make them better than other types of storage tanks. If you are taken over by the benefits of stainless steel water storage tanks and want to buy one, contact Buckeye Fabricating.

Selection of stainless steels for water tank applications

Introduction

Stainless steel grades, such as the 304 or 316 types are generally suitable for storing and handling cold or unheated drinking, (town’s), waters.
Localised corrosion by crevice or pitting mechanisms is not usually a hazard in properly designed, fabricated and finished tanks handling clean waters of drinking quality.

Hot water tanks however may be at risk from stress corrosion cracking, (SCC)

Stress corrosion cracking (SCC) risk factors

The factors that influence SCC attack are: –

• temperature
• chlorides
• tensile stresses
• oxygen level

For these types of applications chlorides and oxygen levels are fixed by the water chemistry, but chlorides can concentrate in splash zones or at the water /air line by evaporation. This can also be a hazard if external insulation to tanks becomes wet.
Temperatures should be fixed by the tank system controls, but hot spots can be a problem, especially if chlorides concentrate, as described.

A design and fabrication method with as few ‘engineering crevices’ as possible is advisable, as this reduces the risk of stress concentrations, and also guards against crevice corrosion attack.
Fully filled welded joints are preferable to seams with laps or mechanically fastened joints.

Controlling residual stresses

The main design and fabrication factor that can be ‘controllable’ is stress. Residual tensile stresses can be a cause of SCC failure.
Relief of these stresses can be advisable where high levels of residual stresses are possible or the application is critical.

A range of treatments for the 304 and 316 type austenitics can be considered: –

• ‘sub-critical’ stress relief treatment, e.g. 450°C and slow cool
• ‘full-anneal’ e.g. 1050-1100°C and ‘quick’ cool, (air)

stress relieving austenitic stainless steels

The restraining effect around welds on austenitic stainless steels such as 304 or 316 types can also be a source of tensile stresses. If it is impractical to post fabricate heat treat, then control of welding parameters may help.
These would include: –

• Careful pre-weld tacking
• Minimising heat input during welding by controlling welding speed

Alternatives to the austenitic stainless steels to reduce the risk of SCC failure

Alternatives to the austenitics, which have nickel levels making them particularly susceptible to SCC are either: –

• Ferritic stainless steels
• Duplex stainless steels

These types have lower nickel levels and so are more resistant to SCC as a result of the ferrite phase present. (Higher nickel level alloys are also more resistant to SCC, but are not considered economically justifiable for these applications.)

The ferritic grade 444, (1.4521), and particularly the lean duplex grades 1.4162 and 1.4362  are routinely used as SCC resistant grades for hot water tank applications.

Forming and welding differences from the austenitics must also be borne in mind when making the steel selection.

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