Welded vs Bolted Tanks: A Complex Choice?

08 Jul.,2024

 

Welded vs Bolted Tanks: A Complex Choice?

In the world of industrial storage, choosing between welded and bolted tanks can be complicated. Both options have their own benefits and drawbacks. The decision often depends on the specific needs of your industry and the type of materials you&#;re storing.

Are you interested in learning more about bolted storage tanks? Contact us today to secure an expert consultation!

In this article, we&#;ll discuss some important factors to consider when deciding which option is best for your project. We warmly invite and value input from others in this industry to comment on this article, as your insights can also aid others in their decision-making process.

Welded Tanks

Welded tanks are typically made of less material than bolted tanks, making them cheaper from a material standpoint. However, assembling a large welded tank is more time-consuming and also requires on-site welding and radiography, which necessitates thorough planning and execution. Therefore, if the cost of assembly (welding) labor is factored in, a welded tank tends to be a more expensive option. In cases where the end-client performs the assembly without considering the labor costs, it may still be the preferred solution. Additionally, the integrity and sealing behavior of a welded tank are superior to those of bolted tanks. Moreover, tank design codes such as API650 and EN have a proven safety record when all specifications are followed.

Bolted Tanks

Bolted tanks, on the other hand, come in different types, each with its own set of advantages and disadvantages. A bolted tank allows for modular sections to be bolted together on-site, enabling significantly smaller and less skilled installation crews to complete the installation in a shorter duration with precise alignment and a perfect fit. An additional benefit is the ability to relocate the tank. Therefore, bolted tanks are an attractive choice for many industries. Some companies claim that the total project savings when opting for a bolted tank instead of a welded tank are around 30%.

Two types of bolted tanks are typically used in the industry: the flange type and the overlapped type.

Bolted Flange Tanks

Bolted flange tanks offer the following key advantages:

  1. External Bolts: The bolts are located on the outside, eliminating the need for internal protection against conditions such as corrosion and hydrogen embrittlement.
  2. Efficient Installation: The installation process is sped up by requiring fewer but larger bolts.
  3. Inspection Ease: The external location of the bolts allows for easy inspection during operation.
  4. Rigidity: The flange adds rigidity to the shell panel, simplifying its handling.
  5. Tolerance in Fabrication: Misalignment in bolt holes can be easily rectified by reaming. If necessary, the flange can be cut and rewelded, whereas an entire panel would need to be discarded in the case of overlapped types.

However, bolted flange tanks also have their drawbacks:

  1. Prying Action: This can increase the risk of bolt failure if the pre-tension is too close to the yield strength of the bolt.
  2. Panel Deformation: Welding a large flange to a thin shell can cause panel deformation, especially in stainless steel.
  3. Joint Separation: The prying action of the joint can cause separation under hydrostatic liquid load, affecting the sealing behaviour of the joint. Therefore, it is advisable to perform Finite Element Analysis (FEA) on the joint to simulate and verify the prying action. In some tanks with dangerous or toxic content, a small seal weld is sometimes used to ensure a leak-tight joint.

Lapped Type Bolted Tanks

Lapped type bolted tanks are another variant of bolted tanks that come with their own set of pros and cons.

Advantages of Lapped Type Bolted Tanks

  1. Less Material: Lapped joints tanks use less material than flanged type.
  2. Sealing: If fabrication tolerances are good the sealing of the joint is better than the flange type that is prone to prying action.

Disadvantages of Lapped Type Bolted Tanks

  1. Fabrication Tolerance: Lapped joints, if not 100% accurate, can cause major problems for aligning the bolts during assembly.
  2. Sealing: Some tank fabricators prefer using bladders instead of gasket types in overlapped bolted tanks. This is because they struggle to achieve a 100% seal using gaskets and therefore prefer the bladder on the inside.
  3. Thin Wall Tanks: The AWWA Code allows one to use a very thin wall from a hydrostatic point of view. However, it is very difficult to work with these thin plates, and they tend to buckle at the connection points to the jacking system used.

Several design codes and standards are available that specify the design and construction of bolted tanks. The most common codes used in the industry are API 12B and AWWA D103. However, a limitation of these standards is that they do not cover flange-type connections; they only cover overlapped panel connections. Therefore, Finite Element Analysis is an important tool to obtain the stresses in the flange and bolts and to determine the deformation at the joint, which is crucial for the sealing of the joint.

In conclusion, the choice between welded and bolted tanks, and among different types of bolted tanks, depends on a variety of factors, including the specific requirements of the industry, the nature of the materials stored, and the experience and preferences of the fabricators and end clients. 

What is your preferred choice? Bolted or welded? What problems do you experience in practice with these tanks, and what other considerations should be taken into account?

Glass Fused to Steel Tanks Pros and Cons

Glass Fused to Steel Tanks is the most common tank specification for CSTR biogas digester reactor tanks. In this article, we discuss their pros and cons.

 

Enamel tanks, GFS tanks (GFtS), and Glass Fused Bolted Steel (Porcelain Enameled) tanks are all terms used to describe this type of tank.

 

It is essential that all anaerobic digestion tanks must be extremely durable, which means they must be resistant to corrosion as well as impact and abrasion. These tanks have that characteristic but as in most things, their advantages come with a few disadvantages. Read on and find out what those pros and cons really are.

 

Advantages of Glass Coating in Steel Technology

 

Undoubtedly, the apex of coating technology in the storage tank industry lies in glass-fused-to-steel technology. These tanks find extensive application in various sectors including bio-energy (especially CSTR biogas plants), municipal sewage, landfill leachate, and industrial wastewater treatment.

 

How Challenging is it to Select the Right Tank Material?

 

Selecting a liquid storage tank might seem straightforward. After all, it's a vessel for holding liquids. Is there truly a substantial difference?

 

The reality is that each type of tank boasts its own set of advantages and disadvantages. The key to choosing the optimal product lies in evaluating these pros and cons against your specific requirements.

 

Tanks Made of Glass Fused to Steel

 

Glass-fused steel, also known as enameled steel, represents an advanced technology offering long-term performance with minimal maintenance requirements.

 

These tanks stand out as the preferred material for biogas digesters due to their fusion of steel toughness with the corrosion resistance of glass. Moreover, they serve as excellent choices for storing potable water, wastewater, industrial chemicals, bio-digesters, sludge, and various dry bulk materials.

 

In a cutting-edge furnace, enamel frit (glass compounds) undergoes chemical fusion with steel sheets at exceptionally high temperatures (ranging between 800 and 1,000 degrees Celsius). This process generates an integrated, porcelain-like coating that is firmly bonded, chemically inert, and impermeable to liquids.

 

Suppliers tout these tanks as capable of withstanding a range of conditions, such as temperatures up to 140°F and pH levels between 3 and 11, without succumbing to corrosion.

 

 

Advantages of Glass-Fused-to-Steel Tanks

 

Glass fused to steel liquid tanks combines the strength of steel with the exceptional corrosion resistance of glass, offering numerous advantages over traditional epoxy-coated or welded painted storage tanks, including:

 

1. Outstanding anti-corrosion properties.

2. Swift installation in the factory, coupled with high-quality design, production, and stringent quality control.

The company is the world’s best direct water tanks supplier. We are your one-stop shop for all needs. Our staff are highly-specialized and will help you find the product you need.

3. Safety and simplicity: Operators require minimal long-term training, and plant owners benefit from reduced maintenance, leading to less time spent by workers in elevated positions.

4. Minimal impact from local weather conditions on these tanks.

5. Low initial investment, especially pertinent for biogas digesters and industrial wastewater treatment projects.

6. Cost-effective maintenance and ease of repair.

7. Reduced life-cycle costs due to the enduring coating.

8. Flexibility for relocation, expansion, and repurposing.

9. Aesthetic appeal with various color options.

10. Simplified cleaning compared to unlined equipment.

11. Customization for specific applications with tailored tank designs.

 

Even stainless steel tanks, while normally an ideal material for these tanks, cannot withstand the high sulphur which may accumulate at the top rim of commercial digester tanks.

 

Disadvantages of Glass-Fused-to-Steel Tanks

 

While Glass Fused To Steel Tanks offer numerous benefits, it's important to acknowledge some drawbacks that, although not extensive, are noteworthy:

 

1. Joint sealing is crucial at the points where the tank is bolted to the concrete base slab to prevent potential leaks.

2. Physical damage, like impacts from moving equipment or machinery, can lead to chipping of the glass coating at the impact site.

3. Concrete-based biogas tanks in Anaerobic Digestion Plants provide superior insulation compared to steel tanks, thereby avoiding the need for additional thermal insulation and associated costs.

4. When considering burial or partial burial, steel tanks might be less suited to withstand soil loads compared to reinforced concrete tanks.

5. Ensure that the purchased Glass Fused To Steel tank includes edge corrosion protection, as untreated panel edges may pose long-term issues in bolted steel tanks.

 

Nevertheless, implementing excellent design, installation, and operational practices can prevent or mitigate these aforementioned issues effectively.

In moderate climates, digester tanks are typically insulated and enveloped with plastic-coated aluminum profile sheeting along their outer edges.

 

This practice serves the purpose of safeguarding the installed insulation and provides additional protection to the tanks, shielding them from accidental impact damage to the fused-to-glass enamel during their operational use.

 

The Primary Drawback of GFS Tanks: Initial Cost

 

While the benefits of GFS tanks are substantial, their most notable disadvantage is often the initial expense. Glass-lined tanks tend to be considerably pricier compared to epoxy tanks.

 

Consequently, some businesses might initially perceive these upfront costs as prohibitive. However, it's crucial to examine the total cost of ownership throughout the tank's lifespan, considering reduced maintenance expenses and longer-lasting durability offered by GFS tanks, which can result in less frequent replacements.

 

Quality Assurance and Standards for Glass-Fused-To-Steel Bolted Tanks

 

Engineers and industry experts worldwide are increasingly selecting glass-fused-to-steel tanks for their resilience in challenging conditions, ensuring decades of trouble-free operation. However, tanks employing this unique technology require strict adherence to quality standards, notably ISO certification, to ensure superior manufacturing and defect-free performance.

 

Well-manufactured porcelain-enameled tanks boast a lasting coating that eliminates the need for recoating.

 

Among various substrates for glass coating like steel, aluminum, cast iron, copper, and brass, steel is commonly used in porcelain-enameled tanks, chosen based on size requirements&#;larger tanks often necessitate a more durable steel grade.

 

Delivering Quality Glass-Fused-to-Steel Tanks

 

It's imperative to procure tanks only from manufacturers holding ISO certification, indicating adherence to over 16 standard inspections before sale approval. Glass Fused to Steel tanks prove highly advantageous for containing potable, municipal, agricultural, and industrial fluids due to their minimal maintenance needs and inherent resistance to contamination.

 

Welded vs Bolted Tanks: A Complex Choice?

In the world of industrial storage, choosing between welded and bolted tanks can be complicated. Both options have their own benefits and drawbacks. The decision often depends on the specific needs of your industry and the type of materials you&#;re storing.

In this article, we&#;ll discuss some important factors to consider when deciding which option is best for your project. We warmly invite and value input from others in this industry to comment on this article, as your insights can also aid others in their decision-making process.

Welded Tanks

Welded tanks are typically made of less material than bolted tanks, making them cheaper from a material standpoint. However, assembling a large welded tank is more time-consuming and also requires on-site welding and radiography, which necessitates thorough planning and execution. Therefore, if the cost of assembly (welding) labor is factored in, a welded tank tends to be a more expensive option. In cases where the end-client performs the assembly without considering the labor costs, it may still be the preferred solution. Additionally, the integrity and sealing behavior of a welded tank are superior to those of bolted tanks. Moreover, tank design codes such as API650 and EN have a proven safety record when all specifications are followed.

Bolted Tanks

Bolted tanks, on the other hand, come in different types, each with its own set of advantages and disadvantages. A bolted tank allows for modular sections to be bolted together on-site, enabling significantly smaller and less skilled installation crews to complete the installation in a shorter duration with precise alignment and a perfect fit. An additional benefit is the ability to relocate the tank. Therefore, bolted tanks are an attractive choice for many industries. Some companies claim that the total project savings when opting for a bolted tank instead of a welded tank are around 30%.

Two types of bolted tanks are typically used in the industry: the flange type and the overlapped type.

Bolted Flange Tanks

Bolted flange tanks offer the following key advantages:

  1. External Bolts: The bolts are located on the outside, eliminating the need for internal protection against conditions such as corrosion and hydrogen embrittlement.
  2. Efficient Installation: The installation process is sped up by requiring fewer but larger bolts.
  3. Inspection Ease: The external location of the bolts allows for easy inspection during operation.
  4. Rigidity: The flange adds rigidity to the shell panel, simplifying its handling.
  5. Tolerance in Fabrication: Misalignment in bolt holes can be easily rectified by reaming. If necessary, the flange can be cut and rewelded, whereas an entire panel would need to be discarded in the case of overlapped types.

However, bolted flange tanks also have their drawbacks:

  1. Prying Action: This can increase the risk of bolt failure if the pre-tension is too close to the yield strength of the bolt.
  2. Panel Deformation: Welding a large flange to a thin shell can cause panel deformation, especially in stainless steel.
  3. Joint Separation: The prying action of the joint can cause separation under hydrostatic liquid load, affecting the sealing behaviour of the joint. Therefore, it is advisable to perform Finite Element Analysis (FEA) on the joint to simulate and verify the prying action. In some tanks with dangerous or toxic content, a small seal weld is sometimes used to ensure a leak-tight joint.

Lapped Type Bolted Tanks

Lapped type bolted tanks are another variant of bolted tanks that come with their own set of pros and cons.

Advantages of Lapped Type Bolted Tanks

  1. Less Material: Lapped joints tanks use less material than flanged type.
  2. Sealing: If fabrication tolerances are good the sealing of the joint is better than the flange type that is prone to prying action.

Disadvantages of Lapped Type Bolted Tanks

  1. Fabrication Tolerance: Lapped joints, if not 100% accurate, can cause major problems for aligning the bolts during assembly.
  2. Sealing: Some tank fabricators prefer using bladders instead of gasket types in overlapped bolted tanks. This is because they struggle to achieve a 100% seal using gaskets and therefore prefer the bladder on the inside.
  3. Thin Wall Tanks: The AWWA Code allows one to use a very thin wall from a hydrostatic point of view. However, it is very difficult to work with these thin plates, and they tend to buckle at the connection points to the jacking system used.

Several design codes and standards are available that specify the design and construction of bolted tanks. The most common codes used in the industry are API 12B and AWWA D103. However, a limitation of these standards is that they do not cover flange-type connections; they only cover overlapped panel connections. Therefore, Finite Element Analysis is an important tool to obtain the stresses in the flange and bolts and to determine the deformation at the joint, which is crucial for the sealing of the joint.

In conclusion, the choice between welded and bolted tanks, and among different types of bolted tanks, depends on a variety of factors, including the specific requirements of the industry, the nature of the materials stored, and the experience and preferences of the fabricators and end clients. 

What is your preferred choice? Bolted or welded? What problems do you experience in practice with these tanks, and what other considerations should be taken into account?

Glass Fused to Steel Tanks Pros and Cons

Glass Fused to Steel Tanks is the most common tank specification for CSTR biogas digester reactor tanks. In this article, we discuss their pros and cons.

 

Enamel tanks, GFS tanks (GFtS), and Glass Fused Bolted Steel (Porcelain Enameled) tanks are all terms used to describe this type of tank.

 

It is essential that all anaerobic digestion tanks must be extremely durable, which means they must be resistant to corrosion as well as impact and abrasion. These tanks have that characteristic but as in most things, their advantages come with a few disadvantages. Read on and find out what those pros and cons really are.

 

Advantages of Glass Coating in Steel Technology

 

Undoubtedly, the apex of coating technology in the storage tank industry lies in glass-fused-to-steel technology. These tanks find extensive application in various sectors including bio-energy (especially CSTR biogas plants), municipal sewage, landfill leachate, and industrial wastewater treatment.

 

How Challenging is it to Select the Right Tank Material?

 

Selecting a liquid storage tank might seem straightforward. After all, it's a vessel for holding liquids. Is there truly a substantial difference?

 

The reality is that each type of tank boasts its own set of advantages and disadvantages. The key to choosing the optimal product lies in evaluating these pros and cons against your specific requirements.

 

Tanks Made of Glass Fused to Steel

 

Glass-fused steel, also known as enameled steel, represents an advanced technology offering long-term performance with minimal maintenance requirements.

 

These tanks stand out as the preferred material for biogas digesters due to their fusion of steel toughness with the corrosion resistance of glass. Moreover, they serve as excellent choices for storing potable water, wastewater, industrial chemicals, bio-digesters, sludge, and various dry bulk materials.

 

In a cutting-edge furnace, enamel frit (glass compounds) undergoes chemical fusion with steel sheets at exceptionally high temperatures (ranging between 800 and 1,000 degrees Celsius). This process generates an integrated, porcelain-like coating that is firmly bonded, chemically inert, and impermeable to liquids.

 

Suppliers tout these tanks as capable of withstanding a range of conditions, such as temperatures up to 140°F and pH levels between 3 and 11, without succumbing to corrosion.

 

 

Advantages of Glass-Fused-to-Steel Tanks

 

Glass fused to steel liquid tanks combines the strength of steel with the exceptional corrosion resistance of glass, offering numerous advantages over traditional epoxy-coated or welded painted storage tanks, including:

 

1. Outstanding anti-corrosion properties.

2. Swift installation in the factory, coupled with high-quality design, production, and stringent quality control.

3. Safety and simplicity: Operators require minimal long-term training, and plant owners benefit from reduced maintenance, leading to less time spent by workers in elevated positions.

4. Minimal impact from local weather conditions on these tanks.

5. Low initial investment, especially pertinent for biogas digesters and industrial wastewater treatment projects.

6. Cost-effective maintenance and ease of repair.

7. Reduced life-cycle costs due to the enduring coating.

8. Flexibility for relocation, expansion, and repurposing.

9. Aesthetic appeal with various color options.

10. Simplified cleaning compared to unlined equipment.

11. Customization for specific applications with tailored tank designs.

 

Even stainless steel tanks, while normally an ideal material for these tanks, cannot withstand the high sulphur which may accumulate at the top rim of commercial digester tanks.

 

Disadvantages of Glass-Fused-to-Steel Tanks

 

While Glass Fused To Steel Tanks offer numerous benefits, it's important to acknowledge some drawbacks that, although not extensive, are noteworthy:

 

1. Joint sealing is crucial at the points where the tank is bolted to the concrete base slab to prevent potential leaks.

2. Physical damage, like impacts from moving equipment or machinery, can lead to chipping of the glass coating at the impact site.

3. Concrete-based biogas tanks in Anaerobic Digestion Plants provide superior insulation compared to steel tanks, thereby avoiding the need for additional thermal insulation and associated costs.

4. When considering burial or partial burial, steel tanks might be less suited to withstand soil loads compared to reinforced concrete tanks.

5. Ensure that the purchased Glass Fused To Steel tank includes edge corrosion protection, as untreated panel edges may pose long-term issues in bolted steel tanks.

 

Nevertheless, implementing excellent design, installation, and operational practices can prevent or mitigate these aforementioned issues effectively.

In moderate climates, digester tanks are typically insulated and enveloped with plastic-coated aluminum profile sheeting along their outer edges.

 

This practice serves the purpose of safeguarding the installed insulation and provides additional protection to the tanks, shielding them from accidental impact damage to the fused-to-glass enamel during their operational use.

 

The Primary Drawback of GFS Tanks: Initial Cost

 

While the benefits of GFS tanks are substantial, their most notable disadvantage is often the initial expense. Glass-lined tanks tend to be considerably pricier compared to epoxy tanks.

 

Consequently, some businesses might initially perceive these upfront costs as prohibitive. However, it's crucial to examine the total cost of ownership throughout the tank's lifespan, considering reduced maintenance expenses and longer-lasting durability offered by GFS tanks, which can result in less frequent replacements.

 

Quality Assurance and Standards for Glass-Fused-To-Steel Bolted Tanks

 

Engineers and industry experts worldwide are increasingly selecting glass-fused-to-steel tanks for their resilience in challenging conditions, ensuring decades of trouble-free operation. However, tanks employing this unique technology require strict adherence to quality standards, notably ISO certification, to ensure superior manufacturing and defect-free performance.

 

Well-manufactured porcelain-enameled tanks boast a lasting coating that eliminates the need for recoating.

 

Among various substrates for glass coating like steel, aluminum, cast iron, copper, and brass, steel is commonly used in porcelain-enameled tanks, chosen based on size requirements&#;larger tanks often necessitate a more durable steel grade.

 

Delivering Quality Glass-Fused-to-Steel Tanks

 

It's imperative to procure tanks only from manufacturers holding ISO certification, indicating adherence to over 16 standard inspections before sale approval. Glass Fused to Steel tanks prove highly advantageous for containing potable, municipal, agricultural, and industrial fluids due to their minimal maintenance needs and inherent resistance to contamination.