Code of Practice for Use of Steel in Gravity Water Tanks

IS 805 – Introduction: Key Formulas, Tables & Specifications

• Tank Shape & Design (Clause 4.1):

  • Steel tanks are primarily cylindrical with vertical axis.
  • Supported tanks without beams can have hemispherical or suspended bottoms (min. riser diameter 1 m).
  • Flat bottoms allowed on steel/concrete beams or slabs.
  • Non-cylindrical shapes allowed by mutual agreement.

• Design Stresses (Clause 7.4):

  • Use permissible stresses from IS 800-1962 and IS 816-1956 for supporting structures.

• Loads (Clause 6.0):

  • Apply load provisions from IS 875-1964 (loads on structures).

• Purchaser Information (Clause 5.1):

  • Purchaser must provide details as per Appendix A (tank dimensions, loads, materials, etc.).

Important References & Specs

Typical Design Considerations

• Permissible Stress, σ_perm from IS 800/816.
• Load Combinations per IS 875 (dead + live + wind).
• Tank dimensions: height, diameter, bottom type.

flowchart LR
    A[Tank Design] --> B{Shape}
    B --> C[Cylindrical]
    B --> D[Hemispherical Bottom]
    B --> E[Flat Bottom]
    A --> F[Loads per IS 875]
    A --> G[Permissible Stresses per IS 800/816]
    A --> H[Purchaser Info per Appendix A]

This summary provides the foundational framework for steel tank design per IS 805. For detailed formulas and tables, refer directly to the respective IS codes mentioned.

IS 805: Scope & Key Specifications

• Scope (Clause 4.1 & 6.0):

  • Steel tanks are primarily cylindrical with vertical axis.
  • Bottoms:
    • Suspended bottom: hemispherical or acceptable alternative; riser diameter ≥ 1 m if fabricated.
    • Flat bottom allowed on steel/concrete beams or slabs.
  • Other shapes allowed by mutual agreement.
  • Loads per IS 875-1964 apply unless otherwise stated.

• Shell Plate Shaping (Clause 22.1):

• Shell plates must be rolled to correct curvature unless purchaser specifies otherwise.

• Purchaser Information (Clause 5.1):

  • Refer to Appendix A for required data with enquiry/order.

Summary Diagram of Tank Form & Plate Thickness

graph TD
A[Cylindrical Steel Tank] --> B[Bottom Types]
B --> B1[Hemispherical/Suspended Bottom (Riser ≥ 1 m)]
B --> B2[Flat Bottom on beams/slabs]
A --> C[Shell Plates]
C --> C1[Thickness 10 mm → Diameter ≤ 9 m]
C --> C2[Thickness 12 mm → Diameter ≤ 18 m]
C --> C3[Thickness 16 mm → Diameter ≤ 36 m]
C --> C4[Thickness >16 mm → Any Diameter]

For detailed design, refer to IS 875 for loads and permissible stresses.

IS 805: Definitions & Key Specifications

1. Definitions (Clause 2.0)

• The steel tank is primarily cylindrical with a vertical axis.
• Bottom forms may be hemispherical, suspended, or flat depending on support:
  • Hemispherical or other suspended bottoms if supported by steel towers without beams.
  • Flat bottoms when placed on steel/concrete beams or slabs.
• Large fabricated risers should be ≥ 1 m diameter.

2. Shell Plate Shaping (Clause 22.1)

• Plates are rolled to correct curvature unless otherwise specified.

3. Applicable Standards

• IS 875-1964 for loadings unless stated otherwise.
• Specifications for structural steel and welding electrodes are referenced but updated versions should be used.

flowchart TD
    A[Steel Tank] --> B{Form}
    B --> C[Cylindrical with vertical axis]
    B --> D[Bottom Type]
    D --> E[Hemispherical / Suspended (if tower support)]
    D --> F[Flat (if supported on beams/slab)]
    A --> G[Shell Plates]
    G --> H{Thickness vs Diameter}
    H --> I[10 mm for ≤ 9 m diameter]
    H --> J[12 mm for ≤ 18 m diameter]
    H --> K[16 mm for ≤ 36 m diameter]
    H --> L[>16 mm for all sizes]

Summary: IS 805 defines tank geometry primarily as cylindrical with specific bottom types and shell plate thicknesses matched to tank diameter for structural integrity.

IS 805: Key Materials Specifications and References

• Steel for Mountings, Plates, and Sections
  Must conform to:

  • IS 226-1962 (Specification for structural steel - standard quality)
  • IS 2062-1962 (Specification for structural steel - fusion welding quality)

• Tank Form and Material Use

  • Cylindrical tanks with vertical axis preferred.
  • Bottoms: hemispherical, suspended, or flat (when supported by beams or slabs).
  • Large fabricated riser diameter ≥ 1 m.

• Purchaser Information (Clause 5.1)
  Purchaser must provide detailed info per Appendix A for design and material selection.

Common Steel Grades (per IS 2062)

Summary of Material Selection

• Use IS 2062 steel for welded tanks.
• Use IS 226 steel for riveted or standard quality tanks.
• Ensure steel meets mechanical properties and welding quality per IS codes.

flowchart LR
  A[Steel Material] --> B{Type}
  B --> C[Mountings: IS 226 or IS 2062]
  B --> D[Plates & Sections: IS 226 or IS 2062]
  C --> E[Standard Quality Steel]
  D --> F[Fusion Welding Quality Steel]

This ensures compliance with IS 805 for safe, durable steel tank construction.

IS 805: General Requirements for Steel Tanks

• Tank Shape: Cylindrical with vertical axis is standard (Clause 4.1).

  • If supported by a steel tower without beams, a hemispherical or acceptable suspended bottom is required.
  • Large fabricated riser diameter ≥ 1 m.
  • Flat bottoms allowed on steel/concrete beams or slabs.
  • Non-cylindrical shapes allowed by mutual agreement.

• Material Specifications:

  • Structural steel quality as per latest revisions of IS standards (e.g., IS 2062 for structural steel).
  • Welding electrodes per IS specifications (covered electrodes for arc welding mild steel).

• Loads and Stresses:

  • Design loads per IS 875-1964 (clause 6.0).
  • Permissible stresses per IS 800-1962 and IS 816-1956 (clause 7.4).

• Purchaser's Information:

  • Must provide details as per Appendix A (clause 5.1).

Key References Summary

Typical Permissible Stress (IS 800-1962)

flowchart TD
    A[Steel Tank] --> B{Shape}
    B --> C[Cylindrical Vertical]
    B --> D[Non-cylindrical (by agreement)]
    A --> E[Bottom Type]
    E --> F[Flat (on beams/slab)]
    E --> G[Hemispherical/Suspended (tower support)]
    A --> H[Material]
    H --> I

IS 805 - Information to be Supplied with Enquiry and Order (Clause 5.1 & Appendix A)

The purchaser must provide the following key information with enquiry/order (Appendix A):

• A-1: Capacity (litres) or dimensions (multiples of 1.25 m); note any future extension.
• A-2: Space/accessibility limits, erection site (indoor/outdoor), and partition details.
• A-3: Water type (hard/soft); water level indicator requirements.
• A-4: Special jointing materials, internal/external coatings or lagging.
• A-5: Connections/drilling details with dimensioned sketches.
• A-6: External ladder requirements.
• A-7: Supporting structure details and bottom weight above ground.
• A-8: Transverse supporting bearers, spans, and end supports.
• A-9: Inspection by purchaser’s representative at manufacturer’s works.
• A-10: Erection and testing by manufacturer at site, site conditions, accessibility, and water availability for testing.
• A-11: Tank type: riveted or welded.

Shell Plate Shaping (Clause 22.1):

Shell plates are rolled to curvature unless purchaser specifies otherwise.

This detailed info ensures correct design, fabrication, and erection per IS 805 standards.

IS 805: Loads and Permissible Stresses Summary

• Permissible Stresses Reference:

  • Use IS 800-1962 and IS 816-1956 for basic permissible stresses in structural steel.
  • For tank plates, multiply IS 800 permissible stresses by 0.8 (Clause 7.2).

• Key Clauses:

  • 7.1: Basic permissible stresses from IS 800-1962 and IS 816-1956 apply.
  • 7.2: Tank plates stresses = 0.8 × IS 800 permissible stresses.
  • 7.4: Supporting structure design follows IS 800-1962 and IS 816-1956 permissible stresses.

Typical Permissible Stresses (from IS 800-1962 for Mild Steel)

For tank plates, multiply these by 0.8, e.g., tensile = 112 N/mm².

Load Considerations (per IS 800 & IS 816 references)

• Dead load
• Live load
• Wind load
• Seismic load (where applicable)

flowchart TD
    A[Start: Structural Steel Design] --> B{Is it tank plate?}
    B -- Yes --> C[Permissible Stress = 0.8 × IS 800 values]
    B -- No --> D[Use IS 800 & IS 816 permissible stresses]
    C --> E[Design tank plates]
    D --> F[Design supporting structure]
    E --> G[Check load combinations]
    F --> G
    G --> H[Final design]

Note: Always refer to the latest versions of IS 800 and IS 816 for updated permissible stresses and load factors.

Permissible Stresses for Tank Plates and Welding (IS 805)

• Tank Plates:

  • Use permissible stresses from IS 800-1962.
  • Multiply these values by 0.8 to get permissible stresses for tank plates (Clause 7.2).

• Welds in Tank Plates:

  • Use permissible stresses from IS 816-1956.
  • Multiply these values by 0.8 to get permissible stresses for welds in tank plate construction (Clause 7.3).

• Basic Stress Values:

  • IS 800-1962 and IS 816-1956 provide basic permissible stresses.
  • These are reduced by 20% (factor 0.8) for tank design (Clause 7.1).

Summary Table:

Additional Notes:

• Shell and bottom plates minimum thickness: 6 mm (Clause 27.1).
• Tack welds (~12 mm) used for alignment before continuous welding.
• Continuous welding starts from bottom edge upwards (Clause 27.1).

flowchart TD
    A[IS 800-1962: Permissible Stress for Plates] --> B[Multiply by 0.8]
    A --> C[Basic permissible stress]
    D[IS 816-1956: Permissible Stress for Welds] --> E[Multiply by 0.8]
    D --> F[Basic permissible stress]
    B --> G[Tank Plate Design Stress]
    E --> H[Weld Design Stress]

This approach ensures safety margins specific to tank construction per IS 805.

IS 805: Design of Joints - Key Points

1. Joint Efficiency (Clause 9.2.1 & 9.9)

• For butt joints with plate edges within permissible offset (Clause 28.2), design must consider:
  • Joint efficiency factor (η) as per Clause 9.2.
  • Eccentricity effects due to offsetting must be accounted for.
• Weld joint efficiency values depend on weld type and inspection level (refer IS 800/816 for typical values).

2. Permissible Stresses (Clause 7.4 & 8.1)

• Use permissible stresses from:
  • IS 800-1962 (General steel structures)
  • IS 816-1956 (Welded steel structures)
• These govern allowable stresses for the supporting structure and welds.

3. Design of Welded Joints (Clause 9.4)

• Welds in supporting structures can be designed for full strength (100% efficiency).

Typical Weld Joint Efficiency Values (from IS 800/816):

Basic Formula for Weld Strength:

[ P = f_w \times A_w \times \eta ]

Where:

• (P) = design load on weld
• (f_w) = permissible weld stress (from IS 800/816)
• (A_w) = effective weld area
• (\eta) = joint efficiency factor

flowchart TD
    A[Plate Edges] --> B{Offset within permissible range?}
    B -- Yes --> C[Design for eccentricity]
    B -- No --> D[Joint not permitted]
    C --> E[Apply joint efficiency factor η]
    E --> F[Calculate weld strength P = f_w × A_w × η]
    F --> G[Design supporting structure per IS 800/816]
``

Welded Joints in IS 805: Key Points & Formulas

1. General Requirements (Clause 29.1)

• Edges must allow complete fusion and penetration.
• For butt joints with a gap > 12 mm, weld metal (except final layer) should be peened to relieve shrinkage stresses.

2. Joint Efficiency (Clause 9.2)

• For tank plate butt welds, joint efficiency, η = 0.85.

3. Butt Weld Specifications (Clause 17.5)

• Follow Appendix C of IS 823-1964 for:
  • Fusion face angle
  • Gap between parts
  • Finish
• Reinforcement limits:
  • Max 20% if welded from one side
  • Max 10% if welded from both sides

4. Typical Joint Efficiency Formula

[ \sigma_{allowable} = \eta \times \sigma_{base} ]

Where:

• (\eta = 0.85) (joint efficiency)
• (\sigma_{base}) = allowable stress of base metal

5. Weld Joint Types (Fig. 1 Reference)

• IB Welded Joint: Used for vertical shell plate joints.
• Hydrostatic pressure is measured at the weld height.

flowchart LR
    A[Preparation of Edges] --> B[Gap ≤ 12 mm or > 12 mm]
    B -->|Gap > 12 mm| C[Peening of weld metal except final layer]
    B -->|Gap ≤ 12 mm| D[Standard welding]
    C --> E[Complete fusion & penetration]
    D --> E
    E --> F[Butt weld with reinforcement limits]
    F --> G[Joint efficiency η = 0.85]

Summary: Ensure proper edge preparation, control gap size, peen if gap >12 mm, limit reinforcement, and use η=0.85 for design calculations. For detailed joint geometry, refer IS 823-1964 Appendix C.

IS 805: Thickness of Metal - Key Points

• Minimum Thickness (Clause 10.1):

  • 6.0 mm minimum thickness for metal members, except for roofs and railings.

• Additional Thickness for Corrosion (Clause 10.2):

  • Add 1.5 mm extra thickness for interior bracing (if unavoidable) to allow for corrosion and maintenance access.
  • Plates in tanks containing salt or alkaline water require an additional 1.5 mm thickness over the calculated value.

• Controlling Thickness for Rolled Sections (Clause 10.1.1):

  • Use the mean thickness of the flange as the controlling thickness for beams and channels, irrespective of web thickness.

Summary Table

This ensures durability and structural integrity, especially in corrosive environments or where accessibility for maintenance is limited.

IS 805: Key Formulas & Specifications for Load Location and Hydrostatic Pressure

1. Load Location (Clause 11.2)

• Hydrostatic pressure is measured 30 mm above the bottom rivet line of the lower horizontal shell joint.
• For welded tanks, pressure is measured 30 cm above the center line of the lower horizontal weld.
• This location defines where thickness and stress checks are made for shell plates.

2. Hydrostatic Pressure Calculation

• Hydrostatic pressure at depth ( h ):

  [ p = \rho \times g \times h ]

  Where:

  • ( p ) = pressure (N/m²)
  • ( \rho ) = density of water = (1000 , kg/m^3) (1 gm/cm³)
  • ( g ) = acceleration due to gravity = (9.81 , m/s^2)
  • ( h ) = height of water above measurement point (m)

3. Thickness of Bottom Cylindrical Courses (Clause 10.3)

4. Live Load (Clause 6.2)

• Live load = weight of liquid overflowing the tank top.
• Use water density = 1 gm/cm³ for calculations.

Summary Diagram: Hydrostatic Pressure Measurement Point

flowchart TB
    A[Bottom Rivet Line / Weld] --> B[30 mm above (riveted)] 
    A --> C[30 cm above (welded)]
    B & C --> D[Measure Hydrostatic Pressure Here]

Use these guidelines to determine shell thickness and stress checks accurately per IS 805.

IS 805: Openings and Connections – Key Points

Hydrostatic Pressure Measurement (Clause 11.2)

• Measured 30 mm above bottom rivet line in lower horizontal shell joint.
• For welded shells, measured 30 cm above center line of lower horizontal weld.
• Use this pressure to determine minimum plate thickness (Clause 10).

Openings & Reinforcements (Clause 12.1)

• Openings (manholes, pipe openings) must be reinforced by additional steel plates.
• Reinforcement must carry the load of the cut-out portion without overstressing.
• Check average tensile stress in the net section; it must not exceed permissible limits (Clause 7).

Connections (Clause 18.1)

• Provide connections for pipes, braces, and walkways.
• Ensure structural integrity by proper design and welding.

Typical Design Approach for Openings:

1. Calculate net area after cut-out.
2. Determine tensile stress in net section:
   [ \sigma = \frac{P}{A_{net}} ]
3. Reinforce if (\sigma) exceeds allowable stress.
4. Use additional plates welded around openings.

Visualization: Reinforcement Around Opening

flowchart LR
    A[Shell Plate with Opening] --> B[Cut-out Portion]
    B --> C[Net Section]
    C --> D{Stress Check}
    D -- Exceeds Allowable --> E[Add Reinforcement Plate]
    D -- Within Limits --> F[No Additional Reinforcement]

For detailed thickness and weld size, refer to Clause 10 (minimum thickness) and Clause 7 (allowable stresses).

IS 805 - Curved-Bottom Plates: Key Specifications & Tables

1. Plate Thickness & Tank Diameter (Clause 22.1)

• Shell plates must be rolled to the correct curvature unless purchaser specifies otherwise.
• This ensures proper fit and structural integrity of curved-bottom tanks.

2. Reinforcement Around Openings (Clause 12.1)

• Manholes, pipe openings, and attachments require additional steel plates.
• Thickness and connection must carry the load of the cut-out portion without overstressing.
• Check average tensile stress in net section against limits in Clause 7.

3. Bottom Plate Jointing (Clause 17.7 & Fig. 6)

• When two bottom plates lap under the shell:
  • The triangular gap must be fully filled with weld metal.
  • Provide a full-size joggle for smooth shell bearing.

flowchart LR
    A[Two Bottom Plates Lap] --> B[Triangular Space]
    B --> C[Fully Filled with Weld Metal]
    A --> D[Full-Size Joggle Provided]
    D --> E[Smooth Bearing for Shell]

4. Welding

• Follow Code of Procedure for Manual Metal Arc Welding of Mild Steel for all joints.

Summary: Use the table for plate thickness selection based on tank diameter, reinforce openings properly, ensure joggle joints with fully filled welds for lap plates, and roll plates to curvature for curved-bottom tanks.

IS 805: Stiffening and Support Angles Key Points

1. Stiffening Angles (Clause 14.1)

• Provided around the top of tanks without roofs.
• Minimum section modulus ( Z ) (in cm³) is calculated by:

[ \boxed{Z = 0.0578 \times D^2 \times H} ]

Where:

• ( D ) = nominal tank diameter (m)
• ( H ) = height of cylindrical shell (m)

This ensures adequate stiffness to resist shell deformation.

2. Bottom Angles (Clause 13.1)

• Suspended bottom plates lap inside the plates of the lowest cylindrical course.
• Ensures proper load transfer and sealing.

3. Design and Permissible Stresses (Clause 7.4)

• Use permissible stresses from IS 800-1962 and IS 816-1956 for supporting structure design.
• These codes provide allowable stresses for steel sections and welds.

Summary Table

flowchart LR
    A[Tank Shell] --> B[Stiffening Angles at Top]
    B --> C[Section Modulus Z = 0.0578 D²H]
    A --> D[Bottom Plates]
    D --> E[Bottom Angles Lap Inside Shell Plates]
    F[Supporting Structure] --> G[Design as per IS 800 & IS 816]

Use this formula and references for design of stiffening/support angles to ensure structural integrity and compliance with IS 805.

IS 805: Bottom Angle and Connections - Key Points

1. Bottom Angle (Clause 2.5 & Fig.6)

• Bottom plates are flat and welded fully under the shell plate.
• Joggle joints are used in bottom plates to ensure proper fit and welding.
• Bottom angles typically support the shell and bottom plate junction.

2. Stiffening Angle (Clause 14.1)

• Used around the top of tanks without roofs.

• Minimum section modulus, Z (cm³), is given by:

  [ Z = 0.0578 \times D^2 \times H ]

  where:

  • (D) = nominal tank diameter (m)
  • (H) = height of cylindrical shell (m)

3. Connections (Clauses 12.1 & 13.1)

• Suspended bottom plates lap inside the lowest cylindrical shell course.
• Openings (manholes, pipes) require reinforcement plates to carry loads of cut-out sections.
• Reinforcement must prevent overstressing, maintaining average tensile stress within limits of Clause 7.

Summary Table:

flowchart LR
    TankShell -->|Supported by| BottomAngle
    BottomAngle -->|Connected to| BottomPlate
    BottomPlate -->|Lap inside| LowestShellCourse
    Openings -->|Reinforced by| ReinforcementPlates
    StiffeningAngle -->|Around top| TankShell

This ensures structural integrity at critical junctions per IS 805.

Key Specifications & Formulas for Riveted Joints (IS 805)

1. Rivet Pitch and Staggering (Clause 16.2 & 16.3):

• Maximum pitch (distance between rivet centers):

  • Single riveted joints:
    [ p_{max} = 10 \times t_{min} ]
  • Multiple rows of rivets:
    [ p_{max} = 12 \times t_{min} ] where ( t_{min} ) = thickness of the thinnest plate (mm).

• Staggering of rivets:

  • Distance between centers of adjacent rows ( \geq 2 \times d )
    ( d ) = rivet hole diameter.
  • Section between rivets in adjacent rows ( \geq 0.6 \times ) section between rivets in line of stress.

2. Rivet Material:

• Rivets must conform to IS 1148-1964 (Rivet Steel).

3. Connection Details (Clause 15.1):

• For tanks ≥ 6 m diameter, sides and bottoms connected by spliced angles caulked along both legs.

Summary Table: Rivet Pitch Limits

Visual Concept: Rivet Staggering

flowchart LR
    A[Rivet Row 1] ---|≥ 2d| B[Rivet Row 2]
    style A fill:#f9f,stroke:#333,stroke-width:2px
    style B fill:#ccf,stroke:#333,stroke-width:2px

Note:

• (d) = rivet hole diameter
• Rows staggered to reduce stress concentration.

This concise guidance ensures riveted joints in tanks are safe and conform to IS 805 standards.

Key Specifications & Formulas for Welded Joints (IS 805):

• Edge Preparation (Clause 29.1):

  • Edges must allow complete penetration and thorough fusion.
  • For butt joints with gap >12 mm at the weld face, peening (except final layer) is required to relieve shrinkage stresses.

• Joint Efficiency (Clause 9.2):

  • For all butt welds in tank plates, use joint efficiency factor, η = 0.85.

• Reinforcement Limits (Clause 17.5):

  • Butt weld reinforcement ≤ 20% if welded from one side.
  • ≤ 10% if welded from both sides.

• Reference for Weld Details:

  • Follow Appendix C of IS 823-1964 for joint form, fusion face angle, gap, finish, etc.

Typical Weld Strength Formula:

[ \sigma_{weld} = \eta \times \sigma_{base} ]

• (\eta = 0.85) (joint efficiency)
• (\sigma_{base}) = allowable stress of base metal

Diagram: Butt Weld Joint Preparation

graph LR
A[Plate Edge] -- Gap ≤ 12 mm --> B[Weld without peening]
A -- Gap > 12 mm --> C[Weld + Peening (except final layer)]
B & C --> D[Complete Fusion & Penetration]

Summary:
Ensure proper edge preparation, control reinforcement, and apply 0.85 joint efficiency for design strength calculations in welded joints per IS 805.

IS 805: Connections Key Points

1. General Requirements (Clause 18.1)

• Connections must be provided for pipes, braces, and walkway supports.
• They should ensure structural integrity without overstressing the shell or bottom plates.

2. Reinforcement of Openings (Clause 12.1)

• Manholes, pipe openings, and connections require reinforcement with additional steel plates.
• Thickness of reinforcement plates must be sufficient to carry the load of the cut-out portion.
• Design stress limits follow Clause 7 (permissible tensile stress in net section).

3. Welding Details

• Space under shell plates at connections is to be completely filled with weld metal.
• Joggle joints (Fig. 6) are used in flat bottom plates for smooth transitions.

4. Design Stresses (Clause 7.4)

• Use permissible stresses as per IS 800-1962 and IS 816-1956 for connections and supporting structures.

Typical Design Formula for Reinforcement Thickness:

[ t_r \geq \frac{A_c \times f}{f_r} ]

Where:

• ( t_r ) = thickness of reinforcement plate
• ( A_c ) = area of cut-out portion
• ( f ) = permissible stress in shell plate (from Clause 7)
• ( f_r ) = permissible stress in reinforcement plate

Summary Table: Connection Design

flowchart LR
    A[Pipe/Brace/Walkway Support] --> B[Connection Plate]
    B --> C[Reinforcement Plate]
    C --> D[Shell Plate]
    B --> E[Full Weld Metal Fill]
    D --> F[Load Transfer]

Note: Always verify connection design with actual load cases and permissible stresses from IS 805 and referenced IS codes.

IS 805: Roof Design and Anchorage Key Points

Roof Anchorage (Clause 19.2)

• Roof plates must be fastened with ≥ 2 connections, spaced ≤ 75 cm apart.
• Fasteners: bolts/rivets ≥ 12 mm diameter or equivalent welding.
• Stitch welding or short fillets recommended for secure attachment.

Roof Hatch (Clause 19.3)

• Hatch size: minimum 50 cm × 55 cm.
• Hatch cover: steel/iron plate, thickness ≥ 3 mm.
• Hinges: heavy-duty with non-corrodible pins, opening to the right.
• Substantial catch to keep cover closed.
• Alternative designs require inspector approval.

Stiffening Angles (Clause 14.1)

For tanks without roofs, provide stiffening angles with section modulus:

[ Z = 0.0578 \times D^2 \times H ]

• (Z) = section modulus (cm³)
• (D) = tank diameter (m)
• (H) = shell height (m)

Supporting Structure Design (Clause 7.4)

• Follow permissible stresses as per IS 800-1962 and IS 816-1956.

Summary Table: Roof Anchorage

flowchart TD
    A[Roof Plate] -->|Fastened by| B[Bolts/Rivets ≥12mm or Welding]
    B -->|Spacing ≤ 75cm| C[Secure Anchorage]
    A --> D[Roof Hatch]
    D -->|Size ≥ 50x55 cm| E[Steel/Iron Plate ≥ 3mm]
    E --> F[Heavy Hinges + Catch]

This ensures structural integrity and safe access per IS 805.

IS 805 - Ladders and Accessories Key Points

Ladder Bars and Rungs (Clause 20.5)

• Side bars:
  • Fixed ladders: Flat steel 50 × 6 mm
  • Movable ladders: Flat steel 65 × 10 mm
  • Spacing: 25 cm apart
• Rungs:
  • Material: Round or square steel, minimum 16 mm diameter
  • Spacing: 30 cm center-to-center
  • Rungs must extend through and be riveted/welded to side bars
• Load capacity: Designed for a concentrated load of 160 kg

Outside Fixed Ladder (Clause 20.2)

• Positioned at least 15 cm away from tank side
• Rigidly bolted/welded to brackets spaced max 3.0 m apart
• Top bracket max 30 cm below shell top, bottom bracket max 1.5 m above tank base
• Ladder sides extend 45 cm above tank top, bent downward to roof and securely fastened

Outside Revolving Ladder (Clause 20.3)

• Max length: 9 m
• Extends from supporting tower ladder to painters' trolley
• Rigidly bolted at top and bottom, aligned with tower ladder and left of roof hatch

General (Clause 20.1)

• Ladders must allow convenient passage through roof hatch without interference
• No outward inclination from vertical
• Welding to tank shell permitted
• Preferably fixed to tank side

Summary Table: Ladder Dimensions & Spacing

flowchart TB
    A[Ladder Side Bars] --> B

Fabrication Procedures as per IS 805

• Welding Standards:

  • Follow IS 816-1956 for general welding provisions.
  • Welding procedure must comply with IS 823-1964.

• Welding Joint Preparation (Clause 29.1):

  • Edges must allow complete penetration and fusion.
  • For butt joints with a gap > 12 mm, weld metal (except final layer) must be peened to relieve shrinkage stresses.

• Design Considerations (Clause 9.4):

  • Use full strength values of weld joints in structural design.

• Thickness of Metal (Clause 10):

  • Thickness selection must ensure structural integrity and weldability (refer IS 805 for detailed thickness tables).

Key Welding Joint Specification (Butt Joint)

Summary Diagram of Butt Joint Welding

graph LR
A[Shell Plate Edges] --> B[Gap ≤ 12 mm] --> C[Standard Weld]
A --> D[Gap > 12 mm] --> E[Weld Layers]
E --> F[Peen all layers except final]
F --> G[Relieve shrinkage stresses]

References:

• IS 816-1956 (Welding of Steel Structures)
• IS 823-1964 (Welding Procedure)
• IS 805 (Fabrication of Steel Structures)

IS 805: Shaping of Shell Plates – Key Points

1. Nominal Plate Thickness vs Tank Diameter (Clause 22.1)

• Shell plates shall be rolled to the correct curvature unless purchaser specifies otherwise.

2. Welding Procedure (Clause 21.3)

• Follow IS 823-1964 for manual metal arc welding of mild steel.
• Use 12 mm tack welds to align shell plates before continuous welding (Clause 27.1).
• Tack welds are chipped out progressively as continuous weld proceeds.

3. Shell to Bottom Plate Connection (Clause 27.1 & 17.7)

• Shell plates aligned by guide lugs or tack welds.
• Vertical seams welded from bottom upwards before shell-to-sketch plate welding.
• Where two bottom plates lap under shell, fill triangular space fully and provide full-sized joggles for smooth bearing (see Fig. 6 & 7).

Summary Diagram: Shell Plate Shaping & Welding Process

flowchart TD
    A[Start: Shell Plate Rolling] --> B{Thickness vs Diameter}
    B -->|10 mm| C[For tanks ≤ 9 m dia]
    B -->|12 mm| D[For tanks ≤ 18 m dia]
    B -->|16 mm| E[For tanks ≤ 36 m dia]
    B -->|>16 mm| F[All tank sizes]
    C & D & E & F --> G[Roll plates to curvature]
    G --> H[Align plates with guide lugs/tack welds (12 mm)]
    H --> I[Chip out tack welds as continuous welding proceeds]
    I --> J[Weld vertical seams from bottom up]
    J --> K[Fill triangular lap spaces with full-sized joggles]
    K --> L[Complete shell-to-bottom welding]

References:

• IS 805 Clause 22.1, 27.1, 17.7
• IS 823-1964 (W

Water-Tightness of Riveted Tanks (IS 805)

Key Specifications & Practices

• Clause 15.1:

  • For flat-bottom riveted tanks ≥ 6 m diameter, sides and bottoms must be connected by spliced angles caulked along both legs.

• Clause 23.1:

  • Riveted joints made water-tight by caulking edges of plates with a round rosed tool before painting.
  • No foreign materials (lead, copper fillings, cement) allowed in joints.

• Clause 31.1:

  • Water test: Fill tank and inspect all visible joints carefully.
  • On detecting leaks, lower water level immediately.
  • Welded joints are not tested by hammering.

Rivet Specifications

• Rivets must conform to IS 1148-1964 (steel rivets for tank construction).

Summary Table: Riveted Tank Water-Tightness

flowchart TD
    A[Tank Construction] --> B[Riveted Plates]
    B --> C[Caulking Edges with Round Rosed Tool]
    C --> D[Water Filling Test]
    D --> E{Leaks Found?}
    E -- Yes --> F[Lower Water Level & Repair]
    E -- No --> G[Proceed to Painting]

This ensures water-tightness by proper caulking and careful inspection during water testing.

IS 805 - Fitting Roofs: Key Specifications & Formulas

1. Roof Plate Thickness & Shape (Clause 19.1)

• Roof Type: Conical or dome-shaped steel/iron roof for outdoor tanks.
• Plate Thickness:
  • Minimum 3 mm thick for tanks ≤ 9 m diameter.
  • Minimum 5 mm thick for tanks ≤ 12 m diameter.
• Roof Slope: Minimum 30° for self-supporting conical roofs.
• Joining: Rivets or bolts spaced ≤ 15 cm apart, or welding.
• Support: Flatter or larger roofs require steel rafters.

2. Lap Joints (Clause 17.2)

• Single full fillet lap joints allowed only:
  • Outside of roof plates.
  • Inside bottom plates resting on sand/concrete.
  • Non-water contact details.

3. Roof Hatch (Clause 19.3)

• Size: Minimum 50 x 55 cm.
• Material: Steel/iron plate, thickness ≥ 3 mm.
• Hinges: Heavy, non-corrodible pins, open right.
• Closure: Substantial catch to keep cover closed.

4. Water-Tightness (Clause 23.1)

• Caulking with round rosed tool before painting.
• No foreign fillers (lead, copper, cement) in joints.

Summary Table: Roof Plate Thickness & Diameter

flowchart TD
    A[Tank Diameter & Roof Slope] -->|≤9 m & ≥30°| B[3 mm Roof Plates]
    A -->|≤12 m & ≥30°| C[5 mm Roof Plates]
    A -->|>12 m or <30°| D[Steel Rafters Support]
    B --> E[Self-support

IS 805: Bottom Plates on Soil or Concrete - Key Points

1. Bottom Plate Thickness (Clause 10.3)

• For suspended bottom plates:
  • Capacity 500,000 to 700,000 litres: min thickness = 8 mm
  • Capacity 700,000 to 1,000,000 litres: min thickness = 10 mm
  • For larger tanks: thickness = calculated thickness + 1.5 mm minimum

2. Reinforcement around Openings (Clause 12.1)

• Manholes, pipe openings, and attachments must be reinforced with additional steel plates.
• Reinforcement must carry the total load of the cut-out portion without exceeding allowable tensile stress.
• Average tensile stress in net section ≤ permissible tensile stress (per Clause 7).

3. Curved Bottom Plates (Clause 13.1)

• Suspended bottom plates lap inside the plates of the lowest cylindrical course for proper load transfer.

4. Load Considerations (Clause 11)

• Bottom plates must be designed considering the location and magnitude of loads, ensuring no overstressing.

Summary Table: Bottom Plate Thickness

Formula for Reinforcement Plate Design:

[ \sigma_{avg} = \frac{P}{A_{net}} \leq \sigma_{allow} ]

• (P) = Load carried by cut-out portion
• (A_{net}) = Net cross-sectional area after cut-out
• (\sigma_{allow}) = Allowable tensile stress (from Clause 7)

flowchart TD
    A[Bottom Plate] --> B[Thickness per Capacity]
    A --> C[Openings Reinforced]
    A --> D[Curved Bottom Lap Inside Cylindrical Course]
    A --> E[Load Location & Distribution]

This ensures bottom plates are safe, durable, and compliant with IS 805.

Assembly and Welding Sequence - IS 805 Key Points

• Welding Sequence (Clause 29.2):
  Sequence must accommodate shrinkage contraction during cooling to reduce residual stresses and avoid rigidity. This typically means welding in a balanced, symmetrical pattern to minimize distortion.

• Fabrication by Welding (Clause 21.2):
  Follow IS 816-1956 for structural steel welding provisions alongside IS 805.

• Welding Procedure (Clause 21.3):
  Comply with IS 823-1964 for welding procedure specifications.

• Shell Plate Edge Preparation (Clause 29.1):

  • Edges must allow complete penetration and fusion.
  • For butt joints with gap > 12 mm, weld metal (except final layer) should be peened to relieve shrinkage stresses.

Summary Table for Welding Sequence and Edge Preparation

Typical Welding Sequence Illustration

flowchart LR
    A[Start Welding at Center] --> B[Alternate Sides Symmetrically]
    B --> C[Allow Cooling Between Passes]
    C --> D[Peen Weld Metal if Gap > 12mm]
    D --> E[Complete Final Surface Layer]

This sequence helps control distortion and shrinkage stresses effectively.

IS 805: Shell Plate Matching and Alignment - Key Points

1. Shell Plate Alignment (Clause 27.1)

• Shell plates are aligned using guide lugs or tack welds (~12 mm long) to bottom plates before continuous welding.
• Tack welds are chipped out progressively as continuous welding proceeds.
• Vertical seams between adjoining shell plates are welded from the bottom upwards before welding shell to bottom plates.
• Minimum thickness:
  • Sketch plates: 6 mm
  • Bottom rectangular plates: 6 mm

2. Shell Plate Matching (Clause 28)

• Offset Limit: Butt joint edges must not exceed ¼ thickness of the thinnest plate.
• Use bars, jacks, clamps, or wedges to align edges.
• Shell plates must be cylindrical, plumb, and free from local irregularities.

3. Shell Plate Shaping (Clause 22.1 Table)

• Plates should be rolled to correct curvature, unless purchaser specifies otherwise.

Diagram: Shell Plate Alignment Concept

flowchart TD
    A[Shell Plate] -->|Guide Lug or Tack Weld| B[Bottom Plate]
    B --> C[Continuous Weld]
    C --> D[Chip Out Tack Welds]
    D --> E[Vertical Seam Welding from Bottom Up]

Summary: Ensure tight alignment with minimal offset, use temporary tack welds for positioning, and progressively weld vertical seams before shell-to-bottom welding. Follow thickness and curvature guidelines per tank diameter.

IS 805: Shell Plate Welding Key Points

Welding Procedure (Clause 21.3)

• Follow IS 823-1964 provisions for welding procedures.
• Ensure qualified welding techniques and inspection as per IS 823.

Shell Plate Alignment & Tack Welding (Clause 27.1)

• Use guide lugs or tack welds (~12 mm long) to align shell plates to bottom plates.
• Tack welds must be chipped out as continuous welding progresses.
• Vertical seams between adjoining shell plates are welded from the bottom before welding shell to bottom plates.
• Minimum thickness:
  • Sketch plates: 6 mm
  • Bottom rectangular plates: 6 mm

Shell Plate Matching & Joint Preparation (Clause 28.2 & 28.3)

• Butt joint plate edges offset ≤ ¼ thickness of thinnest plate.
• Use bars, jacks, clamps, wedges to align edges.
• Erection bolts for lap joints must be removed before welding, replaced by light tack welds.
• Bolt holes sealed by full-formed rivets with seal weld or weld plugs.

Summary Table

flowchart TD
    A[Align Shell Plates] --> B{Use Guide Lugs or Tack Welds (12mm)}
    B --> C[Chip out Tack Welds as Welding Progresses]
    C --> D[Weld Vertical Seams from Bottom Up]
    D --> E[Continuous Welding of Shell to Bottom Plates]
    F[Check Butt Joint Offset ≤ ¼ Thickness] --> G[Use Clamps/Jacks to Align]
    H[Remove Erection Bolts] --> I[Replace with Light Tack Welds]
    I --> J[Seal Bolt Holes with Rivets/Weld Plugs]

This ensures proper alignment, welding quality, and structural integrity of shell plates per IS 805.

IS 805: Painting and Surface Protection - Key Points & Specifications

1. Surface Preparation & Painting (Clause 30.1):

• Clean all steelwork (except rivets, bolts, nuts, machined surfaces) free from rust, scale, dust.
• Apply one coat of red lead paint conforming to IS:102-1962 (ready mixed, non-setting priming).
• Rivets, bolts, nuts, washers: clean and dip in boiled linseed oil.
• Machined surfaces: coat with white lead and tallow mixture.
• Surfaces to be joined by riveting/bolting: paint before assembly, assemble while paint is wet.
• Inaccessible surfaces after riveting/welding: apply two coats of red lead paint per IS:2074-1962 before assembly.
• Welds and adjacent metal: paint only after cleaning, inspection, and approval.

2. Water-Tightness (Clause 32.2):

• Tank must be fully water-tight under test before painting.

3. Corrosion Allowance (Clause 10.2):

• Add 1.5 mm thickness for interior bracing and tanks storing salt/alkaline water.

4. Painter's Trolley (Clause 20.6):

• Provide a substantial trolley device for repainting elevated tanks with secure top connection and a U-bolt at the lower end for painter safety.

Summary Table: Paint Coating Requirements

flowchart TD
    A[Steel Surface Cleaning] --> B[Apply Red Lead Paint (1 coat)]
   

Testing of Steel Tanks as per IS 805

Key Provisions:

• Clause 32.2: The tank must be entirely water-tight under test to the satisfaction of the inspector before painting.
• Testing follows general provisions of IS 875-1964 (loads and testing unless otherwise stated).

Testing Procedure Highlights

• Water Tightness Test:
  • Fill the tank with water to the specified level.
  • Inspect for leaks or seepage throughout the tank surface and joints.
  • Duration and pressure as per IS 875 or purchaser's requirements.

Important Specifications for Testing

Additional Notes

• Information about tank capacity, dimensions, jointing, coatings, and erection conditions must be supplied by purchaser (Appendix A).
• Testing is often done on-site after erection unless otherwise agreed.
• Ensure surface preparation and priming (red oxide-zinc chrome primer as per IS specifications) before painting post-test.

flowchart TD
    A[Start Testing] --> B[Fill Tank with Water]
    B --> C[Inspect for Leaks]
    C -->|No leaks| D[Approve for Painting]
    C -->|Leaks found| E[Repair and Re-test]
    E --> B

For detailed load and testing pressures, refer to IS 875-1964.

IS 805 - Repairs Key Points & Specifications

1. Repairs of Welded Joints (Clause 32.1)

• Repairs by hammering not allowed when tank is full.
• Water level must be lowered at least 60 cm below the joint or tank fully drained.
• Repair involves:
  • Chipping or melting out defective metal.
  • Rewelding to restore full strength.

2. Water-Tightness Test (Clause 32.2)

• Tank must be entirely water-tight under test to inspector's satisfaction before painting.

3. Painting Specification

• Use ready mixed red oxide-zinc chrome priming paint as per specifications.

4. Riveted Tanks (Clause 23.1)

• Water-tightness ensured by caulking edges with round rosed tool before painting.
• No foreign materials (lead, copper fillings, cement) allowed in joints.

5. Information to be Supplied by Purchaser (Appendix A)

• Capacity or dimensions.
• Site conditions, accessibility, erection details.
• Water type (hard/soft).
• Jointing, coating, connections, ladders, supports.
• Riveted or welded tank.

Summary Table: Repair Conditions for Welded Joints

flowchart TD
    A[Start Repair] --> B{Tank Full?}
    B -- Yes --> C[Lower water ≥ 60 cm or drain]
    B -- No --> D[Proceed with repair]
    C --> D
    D --> E[Chip/melt defective metal]
    E --> F[Reweld joint]
    F --> G[Water-tightness test]
    G --> H{Pass?}
    H -- Yes --> I[Painting]
    H -- No --> D

This ensures repair integrity and tank durability per IS 805.

IS 805 - Information to be Supplied with Enquiry and Order (Appendix A, Clause 5.1)

The purchaser must provide the following details with enquiry/order:

• A-1: Capacity (litres) or dimensions (multiples of 1.25 m), and future extension provisions.
• A-2: Space/accessibility limits, erection location (inside/outside), and partition details.
• A-3: Water type (hard/soft) and water level indicator details.
• A-4: Jointing material, internal/external coating, or lagging requirements.
• A-5: Connections/drilling details with dimensioned sketches.
• A-6: External ladders needed and their particulars.
• A-7: Supporting structure details and bottom weight above ground.
• A-8: Transverse supporting bearers, span, and end support info.
• A-9: Inspection by purchaser’s representative at manufacturer’s works.
• A-10: Erection/testing by manufacturer, site conditions, accessibility, and water availability for testing.
• A-11: Tank construction type: riveted or welded.

Additional Relevant Table (Clause 22.1) - Shell Plate Thickness vs. Tank Diameter

Shell plates are rolled to curvature unless purchaser specifies otherwise.

This information ensures clear communication for correct tank design, fabrication, and erection per IS 805.