glass-fibre reinforced plastic (GRP) pipes joints and fittings for use in potable water supply

IS 12709: Scope - Key Specifications & Tables

1. Scope (Clause 1.2):

   • Provisions for fittings made from GRP pipes or molded joints are guidance only.

2. Pipe Diameters:

   • Inside Diameter (ID) Ranges & Tolerances (Table 1, Clause 7.1.1):

   Nominal Diameter (DN)	Min ID (mm)	Max ID (mm)	Tolerance (± mm)
   200	196	204	1.5
   250	246	255	1.5
   300	296	306	1.8
   ...	...	...	...
   800	795	816	4.2
   2000	1995	2020	-

   • Outside Diameter (OD) & Tolerances (Table 2, Clause 7.1.2):

   Nominal Diameter (DN)	Outside Diameter (OD, mm)	Tolerance (mm)
   200	208	+2.0
   250	259	+2.1
   300	310	+2.3
   ...	...	...
   2000	2044	+6.5

3. Workmanship & Defects (Clause 9, Table 10):

   • No cracks or internal delamination allowed.
   • Max allowable defect sizes (e.g., Chips ≤ 6.5 mm, Air bubbles ≤ 3.0 mm).
   • Ensures quality control for GRP pipe fittings.

4. Terminology Update:

   • "Nominal" diameter replaced by "Effective" diameter in clauses 7.2 and 7.2.1.

Summary Diagram: Diameter Specification Flow

flowchart TD
    A[

Classification as per IS 12709

1. Hydrostatic Design Pressure (HDB) Categories (Table 7, Clause 15):

• Use these values to determine the pressure class for pipes or fittings.

2. Extractants for Biological Tests (Clause 16.1.1.2):

• Double/triple glass distilled water
• 0.9% sodium chloride solution prepared in double/triple glass distilled water

3. Statistical Data for Lower Confidence Limit (Table 9, Clause 12.2.3):

• Student's t-values for different degrees of freedom (N-2) are provided to calculate confidence intervals in acceptance testing.
• Example: For df=10, t=2.2281; for df=30, t=2.0423; for infinite df, t=1.9600.

Summary Formula for Lower Confidence Limit (LCL):

[ LCL = \bar{x} - t \times \frac{s}{\sqrt{n}} ]

• (\bar{x}) = sample mean
• (t) = Student's t-value for ((n-1)) degrees of freedom
• (s) = sample standard deviation
• (n) = sample size

flowchart TD
    A[Determine HDB Category] --> B{Check Pressure Class PN}
    B -->|3| C[540 kPa]
    B -->|6| D[1080 kPa]
    B -->|9| E[1620 kPa]
    B -->|12| F[2160 kPa]
    B -->|15| G[2700 kPa]
    H[Biological Tests] --> I[Use Extractants]
    I --> J[Double/Triple Glass Distilled Water]
    I --> K[0.9% Sodium Chloride Solution]

Use these classifications and tables for design verification, acceptance testing, and biological compatibility as per IS 12709.

IS 12709 — Key Formulas, Tables & Specifications for Materials

1. Symbols & Logarithmic Calculations (Clause 11.1)

• ( N ) = Number of data points
• ( f ) = Logarithm (base 10) of failure stress/strain (%)
• ( F ) = Arithmetic average of all ( f ) values
• ( / ) = Logarithm (base 10) of failure time (hours)
• ( H ) = Arithmetic average of all ( / ) values

Use 5-place logarithm tables for precision.

2. Sample Data for Strain Method (Clause 15.1, Table F-15.1)

Log values are used for time-to-failure vs. stress/strain analysis.

3. Dimensional Tolerances for Pipes (Clause 6.5 & Amendments)

4. Minimum Tensile Strengths (Page 6, Tables 5 & 6)

• Longitudinal Tensile Strength (kN/m circumference):

| DN | PN 3 | PN 6

IS 12709: Dimensions and Tolerances for Pipes

1. Outside Diameter (OD) & Tolerances (Clause 7.1.2, Table 2)

• OD tolerance is generally positive, with some exceptions (e.g., DN 700 has ± tolerance).

2. Inside Diameter (ID) & Tolerances (Clause 7.1.1, Table 1)

• ID tolerances are symmetric ± values around declared ID.

3. Measurement (Annex A, Clause 7.3)

• Diameters must be measured accurately using calibrated instruments.
• Both ID and OD should be checked at multiple points to ensure compliance within tolerance.

Summary:

• OD tolerances are mostly positive with occasional negative allowance.
• ID tolerances are symmetric ± values.
• Nominal diameters range from DN 200 to DN 3000 with increasing tolerances for larger sizes.

flowchart LR
    A[Nominal Diameter DN] --> B[Specified OD ± Tolerance]
    A --> C[Specified ID ± Tolerance]
    B --> D[Measurement of OD]
    C -->

IS 12709: Mechanical Properties Key Points

1. Symbols (Clause 11.1)

• N = Number of data points on time-to-failure vs stress/strain plot
• f = log₁₀ of failure stress/strain (%)
• F = Arithmetic mean of all f values
• l = log₁₀ of failure time (hours)
• H = Arithmetic mean of all l values
  Note: Use 5-decimal logarithm tables.

2. Strain Method Data (Clause 15.1, Table F-15.1)

• Time (hours) and Strain (%) are logged for regression analysis.
• Example data points show time and strain logged to base 10 for trend fitting.

3. Calculations (Clause 11.1 & F-11)

• Use Least Squares Method to fit log(stress/strain) vs log(time).
• Calculate mean values F and H.
• Derive long-term stress/strain and confidence limits.

4. Important Parameters (Clause 5.641)

• Mean stress/strain at long time
• Hydrostatic Design Basis (HDB) (Method A or B)
• Test conditions, unusual behavior, and lab details must be documented.

Typical Formula for Least Squares Fit:

[ F = \frac{1}{N} \sum_{i=1}^N f_i, \quad H = \frac{1}{N} \sum_{i=1}^N l_i ]

Where (f_i = \log_{10}(\text{stress or strain}i)), (l_i = \log{10}(\text{time}_i)).

graph LR
A[Data Points: Time & Strain/Stress] --> B[Logarithmic Transformation]
B --> C[Least Squares Regression]
C --> D[Calculate Mean F & H]
D --> E[Derive Long-Term Mechanical Properties]
E --> F[Hydrostatic Design Basis & Confidence Limits]

This approach ensures reliable extrapolation of long-term mechanical behavior from short-term test data.

IS 12709: Jointing and Fittings - Key Points & Formulas

1. Jointing (Clause 8.1.1 & 9.3)

• Joint Type: Coupling or Socket & Spigot with elastomeric gasket retained in groove.
• Watertightness: Gasket is sole sealing element.
• Surface Condition: Joint sealing surfaces must be free from dents, gouges, or irregularities.
• Typical Detail: See Fig. 1 (groove location on spigot or socket).

2. Fittings from Straight Pipe (Clause 11.2)

• Fabricate fittings from complete straight pipes or portions.
• Mitre cuts must be overwrapped externally and, if possible, internally with:
  • Woven roving and/or chopped strand mat.
• Ensure longitudinal and circumferential tensile strength ≥ pipe strength.

3. Pipe Stiffness & Joint Strength (Clause 8.2)

• Joints must withstand internal pressure and longitudinal forces.
• Design joints for:
  • Internal pressure (P)
  • Axial forces (F)
• Typical design checks include hoop stress and axial load capacity.

Typical Joint Strength Formula (Internal Pressure)

[ \sigma_h = \frac{P \times d}{2t} ]

Where:

• (\sigma_h) = hoop stress
• (P) = internal pressure
• (d) = pipe diameter
• (t) = pipe wall thickness

Summary Table: Joint & Fitting Requirements

flowchart LR
    A[Pipe] --> B[Spigot End with Groove]
    A --> C[Socket End with Groove]
    B & C --> D[Elastomeric Gasket]
    D --> E[Watertight Joint]
    F[

IS 12709: Workmanship and Visual Acceptance Criteria (Clause 9 & Table 10)

Workmanship must follow good practices and meet these Visual Acceptance Levels for defects in GRP pipes/fittings:

Additional Specifications:

• Diameter Tolerances (From Amendments):

  • Inside Diameter (ID) tolerance: ±5 mm for DN 1300, 1500
  • Outside Diameter (OD) tolerance: ±5 mm for DN 1300, 1500

• Strength Requirements (Tables 5 & 6):

  • Minimum Longitudinal Tensile Strength and Hoop Tensile Strength vary by DN and pressure class (PN 3 to PN 15).

Summary Diagram of Defect Acceptance:

graph TD
    A[Workmanship] --> B[Visual Inspection]
    B --> C{Defect Type}
    C -->|Chip| D[Max 6.5 mm]
    C -->|Crack| E[None]
    C -->|Surface Crack| F[Max 6.5 mm length]
    C -->|

Pipe Stiffness (IS 12709)

Key Formula (Clause 10.1)

Pipe stiffness ( S ) is calculated as:

[ S = \frac{F}{\Delta y} ]

• F = Load per unit length (kN/m)
• Δy = Vertical deflection at mid-length (m)

Table 3: Minimum Pipe Stiffness at 5% Deflection (kPa)

Deflection Limits Without Damage (Clause 10.1.1)

• Note: Actual use recommends max 5% deflection for service.

Summary:

• Use the formula ( S = \frac{F}{\Delta y} ) to calculate pipe stiffness.
• Verify stiffness meets Table 3 values for your pipe DN and class.
• Ensure deflection limits (Level X & Y) are respected to avoid damage.

flowchart TD
    A[Apply Load F (kN/m)] --> B[Measure Deflection Δy (m)]
    B --> C[Calculate Stiffness S = F/Δy]
    C --> D{Compare with Table 3}
    D -->|S ≥ Min Stiffness| E[Pass]
    D -->|S < Min Stiffness| F[Fail]

This ensures pipe strength and durability per IS 12709 standards.

IS 12709: Testing and Acceptance Criteria - Key Points

1. Stress Calculation (Clause 2.399)

• Stress at long durations (e.g., 100,000 hours, 50 years) is calculated using a log-log plot of stress vs. time or ( f ) vs. ( h ).
• The three test points must lie on a straight line, confirming correctness.
• Example values:

2. Acceptance Tests (Annex G, Clause 3.4.2)

• Samples are taken from a lot for acceptance testing.
• Tests must confirm conformity based on specified criteria.

3. Sampling and Conformity Criteria (Annex G, Clause 17)

• Sampling procedures and conformity criteria are detailed in Annex G.
• Key parameters to report:
  • Mean stress/strain at long time and lower confidence value.
  • Hydrostatic Design Basis (HDB) and its source (Method A or B).
  • Any unusual test behavior.
  • Test dates and laboratory details.

4. Data Analysis (Clause F-11)

• Least squares method is used for long-term stress/strain calculations.

Summary Formula for Stress-Time Relation (Log-Log Scale)

[ \log f = m \log h + c ]

Where:

• ( f ) = stress
• ( h ) = time (hours)
• ( m, c ) = constants from least squares fit

flowchart LR
    A[Sample Collection] --> B[Acceptance Tests]
    B --> C{Conformity?}
    C -- Yes --> D[Lot Accepted]
    C -- No --> E[Reject Lot]
    B --> F[Calculate Stress vs Time]
    F --> G[Plot on Log-Log Graph]
    G --> H[Least Squares Fit]
    H --> I[Determine Long Term Stress]

Note: Always refer to Annex G for detailed sampling and acceptance criteria procedures.

IS 12709: Potability & Chemical Testing Key Points

1. Potability Testing (Clause 16)

• Sample preparation:
  • Cut GRP pipe pieces (5 cm × 5 cm).
  • Surface area: 1 cm² per 2 ml extractant.
  • Chemical tests: 60 ± 1°C for 2 hours.
  • Biological tests: 40 ± 1°C for 24 hours.
• Extractants for chemical tests (16.1.1.1):
  • Distilled water (double/triple glass distilled).
  • 3% acetic acid solution.
  • 8% ethanol solution.
  • 0.9% sodium chloride solution.
• Extractants for biological tests (16.1.1.2):
  • Distilled water.
  • 0.9% sodium chloride solution.

2. Long Term Hydrostatic Design Pressure (Clause 4.1.1 & Table 7)

• Based on 50-year extrapolated strength (Annex F).

3. Mechanical Strength Requirements

• Beam Strength & Longitudinal Tensile Strength (Table 5)
• Minimum Hoop Tensile Strength (Table 6)
  Refer to the nominal diameter and pressure class for design values (kN/m circumference).

Summary Diagram: Potability Testing Process

flowchart TD
  A[GRP Pipe Sample (5x5 cm)] --> B[Prepare Extractants]
  B --> C{Chemical or Biological Test?}
  C -->|Chemical| D[Immerse in Extractants at 60°C for 2 hrs]
  C -->|Biological| E[Immerse in Extractants at 40°C for 24 hrs]
  D --> F[Transfer Extracts to Transparent Bottles]
  E --> F
  F --> G[Conduct Chemical & Biological Tests]

Note: Sampling

IS 12709: Hydrostatic Design Basis (HDB) Summary

• Hydrostatic Design Basis (HDB) is the fundamental hoop stress/strain capacity of the fiberglass pipe under long-term hydrostatic pressure (Clause 2.4, F-2.4).

• Hydrostatic Design Stress/Strain (HDS) is obtained by multiplying the HDB by a Service Design Factor (SDF) (Clauses 3.4, 8.1; F-3.4, F-8.1).

Key Formulas

[ \text{HDS} = \text{HDB} \times \text{SDF} ]

• HDB: Hydrostatic Design Basis (from Method A or B, per F-5)
• SDF: Service Design Factor (from F-2.7, typically < 1 for safety)

Service Design Factor (Typical Values from F-2.7)

Hydrostatic Design Basis Determination (Methods A & B - F-5)

• Method A: Based on short-term hydrostatic strength tests.
• Method B: Based on long-term hydrostatic strength tests (more conservative).

Summary Flow

flowchart LR
    A[Hydrostatic Strength Test] --> B{Select Method A or B}
    B --> C[Determine HDB]
    C --> D[Multiply by Service Design Factor (SDF)]
    D --> E[Hydrostatic Design Stress/Strain (HDS)]

Note: Use the appropriate method and SDF for your service condition to ensure safe design pressure ratings.

IS 12709: Marking and Labelling Key Points

Marking Requirements (Clause 18.1)

• Marking on both pipe ends with bold letters ≥ 12 mm height.
• Marking must be legible under normal handling.
• Must include:
  • Manufacturer's name or trade-mark
  • Nominal pipe diameter
  • Class of pipe (pressure & stiffness)
  • Batch number or date of manufacture

BIS Certification (Clause 18.2)

• Pipes may carry the BIS Standard Mark for certification.

Workmanship & Visual Acceptance (Clause 9, Table 10)

Symbols for Failure Analysis (Clause 11.1)

• ( N ) = Number of points on failure plot
• ( f = \log_{10}(\text{failure stress/strain %}) )
• ( F ) = Average of all ( f ) values
• ( / = \log_{10}(\text{failure time in hours}) )
• ( H ) = Average of all ( h ) values

flowchart TD
    A[Pipe Ends] --> B[Mark

IS 12709: Installation Guidelines - Key Specifications & Tables

1. Workmanship & Defect Acceptance (Clause 9 & Table 10)

• Chip: Max 6.5 mm break
• Crack: None allowed through thickness
• Surface crack: Max length 6.5 mm
• Crazing: Max 2.5 mm
• Delamination edge: Max 6.5 mm; internal none allowed
• Dry-spot: Max diameter 14 mm
• Foreign inclusion: Max 1.5 mm (metallic/non-metallic)
• Fracture: Max 29 mm
• Air bubble (void): Max diameter 3 mm
• Blister: Max diameter 6.5 mm; height within tolerance

2. Dimensional Tolerances (Clause 7.1.2, Table 2 & Amendments)

• Larger diameters (1300, 1500 DN) have ±5 mm tolerance on OD and ID.

3. Mechanical Strength (Tables 5 & 6)

• Minimum Longitudinal Tensile Strength (kN/m circumference) varies with pressure class (PN 3 to PN 15).
• Minimum Hoop Tensile Strength (kN/m circumference) also specified per pressure class.

Installation Tips (General Guidance)

• Follow good workmanship practices per Table 10.
• Ensure dimensional accuracy within specified tolerances for proper jointing.
• Inspect pipes/fittings for defects before installation; reject if defects exceed limits.
• Use specified service design factor (Clause 2.7) for pressure and load calculations.

flowchart TD
    A[Pipe Inspection] --> B{Defects?}
    B -- No --> C[Proceed with Installation]
    B -- Yes --> D{Defect Type}
    D -->|Acceptable| C
    D -->|Unacceptable| E[Reject Pipe/Fitting]
    C --> F[Check Dimensional Tolerances]
    F --> G{Within

IS 12709: Quality Assurance & Certification Key Points

1. Sampling, Frequency & Criteria for Conformity (Clause 17 & Annex G)

• Sampling and acceptance criteria are detailed in Annex G.
• Acceptance tests cover workmanship and defect limits (Table 10).

2. Allowable Defects (Table 10 Highlights)

3. Long-Term Stress Calculation (Clause 2.399 & Step 3)

• Stress at long durations (e.g., 100,000 hours, 50 years) is calculated using log-log plots or empirical formulas.

4. Additional QA Requirements (Clause 5.641)

• Report must include:
  • Mean stress/strain at long time with confidence interval.
  • Hydrostatic Design Basis (HDB) and method (A or B).
  • Test observations, dates, laboratory, and supervisor details.

flowchart TD
    A[Sampling & Testing] --> B[Visual Inspection: Table 10 Defects]
    B --> C{Defects Within Limits?}
    C -- Yes --> D[Accept Batch]
   

IS 12709: Key Formulas, Tables & Specifications for Annexes and Reference Methods

1. Sampling & Conformity (Annex G)

• Sampling procedures and criteria for conformity are detailed in Annex G.
• Follow prescribed frequency and acceptance criteria for quality control.

2. Determination of HDB Category (Clause 6.4, Table 8)

• Use Table 8 to classify Hydrostatic Design Basis (HDB) categories based on material and test data.
• HDB is critical for pressure rating and design.

3. Measurement of Dimensions (Annex A)

• Annex A covers measurement methods for pipe and fitting dimensions.
• Diameters measured as effective diameter (not nominal).
• Precision in measurement ensures proper fit and performance.

4. Workmanship & Defect Acceptance (Clause 9, Table 10)

5. Biological Tests (Clause 16.9)

• Biological testing methods are outlined to ensure material durability.

Summary Diagram: Defect Acceptance Criteria

graph TD
    A[Workmanship Defects] --> B[Chip ≤ 6.5 mm]
    A --> C[No Cracks]
    A --> D[Surface Crack ≤ 6.5 mm]
    A --> E[Crazing ≤ 2.5 mm]
    A --> F[Edge Delamination ≤ 6.5 mm]
    A --> G[No Internal