Polyethene Fittings for use with Polyethylene Pipes for the Supply of Gaseous Fuels, Part 3: Electro Fusion Fittings
2011 Edition

Coverage of IS 15927 Part 3: Polyethylene Electrofusion Fittings

• Intended Use: Underground polyethylene electrofusion fittings with integrated heating elements.
• Compatible Pipes: Polyethylene pipes conforming to IS 14885 and fittings as per IS 15927 Part 2.
• Size Range: Nominal outside diameters from 16 mm to 315 mm.
• SDR Classes: SDR 11 and SDR 17.6.
• Material Types: PE 80 and PE 100.
• Pressure Ratings: 5.5 bar and 7 bar.
• Operating Temperature Range: -5°C to 40°C.
• Purpose: Designed specifically for gas distribution pipelines.

Important Parameters:

Referenced Standards:

• IS 14885: Polyethylene pipes for gaseous fuels.
• IS 15927 Parts 1 & 2: Socket and spigot fittings.
• IS 2530, IS 7328, IS 15430: Material and testing procedures.

Hydrostatic Pressure Endurance Test (Clause 10.7)

Visual and Dimensional Sampling Plan (Table 10)

Essential Formulas, Tables, and Specifications from IS 15927 Part 3

1. Wall Thickness Correlation (Clause 9.1, Table 2)

• E represents fitting wall thickness.
• en denotes pipe wall thickness.

2. Hydrostatic Strength at 80°C (Table 7)

3. Pressure Drop Characteristics for Electrofusion Tapping Tees (Table 8)

4. Acceptance Testing and Sampling (Tables 9-11)

• Includes visual inspection, dimensional verification, melt flow rate, density, carbon black content and dispersion, thermal stability, hydrostatic resistance, among others.
• Sampling sizes depend on lot volumes.

IS 15927 Part 3: Essential Definitions, Formulas & Tabulations

1. Definitions (Clause 5.5 and General Provisions)

• Applies to buried polyethylene electrofusion fittings with embedded heating elements.
• Compatible with polyethylene pipes conforming to IS 14885.
• Covers nominal sizes from 16 mm to 315 mm, SDR classes 11 and 17.6, materials PE 80 and PE 100.
• Rated for operating pressures of 5.5 bar and 7 bar.
• Operational temperature range: -5°C to 40°C.

2. Wall Thickness Relations (Clause 9.1 and Table 2)

• Where E = fitting wall thickness
• en = minimum pipe wall thickness
• For fittings placed beyond two-thirds of the fitting length from the entrance face with same MRS, E ≥ minimum pipe thickness.

3. Lot Definition and Sampling (Clause 11.1 and Tables 10 & 11)

• A lot is defined as production from machine start to shutdown, limited to a maximum of 170 hours or 10,000 units.
• Sampling for visual and dimensional checks (Table 10) and hydraulic and thermal tests (Table 11) is based on lot size.
• Acceptance and rejection criteria for defective fittings are specified.

4. Hydrostatic Pressure Testing (Clause 10.7 and Table 6)

IS 15927 Part 3: Specifications for Electro Fusion Fittings and Their Dimensions

1. Electrofusion Socket Fittings (Clause 4.1, Figure 1A)

• Critical Dimensions:
  • (d_s): Mean inside diameter of the fusion socket zone
  • (L_1): Socket insertion depth
  • (L_2): Effective fusion zone length

2. Electrofusion Tapping Tees (Clause 4.2, Figure 1B)

• Key Dimensions:
  • (h): Height from main pipe axis to service pipe axis
  • (L): Length of tapping tee from main pipe axis to spigot end
  • (H): Total height from main pipe top to tapping tee top

3. Material Requirements (Clause 6.1)

• Polyethylene compounds must meet the specifications outlined in IS 14885 Table 2.
• Additives should be uniformly mixed and must not impair the fusion process.
• No visible moisture content is permitted.

4. Maximum Reducer Lengths (Table 4, Clause 9.3)

5. Spigot Outlet Dimensions for Tapping Tees (Table 5, Clause 9.4.1)

IS 15927 Part 3: Core Material Requirements

1. Material Grade Identification (Clauses 5.2 & 5.2.3)

• Suppliers must provide clear material grade classification.
• This classification ensures traceability and compliance with required properties.

2. Minimum Required Strength (MRS) (Clause 3.14)

• Defined as the minimum long-term hydrostatic strength in MPa.
• Used for pipe and fitting design and classification.

3. Wall Thickness Requirements (Clause 9.1 and Table 2)

• E = fitting wall thickness
• en = minimum pipe wall thickness

4. Additional Wall Thickness Clause (9.1a)

• For fittings and pipes with identical MRS, the fitting thickness E must be at least equal to the minimum pipe thickness beyond two-thirds of the fitting length from the entrance face.

Summary Expression:

[ E \geq \begin{cases} e_{Min}, & \text{if same MRS and beyond } \frac{2L}{3} \ 0.8 \times e_n, & \text{for PE 80 pipe and PE 100 fitting} \ \frac{e_n}{0.8}, & \text{for PE 100 pipe and PE 80 fitting} \end{cases} ]

This ensures compatibility and long-term durability of pipe and fitting assemblies.

IS 15927 Part 3: Marking and Identification Requirements for Polyethylene Fittings

Essential Requirements (Clauses 13.2 & 13.3)

• Markings must be permanent, clearly readable without magnification, and should not induce cracks or degrade the fitting.
• Markings must remain legible throughout handling, storage, and installation.
• Marking methods must not compromise fitting integrity.

Required Marking Details (Clause 13.2):

Practical Considerations:

• Use indelible ink, embossing, or engraving that does not weaken the fitting.
• Marking placement must be accessible and visible after installation.

flowchart LR
    A[Fitting] --> B[Marking]
    B --> C{Is marking legible?}
    C -->|Yes| D[Permanent and Non-damaging]
    C -->|No| E[Re-marking or Rejection]

These requirements ensure traceability, quality assurance, and safe installation as per IS 15927 Part 3.

IS 15927 Part 3: Procedures for Jointing and Fusion Parameters

1. Fusion and Cooling Duration (Clause 8.5)

• Total jointing time is the sum of fusion time plus cooling time.
• Cooling duration follows the method in Annex C; the maximum cooling time declared by the manufacturer applies.

2. Joint Appearance Criteria (Clause 7.4)

• No molten material should extrude outside or into the inner cold zone, except for fusion indicators.
• No major voids or collapse of the pipe should occur at the fusion interface.

3. Dimensional Characteristics (Clause 9)

• Nominal diameters range from 16 to 315 mm.
• Measurements are taken after 24 hours of manufacture.
• Ovality must not exceed 0.015 times the nominal diameter.
• Inner cold zone length of sockets:
  • For diameters ≤ 125 mm: at least (0.1 × d + 5) mm
  • For diameters > 125 mm: at least 0.1 × d mm

4. Coupler Dimensions (Table 3 and Figure 1A)

5. Reheating of Joints (Clause 7.5)

• One reheating cycle is permitted for fittings used with SDR 11 and SDR 17.6 pipes.
• Cooling to 27 ± 2°C is required before reheating.
• No degradation of joint performance is allowed post-reheating.

Diagram: Socket Fitting Dimensions

flowchart LR
    A[Socket Fitting] --> B[Lead-in for Assembly]
    A --> C[Inner Cold Zone]
    C --> D{Diameter d}
    D -->|d ≤ 125 mm| E[At least 0.1d + 5 mm]
    D -->|d > 125 mm| F[At least 0.1d mm]
    A --> G[Ovality ≤ 0.015d]
    A --> H[Minimum Fusion Length per Table 3]

IS 15927 Part 3: Heating Elements and Electrical Characteristics

Key Highlights:

• Heating Element Resistance (Clause 8.2):

  • Manufacturer specifies nominal resistance per size and type.
  • Tolerance on resistance is ±10%.
  • Joint quality must be verified at resistance tolerance extremes using the method in Annex B.

• Definition of Heating Element (Clause 3.28):

  • A resistance wire embedded in the fitting or pipe surface to generate heat for fusion.

• Short/Open Circuit Prevention (Clause 8.3):

  • Design must prevent short circuits and localized overheating.
  • Protective coatings should not impair fusion quality.

Typical Parameters:

Electrical Resistance Formula:

[ R = \rho \frac{L}{A} ]

• (R): Resistance (Ohms)
• (\rho): Resistivity of wire material (Ohm-meters)
• (L): Length of heating element (meters)
• (A): Cross-sectional area (square meters)

Fusion Heating Considerations:

• Uniform heat distribution is essential.
• Avoid local overheating to maintain joint integrity.

flowchart LR
    A[Heating Element] --> B[Resistance Wire]
    B --> C[Heat Generation]
    C --> D[Heating of Pipe/Fitting Surface]
    D --> E[Formation of Fusion Joint]
    B --> F[Resistance Measurement ±10%]
    F --> G[Joint Quality Verification (Annex B)]

For comprehensive testing details, consult Annex B of IS 15927 Part 3.

IS 15927 Part 3: Key Geometrical Features

1. Overall Dimensions (Clauses 9.4.1 & 4.2)

• Important dimensions include:
  • h: Height of outlet (axis of main pipe to axis of outlet)
  • L: Length of branch (axis of main pipe to spigot mouth)
  • H: Overall height (top of main pipe to top of tapping tee)
• Outlet types considered:
  • Spigot type (dimensions per Table 5)
  • Electrofusion type (dimensions shown in Figure 1B)

2. Nominal Diameter Range (Clause 9)

• Sizes included: 16, 20, 25, 32, 40, 50, 63, 75, 90, 110, 125, 140, 160, 180, 200, 225, 250, 280, 315 mm

3. Wall Thickness Relationship (Clause 9.1 and Table 2)

• E: fitting wall thickness
• en: pipe wall thickness
• For fittings and pipes with the same MRS, fitting wall thickness must be at least the minimum pipe wall thickness beyond two-thirds of the fitting length from the entrance face.

4. Jointing Time (Clause 8.5)

• Total jointing time is the sum of fusion time and cooling time.
• Cooling time is per Annex C, with the maximum cooling time declared by the manufacturer.

Diagram: Tapping Tee Dimension Parameters

graph TD
    A[Overall Tapping Tee] --> B[h (Outlet Height)]
    A --> C[L (Branch Length)]
    A --> D[H (Overall Height)]
    B --> E[Spigot or Electrofusion Outlet]

Note: All dimensions should be measured after 24 hours post-manufacture for accuracy.

IS 15927 Part 3: Summary of Performance Requirements and Testing Procedures

1. Lot Definition and Sampling (Clause 11.1)

• Maximum lot size is 170 hours of production or 10,000 fittings.
• Sampling for visual and dimensional tests follows Table 10.
• Hydraulic and thermal tests sampling per Table 11.
• Acceptance limits and rejection criteria are specified in the standard.

2. Hydrostatic Pressure Testing (Tables 6 & 7)

• Testing uses water-in-water medium.
• End cap orientation during testing is not applicable.

3. Sampling Plans

• Visual and dimensional sample sizes vary from 13 to 200 fittings, depending on lot size.
• Hydraulic and thermal testing samples range from 3 to 7, based on lot size.

4. Additional Testing (Table 9)

• Includes visual inspection, dimensional measurements, melt flow rate, density, carbon black content and dispersion, thermal stability, fusion indicator operation, heating element resistance, decohesion, hydrostatic resistance, and end reversion tests.

5. Pressure Drop Testing for Electrofusion Tapping Tees (Table 8)

• Maximum pressure drops range between 0.10 and 0.90 mbar depending on fitting and pipe sizes.

Hoop Stress Calculation Formula for Hydrostatic Test

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

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

IS 15927 Part 3: Outline of Acceptance Tests

1. Hydrostatic Resistance Testing Parameters (Clause 10.7, Table 6)

2. Hydrostatic Strength at 80°C (Stress vs Minimum Failure Time) (Table 7)

3. Sampling Plans

• Visual and dimensional inspections (Table 10) specify sample sizes and acceptance/rejection thresholds based on lot size.

IS 15927 Part 3: Overview of Type Tests

Objective (Clause 12.1)

• Type tests confirm the suitability of new materials, manufacturing techniques, or fitting sizes.
• Required when changes occur in production or for new fitting dimensions.

Sample Selection (Clause 12.2)

• Samples are randomly selected of identical pressure class and size.
• Prepared according to Table 12 and tested per Table 13.

Principal Test Parameters and Acceptance Limits (Table 6 - Hydrostatic Pressure Test)

• Test medium is water-in-water.
• Conditioning includes 1 hour at 20°C and 12 hours at 80°C.
• End cap orientation is not applicable.

Hydrostatic Strength at 80°C (Table 7)

Acceptance Tests (Table 9)

• Includes visual aspects, dimensional accuracy, melt flow rate, density, carbon black content and dispersion, pigment consistency.

IS 15927 Part 3: Guidelines for Marking and Packaging of Fittings

Marking Requirements (Clauses 13.2 & 13.3)

Each fitting shall be clearly marked with:

• Manufacturer’s identification
• Nominal diameter and SDR rating
• Manufacture date or batch number
• Fusion time (seconds)
• Cooling time (minutes)
• Material type (e.g., PE with designation)

Markings must remain legible throughout handling, storage, and installation.

Packaging Requirements (Clause 14.3)

• Individual fittings shall be packaged in clear polyethylene bags with a minimum thickness of 75 microns to prevent damage.
• Outer packaging should consist of cardboard boxes or cartons suitable for stacked storage.
• Outer packaging must be marked with:
  • Manufacturer’s identity
  • Nominal diameter and SDR
  • Batch or manufacturing date
  • Fitting type and quantity

Summary Table of Type Tests (Table 13)

flowchart TD
    A[Individual Fitting] --> B[Polyethylene Bag (≥75μm)]
    B --> C[Outer Carton/Box]
    C --> D[Stacked Storage]
    C --> E[Marking: Manufacturer Info, Type, Quantity]

IS 15927 Part 3: Packaging Requirements (Clause 14.3 and Table 14)

• Inner Packaging: Each fitting must be individually enclosed in transparent polyethylene bags of minimum thickness 75 microns to avoid deterioration.
• Outer Packaging: Use cardboard cartons or boxes designed for stacked storage.
• Markings on Outer Packaging: Must include manufacturer identification, nominal diameter, SDR rating, batch or manufacturing date, fitting type, and quantity.

Packaging Summary Table

Additional Notes:

• Packaging protects against moisture, dust, and mechanical damage.
• Proper marking facilitates identification and inventory control.

flowchart TD
    A[Fitting] --> B[Polyethylene Bag (≥75μm)]
    B --> C[Cardboard Box/Carton]
    C --> D[Stacked Storage]
    C --> E[Marking: Manufacturer Info, Type, Quantity]

This packaging approach ensures fittings are preserved during storage and transit in accordance with IS 15927 Part 3.

IS 15927 Part 3: Summary of Testing Methods and Additional Provisions

1. Hydrostatic Strength Testing (Clauses 10.7 and Tables 6 & 7)

• Note: At 80°C, only brittle failures are counted; ductile failures require adjustment of hoop stress as per Table 7.

2. Hydrostatic Strength Correlation at 80°C (Table 7)

3. Sampling and Acceptance (Clause 11.1 and Tables 9-11)

• Lot size is limited to 170 hours or 10,000 fittings.
• Visual and dimensional sampling follows Table 10.
• Hydraulic and thermal testing sampling follows Table 11.