Unplasticized PVC Pipes (Ducts) and Fittings for Underground Telecommunications Cable Installation
1999 Edition

Overview of Scope - IS 14735 Standard Details

Scope:
Defines dimensional, material, and testing criteria for UPVC fittings used in underground telecom cable ducts.

Essential Specifications:

• Vicat Softening Temperature (Clause 12.3):

  • Minimum requirement: 78°C (in accordance with IS 6307).
  • Specimens supported on a concave surface matching their radius.

• Sulphuric Acid Resistance (Clause 13):

  • Mass change limits:
    • Maximum increase: 0.32 g
    • Maximum decrease: 0.13 g
  • Surface alterations disregarded.

• Wall Thickness (Clause 7.1, Table 1):

• Vent Cowl Dimensions (Clause 11.4, Table 5):

• Pipe Clips (Clause 11.5, Table 6):

Key Normative References and Calculations in IS 14735

1. References and Test Procedures

• Vicat Softening Point (Clause 12.3):

  • Minimum temperature: 78°C per IS 6307.
  • Samples supported on concave surfaces matching radius.

• Sulphuric Acid Resistance (Clause 13):

  • Mass change limits after IS 12235 Part 7 test:
    • Increase ≤ 0.32 g
    • Decrease ≤ 0.13 g

• Titanium Dioxide Content (Clause 14):

  • Calcination performed until weight stabilizes (difference ≤ 0.5 mg), max 3 hours.

  • Sulphated ash percentage computed as:

    [ \text{Sulphated ash %} = \frac{M_2 - M_1}{M_3 - M_1} \times 100 ]

    where

    • (M_1) = mass of crucible
    • (M_2) = mass of crucible plus sample
    • (M_3) = mass of crucible plus residue

2. Tables of Importance

Colour Standards and Related Requirements in IS 14735

Important Points on Colour and Visual Inspection (Clause E-2)

• Colour compliance is verified by sampling each production lot independently (Clause 1.2).
• Colour checking is an acceptance test as per Table 7 (Clause 18.1).
• Visual quality, workmanship, and dimensional accuracy are also acceptance criteria.

Sampling and Acceptance Thresholds (Table 8)

• Lots exceeding acceptance defect counts are rejected.

Related Technical Specifications

• Vicat Softening Point: ≥ 78°C (Clause 12.3)
• Sulphuric Acid Resistance: Mass change limits ±0.32 g / -0.13 g (Clause 13)
• Titanium Dioxide Content: Verified during type testing (Clause 14)
• Stress Relief and Impact Tests: Conducted post colour acceptance (Clause E-3.1.1)

Sampling and Acceptance Workflow Diagram

flowchart TD
    A[Production Lot] --> B{Determine Lot Size}
    B -->|≤ 500| C[Sample 50 Units]
    B -->|501-1200| D[Sample 80 Units]
    B -->|1201-3200| E[Sample 125 Units]
    B -->|3201-10000| F[Sample 200 Units]

    C --> G{Defects ≤ 0?}
    D --> H{Defects ≤ 1?}
    E --> I{Defects ≤ 1?}
    F --> J{Defects ≤ 2?}

    G -->|Yes| K[Accept Lot]
    G -->|No| L[Reject Lot]
    H -->|Yes| K
    H -->|No| L

Material Requirements According to IS 14735

Vicat Softening Temperature (Clause 12.3)

• Minimum Vicat softening temperature required: 78°C per IS 6307.
• Test specimens supported on a concave surface matching their radius.

Sulphuric Acid Resistance (Clause 13)

• Mass change limits after exposure per IS 12235 Part 7:
  • Mass increase ≤ 0.32 g
  • Mass decrease ≤ 0.13 g
• Surface appearance changes are disregarded.

Wall Thickness for Fittings (Clause 7.1, Table 1)

• Note: A 5% thickness reduction is permitted due to core shifting; however, the average of measurements on opposite sides must meet the minimum thickness.

Vent Cowl Dimensions (Clause 11.4, Table 5)

Pipe Clip Dimensions (Clause 11.5, Table 6)

Dimensions and Permissible Variations (Clause 7.2)

Highlights:

• Socket and spigot dimensions for ring seal and solvent cement fittings are detailed in Tables 2 and 3.
• Out-of-roundness tolerance for socket inside diameter: [ \text{Max Diameter} - \text{Min Diameter} \leq 0.7% \times DN ]

Selected Data from Table 3: Ring Seal Fittings

Selected Data from Table 2: Solvent Cement Fittings

Notes:

• The socket inside diameter is averaged from two measurements taken at 90° apart at the socket midpoint.
• Maximum taper angles:
  • For DN ≤ 75 mm: 0°40' total included angle
  • For DN ≥ 90 mm: 0°30' total included angle

Specifications for Sealing Rings in IS 14735

1. Material Characteristics

• Sealing rings are fabricated from elastomeric material with an IRHD hardness of 50 ± 5.
• They must not negatively impact the fitting’s mechanical or physical properties.
• The ring’s width must fit precisely within the designated groove of the socket.

2. Socket and Spigot Dimensions for Ring Seal Fittings (Table 3, Clause 7.2)

Workmanship Criteria and Sampling as per IS 14735

Requirements (Clause 10 & E-2)

• Workmanship encompasses colour uniformity, visual appearance, and dimensional precision.
• Reworked material generated internally by the manufacturer is permitted up to 10% of the batch.
• Use of any other reworked material is prohibited.

Sampling and Evaluation Criteria (Table 8, Clause E-2.1)

• Batches exceeding the accepted defect level are rejected.
• After passing workmanship evaluation, samples undergo stress relief and impact (drop) testing.

Acceptance Tests (Clause 18.1, Table 7)

Summary Workflow

flowchart TD
    A[Batch of Fittings] --> B[Sample per Table 8]
    B --> C{Defect Count ≤ Allowed?}
    C -- Yes --> D[Batch Accepted]
    C -- No --> E[Batch Rejected]
    D --> F[Perform Acceptance Tests]
    F --> G[Include Workmanship, Colour, Dimensions, Stress Relief]

Design Specifications and Relevant Tables in IS 14735

1. Socket and Spigot Dimensions (Clause 7.2, Table 3)

2. Wall Thickness (Clause 7.1, Table 1)

Note: A 5% reduction allowance is made for core shifting effects; the average of two opposite wall thickness measurements must meet the minimum value.

3. Vicat Softening Temperature (Clause 12.3)

• Minimum required: 78°C as per IS 6307.

4. Sulphuric Acid Resistance (Clause 13)

• Mass change limits:
  • Increase ≤ 0.32 g
  • Decrease ≤ 0.13 g

Summary of Physical Testing Protocols per IS 14735

1. Acceptance Tests (Clause 18.1, Table 7)

2. Sampling and Acceptance (Annex E, Table 8)

Applies to colour, workmanship, visual, and dimensional tests.

3. Key Physical Test Details

• Vicat Softening Test (Clause 12.3):
  Minimum temperature of 78°C according to IS 6307.
  Specimens supported on a concave surface matching the specimen radius.

• Sulphuric Acid Resistance (Clause 13):
  Mass change limits per IS 12235 (Part 7) test:

  • Increase ≤ 0.

Chemical Resistance Requirements in IS 14735

1. Vicat Softening Point (Clause 12.3)

• Minimum Vicat softening temperature: 78°C following IS 6307.
• Samples supported on concave surfaces matching their radii.

2. Sulphuric Acid Resistance (Clause 13)

• Conducted per IS 12235 Part 7.
• Limits on mass change:
  • Increase ≤ 0.32 g
  • Decrease ≤ 0.13 g
• Surface visual changes such as roughening, bleaching, or blackening are disregarded.

3. Relevant Acceptance and Type Tests (Clause 18.1, Table 7)

Summary:

• Ensure chemical stability with Vicat softening point ≥ 78°C.
• Verify resistance to sulphuric acid by mass change limits.
• These assessments are performed as type tests to confirm chemical durability.

flowchart TD
    A[Sample Preparation] --> B[Vicat Softening Test]
    B --> C{Temperature ≥ 78°C?}
    C -- Yes --> D[Pass]
    C -- No --> E[Fail]
    A --> F[Sulphuric Acid Exposure Test]
    F --> G{Mass Change Within Limits?}
    G -- Yes --> D
    G -- No --> E

Titanium Dioxide Content Specifications in IS 14735

• Minimum TiO₂ Content: As stated in Clause 2.5, titanium dioxide content must be at least 2.5% by weight.

• Test Procedure (Annex A):

  • Prepare standard TiO₂ solutions with volumes and concentrations as follows:

    Volume (ml)	TiO₂ Concentration (mg/ml)
    0.00	0.00
    5.0	0.02
    10.0	0.04
    15.0	0.06
    20.0	0.08
    25.0	0.10

  • Procedure steps:

    1. Transfer specified volume into a 50 ml volumetric flask.
    2. Dilute nearly to mark with 10% H₂SO₄.
    3. Add 2 ml of 30% H₂O₂.
    4. Fill to volume with 10% H₂SO₄, shake, and keep in dark for approximately 30 minutes.

• Sample Measurement:

  • Determine TiO₂ content from absorbance measurements following Clause 5.4.
  • Average assay for rutile TiO₂ is about 93% TiO₂ (Clause 2.6).

Formula for TiO₂ Concentration:

[ C = \frac{V_s}{50} \times C_{std} ]

Where:

• (C) = concentration in mg/ml
• (V_s) = volume of standard solution (ml)
• (C_{std}) = concentration of standard TiO₂ solution (assumed 0.10 mg/ml)

flowchart LR
    A[Standard TiO₂ Solution] --> B[Measure Volume (0-25 ml)]
    B --> C[Dilute to 50 ml with 10% H₂SO₄]
    C --> D[Add 2 ml 30% H₂O₂]
    D --> E[Dilute to volume, shake]
    E --> F[Measure Absorbance]

Sulphated Ash Content as Defined in IS 14735

Definition:
Sulphated ash content is the residue left after complete combustion of the sample, followed by treatment with concentrated sulphuric acid and heating at 850°C until the mass remains constant.

Calculation for Titanium Dioxide Content (Clause 5.4.3 & Annex A)

[ \text{TiO}_2 % = \frac{C \times V_1 \times V_2 \times 100}{M \times V_3} ]

Where:

• (C) = concentration of TiO₂ in final solution (mg/ml)
• (M) = mass of test sample (mg)
• (V_1) = total volume of sample solution (500 ml)
• (V_2) = volume of prepared solution (50 ml)
• (V_3) = volume transferred from total solution (50 ml)

Limits for Sulphated Ash and Titanium Dioxide Content (Clause 15 & 2.5)

Testing Procedure (Annex B)

1. Completely burn the sample.
2. Treat residue with concentrated H₂SO₄ to convert it into sulphates.
3. Heat residue at 850°C until constant weight is achieved.
4. Calculate sulphated ash as percentage of original sample mass.

Notes

• Use a desiccator with a non-reactive drying agent to prevent moisture absorption (Clause 3.6).
• Constant mass is confirmed by repeated heating until weight variation is negligible.

flowchart TD
    A[Sample] --> B[Combustion]
    B --> C[Residue]
    C --> D[Treatment with H₂SO₄]
    D --> E[Heating at 850°C]
    E --> F[Constant Mass Residue]
    F --> G[Calculate Sulphated Ash Content]

This procedure ensures accurate quantification of inorganic residue in UPVC fittings.

Mechanical Properties as per IS 14735

1. Wall Thickness (Clause 7.1, Table 1):

• Note: Core shifting allows up to a 5% reduction, provided the average thickness measured on opposite sides meets or exceeds minimum values.

2. Vicat Softening Temperature (Clause 12.3):

• Minimum required: 78°C as per IS 6307.

3. Sulphuric Acid Resistance (Clause 13):

• Mass change limits:
  • Increase ≤ 0.32 g
  • Decrease ≤ 0.13 g
• Surface appearance changes ignored.

4. Sampling for Stress Relief and Impact Testing (Clause 3.1.1, Table E-3.1):

Wall Thickness Compliance Diagram

flowchart TD
    A[Nominal Diameter] --> B{Diameter Range}
    B -->|40-125| C[Wall Thickness: 3.2-3.8 mm]
    B -->|140| D[Wall Thickness: 3.6-4.2 mm]
    B -->|160| E[Wall Thickness: 4.0-4.6 mm]

Water Tightness Test Procedure per IS 14735

1. Test Arrangement (Annex D, Clause 17)

• Assemble fitting with pipe and seal all open ends using end-sealing devices.
• Connect one end to a hydraulic pressure source capable of bleeding air.
• Use water at ambient temperature.

2. Testing Method

• Gradually increase hydrostatic pressure to 0.05 MPa (0.5 bar).
• Maintain this pressure for 15 minutes.
• Inspect the assembly for any visible leakage.

3. Pass Criteria

• No visible leakage should occur during or after the test period.

Summary Table

Additional Information

• This test confirms the sealing integrity of joints under operational pressure.
• Conducted after successful visual, dimensional, and impact tests (Annex C).
• Failure indicates joint or fitting defects.

flowchart LR
    A[Assemble Fitting and Pipe] --> B[Seal Open Ends]
    B --> C[Connect to Hydraulic Pressure Source]
    C --> D[Fill with Ambient-Temperature Water]
    D --> E[Increase Pressure to 0.05 MPa]
    E --> F[Maintain Pressure for 15 Minutes]
    F --> G[Inspect for Leakage]
    G --> H{Leakage Detected?}
    H -- No --> I[Test Passed]
    H -- Yes --> J[Test Failed]

This test is vital to ensure joints retain watertightness under applied hydraulic pressure.

Sampling Procedure and Acceptance Standards in IS 14735

1. Sampling Approach (Clause 3.1.2 and Annex E)

• Sampling adheres to Clause E-2.2, utilizing Table 9 (not fully included here).
• Samples must be drawn independently from each production lot (Clause E-1.2).

2. Acceptance Tests (Clause 18.1 and Table 7)

3. Key Testing Details

• Sulphated Ash Content Calculation (Clause 4.7 B-6):

[ \text{Sulphated Ash %} = \frac{M_2 - M_1}{M_3 - M_1} \times 100 ]

Where:

• (M_1) = mass of empty crucible

• (M_2) = mass of crucible plus test portion

• (M_3) = mass of crucible plus residue after calcination

• Impact Test (Annex C):

  • Specimens conditioned at 0 ± 1°C for 30 minutes.
  • Dropped from 2 m height for DN ≤ 75 mm, or 1 m for DN > 75 mm, onto concrete.
  • No visible cracking or breakage allowed.

• Water Tightness Test (Annex D):

  • Apply hydrostatic pressure of 0.05 MPa for 15 minutes.
  • No leakage permitted.

Marking and Certification Details in IS 14735

1. BIS Certification Mark (Clause 19.2)

• Fittings may bear the BIS Standard Mark to indicate compliance.

2. Acceptance and Type Testing Matrix (Clause 18.1, Table 7)

3. Critical Specifications

• Vicat Softening Temperature (Clause 12.3): Minimum 78°C (IS 6307 method).

• Sulphuric Acid Resistance (Clause 13): Mass change limits:

  • Increase ≤ 0.32 g
  • Decrease ≤ 0.13 g (Test method IS 12235 Part 7).

• Sulphated Ash Content Formula (Clause 4.7): [ \text{Sulphated Ash %} = \frac{M_2 - M_1}{M_3 - M_1} \times 100 ] Where:

  • (M_1) = crucible mass
  • (M_2) = crucible plus sample mass
  • (M_3) = crucible plus residue mass after calcination

4. Impact (Drop) Test (Annex C)

• Condition specimens at 0 ± 1°C for 30 minutes.
• Drop height:
  • 2 meters for DN ≤ 75 mm
  • 1 meter for DN > 75 mm
• Inspect for any visible cracks or breaks.