Guniting: Method for Fireproofing of Pipes

1.0 Introduction to Fireproofing

Fireproofing is employed in refineries and petrochemical plants to minimize the escalation of a fire that would occur with the failure of structural supports and the overheating of pressure vessels. The damage that fire could potentially do very early on, could add significant fuel to the fire.

This section is for the materials and construction of fire resistant casings to pipes.

The thickness of fire proofing cover shall not be less than the requirement of BS 476 for a two hour rating.

2.0 Types of Fireproof casing for Pipes:

The following type of casing is approved:

  1. Gunite
  2. Lightweight cements
  3. Prefabricated cementitious board
  4. Intumescent coatings

Guniting is most widely used method for fireproofing of pipes.

The methods lightweight cements, prefabricated cementitious board & intumescent coatings are used in less critical areas and where weight reduction is of significant benefit.

3.0 Fireproofing materials for Pipes: Gunite

  • 3.1 Reinforcing fabric shall be 50mm x 50mm x 2.5mm, galvanised.
    The fabric shall be secured by 1.3mm galvanised tie wire to studs or spaces to maintain a clearance of not less than 20mm from the face of the member, and with a minimum cover of 20mm from the outside face of casing. Adjacent sheets shall be lapped at least 50mm, and securely tied together.
  • 3.2 Steel surfaces to be cased shall be cleaned of all loose paint, dirt, rust, scale, etc.; oil and grease deposits shall be removed with detergents, and the steel left in a clean and dry condition. Sound paint work may remain on the steel.
  • 3.3 The thickness of concrete cover for the casing to pipe shall be 50mm, to a tolerance of -2/+3mm. The concrete may be plaster applied and trowelled smooth.
  • 3.4 The fixings for the reinforcing fabric shall be robust, and in sufficient quantity, to secure the fabric in the required position, at all stages of the concrete application.
  • 3.5 The junction between fireproofing and bare steel shall be sealed against the ingress of water.
  • 3.6 Heat resistant/refractory base cement (approved Portland cement) with W/C ratio of 0.4 to 0.5 shall be used. The cement, gravel, sand mix shall be in the ratio 1:1.5:3. The gravel shall be 4.5mm to 6.0mm and the sand shall contain at least 4.0% moisture.
  • 3.7 Guniting shall not be carried out in the vicinity of disconnected piping where rebound and splatter can enter unless the openings in such lines are closed with wooden plugs or other suitable shields.
  • 3.8 The gunite shall be trowel finished and exhibit a dense mass.
  • 3.9 Materials, equipment, and method of application shall be in accordance with A.C.I standards “Recommended Practice for Shotcreting” No. 506-66 and “Specification for Materials Proportioning and Application of Shotcrete”, No. 506.2-77 published by the American Concrete Institute or, Indian equivalent. Guniting shall be done only by skilled operators. Care shall be taken to ensure the gunite fully penetrates through the mesh to the steel.

4.0 Temperature Limitations (Cementitious Materials)

No fireproofing shall commence when the bare steel temperature is 38°C or higher. In hot climates the ideal time to commence fireproofing is later afternoon, to allow curing overnight. Similarly, no fireproofing shall commence when the bare steel temperature, or the air temperature is 4°C or less.

5.0 Valves

The fireproofing shall comprise of either a weatherproof flexible bag or an insulated prefabricated steel box. The construction of the enclosure shall permit easy access to the actuator controls. Manual valve operation shall be achieved without removing or opening the fireproof enclosure. The enclosure shall maintain the valve operable under normal site conditions without over heating due to the absence of ventilation and also maintain it operable for a minimum of 15 min when exposed to a hydrocarbon fire. Vendor to provide third party certification of his proposed construction. The basis for certification shall be exposure to a temperature of at least 1100°C for the entire 15 min period. That is to say any period of time required to arrive at the subject temperature shall not be deemed as a part of the test.

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