Calculations and justification: fire protection thicknesses and coating durability

The thickness of a protective coating is a calculated value. For fire protection, it depends on the section, the required fire resistance rating, the fire curve and the test data of the specific material. For corrosion protection, it depends on the environment and the service life the client expects. We carry out these calculations and document the justification so that any participant in the project can check it.

Fire protection of structural steel

What we take into account

  • the required fire resistance rating of each member — from the building’s degree of fire resistance (ShNK 2.01.02-04; ShNK = Uzbekistan’s Urban Planning Norms and Rules) or from the project requirements;
  • the fire curve: standard or hydrocarbon;
  • the reduced metal thickness or the section factor Hp/A, taking into account on how many sides the member is exposed to fire;
  • the critical temperature of the steel: either the value adopted in the test method or one calculated from the member’s load level if the design follows EN 1993-1-2;
  • the test data of the selected material: the thickness tables and the limits within which they apply.

How the calculation proceeds

  1. We compile a list of members from the steelwork drawings and group them by section.
  2. For each section, we determine the reduced metal thickness or Hp/A, taking the fire exposure configuration into account.
  3. We select the dry film thickness from the material’s test data and check that the section and the fire resistance rating fall within the tested range.
  4. If a member falls outside the tables or is loaded more heavily than the adopted critical temperature allows, we consider calculating the critical temperature, a different material or non-reactive fire protection.
  5. We calculate the areas and consumption, allowing for application losses.

Thicknesses from the documents of different materials and different test methods cannot be transferred from one to another: GOST R 53295, EN 13381-8 and UL 1709 have different heating regimes and criteria. For details, see the article “How fire protection tests are carried out”.

Deliverables

  • a table by member: section, reduced metal thickness or Hp/A, required fire resistance rating, dry film thickness, area, consumption;
  • an explanatory note: the method, the input data, references to the material manufacturer’s documents;
  • where required, a comparison of options: paint, plaster, boards, combined protection.

Durability of corrosion protection

ISO 12944-1 expresses the durability of a coating system as the time to the first major maintenance and defines four ranges: low (L) — up to 7 years, medium (M) — 7 to 15 years, high (H) — 15 to 25 years, very high (VH) — more than 25 years. This is a guide for choosing a system, not a guarantee period — the standard states this explicitly.

  • we determine the corrosivity category to ISO 12944-2 for each zone of the facility: indoors, outdoors, and in areas exposed to condensation, spillage and immersion;
  • we select a system that meets ISO 12944-5 for this category and durability range: type of primer, number of coats, nominal thickness;
  • we check whether the system has laboratory test results to ISO 12944-6;
  • we separately take into account what the standard does not cover: elevated temperature, intense sunlight, abrasive wear, chemical exposure.

Life-cycle cost

A system that is cheap to buy can turn out to be expensive over the life of the facility if it has to be repaired more often and each repair requires a production shutdown, scaffolding or work at height. On request, we compare the options by total cost: the initial protection plus the maintenance cycles over a given period.

Material quantities and consumption

We calculate the theoretical consumption from the volume solids and the dry film thickness, and the practical consumption with allowances for the application method, the shape of the structures and the working conditions. That way the schedule of materials matches what will actually be needed on site.

Input data

  • steelwork drawings or a specification of the sections;
  • the required fire resistance ratings or the building’s degree of fire resistance;
  • service conditions and the required service life of the coating;
  • the material, if one has already been chosen, and its technical documents.

Send us the drawings and requirements and we will calculate and justify the thicknesses for your project. Phone, WhatsApp, Telegram: +998 94 094 52 27. Documents: info@ognezashita.uz.