API API-936 - API 936 - Refractory Personnel

Chemically bonded refractories, such as phosphate-bonded or acid-bonded types, develop strength through chemical reactions that requireexposure to ambient air. These materials must remainuncovered and dry during curing, as moisture or covering may inhibit the required chemical bonding or lead to improper set.

Covering chemically bonded linings (e.g., with plastic sheeting or wet burlap) — practices appropriate forhydraulic bonded(cement-based) refractories — would trap moisture and interfere with the chemical reaction process in chemical bonds.

Shelf life is defined as the maximum period during which a material may be stored under specified conditions and still remain in a usable condition. API 936 emphasizes that materials such as monolithic refractories, when stored properly, should be used within their specified shelf lives to ensure they retain the required properties for performance.

According to API TR 980, a form must be able to support its own weight and the pressure from the refractory material:

“Formwork shall be self-supporting and capable of withstanding the static and dynamic loads imposed during installation.”

— API TR 980, Section 4.2.1, Form Requirements​

Transparency and chemical resistance are not required characteristics for refractory formwork in installation.

When drying out units withmultiple types of refractories, API 936 and API Technical Report TR 980 emphasize that the most conservative dryout schedule must be followed to avoid premature failure orexplosive spalling. This meanschoosing the refractory material or lining system that requires the longest duration or slowest heating rate.

Different refractory types—gunned, cast, plastic, or fiber—have varying sensitivities to moisture and thermal gradients. Selecting the schedule with the longest duration ensures full water removal, especially from thick sections or materials with high water retention capacity.

The correct method for determining the size distribution of aggregate particles used in refractory castables isscreen analysis. This is a standardized technique for analyzing particle size distribution by passing material through a series of sieves with progressively smaller openings.

As specified in API 936 and related technical literature such as API TR 978 and API TR 980, aggregate grading and size distribution directly affect the packing density and therefore the performance of monolithic refractories. The screen analysis is fundamental in determining if aggregates fall within the prescribed grading ranges, which is critical for workability, density, and mechanical strength.

According to API 936, theinstallation contractor must secure prior written approval or agreement from the ownerregarding all details of the installation. This includes procedures for curing, dryout, anchoring, repairs, and quality control. The owner or their authorized representative is the ultimate authority for project specification conformance.

Phosphate-bonded plastic refractories develop their final bonding during high-temperature exposure. As described in TR 980:

“Phosphate-bonded plastics require temperatures between 500°F and 700°F (260°C and 370°C) to form a permanent ceramic bond.”

— API TR 980, Section 5.2.3​

Pigment in curing compounds serves a visual function to verify that the applied coating has achieved full and even coverage across the refractory surface. This aids inspectors in confirming compliance with curing requirements.

API TR 980 provides guidance for hot weather installation, recommending:

“Preventive measures include shading material and equipment, cooling of mix water and forms, and in some cases, air conditioning of ambient air. Spraying water on equipment may be used to reduce radiant heat.”

— API TR 980, Section 4.5.2​

However, decreasing mixing time is not advised; it can result in insufficient material wet-out or inconsistent dispersion. Therefore:

A (air conditioning): Acceptable

B (decreasing mixing time): Not acceptable

C (shading): Acceptable

D (spraying water): Acceptable

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