The API 936 - Refractory Personnel (API-936)

Chemically bonded refractories , such as phosphate-bonded or acid-bonded types, develop strength through chemical reactions that require exposure to ambient air . These materials must remain uncovered 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 for hydraulic bonded (cement-based) refractories — would trap moisture and interfere with the chemical reaction process in chemical bonds.

The curing of newly installed refractory linings must adhere strictly to manufacturer guidelines to ensure integrity and performance:

“Forms shall not be stripped until the lining has cured per the manufacturer’s recommendation.”

— API Std 936, Section 5.4.2.1​

The manufacturer's recommendations ensure that the product reaches sufficient strength before demolding.

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According to API Standard 936, the correct specimen dimensions for cold crush strength testing are:

“Test specimens for cold crushing strength shall be 2 in. (50 mm) cube samples prepared in accordance with ASTM C133.”

— API Std 936, Section 6.4.2 ​

This directly invalidates option A, which incorrectly states the specimen size as 4-1/2 inches.

For the other options:

Option B – Density determination:

API 936 states that density shall be measured using the same specimens used for linear change and abrasion resistance:

“Bulk density shall be determined using the same specimens prepared for the linear change and abrasion resistance tests.”

— API Std 936, Section 6.4.3 ​

“These specimens include cubes, linear change bars, and erosion plates.”

— Appendix A, API Std 936 ​

Option C – Abrasion resistance specimen size:

“Two 4-1/2 in. × 4-1/2 in. × 1 in. (114 mm × 114 mm × 25 mm) specimens shall be prepared for abrasion resistance testing.”

— API Std 936, Section 6.4.4 ​

Option D – Permanent linear change specimen size:

“Permanent linear change (PLC) is determined with a bar 2 in. × 2 in. × 9 in. (50 mm × 50 mm × 230 mm) cast in steel molds.”

— API Std 936, Section 6.4.1 ​

Therefore, Option A is the only false statement.

TR 980 outlines curing and dryout best practices for monolithic refractories. For high-purity low-cement castables, gradual heat-up is necessary to avoid thermal shock and cracking:

“A minimum 24-hour air cure at ambient temperature should be followed by a controlled dryout ramp not exceeding 50°F (28°C) per hour up to 600°F (316°C).”

— TR 980, Section 6.4.2​

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Removable back panels in gunning test panels are required to allow inspection for internal defects , particularly voids, laminations, and rebound pockets that are not visible from the surface. These panels are taken off after gunning so that the interface between layers or the entire cross-section can be visually examined.

This approach ensures that the test section is representative of actual field performance and that the gunning technique (angle, nozzle distance, rebound control) is achieving full compaction without defects.

The cure period before initiating the dryout process is a critical phase of installation:

“Newly installed air-setting, hydraulic, and chemically bonded materials shall be allowed to cure for a minimum of 24 hours at 60 °F (16 °C) or above prior to initial heating.”

— API TR 980, Section 6.2.1​

This condition ensures chemical bonding processes are complete before exposure to thermal stress.

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According to API 936, the installation contractor must secure prior written approval or agreement from the owner regarding 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.

According to API TR 980 – Monolithic Refractories: Installation and Dryout, when multiple heat sources are used during refractory dryout, the final approval must come from the Owner:

“If more than one heat source is used, the contractor shall obtain written approval from the Owner for the dryout procedure.”

— API TR 980, Section 6.2.2​

While the contractor may propose or execute the dryout, the responsibility for ensuring its validity and safety—especially when multiple heat sources are involved—rests with the Owner.

Apparent porosity is a measure of the volume of open pores (voids that can absorb water) within a refractory sample, relative to the total volume. It is always expressed as a percentage . Testing is done using standards such as ASTM C20, which API 936 references. This metric is crucial for understanding a material’s permeability, thermal shock resistance, and mechanical integrity.