API-936 API 936 - Refractory Personnel Free Practice Exam Questions (2025 Updated)

Hydrationrefers to the chemical reaction between water and cement components in refractory concretes (hydraulic bonded castables), resulting in the formation ofcalcium-aluminate hydrates, which are responsible for initial strength—known asgreen strength. This strength enables the lining to be demolded and eventually dried without mechanical failure.

Hydration is not related to final heat resistance or dryout; those come later during the firing or heat-up stages. It is distinct from setting in air-setting refractories or sintering in ceramic-bonded types.

According to API Standard 936, water used in the preparation of refractory mixes is subject to quality limitations, especially when stainless steel anchors are embedded in or come into contact with the refractory that is installed on a carbon steel surface. High chloride concentrations in the mixing water may promote corrosion in stainless steel anchoring systems.

API 936 explicitly states:

“When water is used for refractory installed on a carbon steel surface with a stainless steel anchorage, the chloride content of the potable water shall not exceed 50 ppm.”

— API Std 936, Section 5.1.2​

This clause is intended to protect the integrity of stainless steel anchors from chloride-induced stress corrosion cracking or pitting, which can compromise the mechanical support of the refractory lining.

Therefore, Option A (50 ppm) is the only correct and code-compliant answer.

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API Std 936 specifies in Section 6.6.1.1 that the test panels for pneumatic gunning must be cast to a minimum thickness of 2 inches with an acceptable tolerance:

"The minimum gunned thickness shall be 2 in. (50 mm), and the final thickness shall be within ±0.25 in. (6 mm) of the target."

— API Std 936, Section 6.6.1.1​

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The ASTM C704 standard requires the use of two specimens per sample for testing abrasion resistance:

“The abrasion resistance shall be determined using two 4½ in. × 4½ in. × 1 in. (114 mm × 114 mm × 25 mm) specimens per test sample.”

— API Std 936, Section 6.4.4, Abrasion Resistance​

This ensures accurate and reproducible results for quality control in refractory installations.

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