Which two actions are mandatory when using API 936?

Sampling and testing the refractory material to ensure compliance is a critical step in the process outlined in API 936. This action ensures that the refractory material meets specific performance criteria and standards as dictated by the relevant guidelines. Without proper sampling and testing, there is no assurance that the materials will perform as expected under operational conditions, potentially leading to premature failure of the refractory lining, which can result in safety hazards, environmental issues, and increased operational costs.

Ensuring compliance through sampling and testing also helps to maintain the integrity of the entire process, as it verifies that the materials used are suitable for the specific application and will perform adequately in high-temperature environments. This adherence to specification is paramount in industries where high-performance and durability are critical, such as in petrochemical and refining sectors.

The other options, while related to the overall process, do not carry the same mandatory weight as sampling and testing in terms of ensuring the quality and suitability of the installed refractory.