Use only the attached synthetic input. Return a JSON object with these exact fields: equipment_tag, revision, design_temperature_c, operating_temperature_c, design_pressure_barg, operating_pressure_barg, material. Use null for information not stated. Preserve identifiers, units and revision states. Lists follow first appearance in the input, except an explicitly requested chronological order. Use snake_case for categorical labels. Do not add inferred engineering decisions.
Field types: {"equipment_tag": "string", "revision": "string", "design_temperature_c": "number", "operating_temperature_c": "number", "design_pressure_barg": "number", "operating_pressure_barg": "number", "material": "null when unstated"}

Task: Use field extraction with source references. Keep design and operating values in separate columns and require an explicit null for absent fields.
Do not swap design and operating values.
Keep gauge pressure distinct from absolute pressure.
Return null for material, not a guessed alloy.