According to 46 CFR §56.50-60, oil piping that conveys fuel oil or lubricating oil and is in proximity to equipment having parts operating above what temperature must be of seamless steel?

Why C is correct

46 CFR §56.50-60(j) states that piping conveying fuel oil or lubricating oil to equipment in proximity to equipment or lines having an open flame or having parts operating above 500 °F must be of seamless steel. The other temperatures listed are not the regulatory threshold.