I'm writing a Rails service in which a series of operations are performed on a record:

class RecordBaseAmountService

   self.build
      new
   end

   def call(record, subrecord)
      record = calculate_base_amount(record, subrecord)
      record = adjust_base_amount(record, subrecord)
      record = pro_rate_record(record, subrecord) if subrecord.is_prorated?
      
      return record
   end

   private

   def calculate_base_amount(record, subrecord)
      if subrecord.type == 0
         base_amount = 10
      elsif subrecord.type == 1
         base_amount = 20
      else
         base_amount = 30
      end
       
      record.base_amount = base_amount
      record.audit_field += "=>base amount calculated"
      record
   end

   def adjust_base_amount(record, subrecord)
      record.base_amount = record.base_amount*30
      record.audit_field += "=>base amount adjusted"
      record
   end

   def pro_rate_record(record, subrecord)
      record.pro_rated_amount = record.base_amount*subrecord.pro_rate
      record.base_amount = record.base_amount - record.pro_rated_amount
      record.audit_field += "=>prorated"
      record
   end
end

Is this code thread safe? Any comments on how to improve it?