Managing Fired Furnace Tubes in Refineries

Introduction

Fired furnaces in the petrochemical and refining industry are critical pieces of equipment that can have a major impact on process unit safety, reliability, and economics. They are complex pieces of equipment, where tubes and other pressure boundary components might fail due to relatively short periods of upset conditions. There are several factors playing key roles in the life span of fired furnace tubes. Management, engineering practitioners, operators, and inspection/ maintenance personnel are continuously challenged to operate furnaces for longer runs, with higher throughput, and with minimum business interruption. Material selection, monitoring of process and operating conditions, routine maintenance, repairs, inspection, sample selection/removal, material evaluation and testing, fitness-for-service (FFS), and remaining life assessment, are some of the instances where decisions, assumptions, and approaches used might significantly affect the management of fired furnace tubes. In this article, numerous areas of concern or factors are discussed.

Typical Fabrication Materials of Fired Furnace Tubes

The fabrication materials of fired furnace tubes vary with the type of service, owner-user preference, and previous experience. Typical alloys for some of the common furnaces in refining processes are as follows:

• Crude Units: convection tubes are usually carbon steel, and sometimes low alloy steel (5Cr-1Mo, 7Cr-1Mo or 9Cr-1Mo); radiant tubes are generally low alloy steel (5Cr-1Mo, 7Cr-1Mo or 9 Cr-1Mo), and in a few cases radiant sections of carbon steel are found; stainless steel Type 316L or 317L is typically used in the outlet and areas of high velocity.
• Vacuum Units: materials of construction are similar to those used in Crude Units for both radiant and convection tubes; some furnaces are built with radiant sections of stainless steel Type 347.
• Delayed Coker Units: 9Cr-1Mo is the “work horse” alloy for both the radiant and convection section; in a few old furnaces the tubes in the radiant section are either 5Cr-1Mo or 7Cr-1Mo. Nowadays, upgrades to stainless steel Type 347 or Incoloy 800H/HT are common.
• Hydroprocessing Units: radiant section tubes of recycled hydrogen and feed heaters are typically 300 series stainless steel; thermally stabilized Type 347 tubes are a common choice for new tubes or replacements. It is also common to find carbon steel convection section tubes with 12Cr alloy fins. Radiant tubes in feed and 2nd stage heaters of older units are typically made of low alloy steel (5Cr-1Mo, 7Cr-1Mo or 9 Cr-1Mo). Many older units run with SS304, 316, 321, HF modified and non-thermally stabilized Type 347.
• Steam Methane Reformer Units: HP modified and microalloys are today’s industry standard metallurgy for these furnaces.