What Are APH Tubes and Why Does Tube Construction Matter?
APH Tubes carry flue gas and combustion air through the air preheater bundle, so heat from the exhaust side gets passed back into the incoming air. Power plants and refineries use this step to reduce fuel use and get more out of the boiler. There are two main ways these tubes get made. ERW APH Tubes are rolled from strip and welded along a seam. Seamless APH Tubes come from a solid billet, pierced or extruded, with no weld at all. One isn’t automatically better than the other. Engineers usually look at material, size, expected service conditions, and the specification the project is following. The tube construction is just one part of that list. Have a look at our APH Tubes range if you want to check sizes against your drawing.
ERW vs Seamless APH Tubes: Key Differences
Manufacturing construction: ERW tubes are rolled from flat strip and welded along a seam. Seamless tubes come from a pierced or extruded billet, no weld involved.
Dimensional requirements: ERW mills handle a broad diameter range with fairly tight tolerances. Seamless mills tend to work around set diameter-to-thickness ratios per drawing.
Wall thickness: ERW covers thin to moderate walls at a reasonable cost. Seamless handles thicker walls when the design actually requires it.
Service conditions: Both can work in APH service. It depends on what the code allows, what the gas exposure looks like, and how the equipment is designed.
Inspection requirements: ERW tubes usually get the weld seam checked, eddy current or ultrasonic testing. Seamless tubes go through volumetric testing per the standard referenced.
Fabrication considerations: ERW tubes weld and roll into tube sheets using normal shop methods. Seamless tubes are joined in a similar way, depending on how the fabricator works.
Availability: ERW tubes generally move faster in standard sizes since the mills run continuous production. Seamless can take longer for certain diameters.
Project cost: ERW usually costs less per length. Seamless can carry a premium because of billet processing and mill setup.
What Should You Consider When Selecting APH Tubes?
Operating Conditions
Temperature, pressure, how much heat transfer is needed, and gas-side fouling all play into which construction fits the design. It’s worth checking the equipment manufacturer’s data sheet rather than guessing at a limit that might not apply to your unit.
Material and Corrosion Requirements
Flue gas makeup, moisture, and condensate at the cold end all affect which material grade is right. This is a separate decision from ERW versus seamless, and it shouldn’t get mixed in with the construction choice.
Tube Diameter and Wall Thickness
Outside diameter, wall thickness, length, tolerances, and end configuration all need to line up with the tube sheet layout and whatever ASME or ASTM spec applies. Check these against the drawing before placing an order.
Fabrication and Installation Requirements
How the tube joins to the tube sheet, whether it’s rolled or welded, how easy it is to access for cleaning, and what the inspection schedule looks like during shutdowns, all of this can push the decision one way or the other. Best to talk it through with whoever’s handling the tube bundle assembly.
When Can ERW APH Tubes Be Considered?
ERW APH tubes work when the specification, the service conditions, the dimensional requirements, and the inspection procedure all allow welded construction. BS 6323 and several ASME specifications specifically cover ERW tubing for air preheater use, and plenty of designers choose it when the drawing and material certificates support welded tube. Check the code section that applies to your project.
When Can Seamless APH Tubes Be Considered?
Seamless APH tubes get used when the specification, the design pressure and temperature, or the material standard needs it. Some specifications ask for seamless tube on particular tube sheet setups or material grades, and this isn’t always tied to how high the pressure or temperature is. Look at the design basis and the procurement specification, that tells you whether seamless is actually required.
ERW or Seamless APH Tubes: How to Make the Final Selection
Start with the air preheater’s design basis and expected service conditions, that’s in the equipment documentation. Then work out the material grade and the governing specification, since this often narrows things down before you even get to diameter or thickness. Check outside diameter and wall thickness against the tube sheet layout. Look at temperature, pressure, corrosion, and condensate risk at the cold end. Go through fabrication and installation requirements with whoever’s rolling or welding the tube sheet, and check what inspection and testing the code demands. Compare lead time and availability for both options. Then pick whichever construction the specification and material standard actually allow. This keeps things based on the paperwork rather than a fixed preference for one type over the other.
Contact Amco Metals for a quote on APH tube sizes matching your air preheater drawing.