What are the Best Material Choices for Heat Exchanger Pipe?
Introduction
Heat exchangers are widely used in power plants, petrochemical facilities, ships, industrial processes and more to transfer heat between fluids without direct contact. At the heart of any heat exchanger are the tubes or pipes carrying the fluids, and material selection is critical to ensure long-term performance under heat transfer requirements, environmental conditions and constraints like weight or costs. This report examines the key material properties affecting heat exchanger pipes and provides an overview of the most common and advanced alloy options available today.
Material Requirements
First, the operating demands on heat exchanger pipe materials must be understood. Key factors include:
- Thermal conductivity: Transfers heat efficiently between fluids flowing inside/outside the pipe wall.
- Strength: Withstands pressures/mechanical stresses from fluid flow and pipe handling.
- Temperature limits: Resistance to degradation from high/low operating temperatures.
- Corrosion resistance: Chemical inertness towards fluids as well as environmental exposure.
- Weight: Lighter materials ease assembly/maintenance especially offshore.
- Cost: Affordability must be balanced with performance benefits.
No single material possesses the entire spectrum of ideal properties. Instead, selections depend strongly on the heat exchanger’s specific service conditions and design constraints.
Carbon Steel
As the most economical choice, carbon steels like ASTM A53 Grade B remain prevalent for lower temperature heat exchangers below approximately 400°F. Strengths range up to 60 ksi with satisfactory general corrosion resistance achievable through protective coatings. However, carbon steel is susceptible to scaling and pitting if exposed to corrosive fluids.
Stainless Steel
The chromium-containing stainless steels encompass diverse grades optimized over wide temperature ranges. Austenitic alloys like UNS S30400 exceed carbon steel in corrosion resistance, thermal conductivity and strength up to 800°F, while ferritic/ martensitic grades withstand higher temperatures to 1200°F. Special materials like duplex provide the best overall balance though at increased costs versus carbon steel. However, sensitization must be prevented during stainless fabrication to avoid cracking.
Nickel Alloys
Heat exchangers for seawater or flue gas duties involving temperatures above 1200°F require the corrosion resistance only nickel alloys can provide, represented by Inconel 600 and 625. Yet greater strengths and thermal shock resistance come from harder alloy families like Hastelloy C-276 and Inconel 690. Despite costs several times higher than carbon steel, nickel remains indispensable for the most aggressive non-ferrous applications like fossil energy plants.
Titanium
Boiling water reactors counting on its exceptional corrosion resistance employ pure grade 2 titanium in smaller heat exchanger components. However, low thermal conductivity requires thick walls affecting weight and costs, limiting broader adoption. Joining also challenges conventional fabrication methods. Nonetheless, new applications emerge in seawater desalination heat exchangers.
Coatings & Claddings
Advanced surface modification provides enhanced performance at reasonable costs over bulk alloy upgrades. Nickel-aluminum and zinc-nickel coatings by torch spray techniques surpass carbon steel’s limits up to 1200°F while retaining lower costs. Cladding tubes using overlay welding introduces high-alloy materials for localized corrosion protection at critical portions exposed to fluids. Ceramic insulators too can lower tube wall temperatures to widen carbon steel service ranges.
Material Selection Example
Consider a heat exchanger for a sulfuric acid alkylation unit continuously operating between 200-300°F. Carbon steel tubing satisfies the moderate temperature needs, with fiberglass or Gilsil thermal insulation maintaining wall temperatures. However, concentrated sulfuric acid demands something more corrosion resistant. Stainless 316 offers superior resistance versus 304, despite a 40% higher price premium over carbon steel. Here the performance merits upgrading given the heat exchanger’s role in a major plant process. Lining could represent a more cost-effective alternative for occasional high temperature excursions.
Conclusions
Material selection represents a key design factor governing long-term heat exchanger reliability and costs. While carbon steel dominates many lower temperature applications, excellent corrosion resistance and high temperature strength motivate using stainless steels, nickel alloys or linings/coatings especially for demanding service conditions. Performance must be balanced judiciously against constraints like budgets or weight to procure piping optimized for a heat exchanger’s full service life.
DIN 17175 is designed for elevated temperature purposes, ABTER STEEL supplies following steel grades: St35.8, St45.8, 15Mo3, 13CrMo44, 10CrMo910. DIN 17175 seamless steel pipes are widely used in heat exchange appliances.
ASTM A179 covers minimum-wall thickness, seamless cold-drawn steel tubes for tubular heat exchangers, condensers, and similar heat transfer apparatus. It is a kind of low-carbon tubes shall be made by the seamless process and shall be cold drawn.
EN10216-2 is specification made for seamless steel tubes for specified elevated temperature purposes as boiler tube, power plants, etc, it has following steel grades: P195GH, P235GH, P265GH, 16Mo3, 14MoV6-3, 13CrMo4-5, 10CrMo9-10, with non-alloy and alloy steel included.
The EN 10217-1 standard is the European standard for welded pressure pipes, it governs the technical requirements for carbon steel tubes. This standard is suitable for welding carbon steel tubes which having specified room temperature properties and rated pressures. The essential requirements of this standard are minimum yield point strength and tensile strength, elongation, weldability, Impact values, non-destructive test, etc. This standard is widely used in the construction of pressure vessels and piping systems in the oil and gas, petrochemical, and Power industries.
A heat exchanger is a device that transfers heat from one medium to another, often with the goal of reusing or recycling heat that would otherwise be wasted or lost. The process of heat exchange is fundamental to many everyday appliances, such as refrigerators and air conditioners, and is also critical in many industrial applications.
ASTM A179,ASME SA179 steel tubes covers minimum-wall-thickness, seamless cold-drawn low-carbon steel tubes for tubular heat exchangers, condensers, and similar heat transfer apparatus.
