Anchors are critical components in pressure equipment with internal linings, such as pressure vessels and reactors, to secure refractory or corrosion-resistant linings to the vessel shell. They ensure structural integrity, prevent lining detachment under thermal or mechanical stresses, and help maintain the lining’s position during operation.
Types of Anchors
Ceramic Anchors:
Designed for high-temperature and highly corrosive environments, ceramic anchors are often used to secure refractory linings. Common materials include reaction-bonded silicon carbide (SiC) and silicon nitride (Si₃N₄), chosen for their resistance to heat and corrosion.
Ceramic anchors come in various shapes:
- Spike or nail forms, often with serrated or threaded shafts for improved grip.
- Designs with enlarged or truncated heads to enhance holding strength.
- Variations with helical spiral threads or semi-circular peripheral lands to further secure the lining.
Metallic Anchors:
Stainless steel anchors (such as those made from high-grade steel) are frequently used, especially where high mechanical strength is needed or in less aggressive environments. These are commonly used to optimize refractory lining performance and are available in several configurations, such as V-shaped, Y-shaped, or corrugated designs.
Anchors are typically installed at various angles (often between 45° and 90° to the surface) and in random patterns to avoid creating planes of weakness in the lining. This randomization helps distribute stresses and enhances the mechanical bond between the lining and the vessel wall. The inner or “hot face” refractory layer is then gunned, sprayed, or cast in place to surround the anchor heads, securing the lining.
Anchor Grades
Anchors are a fundamental part of internal lining systems in pressure equipment, with their selection and design tailored to the specific operating environment and lining material. Proper use of anchors ensures the long-term durability and safety of pressure vessels and similar equipment.
Steel Anchor Selection
Steel grade selection is crucial for the durability of metallic anchors used in internal linings of pressure equipment, as it directly impacts resistance to corrosion, high temperatures, and mechanical stresses.
Stainless Steel Grades
(e.g., 304, 316, 310)
Stainless steels contain chromium (often nickel), forming a passive layer that protects against rust and corrosion.
Grades like 316 are especially resistant to harsh environments, including high moisture and chemical exposure, making them ideal for outdoor, marine, or corrosive process conditions.
Higher alloy grades (e.g., 310, 330, Inconel 601) provide superior resistance to oxidation and sulfidation at elevated temperatures, further enhancing durability in extreme applications.
Carbon Steel and Low-Alloy Steel
While cost-effective and strong, carbon steels are prone to corrosion, especially in moist or chemically aggressive environments. Without protective coatings, their durability is significantly reduced over time.
Zinc-plated or galvanized steels offer some corrosion resistance but are still less durable than stainless steel in aggressive settings.
High-Temperature Stainless Steels (e.g., 309, 310, 330, Inconel 601)
These grades maintain strength and resist oxidation at temperatures up to and above 2000°F (1093°C), making them suitable for refractory linings and high-temperature vessels.
Lower-grade stainless steels (e.g., 304, 316) are suitable for moderate temperatures but may lose mechanical properties or oxidize at extreme heat.
High-Tensile Steels
The mechanical strength of an anchor depends on both the steel grade and its diameter. High-tensile stainless and alloy steels provide better load-bearing capacity and resistance to deformation under stress, which is critical for maintaining anchor integrity over time.
Some stainless-steel grades, such as 316L, offer excellent corrosion resistance but lower tensile strength than high-tensile carbon steels.
Anchor Design and Steel Quality
Using inferior or low-quality steel grades, even if labelled as stainless, can result in weak anchors that may fail under load or corrode prematurely.
For critical applications, reputable manufacturers use high-tensile stainless or alloy steels, sometimes with additional treatments for enhanced durability.
Selecting a higher-grade, corrosion- and heat-resistant steel significantly improves the long-term durability of metallic anchors in pressure equipment. Stainless steels (especially 316, 310, and higher alloys) are preferred for harsh or high-temperature environments, while carbon steels may suffice for less demanding indoor applications but offer lower durability in aggressive conditions