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ASME B29.21-2013 (2018) — 700 Class Chains, Attachments, and Sprocket Teeth for Water and Sewage Treatment Plants
⚙️ ASME B29.21-2013 (reaffirmed 2018), 700 Class Chains, Attachments, and Sprocket Teeth for Water and Sewage Treatment Plants, is the American National Standard dedicated to chains used in water and sewage treatment plants. This “700 Class” chain was first standardized in 1975 and revised in 1981 and 1996; since the marketplace increasingly uses chains made from plastics or stainless steels, this revision adds product groups not found in previous editions — stainless steel fabricated chains (SS715 and SS709) and nonmetallic (plastic) chains (NM720) — on top of the traditional cast iron and welded steel chains. It was approved as an American National Standard on November 26, 2013, and reaffirmed in 2018. These chains serve bar screens, grit collectors, primary and secondary sludge collectors, and sludge thickener mechanisms — slow-speed, heavy-duty service in wet, corrosive environments.
💡 The 700 Class chain is the heart of a treatment plant’s “underwater moving parts”: continuously immersed in sewage, sludge, and grit, it faces corrosion and abrasive wear together. Correct selection of material (cast iron/welded steel/stainless/plastic), sprockets, and chain savers directly determines maintenance intervals and operating reliability.
1. Scope and Overview 📌
The Standard specifies dimensions, construction, ultimate strength, proof load, strand length, attachments, and sprocket tooth form for 700 Class chains in water and sewage treatment plants. The principal product groups are:
- Cast iron chain: with and without chain saver, the traditional mainstay of 700 Class chains;
- Welded steel chain: with and without chain saver, stronger for longer spans and heavier loads;
- Stainless steel fabricated chain (SS715, SS709): added in 2013 for excellent corrosion resistance in aggressive service;
- Nonmetallic (plastic) chain (NM720): added in 2013, lightweight, corrosion-resistant, and quiet.
The Standard also specifies attachment types F22-6, F22-8, A-42, F-2, K-2, and M-1 (Tables 4 through 9), sprocket tooth-form parameters including pressure angle, pitch diameter, and clearance circle, maximum eccentricity and face runout tolerances (Tables 10 and 11), and chain saver rim diameters for curved-sidebar chains (Table 12). Mandatory Appendix I provides engineering characteristics requirements.
2. Chain Types and Material Selection 🔧
A 700 Class chain link is generally a sidebar-pin-bushing construction: cast iron chains use cast links and welded steel chains use welded links, while stainless and plastic chains use stainless steel and engineering plastic link materials respectively. A chain saver is a wear ring fitted over the sprocket to protect the teeth and extend sprocket life. The table summarizes the characteristics and applications of each chain type:
| Chain Type | Typical Designation/Notes | Key Advantages | Typical Applications |
|---|---|---|---|
| Cast iron (with/without saver) | 700 Class cast iron | Low cost, good load capacity, wear resistant | Bar screens, grit and sludge collectors |
| Welded steel (with/without saver) | Welded steel construction | High strength, shock resistant | Long-span, heavy-load sludge collectors |
| Stainless steel fabricated | SS715, SS709 | Excellent corrosion resistance | Aggressive sewage, chloride-bearing service |
| Nonmetallic (plastic) | NM720 | Lightweight, corrosion resistant, quiet | Light-load, corrosive, low-noise duty |
⚠️ Material selection must follow water and sludge chemistry: for sulfide-, chloride-, or pH-fluctuating service, prefer stainless chains (SS715/SS709); cast iron chains lose life quickly in aggressive environments. Plastic chains (NM720) have limited load and temperature capability and suit light duty only.
3. Strength and Chain Length Parameters 📏
Table 1 of the Standard gives general chain dimensions, ultimate strength, proof load, strand length, and chain length measuring load for each chain number. Unlike many chain standards, treatment-plant chains specify both ultimate strength and proof load — the load a chain must withstand in factory inspection without permanent deformation, an important quality-control index. Strand length tolerance and measuring load ensure synchronization and load sharing of multiple parallel chains (as in double-strand sludge collectors).
| Parameter | Meaning | Engineering Significance |
|---|---|---|
| Ultimate strength | Breaking load in a single tensile test | Upper reference for safety factor; not a working load |
| Proof load | Load sustained in factory inspection without permanent set | Quality control and chain consistency |
| Strand length | Length of a standard strand under measuring load | Multi-strand synchronization, tension adjustment |
| Chain length measuring load | Specified tension when measuring chain length | Comparable measurement results |
🚨 Ultimate strength must never be used as a working load! Treatment-plant chains run long-term in corrosive and abrasive conditions — select from manufacturer rated loads and inspect for wear and corrosion thinning. Replace promptly when corrosion thinning or significant pitch elongation appears, or breakage can shut down the plant and damage equipment.
4. Attachments and Sprocket Tooth Form 🔩
The Standard specifies attachments F22-6, F22-8, A-42, F-2, K-2, and M-1 (Tables 4 through 9) for mounting scrapers, sludge-collector arms, screen bars, and other load elements. The sprocket section gives the pressure angle, pitch diameter, and clearance circle, together with maximum eccentricity and face runout tolerances (Tables 10 and 11); for curved-sidebar chains it also specifies chain saver rim diameters (Table 12), so the sprocket teeth can continue in service after the saver wears — lowering maintenance cost. Mandatory Appendix I defines the chains’ engineering characteristics for design selection.
💡 The chain saver is the “consumable” of a treatment-plant chain system: it protects the sprocket teeth, is easy to replace, and costs little. Select saver rim diameter per Table 12 and inspect saver wear regularly — timely replacement significantly extends sprocket life.
5. Engineering Practice Essentials 🛠️
- 🔍 Selection workflow: determine sludge/screen load and chain speed → choose chain type (cast iron/welded steel/stainless/plastic) → verify ultimate strength and proof load → choose attachment type → design sprockets and chain savers to the Standard.
- 🔧 Corrosion and wear: prefer stainless chains in aggressive service; for cast iron chains inspect coating and saver condition to prevent strength loss from corrosion thinning.
- 📊 Maintenance: periodically inspect link wear, sprocket teeth, and saver wear; measure chain length under measuring load to judge elongation; keep both sides of double-strand systems synchronized.
- 📋 Interchangeability management: only links, attachments, and sprockets made to B29.21-2013 are guaranteed interchangeable; do not freely mix material families — select as a matched system per the Standard.
6. Frequently Asked Questions ❓
❓ Q: What does “700 Class” mean?
A: “Class 700” is the series designation for this family of water-treatment chains, deriving from its chain-number and size system rather than a single dimension. Since standardization in 1975, the series has expanded to cast iron, welded steel, stainless, and plastic product groups.
A: “Class 700” is the series designation for this family of water-treatment chains, deriving from its chain-number and size system rather than a single dimension. Since standardization in 1975, the series has expanded to cast iron, welded steel, stainless, and plastic product groups.
❓ Q: What is the function of a chain saver?
A: A chain saver is a wear ring mounted on the sprocket that absorbs the chain’s meshing wear, protecting the sprocket teeth, being easy to replace, and costing little. Table 12 specifies saver rim diameters for curved-sidebar chains.
A: A chain saver is a wear ring mounted on the sprocket that absorbs the chain’s meshing wear, protecting the sprocket teeth, being easy to replace, and costing little. Table 12 specifies saver rim diameters for curved-sidebar chains.
❓ Q: What did the 2013 edition add compared with earlier editions?
A: The 2013 edition added stainless steel fabricated chains (SS715 and SS709) and nonmetallic plastic chains (NM720) to meet current demand for corrosion-resistant, lightweight, and quiet chains, while retaining the traditional cast iron and welded steel series.
A: The 2013 edition added stainless steel fabricated chains (SS715 and SS709) and nonmetallic plastic chains (NM720) to meet current demand for corrosion-resistant, lightweight, and quiet chains, while retaining the traditional cast iron and welded steel series.
🔍 Q: What is the difference between ultimate strength and proof load?
A: Ultimate strength is the breaking load in a single tensile test — a destructive index; proof load is the load a chain must sustain in factory inspection without permanent deformation, used for quality control and consistency. Neither may be used directly as a working load.
A: Ultimate strength is the breaking load in a single tensile test — a destructive index; proof load is the load a chain must sustain in factory inspection without permanent deformation, used for quality control and consistency. Neither may be used directly as a working load.
