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Welded Steel, Drag, and Engineering-Class Chain: ASME B29 Explained

Engineering-class chain is, in CEMA's words, the chain most often used for the movement of materials, as distinct from roller chain, which is primarily used to transmit power, and ASME's publisher descriptions of the B29 standards describe most of its families by the part of the link that meets the sprocket. UTEC Industrial designs, engineers, machines, fabricates, and installs custom material handling systems for aerospace and heavy industry from its Spokane Valley, WA facility, integrating Allen-Bradley PLC and motion control with in-house CNC machining, heat treating, and stress relief. This article sets out what ASME's and CEMA's public documents say about the welded-steel mill and drag, combination, H-type, bushed rollerless, roller conveyor, and double-pitch families, how conveyor chain is rated, how parallel strands are matched, and how wear is measured and chain replaced. Chain sits in the build chain, design → engineering → parts machining → fabrication → assembly → weld fatigue → stress relief → drives → controls → tuning → monitoring, between the sprockets machined for it and the drive and monitoring that run it.

What is engineering-class chain, and how does it differ from roller chain?​

CEMA's Conveyor Chain and Sprocket Section draws the line by use. Its fact sheet states that roller chains are primarily used for the transmission of power, while engineering class chains are most often used for the movement of materials, and that there are some exceptions, "but the rule to remember is: Roller Chains for Power Transmission and Engineering Class Chains for Material Handling".

The two families are identified differently:

  • Roller chain. Highly standardized, with a universal code in which the number 80 equals a 1-inch pitch, so 60 is a 3/4-inch pitch and 40 a 1/2-inch pitch, regardless of the manufacturer or country of origin.
  • Engineering-class chain. There is no standard numbering system, and each manufacturer uses its own system. CEMA says there has been agreement on pitch and dimensional sizes, but a customer who wants to compare value must refer to a catalog or interchange list, and that even then the question of manufacturing controls, steels used, heat treatment processes, and dimensional controls is left unanswered.

CEMA's technical report on conveyor chain types lists the general types it covers as roller chains, forged chains, cast chains, welded steel chains, agricultural chains, steel bushed chains, chain drive belt, and plastic chains, and says the list is not intended to be exhaustive but covers most of the typical chains used in conveying applications. Plastic conveyor chain and polymer wear strips are compared with steel in the engineering plastics article. The report's publisher page says its scope includes descriptions and definitions of several chain types along with some typical applications; the definitions themselves are not quoted here (CEMA Conveyor Chain Fact Sheet 2007-02, 2007; CEMA Technical Report 2018-01, 2018).

Which ASME B29 standards cover conveyor, mill, and drag chain?​

Five ASME B29 standards cover the families in this article. Each is cited at standard level, from its publisher description:

StandardEdition statusChain families
B29.200-2001 (R2021)Reaffirmed 2021Welded-steel-type mill chains and welded-steel-type drag chains, attachments, and sprocket teeth; a consolidation of B29.16M-1995 and B29.18M-1993
B29.400-2001 (S2025)Stabilized 2025Combination and "H"-type mill chains and sprockets; a consolidation of B29.11M-1994 and B29.14M-1996
B29.12M-1997 (S2025)Stabilized 2025Steel bushed rollerless chains, attachments, and sprocket teeth
B29.15M-1997 (S2025)Stabilized 2025Steel roller type conveyor chains, attachments, and sprocket teeth
B29.100-2011 (S2025)Stabilized 2025Double-pitch roller chains of both the conveyor and power transmission types

ASME's pages say B29.200 combined its two predecessors "because of the similarity of construction and the usual applications for the two types of chains", and ANSI's listing of the 2001 edition of B29.400 says its two predecessors were combined "because of the similarity of construction and the unusual applications for the two types of chains". ASME's pages for B29.12M, B29.15M, and B29.100 say each was last reviewed and placed on stabilized maintenance in 2025 and remains in effect, and the ANSI webstore marks B29.400-2001 (S2025) as its most recent listing. The American Chain Association's Standard Handbook of Chains (2nd edition, 2005) covers chains for power transmission and material handling and is cited here at book level only (ASME B29.200-2001 R2021; ASME B29.400-2001 S2025; ASME B29.12M-1997 S2025; ASME B29.15M-1997 S2025; ASME B29.100-2011 S2025; American Chain Association 2005).

How is a welded-steel mill or drag chain built?​

ASME's description of B29.200 gives both chains the same construction: a series of identical welded offset links having barrels to contact the sprocket teeth, and pins which articulate in the barrels of the links. Pins are fixed in the sidebar pitch holes by press fits, mechanical locks such as flats, or both, to prevent the pins rotating in the sidebar pitch holes.

The two differ in what they were developed to replace:

  • Mill chains. Developed to provide a series of steel chains similar to cast chains of the detachable, mill, and combination types. ASME says they were introduced many years ago for the forest products industries, and that their extended usage in a variety of materials handling and drive applications stimulated standardization of the basic types.
  • Drag chains. Developed to provide a series of steel chains similar to cast drag chains in the offset and combination types. ASME says they were originally introduced for the forest products industries, and that their expanded usage called for standardization of basic sizes.

As engineering reasoning, the welded offset link with its own barrel is what lets one link design serve as both a running and a dragging chain: the barrel carries the sprocket contact, and the sidebars carry the tension and the sliding wear. As this article understands B29.200, its general proportions and designations, its tables of minimum ultimate tensile strength and measuring load, and its sprocket tooth form are set out in the standard; those values are read from the book (ASME B29.200-2001 R2021).

How do combination, H-type, bushed, and roller conveyor chains differ?​

The publisher descriptions name, for most of these chains, the part that meets the sprocket:

  • Combination chain (B29.400). A series of block links having barrels to contact the sprocket teeth, alternating with links of sidebars and pins that articulate in the barrels of the block link. Pins are fixed against rotation in the sidebar pitch holes by mechanical locks such as flats, by interference fits, or both.
  • "H"-type mill chain (B29.400). A series of identical cast offset links having barrels to contact the sprocket teeth and pins that articulate in the barrels of the links.
  • Steel bushed rollerless chain (B29.12M). A series of block links having steel bushings to contact the sprocket teeth, alternating with links of sidebars and pins that articulate in the steel bushings of the block link.
  • Steel roller type conveyor chain (B29.15M). A series of roller links having steel bushings with rollers to contact the sprocket teeth, alternating with links of sidebars and pins that articulate in the steel bushings of the roller link.
  • Double-pitch conveyor roller chain (B29.100). Alternately assembled roller links and pin links, with the pins articulating inside the bushings and the rollers free to turn on the bushings; the pitch of the link plates is twice that of the base series chain.

The contact element changes the wear. Renold's 2010 guide says sprocket tooth wear generally occurs faster on sprockets driving bush chains than on sprockets driving roller chains, because of the sliding engagement of the bush on the tooth, as opposed to the rolling engagement of the roller. As this article understands B29.400, B29.12M, and B29.15M, each gives designations, attachment dimensions, and sprocket data for its families; those are read from the books (ASME B29.400-2001 S2025; ASME B29.12M-1997 S2025; ASME B29.15M-1997 S2025; ASME B29.100-2011 S2025; Renold REN16/ENG/10.10, p. 14).

What do the B29 tables give, and what do they leave to the chain maker?​

The publisher descriptions list the tables each standard carries:

  • Strength and length. B29.200, B29.12M, and B29.15M list general chain dimensions, minimum ultimate tensile strength, strand length, and a measuring load for checking chain length. B29.400 lists a proof test load in place of a minimum ultimate tensile strength.
  • Interchangeability. Each of those four lists maximum and minimum controlling dimensions for interchangeable chain links, and chain clearance dimensions.
  • Attachments. Each of those four lists its attachments by letter code; for welded-steel mill chain these are A1, A2, A22, F2, F4, K1, K2, and W1, and for welded-steel drag chain C1, C3, C4, RR, and wing-type attachments.
  • Sprockets. B29.200 and B29.12M list sprocket tooth form factors and B29.15M sprocket factors, and all three list maximum eccentricity and face runout tolerances for sprockets; the H-type part of B29.400 gives maximum eccentricity and face runout at root diameter and sprocket factors.

What the tables standardize is interchangeable geometry. CEMA's fact sheet makes the same point from the buyer's side: there has been agreement on pitch and dimensional sizes, but manufacturing controls, steels, heat treatment, and dimensional controls are left for the buyer to ask about. As engineering reasoning, a chain that fits a B29 sprocket and attachment pattern can still differ from another maker's chain in hardness, pin fit, and fatigue life, so a specification asks for those properties in addition to the designation (ASME B29.200-2001 R2021; ASME B29.400-2001 S2025; ASME B29.12M-1997 S2025; ASME B29.15M-1997 S2025; CEMA Conveyor Chain Fact Sheet 2007-02, 2007).

How is conveyor chain rated for working load?​

CEMA's 2022 technical paper on corrosion-resistant chains, written by a chain maker's product manager, states the basis plainly: conveyor chain selections are based on working loads that are determined by bearing pressure between pin and bushings, with working load equal to bearing area times bearing pressure, and bearing area defined as the length of bushing times the pin diameter. It adds that in conveyor applications the limiting factor may not be pin/bushing wear but roller/bushing wear when the chain is tracked by the roller, in which case the roller material may need to be altered.

Renold's guide gives the same mechanism from the other end. On drive chain, it says, the major factor determining chain life is extension due to wear between the bearing pin and bush, but on conveyor chain the life may be determined by wear on other components, depending on the environment. On long-centred conveyors where rollers carry the load along a track, the rollers turn continually under load against the bushes, while the pin and bush turn against each other only four times per circuit, one of them under full load, so roller wear can be the limiting factor in chain life.

Renold's factor-of-safety method, its 24 N/mm² bearing-pressure basis, and the makers' service and temperature factors are set out in the conveyor chain selection article and are not repeated here (Neuhengen 2022, CEMA Conveyor Chain and Sprocket Technical Paper 2022-01; Renold REN16/ENG/10.10, p. 13).

What changes when engineering-class chain must resist corrosion?​

The CEMA paper lists the standard options and how each is rated:

  • Nickel-plated carbon steel. A temperature range of 32 °F to 350 °F, with working loads based on carbon steel horsepower tables or the fatigue strength of the chain. Components are plated before assembly, so pressing them into the link-plate pitch holes removes a limited amount of plating, where corrosion can initiate.
  • Zinc-coated carbon steel. 32 °F to 350 °F; the paper says zinc-coated chains should not be used in sulfur dioxide or chlorine environments. Coated chains cannot be used in direct contact with food, per FDA restrictions.
  • Austenitic stainless (304 and 316). −40 °F to 750 °F for 304 and −40 °F to 930 °F for 316. Working loads are based on a bearing pressure of 1,420 psi between pin and bushing, which "can be doubled if the chains are effectively lubricated, and the chain is totally resistant to chemical".
  • Martensitic stainless (400SS). −20 °F to 500 °F, with working loads based on 2,130 psi, which can be doubled if the chains are effectively lubricated and the chain is highly resistant to chemicals.

Against heat-treated carbon steel chain, the paper says the working loads of conveyor engineered chains are reduced by "Approximately 1/3" for austenitic stainless and "Approximately 1/2" for martensitic stainless. It gives a speed limitation of 230 fpm for both stainless families, and says to consult the chain manufacturer's catalogs to choose the stainless material for the chemicals involved (Neuhengen 2022, CEMA Conveyor Chain and Sprocket Technical Paper 2022-01, pp. 1–4).

Why must parallel strands be matched, and how are they specified?​

CEMA's matched-strands report gives three ordering points for multiple-strand conveyors:

  • Hand. Right-hand and left-hand strands may be required where the chain or the attachments are not symmetrical, and should then be specified when ordering.
  • Direction. Many such chains have a recommended direction of travel relative to the head sprocket, which should be clearly shown on the conveyor drawings or be part of the contractor's specifications.
  • Length. When pairs or groups of chain run in parallel, it is best practice to use matched strands to minimize differences in overall length, because chain made to length tolerance can vary within the tolerance range, especially between manufacturing lots. Matched strands share load more equally, which the report calls particularly important where through rods, scraper flights, or other carrying attachments rigidly connect the strands; unmatched strands may cause unequal loading, uneven wear, and racking.

The report describes a pre-stress operation that may be added if a tighter range or improved consistency is required, a one-time tensile load usually between 30% and 50% of the chain's tensile or breaking strength, which it says is common on smaller chains but becomes less effective or may not be practical on larger chains. It recommends discussing the matching tolerance with the manufacturer, ideally during quotation, and identifying the requirement when the chain is ordered; matched sets are commonly tagged. Renold's guide on the same subject says chains can be matched only on chain pitch length, not relative to attachments, and its guidance is covered in the sawmill chain transfer article (CEMA Technical Report 2016-01, 2016, pp. 1–2; Renold REN16/ENG/10.10, p. 32).

How is chain wear measured, and when is chain replaced?​

Renold's 2010 guide gives a direct measure of pin and bush wear. A length of chain is measured over as many pitches as possible, on a straight section of track and under tension, and the percentage extension is [M − (X × P)] × 100 ÷ (X × P), where M is the measured length in mm, X the number of pitches, and P the pitch in mm. When the extension reaches the maximum the guide tabulates for that chain series, the chain is due for replacement, and the guide says regular, recorded measurements make it possible to predict when replacement will be required. Its other limits, for its own chain, are:

  • Roller wear. If the rollers have worn until the link plates are near to or rubbing on the tracks, replacement is necessary; less wear is allowable at bends in the track.
  • Link-plate edge wear. Where chain runs on its plate edges, wear should not exceed half the original plate depth above the bush, otherwise a chain breakage could occur.
  • Plate thickness. If inner or outer plate thickness has been reduced by more than 1/3 of its original thickness, the chain strength is substantially reduced, and the chain should be replaced after the misalignment that caused it is corrected.
  • Bush wear. On a bush chain, if the bush is worn through so that the pin is exposed, the chain should be replaced.

Tsubaki's 1997 guide says that in conveyor chains, in which the number of working teeth in sprockets is less than in transmission chains, the stretch ratio is limited to 2 percent, and that testing shows that when wear elongation is less than or equal to 2 percent for conveyor chain there is almost no risk of fatigue failure. It notes that this replacement limit applies where every pin and bushing wears equally. CEMA's fact sheet adds the visual checks, after three months' service and every six months thereafter, including joints "wallowing out", which it says will result in chain stretch, jumping of sprockets, a surging conveyor, and more likely early pin or sidebar breakage. The OSHA sawmill rule's one-third-link stretch figure, and whether it reaches conveyor chain, is covered in the sawmill conveyor and deck safety article (Renold REN16/ENG/10.10, pp. 13–14; U.S. Tsubaki 1997, The Complete Guide to Chain, §2.1.2 p. 15 and §2.2.3.2 p. 20; CEMA Conveyor Chain Fact Sheet 2007-03, 2007).

What safety guidance covers drag-chain conveyors and chain drives?​

CEMA issued a drag-conveyor safety bulletin in 2026, developed by its Joint Screw Conveyor and Bucket Elevator Section. Its publisher page says it provides guidance for the installation, operation, inspection, cleaning, and maintenance of drag conveyors, emphasizes proper guarding, risk assessment, energy isolation, and lockout procedures, and outlines minimum safety provisions for contractors, installers, owners, and users. The listed topics include covers, guards, railings, and fences; lockout for inspection, cleaning, maintenance, and jam removal; guarding of conveyor feed openings; stored-energy hazards; and conveyor interlocking and secondary safety devices. The bulletin's text is not cited here.

For the drive, 29 CFR 1910.219(f)(3) requires all sprocket wheels and chains to be enclosed unless they are more than 7 ft above the floor or platform, with protection against falling where the drive extends over other machine or working areas. The section covers mechanical power-transmission apparatus and does not say whether a conveyor's carrying strand is a power-transmission chain. As engineering reasoning, a drag chain running in a closed trough has its nip points at the head and tail sprockets and at feed openings; of those, the bulletin's listed topics name the feed openings (CEMA Safety Bulletin DC 2026-03, 2026; OSHA 29 CFR 1910.219, §1910.219 paragraph f.3).

What sensing and controls track chain wear and strand condition?​

The sources give the signals; the instruments are this article's engineering practice. CEMA's fact sheet names a surging conveyor and jumping sprockets as results of worn joints, and its checklist names a hooking wear pattern on sprocket teeth as a sign of misalignment and a shiny surface on the inner face of the sidebars as something that could signal a misalignment problem. Renold's guide says regular, recorded extension measurements make it possible to predict when replacement will be required.

The intelligence layer below is engineering practice, not a requirement of these sources:

  • Stretch. Two proximity sensors a known number of pitches apart time a pin or attachment past each, and the drive's speed converts the timing to an extension trend between manual measurements.
  • Take-up travel. A position sensor on a screw or gravity take-up records how far the take-up has moved, which rises as the chain lengthens.
  • Surge and stall. Drive current and a tail-shaft speed sensor show surging and a broken or jumped chain while the drive still turns.
  • Logging. In Logix controllers, a periodic task performs a function at a specific time interval, which suits sampling these trends.

UTEC Industrial, a Rockwell Automation Recognized System Integrator, integrates Allen-Bradley ControlLogix and CompactLogix controllers with VFD drives for this kind of condition monitoring (CEMA Conveyor Chain Fact Sheet 2007-03, 2007; Renold REN16/ENG/10.10, p. 13; Rockwell Automation 1756-RM094N-EN-P-2025, Ch. 5 p. 41).

Where does chain sit in the design-to-monitoring chain?​

The steps upstream of a bought chain decide how evenly it wears:

  • Design and engineering. As engineering reasoning, the B29 family, pitch, attachment pattern, strand count, and working-load basis are fixed from the material and duty before the sprockets are drawn.
  • Parts machining. B29.200, B29.12M, and B29.15M carry sprocket eccentricity and face runout tolerances, and Renold's guide says that where chains have been matched, the drive sprockets should be bored and keywayed as a set in relation to a tooth, with a machine-cut tooth form recommended to ensure equal load sharing.
  • Fabrication, weld fatigue, and stress relief. Renold says inner-plate wear that appears before other wear is a sign of misalignment in the conveyor, and lists alignment of head and tail wheels, shaft alignment, and level across the tracks as the checks. As engineering reasoning, a frame that distorts after machining produces exactly that misalignment. Stress relief ahead of final machining is covered in the stress-relief article for machine bases and frames.
  • Drives, controls, and monitoring. The trends in the previous answer, against the maker's replacement limits.

UTEC Industrial machines to tolerances as tight as ±0.001 in and performs CMM inspection on the parts it machines, which is where sprocket bores, keyways, and shaft seats can be made and checked (ASME B29.200-2001 R2021; ASME B29.12M-1997 S2025; ASME B29.15M-1997 S2025; Renold REN16/ENG/10.10, pp. 14 and 32).

What should an engineering-class chain specification state?​

As engineering practice, a chain request gives the chain maker and builder what the documents above call for:

  • The family and standard. The B29 standard and family, pitch, and attachment codes, or the maker's designation where no B29 family applies.
  • The properties the designation does not fix. Material, heat treatment, and pin fit, which CEMA's fact sheet says a catalog comparison leaves unanswered.
  • The working-load basis. Bearing area and bearing pressure, or the maker's own method, with the lubrication and chemical conditions any doubled bearing pressure depends on.
  • The environment. Plating or stainless grade, with its temperature range, chemical exposure, food contact, and the 230 fpm stainless speed limit in the CEMA paper.
  • Multiple strands. Right- or left-hand strands, direction of travel on the drawings, and the matching tolerance and tagging, identified when the chain is ordered.
  • Inspection and replacement. The extension measurement method, the maker's replacement limits, and the inspection interval.

The standard and family items trace to ASME's publisher descriptions; the rating, matching, and wear items trace to CEMA's documents and the makers' guides, cited as dated sources, not as current general practice (ASME B29.200-2001 R2021; CEMA Conveyor Chain Fact Sheet 2007-02, 2007; Neuhengen 2022, CEMA Conveyor Chain and Sprocket Technical Paper 2022-01; CEMA Technical Report 2016-01, 2016, p. 2; Renold REN16/ENG/10.10, p. 13).

Related Articles

References​

  • CEMA Conveyor Chain and Sprocket Section. Engineering Class and Roller Chains -- There is a difference (Conveyor Chain Fact Sheet 2007-02). CEMA, 2007.
  • CEMA Conveyor Chain & Sprocket Committee. Conveyor Chain Types & Definitions (Technical Report 2018-01). CEMA, 2018.
  • ASME B29.200-2001 (R2021): Welded-Steel-Type Mill Chains, Welded-Steel-Type Drag Chains, Attachments, and Sprocket Teeth. ASME, 2001.
  • ASME B29.400-2001 (S2025): Combination, "H"-Type Mill Chains, and Sprockets. ASME, 2001.
  • ASME B29.12M-1997 (S2025): Steel Bushed Rollerless Chains, Attachments, and Sprocket Teeth. ASME, 1997.
  • ASME B29.15M-1997 (S2025): Steel Roller Type Conveyor Chains, Attachments, and Sprocket Teeth. ASME, 1997.
  • ASME B29.100-2011 (S2025): Double-Pitch Roller Chains, Attachments, and Sprockets. ASME, 2011.
  • American Chain Association. Standard Handbook of Chains: Chains for Power Transmission and Material Handling, 2nd ed. CRC Press, 2005. ISBN 9781574446470.
  • Renold REN16/ENG/10.10: Conveyor Chain Installation, Maintenance & Designer Guide. Renold Power Transmission, 2010.
  • Neuhengen R. Corrosion Resistant Chains (Conveyor Chain and Sprocket Technical Paper 2022-01). Conveyor Equipment Manufacturers Association, 2022.
  • Conveyor Equipment Manufacturers Association. Conveyor Chain - Matched Strands (CEMA Technical Report 2016-01). CEMA, 2016.
  • Otoshi K (supervising ed.), Kanehira M (ed.). The Complete Guide to Chain, 1st English ed. U.S. Tsubaki, 1997. ISBN 0-9658932-0-0.
  • CEMA Conveyor Chain and Sprocket Section. Common Sense Facts About Chain Design, Maintenance, and Uses (Conveyor Chain Fact Sheet 2007-03). CEMA, 2007.
  • CEMA Safety Bulletin DC 2026-03: Warning and Safety Reminders for Drag Conveyors. Conveyor Equipment Manufacturers Association, 2026.
  • OSHA 29 CFR 1910.219: Mechanical Power-Transmission Apparatus. U.S. Department of Labor, 1974 (as amended through 2004).
  • Rockwell Automation 1756-RM094N-EN-P-2025: Logix 5000 Controllers Design Considerations. Rockwell Automation, 2025.

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