ASME B29.21M

Description / Abstract: An ANSI B29 Subcommittee was established in 1975 to develop a standard which would aid municipalities and others in specifying chains for water and sewage treatment plants. This Standard is the result of that effort.

Previous ANSI chain standards have covered dimensions which assured interchangeability and listed ultimate strengths. This Standard serves a dual purpose. It was developed to assure consistency with previous standards and does replace ANSI B29.13-1972. However, it also contains a supplementary section which is unique to ANSI B29 standards. The supplement identifies "Engineering Characteristics" of 700 Class Welded Steel and Cast Chain including attachments and sprockets in common use for rectangular straight line collectors in water and sewage treatment tanks. "Engineering Characteristics" as used in this Standard identify those properties of the chains, attachments and sprockets which are required to assure that they will operate successfully.

Use of this Standard and supplement offers sufficient information to use as a minimum or base requirement when specifying chain attachments and sprockets for water and sewage treatment plants. The Standard specifies a minimum chain "quality". The user must identify those options, not affecting chain "quality", but which do describe the chain features for a specific application. User specifications should include the following:

- Chain type and number

- Attachment and spacing

- Pin and cotter or riveted

- Pearlitic malleable-cast chain

- Heat treated or nonheat treated (welded steel chain only)

- Destructive tests, if any

- Sprocket construction details

- Special materials or plating

- Shipping Instructions

In the event that any chain, attachment or sprocket produced in accordance with this Standard does not comply with the listed "Engineering Characteristics" of the supplement for new and unused chain, it would be anticipated that the supplier would like an appropriate corrective action.

The function of the chains in a collector tank is to remove the separated solids from the tank by means of moving scraper flights. The operating conditions are both corrosive and abrasive to varying degrees. Successful past operation suggests that adherence to the "Engineering Characteristic" will provide satisfactory operation of chains in this application. Further, it provides for similar operating results with chains from various manufacturers.

Historically, small amounts of copper have been added to materials used in cast and fabricated steel chains for this application. While it is reported in scientific literature that small additions of copper enhance resistance to atmospheric corrosion, it is as yet undetermined whether the benefits of this practice apply to this application, and therefore, no requirement for copper is included.

The subcommittee encourages comparison testing where additional data is desired to confirm the advantage, non-advantage or disadvantage of copper addition. Additional consideration was also given to the commercial problem of the unavailability of copper in wrought steel materials except for very large orders.

This Standard was approved by the B29 Standards Committee and was subsequently approved by the secretariat and submitted to the American National Standards Institute for designation as an American National Standard. This was granted on April 3, 1981.

The current revision was approved as an American National Standard on March 8, 1996.