ANSI API RP 10D-2-2004 pdf free download – Petroleum and natural gas industries — Equipment for well cementing — Part 2: Centralizer placement and stop-collar testing.
5 Procedure for testing stop collars
5.1 General
For the purposes of this procedure, the term “stop collar” is used to indicate any type of device employed to prevent or limit movement of a centralizer on the casing. This includes stop collars that are independent of the centralizer and holding devices that are built into the centralizer, as in the case of solid or rigid centralizers. In this clause, the principles described for centralizers apply to other casing hardware that incorporate the use of a stop collar. Examples of these include cement baskets, scratchers, etc.
The holding device used to prevent the slippage of a centralizer can be an independent piece of equipment, as in the case of a stop collar, or can be integral within the centralizer itself. Several types are available that include the use of screws, nails and mechanical dogs. Some manufacturers also recommend the use of resins in conjunction with their particular holding device.
Regardless of the mechanism used to hold the centralizer in place, the holding device shall be capable of preventing slippage. While the holding force of the stop collar should be greater than the starting force of the centralizer, some multiplier should be applied depending on the particular well conditions. In the case of either solid or rigid centralizers, it is recognized that these types of centralizer do not have a starting force, as they have a constant outside diameter. The minimum holding force applied to these centralizers should follow the same guidelines as a bow-type centralizer that would be used in the same hole configuration. This same recommendation also applies to other casing hardware incorporating a stop collar.
It should be noted that the data obtained for centralizer starting, running and restoring forces can vary depending on how the centralizer is installed on the casing. The use of a stop collar either as an integral part of the centralizer or with the centralizer placed over the stop collar can provide different results for some centralizers.
Further information indicates that the casing grade, mass, and surface finish can affect the results obtained from stop-collar tests. Changes in the hardness of the casing, as well as the casing wall thickness, have been shown to cause variations in the results by as much as a factor of four. It is therefore recommended that in a critical situation, the testing be performed using the same casing grade and mass as are to be used for the well.
The rate at which the load is applied during the test can have a minor effect on the results. While small changes in the loading rate should have minimal effects, shock loading can alter the results. In some instances it may be desirable to equate the loading rate to the anticipated casing running speed, and adjust the rate accordingly. There are insufficient data currently available to make a firm conclusion or recommendation on loading rates. Associated with the loading rate is the manner in which the load is applied. This test procedure incorporates a concentric loading pattern, which may not match precisely the type of loading that can occur during actual field use. The purpose of this procedure is to provide a consistent method for performing routine tests. If the actual field conditions warrant, individual customized testing may be appropriate. Note that this is a destructive test, and may require replacement of the test casing and the stop collar following each test.ANSI API RP 10D-2 pdf download.