Casing Bow-spring Centralizers

API SPECIFICATION 10D SEVENTH EDITION, APRIL 2021

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Copyright © 2021 American Petroleum Institute

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Foreword

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Contents

Page

1. Scope 1

2. Normative Reference 1

3. Terms and Definitions, Symbols, and Abbreviations 1

   1. Terms and Definitions 1

   2. Symbols and Abbreviations 3

4. Requirements 4

   1. Functions of a Centralizer 4

   2. Starting Force 4

   3. Standoff Ratio at API Test Load 4

   4. Establishing Initial Centralizer Performance Values 7

5. Testing Equipment 9

   1. Test Stand 9

   2. Instrumentation 10

   3. Accuracy 10

   4. Test Pipe 10

6. Testing Bow-spring Centralizers to be Used in Conventional Applications 11

   1. Starting, Restarting, and Running Force Test 11

   2. Measuring Standoff at API Test Load—Procedure 13

   3. Pass or Fail Criteria 16

7. Testing Bow-spring Centralizers to be used in Under-reamed Applications 16

   1. General 16

   2. Testing Sequence for Under-reamed Applications 16

   3. Pass or Fail Criteria 17

8. Marking 17

   1. General 17

Annex A (informative) Miscellaneous Information 19

Bibliography 26

Figures

1. Conventional and Under-reamed Bow-spring Centralizer Applications 4

2. Bow-spring Centralizers—Criterion to Define Retesting Requirements 8

3. Typical Bow-spring Centralizer Starting Force Test Equipment 9

4. Typical Test Equipment for Bow-spring Centralizer Standoff at Test Load 10

5. Outer Pipe Inner Edge Bevel 11

6. Bow-spring Centralizer Conventional Application: Starting Force Test 13

7. Standoff Test and Bow-spring Casing Centralizer Test Positions 15

8. Casing Standoff 16

Contents

A.1 SOR vs. Load Curve Example [298.5-mm (11 ¾-in.) bow-spring centralizer in 374.7-mm (14 ¾-in.)

Page

hole] 19

Tables

1 Casing Bow-spring Centralizers Specification—API Test Load and Maximum Starting Force 5

Introduction

This edition is based on API Specification 10D, 6th Edition, March 2002.

Users of this standard should be aware that further or differing requirements may be needed for individual applications. This standard is not intended to inhibit a vendor from offering, or the purchaser from accepting, alternative equipment or engineering solutions for the individual application. This may be particularly applicable where there is innovative or developing technology. Where an alternative is offered, the vendor should identify any variations from this standard and provide details.

In this standard, quantities are expressed in international System of Units (SI) and/or in U.S. customary units (USC). The values associated with the different units do not necessarily represent a direct conversion of SI units to USC units, or USC units to SI units. Consideration has been given to the precision of the instrument making the measurement.

Calibrating an instrument refers to ensuring the accuracy of the measurement. Accuracy is the degree of conformity of a measurement of a quantity to its actual or true value. Accuracy is related to precision, or reproducibility, of a measurement. Precision is the degree to which further measurements or calculations will show the same or similar results. Precision is characterized in terms of the standard deviation of the measurement. The results of calculations or a measurement can be accurate but not precise, precise but not accurate, neither accurate nor precise, or both accurate and precise. A result is valid if it is both accurate and precise.

This document uses a format for numbers which follows the examples given in API Document Format and Style Manual, October 2020. This numbering format is different than that used in API 10D, 6th Edition. In this document, the decimal mark is a period and separates the whole part from the fractional part of a number. No spaces are used in the numbering format. The thousands separator is a comma and is only used for numbers greater than 10,000 (i.e., 5000 items, 12,500 bags).

Casing Bow-spring Centralizers

1. Scope

   
   

   This specification provides testing, performance, and marking requirements for casing bow-spring centralizers to be used in oil and natural gas well construction. The procedures provide verification testing for the manufacturer’s design, materials, and process specifications, and periodic testing to confirm the consistency of product performance. This specification is not applicable to other devices, such as rigid centralizers and cement baskets, or bow-spring centralizers used for other purposes (e.g., wireline tools, gravel pack, inner string).

   
   

2. Normative Reference

   
   

   This document contains no normative references. For a listing of other articles associated with this publication, refer to the bibliography.

   
   

3. Terms and Definitions, Symbols, and Abbreviations

3.1 Terms and Definitions

For the purposes of this specification, the following terms and definitions apply.

3.1.1

annular clearance

Radial clearance between the outside diameter of the casing and the wellbore.

3.1.2

API test load

Specified normal force applied to a bow-spring centralizer to evaluate standoff performance.

3.1.3

bow-spring centralizer

An apparatus comprised of a plurality of bow-shaped springs biased outwardly from a tubular body, the outside diameter of which can vary under a change in applied load, and connected by two end collars, that is placed on the outside of a tubular (e.g., casing or tubing) and used to centralize the tubular in a wellbore.

3.1.4

bow-spring centralizer sub

A bow-spring centralizer installed on a tubular body having an integral holding method where the tubular body becomes its own section of the casing string.

3.1.5

casing nominal diameter

Theoretical outside diameter of the casing.

3.1.6

conventional application

An application where the smallest wellbore diameter that the bow-spring centralizer will pass through is at the centralizer setting depth (see Figure 1).

3.1.7

holding device

A device employed to limit the axial movement of the stop collar or bow-spring centralizer on the casing.

EXAMPLESet screws, nails, machined tubular, mechanical dogs, epoxy resins, or machined features (integral).