Agenda Item 650-520



Agenda Item 650-520

Title: PVT Metrication Methodology

Date: August 12, 2003

Handled By: Ty Hagen

Company Hagen Engineering International, Inc.

Phone 651-686-5686

Fax 651-686-5685

Email: ty@

_________________________________________________________________________________________

Purpose: To establish agreed upon rules and procedures for use by the API PV&T Subcommittee in converting API Tank Standards, API STD 620, 650 and 653, from a single set of units (in-lbs) to a dual set of units (SI and in-lbs).

Source: Inquiry 650-I-03/00

Revision: 0

Impact: The guide document will lead to metricated versions of API 620, 650 and 653 that follow metrication best practices and serve well the needs of tank purchasers and manufacturers.

Background: The metrication of API 650 that was published as the 10th edition (Nov 98) raised a number of questions in inquiry 650-I-03/00. A metrication task group was formed to address these issues and to metricate API 620 and API 653. The task group approach has been to first work through the issues and produce this guide document to express what the TG feels is the right way to do the metrication. During this process all of the issues raised in 650-I-03/00 have been addressed along with additional issues.

Rationale: Rationale for the position taken on certain key issues is as follows:

|Issue and Position |Rationale |

|SI and in-lb unit rules will be similar but not identical. |Already settled in item 650-539 |

|These rules are not to be mixed by the standard user. | |

|Rounded conversions to SI with few exceptions |Makes standards user-friendly in metric units |

|Critical dimensions such as bottom plate thickness are to be |Rounded values of 6mm and ¼ in. considered to have significantly different |

|exact converted (6 mm and 0.236 in.) |expected life. ¼” can still be user specified when desired. |

|Single set of standards for mating parts, such as API |Owners and appurtanance venders will have only one physical API manhole |

|manholes |flange series rather than two. This helps standardization, |

| |interchangability and reduced inventory. |

|Equations will be re-written in dimensionless units. |This reduces the bulk of the standards and helps make the equation basis |

| |clearer. |

Proposed Change:

| |

|This ballot item does not directly contain any changes to the content of API 620, 650 or 653. What is being balloted is a separate |

|document titled: |

| |

|“Rules for the Development of Dual Unit API Tank Standards” |

Rules for the development of Dual Unit API Tank Standards

April 1, 2003

1. Scope

1. This document provides rules and procedures for use by the API PV&T Subcommittee in converting API Tank Standards , API STD 620, 650 and 653, from a single set of units (in-lbs) to a dual set of units (SI and in-lbs)

2. References

1. IEEE/ASTM SI 10 Standard for Use of the International System of Units (SI): The Modern Metric System

2. API Manual of Petroleum Measurement Standards Chapter 15 (formerly API Publication 2564) Guidelines for the Use of the International System of Units (SI) in the Petroleum and Allied Industries. 3rd ed, 2001.

3. API STD’s 620, 650 and 653

4. NIST website . “General Tables of Units of Measurement” defines US Customary System and includes discussion on where there are differences between US and British units. The main differences are imperial gallon and imperial bushel which are larger than in US.

3. Definitions

1. in-lb: Units of measurements based upon the inch and pound and commonly used in the USA and referred to as the US Customary System (USCS). These units of measurement are similar but not necessarily equivalent to the English system, or the imperial system of units.

2. SI: The International System of Units, symbolized SI. This system is based on the meter and kilogram and defined by the General Conference on Weights and Measures (CGPM). This is a simplified modern version of the metric system and has been adopted on an international basis.

3. Rounded conversions: (a.k.a. Hard Conversion). This converts in-lb units to SI units that do not exactly numerically match the old in-lb unit values. e.g. 1 in = 25 mm.

4. Exact conversions: (a.k.a. Soft Conversion). This exactly converts the in-lb unit to a numerically equivalent SI unit, thereby maintaining the in-lb value, specified in SI units. e.g. 1 in = 25.4 mm.

4. Philosophy

1. The following guiding values underlie the rules and procedures for units conversion expressed in this document.

2. Dual units must not create ambiguity regarding which rules in the standards must be followed.

3. Compatibility of mating parts should be assured.

4. Standards should minimize number of different tank and appurtenance spare parts required.

5. Good availability of materials should be considered in required part sizes.

6. Tank and tank appurtenance manufacturer standardization should be fostered.

7. Round numbers are desired in both systems of units where possible.

8. Minimizing the length of the standards is desirable (e.g. non-dimensional equations help this)

5. Rules

1. General

Dual units standards shall contain a policy statement to the effect that:

1) Requirements are stated in two alternate systems of units

2) The two alternate systems of units creates a standard containing similar but not identical sets of requirements

3) Either one set of requirements or the other must be used on a given structure rather than a mixture of the two sets of requirements.

5.2 Rounded Conversions vs. Exact Conversions

When determining a new SI value corresponding to an existing inch-pound value the key question is “how exact should be conversion be?” 3.3 and 3.4 above define two general categories, rounded conversion and exact conversion. This section provides direction on when each type of conversion practice should be used.

5.2.1 Normal practice shall be to use rounded conversion in all cases except where an exception is justified as discussed in 5.2.1.4 below. This will create tank standards containing two similar but not identical rule-sets. However this will not create confusion as long as each tank standard contains policy as per 5.1.1 that the two rule-sets should not be mixed on one tank

5.2.2 Exceptions where exact conversions shall be used:

• Mating parts: It is intended that where API tank standards define dimensions of standard removable parts, there will be only one physical set of dimensions. Corresponding mating parts that are not removable shall utilize dimensions that allow a standard part to mate to tanks built to either rule set. (e.g. In API 650: Table 3-3, columns 3 to 6; Table 3-5, columns 2 to 3; Table 3-8, columns 3 to7; Table 3-13, columns 2 to 8; etc)

• Where industry standards in general use both in the USA as well as in SI-dominated locations utilize the same physical dimensions. (e.g. pipe dimensions as given in Table 3-6, columns 2-3)

• Materials Specifications: The converted standard shall provide for an exception to the policy statement given in 5.1.1 above. The exception shall permit any material listed in the API standard to be used on non-structural components such as clips regardless of the units selected for the tank. For example clip material certified to A36 shall be permitted in a tank even if SI rules are being applied; A36M is not required.

• Critical quality dimensions: One critical dimension that should be exact converted is the bottom thickness, since it directly relates to tank longevity. Minimum thickness should be 6 mm (0.236 in.). This reflects that fact that a 6 mm bottom is considered technically adequate, and may be used anywhere any where in the world and following either rule-set if 6 mm plate is available. At the same time 6.35 mm (¼ in.) is acceptable too and will be used if 6 mm is not available or if purchaser so specifies.

5.3 Equations

5.3.1All equations are written so that any consistent set of units may be used to obtain correct results. For example, where variables with length dimensions are required, the user will obtain correct results whether the user inputs all such variables in in., ft., mm, m, or any other measure of length.

5.3.2All variable names used in equations are defined in one section titled “Nomenclature” placed at the beginning of the document in which they appear. Each variable name has a unique definition in the document. For example:

D = centerline diameter of the bottom shell course

5.2.3Where an equation contains a term that is a constant with dimensions, the term in the equation appears as a variable and the variable is defined immediately following the equation. For example, for the 1 ft rule in section 3.6.3.2, the equation for determining shell thickness is given as:

[pic]

where A = 0.3 m (1 ft)

Note that the other terms of the equation (tt, (w, D, H, and St) are defined in the nomenclature section.

5.4 Formatting Rules

5.4.1 Text Format

• Spelling For the API tank standards, use the following spellings: “meter” and “liter”. These terms have alternate spellings that should not be used in API documents.

• Space Units and symbols must be separated by a space, e.g. 100 kg. However, use commas, not spaces, to separate by thousands in number grouping.

• Symbols The short form of units, such as mm for millimeter, are called symbols, not abbreviations.

• Punctuation Symbols do not end with a period, except at the end of a sentence and “in.” for inch.

• Singularity Symbols are always written in the singular form, even if more than one is the intent. If the symbol is not abbreviated, then adding as “s” is correct for the plural form. Correct Examples: 100 m, 500 millimeters

• Quotients For terms that are a quotient of two or more units, such as velocity terms, use a slash, rather than a negative exponent, or the letter “p”. Correct usage for the tank standards is: km/h, not kph, or kmh-1. This may also be written as “kilometers per hour”.

• Products For terms that are multiplications of symbols, use raised dot to string them together, (e.g. N.m for Newton meter).

• Prefixes The SI symbols can be modified with one prefix for each base symbol, but no more, to keep the value in the preferred range of 0.1 to 1000. Correct examples are: 0.5 mm, 800 kPa.

• Temperature The SI term for temperature is the Kelvin (K), which is used to express temperature intervals and thermodynamic temperature. However, for the tank standards, use “degree Celsius ((C)”, and “degree Fahrenheit (oF)”. Do not use centigrade temperature.

• Pressure The correct SI term is kPa. The correct in-lb term is psi. To specify absolute pressure or gage pressure, add a space, then (abs) or (ga). Do not append “a” or “g” to the symbols. Do not use the term “bar”. Do not express pressure in meters or feet of head. Correct examples are 15 kPa, 0 kPa (ga), 2 kPa (abs), 1.5 psi.

• Stress The correct SI term is MPa. Do not use kg/mm2. The correct in-lb term is psi.

• Angles Use degrees and its decimal submultiples (e.g. 30.5 degrees) rather than radians or use of minutes and seconds.

• Capitalization Capitalize the following:

-only those prefixes representing values of a million or greater,

-the symbol for liter (L),

-the word Celsius,

-symbols derived from person’s names (e.g. W for watt, Pa for pascal, etc.),

-G (giga, 1,000,000,000), and M (mega, 1,000,000), and

-whenever grammar rules require capitalization.

• Order of Terms In the API tank standards, place the SI term first, followed by the inch-pound term in brackets (e.g. 25 mm [1 in.]).

• Units not Allowed Do not use the following units: kilogram-force; millimeter, centimeter, in. of mercury; millimeter, centimeter, meter, or in. of water; standard atmosphere (101.325 kPa); micron.

• Special API-Related Terms Do not use the terms “API gravity”, and “API Density”. Instead, us absolute density and relative density.

• References For SI format issues not addressed above, refer to API Publication 2564.

5.4.2 Table Format

a) Separate Tables: Tables are to be shown with the SI units displayed in tables separate from the inch-pound unit tables. The purpose is to minimize reader errors, to improve readability, and to provide for the eventual all-metric edition of the standard.

b) Sequence of Tables: Show SI table first, then in-lb.

c) Table Numbering: The SI table number shall be followed by “(SI)” and the inch-pound table number shall be followed by “(in-lb)”; for example, “Table 3-2 (SI)” and Table 3-2 (in-lb)”.

5.4.3 Figure Format

a) Graphs: Use all 4 scales to show dual units, with the metric units on the left and bottom axes and in-lb on right and top axes. Normally, do not use separate graphs to show the two sets of units.

b) Other Figures: Use a single dual-unit figure for each. Where text is included in the figure it shall be handled as per 5.4.1.

-

6. Procedures

1. Identify the number or equation that requires dual units.

2. Understand the basis and accuracy of the number or equation. Especially in the case of rounded conversions, this will lead to appropriate decisions regarding the amount of precision to carry from the initial exact conversion into the final rounded SI value. Refer to Annex B of IEEE/ASTM SI-10 for details on this issue.

3. If the number comes from an equation, adjust the equation so that it is unit less.

4. Determine if the number should be rounded converted or exact converted.

5. How conversions are done

6.5.1 Rounded Conversion

6.5.1.1 General

1) Rounded conversions shall round to the nearest convenient or whole number. The conversion of units shall normally follow the chart given in Appendix A (e.g. inches will always convert to mm, feet will always convert to meters.)

2) See appendix B for typical rounded conversions for typical values.

3) Example 1” = 25 mm.

6.5.1.2 Rounded conversions provided by documents referenced by API standards (e.g. ASTM and AWS) should be used where applicable. We should not attempt to revise the conversions in these specifications just to be consistent with this API PV&V conversion rules document. The yield strength and tensile strength given in SI in ASTM is one relevant example. The amount of permitted thickness under-run is another example (0.3 mm as given in A6 and A20 should be used in API 650, 2.2.1.2.3 rather than 0.25 mm).

6.5.1.3 Rounded conversions that have been widely adopted by industry or manufacturing practice should be followed. For example, structural shapes such as angles need to be converted based on availability of SI sizes of angles. Do not convert to a size for a part or component that is not readily available.

6.5.2 Exact Conversion

1) Exact conversions shall maintain the original precision of the original number, keeping the same number of significant digits. Appendix A provides the exact conversion factors for the various units. The converted value must be carried to a sufficient number of digits to maintain the accuracy implied or required in the original value.

2) See Appendix B for typical exact conversion factors for typical values.

3) Example 1” = 25.4 mm

7. Implementation

1. Authority

PV&T subcommittee approves this guide document and provides authority to the Metrication Task Group. The API 620/650/653 documents are to be metricated in accordance with this guide document at the direction of the PV&T subcommittee.

2. Changes/Questions/Revisions

On going metrication task group will answer any questions that arise that are not covered in the guide and update the guide document. Substantial changes to the guide document requires subcommittee approval.

3. Agenda items need to meet metrication requirements given in this guide document, this is not an API staff function. The handler of each agenda item is responsible for meeting these guidelines.

4. This document will be made available and updated on the PV&T website.

8. Appendices

A. Unit Chart

B. Conversions

|Appendix A |Units | | |

| | | | |

|  |in-lb Unit |SI Unit |Exact Conversion factor |

|  |  |  |in-lbs to SI |

|  |  |  |  |

|Length |in. |mm |2.54 * 101 |

|  |ft |m |3.048 * 10-1 |

|  |  |  |  |

|  |  |  |  |

|Area |in.2 |mm2 |6.4516 * 101 |

|  |ft2 |m2 |9.2903 *10-2 |

|  |  |  |  |

|  |  |  |  |

|Volume |bbl |m3 |1.590 * 10-1 |

|  |  |  |  |

|  |  |  |  |

|Force |lb |N |4.4482 |

|  |  |  |  |

|  |  |  |  |

|Pressure ( Stress) |psf |kPa |4.7880 * 10-2 |

| small |psi |kPa |6.8948 |

| large |psi |Mpa |6.8948 * 10-3 |

|  |ksi |Mpa |6.8948 |

|  |  |  |  |

|  |  |  |  |

|Moment |ft-lb |N*m |1.3558 |

|  |  |  |  |

|Energy |ft-lb |J |1.3558 |

|  |  |  |  |

|Section Modulus |in.3 |cm3 |1.6387 * 101 |

|  |  |  |  |

|Temperature |oF | °C |(F-32) * (5/9) |

|  |  |  |  |

|  |  |  |  |

|Flow |bbl/h |m3/h |1.590 * 10-1 |

|  |in./hr |mm.hr |2.54 * 101 |

|  |  |  |  |

|Velocity |mph |km/h |1.6093 |

|Appendix B - Conversion Examples | |

| | | | | |

|in-lb value |in-lb unit |SI unit |Rounded |Exact |

|  |  |  |SI Value |SI Value |

|  |  |  |  |  |

|3/16 |in |mm |5 |4.7625 |

|1/4 |in |mm |6 |6.35 |

|5/16 |in |mm |8 |7.9375 |

|3/8 |in |mm |10 |9.525 |

|1/2 |in |mm |13 |12.7 |

|1 |in |mm |25 |25.4 |

|50 |ft |m |15 |15.24 |

|120 |ft |m |36 |36.576 |

|200 |ft |m |61 |60.96 |

|200 |degrees F |degrees C |90 |93.3 |

|36,000 |psi |Mpa |250 |248 |

|25 |psf |kPa |1.2 |1.2 |

| | | | | |

|SI Unit Value |SI Unit |in-lb unit |Rounded |Exact |

|  |  |  |in-lb Value |in-lb Value |

|5 |mm |in |3/16 |0.1969 |

|6 |mm |in |1/4 |0.2362 |

|8 |mm |in |5/16 |0.315 |

|10 |mm |in |3/8 |0.3937 |

|13 |mm |in |1/2 |0.5118 |

|25 |mm |in |1 |0.9843 |

|15 |m |ft |50 |49.2126 |

|36 |m |ft |120 |118.1102 |

|61 |m |ft |200 |200.0722 |

|90 |degrees C |degrees F |200 |194 |

|250 |Mpa |psi |36,000 |36,259 |

|1.2 |kPa |psf |25 |25 |

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