Pipe Size Selection

1. Purpose

This procedure identifies commonly available pipe sizes and piping components through 60 inch pipe size.

2. General

Throughout this procedure pipe sizes are referenced as numeric inch with the term “size” implied. Customary pipe sizes are nominal up through and including 12 inches, and the outside diameter measurement for 14 inches and larger. Inflection Point Engineering designates pipe sizes in inches for English, metric, and SI units. This is a commonly accepted international practice. Inch pipe sizes may not be directly converted to metric pipe sizes; take care if converting to metric. There is no clear correlation of nominal and true metric to inch pipe size with potential adverse affect to hydraulics.

3. Pipe Size Selection

First determine the required inside pipe diameter based upon process hydraulic requirements such as pressure drop and velocity limitations. Select a pipe size based upon the availability of pipe (and any additional applicable piping components) in the required size and metallurgy. Refer to Table 1 for typical pipe sizes along with the availability of valve, flange and fitting piping components.

3.1 Pipe Availability

a. Seamless pipe up to and including 24 inches, along with a full complement of flanges and fittings, is widely available in the metallurgies that Inflection Point Engineering commonly specifies. For most flange classes (see Tables 2 and 3) there is good availability of flanges and fittings in the tabulated sizes. The use of 22 inch pipe is discouraged because there are no ASME standard flanges or valves available. In most situations, an increase to 24 inch or decrease to 20 inch is feasible. Consequently, the 22 inch pipe size has been omitted from Tables 1, 2, and 4. Seamless pipe may be obtained up to and including 60 inches; however, world suppliers are limited, cost may be prohibitive, and delivery may also be extended when compared to welded pipe.

b. Welded pipe up to and including 60 inches, along with a full complement of flanges and fittings, is widely available in the metallurgies that Inflection Point Engineering commonly specifies. For most flange classes (see Tables 2 and 3) there is good availability of flanges and fittings in the tabulated sizes.

c. When wrought fittings are not available for a particular size of piping, use mitered elbows and fabricated fittings. The design engineer shall account for the additional pressure drop when using mitered elbows.

d. As a point of reference, seamless carbon steel pipe may cost from 15% to 30% more than welded. If full radiography is required for the longitudinal weld, this cost differential is greatly reduced.

3.2 Valve Availability

Tables 1 and 4 indicate the availability of gate valves in various sizes. The availability of gate valves in the tabulated sizes depends upon the ASME class (see Table 4). For other types of valves refer to the applicable Inflection Point Engineering Pipe Class.

4. Minimum Pipe Size

One inch is the smallest size specified for process lines. Smaller sizes may be used for miscellaneous services such as instruments, vents, drains, and injection piping.

5. Special Applications

Pipe for special applications (such as: instruments, refrigeration circuits, catalyst transfer piping, Parex port piping, heater tubes, and special nozzle connections) is available in commonly used metallurgies in the following inch sizes:

These sizes are not recommended for process piping due to long material delivery, high cost, and/or lack of availability of valves, flanges and fittings.

6. Substitutions

6.1 Larger Sizes

Larger pipe sizes may be substituted except where:

(1) Piping volume is critical; e.g., Parex

(2) Hot residence time is critical; e.g., Oleflex

(3) Velocities must be maintained; e.g., carrying solids or

(4) The flow regime is critical

6.2 Smaller Sizes

Smaller pipe sizes may be substituted if the unit hydraulics are suitably adjusted, unless the velocity increase is a concern; erosion from carried materials, vibration, flow regime, or corrosion from stripping a protective film.

Table 1 - Pipe, Valves, Flanges and Fittings Common Size Availability

Notes:

(1) For valve availability see Table 4.

(2) Standard flange availability depends on the ASME B16.5 flange Class. See Table 2.

(3) Standard flange availability depends on the ASME B16.47 flange Class. See Table 3.

(4) Available pipe and fitting sizes are based upon ASME B16.5, B16.9, B16.11, B36.10M, and B36.19M.

(5) Seamless pipe may be special ordered, however availability restrictions and higher cost must be considered.

Table 2 - Standard Flanges Available per ASME B16.5 Up to Size 24 Inches

Note:

(1) Flanges up to 24 inches not included in ASME B16.5 must be designed in accordance with accepted methods; i.e., ASME Section VIII, Division 1, Appendix 2.

Table 3 - Flanges Available per ASME B16.47 Sizes 26 to 60 Inches, Series A and B.

Notes:

(1) Flanges from 26 to 60 inches not included in ASME B16.47 must be designed in accordance with accepted methods; i.e., ASME Section VIII, Division 1, Appendix 2.

(2) Flanges not available in Series B.

Table 4 - Availability of Gate Valves

Note:

(1) Longer lead times may be required for valve manufacture.