Ellenberger Piping and Pipeline Calculations Manual

Construction, Design Fabrication and Examination
2. Auflage 2014
ISBN: 978-0-12-416968-5
Verlag: Elsevier Science & Techn.
Format: EPUB
Kopierschutz: 6 - ePub Watermark

E-Book, Englisch, 412 Seiten

Piping and Pipeline Calculations Manual, Second Edition provides engineers and designers with a quick reference guide to calculations, codes, and standards applicable to piping systems. The book considers in one handy reference the multitude of pipes, flanges, supports, gaskets, bolts, valves, strainers, flexibles, and expansion joints that make up these often complex systems. It uses hundreds of calculations and examples based on the author's 40 years of experiences as both an engineer and instructor. Each example demonstrates how the code and standard has been correctly and incorrectly applied. Aside from advising on the intent of codes and standards, the book provides advice on compliance. Readers will come away with a clear understanding of how piping systems fail and what the code requires the designer, manufacturer, fabricator, supplier, erector, examiner, inspector, and owner to do to prevent such failures. The book enhances participants' understanding and application of the spirit of the code or standard and form a plan for compliance. The book covers American Water Works Association standards where they are applicable. - Updates to major codes and standards such as ASME B31.1 and B31.12 - New methods for calculating stress intensification factor (SIF) and seismic activities - Risk-based analysis based on API 579, and B31-G - Covers the Pipeline Safety Act and the creation of PhMSA

J. Phillip Ellenberger, P.E., retired as Vice President of Engineering at WFI International (a division of Bonney Forge ) in Houston, Texas, a design and manufacturing firm specializing in machined branch connections. He is a life member of ASME, for which he serves on several codes and standards committees. He is active with the B16 F & C subcommittees, the B31.3 design task group, and the B31 mechanical design and fabrication committee. Mr. Ellenberger is also the MSS Chairman of the Coordinating Committee and Committee 113, and IS member of WG 10 SC67. He has taught piping stress analysis at the University of Houston, and numerous professional seminars on B31.3 and related topics.

Autoren/Hrsg.

Ellenberger, Philip

Leseproben

Chapter 2

Metric versus U.S. Customary Measurement

Abstract

This chapter confronts the difficulties and challenges encountered when dealing with standards and codes that use different systems of measurement. Many U.S. codes and standards were originally written in a period when the metric system was not necessarily the dominant world system. While the United States has played with converting to the SI system, it has not yet occurred and conversion is still something that must be deal with. The chapter discusses the difference between hard conversion and soft conversion: hard conversion involves converting a physical object (i.e., actually replacing the part), while soft conversion involves merely renaming a part and expressing its size in metric. The chapter continues with a brief look at the basics of the SI units of measurement, and outlines various methods of conversion that piping codes have used to convert units from U.S. customary to metric. Finally, the challenges encountered when undertaking conversion in the piping context are detailed.

Keywords

International System of Units (SI)U.S. customary systemmetrichard conversionsoft conversionpipingASTMSI-10ASME

Contents

Overview

Hard versus Soft Metric Conversion

SI System of Measurement

Methods of Conversion from One System to the Other

Challenges for Converting from One System to the Other

Overview

Whenever one writes anything that includes a measurement system in the United States, he or she is confronted with the problem of what system to use in presenting the data and calculations. This is especially true when writing about codes and standards. Most U.S. codes and standards were originally written some time back when the metric system was not necessarily the dominant world system.

The metric system itself has several minor variations that relate to the base units of measure. This will be discussed more thoroughly in the remainder of the chapter. The metric system has evolved in dominance to the point that only three countries do not use it as their primary measurement system: Myanmar, Liberia, and the United States. It is now known as the International System of Units (SI).

The United States has played with converting to the SI system for as long as I have been working in this field, which is a long time. Americans have not made the leap to make it our primary system. This lack of tenacity in converting to this system is difficult to understand completely. The most plausible argument revolves around the installed base of measurement and a modicum of inertial thought regarding the seemingly inevitable conversion. This argument is belied by the fact that England has converted, and it only took a few years.

To those who have worked with the SI system it is immensely preferred due to its decimal conversion from larger to smaller units. What could be simpler than converting a length measurement from something like 1.72 meters to 1720 millimeters? Compare that to converting 1 yard, 2 feet, and 6 inches to 66 inches or 5.5 feet.

On the other side, there is the problem of what you grew up with. It is rather like translating a language that is not your native language. You first have to perform some mental conversion of the words into some semblance of your native tongue. As one becomes fluent in another language, he or she can begin to think in that language.

Hard versus Soft Metric Conversion

All of this is a descriptive example of some of the difficulties of converting an ASME code into a metric code. The generic classification of this problem is hard versus soft conversions. The terms hard conversion and soft conversion refer to approaches you might take when converting an existing dimension from nonmetric units to SI. “Hard” doesn’t refer to difficulty, but (essentially) to whether hardware changes during the metrication process. However, the terms can be confusing because they’re not always consistently defined and their meanings can be nonintuitive.

It’s simplest to consider two cases: “converting” a physical object and conversions that don’t involve an object.

When converting a physical object, such as a product, part, or component, from inch-pound to metric measurements, there are two general approaches. First, one can replace the part with one that has an appropriate metric size. This is sometimes called a hard conversion because the part is actually replaced by one of a different size—the actual hardware changes. Alternatively, one can keep the same part, but express its size in metric units. This is sometimes called a soft conversion because the part isn’t replaced—it is merely renamed.

Another, and possibly simpler way, to explain it is that in a soft conversion a dimension of one foot would be converted to 305 millimeters or 304.8 depending on the accuracy required. In a hard conversion one might convert to 300 millimeters, as that would probably be the size one who was doing the design would choose if he were designing in a metric system.

If the latter sounds odd, note that many items’ dimensions are actually nominal sizes—round numbers that aren’t their exact measurements—such as lumber, where a 2 × 4 isn’t really 2 by 4 inches, and pipe, where a 0.5-in. (NPS ½) pipe has neither an inside nor an outside diameter of 0.5 in. With pipe, the international community has come to a working solution to this anomaly because comparable SI pipe has different dimensions than U.S. schedule pipe. However, when working with pipe above NPS 4, the metric or DN number is 25 × NPS; for smaller or fraction pipe it is made an even number like DN 15 for a NPS ½ pipe.

An even more difficult problem comes about when one is making nonproduct-type decisions while determinign pipe calculations. For instance, how does 1720 mm compare to 5.5 ft in your sense of the two distances? That is to ask, which is longer?

The answer is 1720 mm converts mathematically to 5.643045 ft. However, for some of us, even those who have worked with but are not fluent in metrics, the answer is not obvious—until we do the conversion. We may sense that they are close. In some calculations 5.643045 may not make a significant difference. In others, it may make the difference between meeting or not meeting a certain requirement.

This points to another problem in working with things developed in one system as opposed to other systems. As it relates to conversion, there are often many decisions to be made. If for some reason we were developing a U.S. customary design and arrived at an answer that came to 5.643045 ft, we might call it any of several dimensions in our final decision. It woul depend on the criticality of the dimension in the system.

This would bring us face to face with the oddness of our fractional notation. Normally we think of fractions of an inch. However, we could be dealing with fractions of a foot. Where we are concerned with a dimension that only needs to be within the nearest in. to be effective, we might choose (5 ft, 7.5 in.) or (5 ft, 9 in.). The original 5.643 can be converted to something within of an inch as 5 ft, 7 inch, and so on. Mind you, all this is for converting 1720 mm into U.S. customary dimension. A similar exercise could be presented for converting something like (5 ft, 9 in.) into millimeters, which would be 1752.6 mm. One would then have to make comparable decisions about the criticality of the dimension.

SI System of Measurement

As mentioned earlier, there are several variations of metric systems. Fortunately, they are not as complex as the U.S. customary system (USC). For instance, in distance measurement the name and unit of measure changes with the size of the distance. We have miles, furlongs, chains, yards, feet, inches, and fractions of an inch, all of which can be converted to the other, but not in a linearly logical base 10 fashion as the SI system does.

One system for length, weight, and time in metric is the centimeter, gram, and second system. Another is the kilometer, kilogram, and second system. Note that the change here is just the prefixes for length and weight; the decimal relationship is constant and thus the conversions between the two systems are simple.

The International System of Units (SI) includes some other base units for use in other disciplines:

1. Meter, the distance unit. USC usually uses the inch in pipe work.

2. Kilogram, the weight and force unit. In USC it is the pound.

3. Second, the time unit. Interestingly, a second in France is the same as a second in New York.

4. Ampere, the electrical unit.

5. Kelvin, the temperature unit. Since most of us live and work in the atmosphere, the Celsius measure is more commonly used. But a degree in either is the same; the difference is the 0 reference point....