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There’s no such thing as too large a compressed air line. A common error in compressed air systems is line sizes too small for the desired air flow.
By Hank van Ormer, Don van Ormer and Scott van Ormer
Mar 14, 2005
Energy Savings are Often Disguised as Problems
A common error we see in compressed air systems, in addition to poor piping practice, is line sizes too small for the desired air flow. This isn’t limited to the interconnecting piping from compressor discharge to dryer to header. It also applies to the distribution lines conveying air to production areas and within the equipment found there. Undersized piping restricts the flow and reduces the discharge pressure, thereby robbing the user of expensive compressed air power. Small piping exacerbates poor piping practices by increasing velocity- and turbulence-induced backpressure. (See “There’s a Gremlin in your air system â€“ Its name is turbulence,” pg 37, Plant Services, July 2002).
Pipe size and layout design are the most important variables in moving air from the compressor to the point of use. Poor systems not only consume significant energy dollars, but also degrade productivity and quality. How does one properly size compressed air piping for the job at hand? You could ask the pipefitter, but the answer probably will be, “What we always do,” and often that’s way off base.
Another approach is matching the discharge connection of the upstream piece of equipment (filter, dryer, regulator or compressor). Well, a 150-hp, two-stage, reciprocating, double-acting, water-cooled compressor delivers about 750 cfm at 100 psig through a 6-in. port. But most 150-hp rotary screw compressors, on the other hand, deliver the same volume and pressure through a 2-in. or 3-in. connection. So, which one is right? It’s obvious which is cheaper, but port size isn’t a good guide to pipe size.
Do I Want to Be a Piping Designer?
Piping designers draft drawings for the construction of piping systems. They utilize computerized drafting systems, such as computer-aided drafting (CAD). A great deal of their work takes place seated at a computer, although visits to job sites might be required.
Students can acquire the skills needed to work as a piping designer through an associate's degree program. Industry certifications are available at various levels based on education, experience and exams. The following steps detail how to become a piping designer.
Step 1: Obtain a High School Education
A piping system transports various gases and liquids from one place to another. Piping systems are used in buildings to move air throughout the premises and in petroleum distillation, chemical processes and paper pulping among other industrial areas. A piping designer creates the drawings for the operation, construction and layout of the system of pipes.
For those wishing to become a piping designer, it is necessary to learn computer-aided drafting (CAD) at a 2-year postsecondary school. To prepare for entry into one of these schools, high school courses in mathematics, science, computer technology, design, computer graphics and, if possible, drafting should be taken. In addition, he or she should know algebra. The student should ideally have a laptop computer (and be visually capable of reading the screen) as well as knowing how to use digitizing equipment.
Step 2: Obtain an Associate's Degree
Most employers prefer applicants who have had training at a 2-year school. Many public community colleges offer a program in CAD. A typical program consists of courses in drafting procedures, materials, manufacturing processes, science and mathematics. The student acquires theoretical and practical training in drafting principles, drafting skills, CAD drafting, manufacturing processes and machine and tool design. The program teaches students to produce detail and assembly drawings, piping process layouts and instrumental and piping diagrams, along with how to use control systems (hydraulic and pneumatic). Alternatively, a student may enter an apprenticeship in order to learn the trade.
Step 3: Acquire Experience
Job opportunities for piping designers are best for those with at least two years of postsecondary training, according to the Bureau of Labor Statistics (BLS); however, growth may be slower than average due to outsourcing overseas (www.bls.gov). Expertise with CAD may open doors to employment, and piping designers should look for temporary jobs or jobs hired on a contractual basis.
Step 4: Acquire Certification
Professional Piping Designer certification (PPD) is available for piping designers who have the required experience and pass certain exams. Certification is a five level process. Level I stresses piping layout. Level III stresses equipment placement, spacing and orientation. Levels I and III require passing an exam. Levels II, III and IV demand four, eight and twelve years of experience, respectively. Level II exam consists of 45 questions and Level III, 1,000 questions. Level IV requires management experience.
Unlike orthographics, piping isometrics allow the pipe to be drawn in a manner by which the length, width and depth are shown in a single view. Isometrics are usually drawn from information found on a plan and elevation views. The symbols that represent fittings, Valves and flanges are modified to adapt to the isometric grid. Usually, piping isometrics are drawn on preprinted paper, with lines of equilateral triangles form of 60°.
The Iso, as isometric are commonly referred, is oriented on the grid relative to the north arrow found on plan drawings. Because iso's are not drawn to scale, dimensions are required to specify exact lengths of piping runs.
Pipe lengths are determined through calculations using coordinates and elevations. Vertical lengths of pipe are calculated using elevations, while horizontal lengths are caculated using north-south and east-west coordinates.
Piping isometrics are generally produced from orthographic drawings and are important pieces of information to engineers. In very complex or large piping systems, piping isometrics are essential to the design and manufacturing phases of a project.
Piping isometrics are often used by designers prior to a stress analysis and are also used by draftsmen to produce shop fabrication spool drawings. Isometrics are the most important drawings for installation contractors during the field portion of the project.
Why plastic piping? by David A. Chasis
wo major criteria for purchasing a car
or for that matter any non-commodity
product are performance and cost. These
should be the exact same parameters
when choosing piping systems — performance
and cost. Yet in the piping
mythology, adhered to by some unscientific
and myopic agenda activists, these
two major factors are laid aside or treated
as insignificant. Maybe the reason for the
activist’s illogical conclusions is due to
the Western World’s need to bash or find
fault with any hugely successful, company,
product or celebrity. Certainly this
could be a major reason for all the negativity
in recognizing the unbelievable
revolutionary success of thermoplastic piping
during the last 40 years.
Throughout the world, polyvinyl chloride
(PVC), polyethylene (PE), polypropylene
(PP), chlorinated polyvinyl chloride
(CPVC), cross-linked polyethylene (PEX),
acrylonitrile-butadiene-styrene (ABS) and
polyvinylidene fluoride (PVDF) piping systems
have made tremendous inroads in
such applications as residential and commercial
drain/waste/vent, hot and cold
water distribution, chemical processing,
acid waste draining, irrigation systems,
fire sprinkler systems, swimming pools,
T well casing, natural gas distribution and
several others. So why in just four decades
have plastics overtaken metal, asbestoscement
and clay pipe in many applications?
Right, you guessed it — performance
Let me explain. (cont.)
Selection criteria for lines subject to comprehensive stress analysis
As a general guidance, a line shall be subject to comprehensive stress analysis if it falls into any of the following categories:
• All lines at design temperature above 180C.
• 4" NPS and larger at design temperature above 130°C.
• 16" NPS and larger at design temperature above 105°C.
• All lines which have a design temperature below -30°C provided that the difference between the maximum and minimum design temperature is above:
-190°C for all piping
-140°C for piping 4" NPS and larger
-115°C for piping 16" NPS and larger
• Note: These temperatures above are based on a design temperature 30°C above maximum
operating temperature. Where this is not the case, 30°C must be subtracted from values above.
• Lines 3" NPS and larger with wall thickness in excess of 10% of outside diameter. Thin walled
piping of 20" NPS and larger with wall thickness less than 1% of the outside diameter.
• All lines 3" NPS and larger connected to sensitive equipment such as rotating equipment.
However, lubrication oil lines, cooling medium lines etc. for such equipment shall not be
selected due to this item.
• All piping subject to vibration due to internal forces such as flow pulsation and/or slugging or external mechanical forces.
• All relief lines connected to pressure relief valves and rupture discs.
• All blowdown lines 2" NPS and larger excluding drains.
• All piping along the derrick and the flare tower.
• All lines above 3" NPS likely to be affected by movement of connecting equipment or by
• GRE piping 3" NPS and larger.
• All lines 3" NPS and larger subject to steam out.
• Long vertical lines (typical 20 meter and higher).
• Other lines as requested by the stress engineer.
• All production and injection manifolds with connecting piping.
• Lines subject to external movements, such as abnormal platform deflections, bridge movements, platform settlements etc.