All Important Things You Need to Know About Piping Design Engineering

30_Mechanical_piping__April_2019_Credit_Raimund_Koch
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All Important Things You Need to Know About Piping Design Engineering

Piping Design Engineer is a specialized discipline of Mechanical Engineering which covers the design of piping and layout of equipments and process units in chemical, petrochemical or hydrocarbon facilities. Piping Engineers are responsible for the layout of overall plant facilities, the location of equipments and process units in the plot and the design of the connected piping as per the applicable codes and standards to ensure safe operation of the facilities for the design life. Piping can be defined as an assembly of piping components used to convey or distribute process fluid from one item of equipment to another in a process plant. The piping components that form a part of this assembly are pipes, fittings, flanges, valves, piping specials, bolts and gaskets. This definition also includes pipe-supporting elements such as pipe shoes but does not include support structures such as pipe racks, pipe sleepers and foundations.

 

Piping Design Engineer GOAL

 

Piping Engineering is a discipline that is rarely taught in a university setting, but is extremely important for the safety of plant personnel, safety of the public, and reliability of a facility.

The Goal of Piping Engineering is:


ASSURE A PIPING SYSTEM IS

  • SPECIFIED AND DESIGNED
  • FABRICATED AND ERECTED
  • INSPECTED AND TESTED
  • OPERATED AND MAINTAINED

TO PERFORM RELIABLY AND SAFELY IN ALL EXPECTED CONDITIONS, FOR ITS DESIGN LIFE.

piping

When plant evaluations and repairs of existing pipe, are being performed, often plant operations and maintenance personnel ask, “Is it going to be safe to work around here?” An answer they always appreciate from the piping engineer; “I’ll be out here checking on the pipe when the plant starts up.” The plant personnel just want to be assured that we are doing everything in our power to make the piping system safe to operate. This experience leads to a more personal definition of Piping Engineering:

“WHAT IS REQUIRED FOR ME TO BE SAFE STANDING NEXT TO THIS PIPE WHILE IT IS OPERATING?”

To the uninitiated, this personal definition may seem a little alarmist, but it is based on reality. Pipes do fail, and sometimes with catastrophic results. Operations and maintenance personnel at plants understand the potential risks. While some major failures of high pressure lines have killed personnel, sometimes even relatively low pressure releases can cause injury and extended plant shutdowns. A release of toxic, flammable fluids or hazardous chemicals is a tremendous risk to personnel and neighbors and a large financial risk to operators.

Engineers sometimes get caught up in the numbers and minute detail of the designs. While details are important, it is also important to personalize the work and think about the full picture of the installation, and the long – term equipment’s use. While you may not be standing next to that pipe or equipment, someone will be – and their safety should always be in your mind when considering if all appropriate considerations have been made, and the calculations are accurate.


WHY IS PIPING ENGINEERING SO DIFFICULT?


On the surface, pipe is pretty simple – a round bar with a hole in it to transport a fluid or gas. However, there is no other equipment within a typical plant that is subjected to so many different loading conditions over its life.

  • Pipe is supported at point locations, and must be able to support itself without undue  sagging or bowing.
  • The weight of the pipe may change from empty to full at times, which on large diameter pipes can create dead weight double or triple the empty weight.
  • Temperatures vary from ambient to operating, sometimes greater than 1200F in process or steam systems, or less than -300F in a cryogenic application.
  • As the pipe heats and cools it moves due to thermal expansion. Pipe flexibility and pipe supports must accommodate this movement.
  • Pipe is attached to equipment, which has a limited capacity to support the pipe.
  • As the pipe ages, it tries to find its lowest stress level, and thus it “relaxes” – almost always into a different position than the theoretical analysis calculates.
  • Flexible pipe is sometimes analogous to supporting spaghetti, as it bends and twists from all of its various loading conditions. Changing a support in one location sometimes has a major effect on pipe movement 80 feet away.
  • Depending on the operating conditions, the pipe material may degrade over time due to creep, embrittlement or some other metallurgical phenomena.
  • Pipe stress analysis is not very exact. There is a great deal of judgment that is required in evaluating the results.
  • Standard pipe specifications allow +, – 12.5% variation in wall thickness. While most pipe thickness is within 1% to 2% of nominal; at any welded joints, the actual wall thickness may be 12.5% different than  expected.
  • There are a high number of different components in each piping system: elbows, straight pipe, reducers, valves, flow meters, thermowells, pressure taps, branch connections, flanges, gaskets, bolts, etc. In a typical plant, when the sizes and schedules of all these components are counted, there may be much more than 10,000 different components. This represents a large quantity of data to understand, and to properly identify and track through the design, installation and operation of plants.
  • Even with great engineering and design, the installation is subject to irregularities in the fabrication and erection of the pipe. Pipe fitters will rotate weld joints and pull pipe to “make the pipe fit”. While some of this can be controlled with very strict Quality Assurance, the reality is that it will occur. Engineering must try to control and then assure enough conservatism in the design that fabrication tolerances do not create significant problems.
  • Pipe has its limitations in age and usage. Pipe may corrode, erode, metallurgical characteristics may age; all of which will change its strength and flexibility characteristics.
  • Pipe supports springs can wear out, or fail due to overload, corrosion or other external factors.
  • Modifications have often been made to existing piping systems without sufficient consideration, and the result has been damaged pipe and an unreliable plant.
 

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