Problem:

What are some typical modeling approaches for different types of piping?

Answer:

1. Coated PIPE (ex. concrete encased steel pipe):
   
   There is no accurate way to simulate this analysis. In order to correctly account for the pipe & concrete stiffness, you would need outside program values for total pipe stiffness (pipe & coating), 
   
   OR, suggest to calculate an equivalent steel thickness by calculating the equivalent moment of inertia.
   
   Es*Ie = Es*Is + Ec*Ic
   
   Where Es, Ec stand for modulus of elasticity of steel and concrete respectively.
   
   Ie, Is and Ic are the equivalent moment of inertia, steel pipe inertia and concrete pipe coating inertia. The inertia can be approximated by
   
   Pi * R^3 * t
   
   R is the mean radius of the pipe or coating.
   
   Assume equivalent radius is same as steel radius and solve for equivalent thickness. You can recompute equivalent radius and solve again for new thickness.
   
   Please note you may use 1/2 or so (cannot recall exact number as neutral axis will move) of the concrete inertia as it will crack in tension. AutoPipe will give you stress in the equivalent steel pipe. You may need to evaluate the stress at most stress point by splitting the moment between pipe
   and coating proportional to their E*I.
   
   For example Ms = M * EsIs/EsIe and Mc = M* EcIc/EsIe
   
   And calculate stress for pipe and concrete using their actual diameter,thickness and material.
   
   So in conclusion, of modeling a concrete encased steel pipe, based on the information above:
   
   1. Insert a pipe property
   
   2. Combined Concrete / Steel Stiffness:
         a. Set Pipe material = Ns (nonstandard)
         b. Calculate / insert the pipe properties for the combined Concrete / Steel Pipe
   
   3. Account for weight and correct size:
         a. Set insulation thickness = XXX inches
         b. Set Insulation material = Other
         c. Set Insulation density = XXX lbs/cuft ( for concrete only).
         d. Set Density = XXX lbs/cuft ( for steel only)
   
   Note: setting the correct insulation thickness, insulation density, and pipe density will accurately account for the weight and outside dia of the combined pipe/ concrete for the wind / wave / current loading.
   
   4. Because the material is set to NS, update the data on the Press / Temp/ PipeID tab.
   
         a. Calculate and insert the expansion coeff, hot mod, and hot allowable based on the combined
              concrete / steel pipe.
   
   Notes: Take care not to double up on insulation/lining density and pipe density
   
   

2. Corroded PIpe or Spot corrosion?:
   
   Question: Does AutoPIPE offer a function or upgrade that will analyze corroded pipe with the following user informaiton:
   
   a. Corrosion network sizes
   b. Longitudinal and rotational positions
   c. Minimum wall thickness at pit depths
   
   Answer:
   The following enhancment has been logged: CAE-CR-10121, Add ASME B31G: Remaining Strength of Corroded pipeline.
   
   
3. Corrugated Straight pipe
   
   There are 3 options to choose from:

   A. Apply a special pipe id to the legth of corrugated piping changeing that pipe id's Pipe material to NS (NonStandard), update pipe properties using equivalent stiffness values in Long Modulus, Hoop Modulus, and shear Modulus; adjusting other pipe properties as needed.

   B. Place back to back Flexible joints over the length of straight pipe using the correct stiffness values.

   C. Insert back to back bends over the length of straight pipe, for example 10/1000 angle at each bend, but ending with straight end connections. In the model input grid change the bend's Flexibility Factor from Automatic to the correct value.
           Note: there has been no official testing done using option C, but appears to work in theory
   

4.  Jacketed Piping
   
   Please see the following AutoPIPE help section:
   Help > Contents> Contents Tab> Modeling Approaches> Modeling Approaches> Pipes> Jacketed Pipe
   
   First create the carrier pipe with locations of all spider supports along the inside of the jacket piping. Then easily create the Jacket by using the graphical Select and Copy / Paste functions. Select the range of carrier pipe including valves, flanges, reducers etc and pasting then connecting back onto itself with a small offset (remember - no 2 node points should be in the exact same point, small offset). This modeling technique is covered in advanced training.
   
   Notes:
   
   a. Carrier pipe and jacket modeled as two separate segments with different pipe identifiers e.g. Jacket6 and carrier8
   
   b. Segments may be made of different materials and have different operating conditions
   
   c. Carrier pipe is supported by the jacket at regular intervals using spacers (spider support) and at flanged ends.
   
   d. Spacers are modeled as two point supports e.g. guide between acarrier segment point and a jacket segment point.
   
   e. If both carrier and jacket are liquid filled wiht the same liquid then adjust jacket SG accordingly, while settng the carrier piping SG = 0.000 over the length of jacket piping. The model would bo double counting weight of contents if both pipes SG were entered.
   
   f. Remember to only apply hydrodynamic (e.g. submerged piping), wind, and insulation only to jacket.
   
   g. Ideally suited for graphical copy/paste operations
   
   h. New segment cannot be inserted at the start of a 2 point componentlike a valve. New segment at end of the valve is ok therefore need to insert small run point before the valve to connect the jacket segment.
   
   i. Be sure to check any interference between inner and outter jacket. AutoPIPE does not perform clash detection. Recommend export model to Bentley Navigator.
   
   j. Consider taking an offical AutoPIPE training class, this is covered in the class with extra documentation.
   
   i. For underground jacketed pipe, apply soil properties to the Jacket (outside) pipe only, the carrier pipe insde of the jacket is supported by spacers, not soil. Agian, confirm soil properties are only applied to the outside pipe for the length of jacketed piping underground.  
   
   k. Recommend setting pipe graphics to be transparent, View> Transparency> toggle the check box ON for Pipe, and press OK button. View model is solid model view, similar to screen shot above.
   
   L. Model multiple carrier pipes using the same technique as shown above, connecting all carrier pipe supports to the same node point on the jacketd pipe.  
   
    
   
   
   
   
5. Large Bore Piping:
   
   Question: Are there any problems analyzing big diameter pipe systems? It was indicated that some issues with regards to Caesar's analysis of big diameter pipe analysis?
   
   Answer: This is a long standing issue with the Piping codes and this question comes up often. Basically the piping codes only supports SIF calculations for D/t < 100, hence large diameter pipes fall outside this limit.  Caesar prints a warning when this occurs and AutoPIPE will be doing the same in v9.1. We recommend for users to perform a local stress analysis at these connections and/or determine a SIF from e.g. FEA and add back into the program
   
   Question:
   
   Can AutoPipe handle 12 to 30 foot diameter welded steel pipes with internal veins? Mostly for steam flow…

   Answer: Yes, AutoPIPE can be trusted to model large diameter piping systems as long as it does not exceed the code requirements. However, when D/T > 100, AutoPIPE can be used to provide the correct forces, moments, and displacements in the piping system by applying these user-defined SIF and flexibility factors. Care should be taken with such systems as they are susceptible to ovaling and denting and that should be considered while lifting or supporting the pipes.
   
   Modeling, an equivalent pipe section with same section modulus for this large pipe with stiffeners could be calculated. Then adjust the density of pipe to get the equivalent weight of stiffened pipe when selecting a non-standard material (NS).
   

6. Rigid Pipe Element with "ZERO" Mass (Pipe & Water S.G.=0)
   
   Select a range of pipe, press Insert> Rigid options over Range> uncheck "Include Weight" and user choice to consider "Include Thermal Expansion".
   

See Also

Bentley AutoPIPE

External Links

Bentley Technical Support KnowledgeBase

Bentley LEARN Server

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