autopipe manual

AutoPIPE Modeling Approaches

Modeling Approaches This help has been provided in order to give users ideas for modeling typical piping arrangements. The steps shown in

each example should not be taken as the only method available to create models. In addition, the intent of the

examples is to present ways to create adequate models of specific piping components for analytical purposes. It is not

the intent of the examples to represent proper design of the overall piping system. If you have a specific modeling

problem which you feel is not fully explained in this section, you are urged to contact Bentley Technical Support for

further discussion.

Example Systems This help has been provided in order to aid users in modeling more complex piping arrangements. The steps shown in

each Example System should not be taken as the only method available to create models. In addition, the intent of the

examples is to present ways to create adequate models for analytical purposes.

Choose from the following topics:

PipeSOIL Interaction: Transition Example

Water Hammer (Time History) Example

Steam Relief (Time History) Example

Harmonic Analysis Example

Anchors Pipes

Bends Reducers

Cuts Rotating Equipment

Flexible Joints Supports

Frames Tees

Hangers Valves

Nozzles Vessels

Anchors Select from the following anchor-related examples:

Rigid Anchor with Thermal Movement

Flexible Anchor

Anchor Releases for Hanger Selection

Rigid Anchor with Thermal Movement An anchor is used at locations where the piping system ties into a wall, anchor block, foundation, or a piece of large

equipment. Most large equipment such as pumps, turbines, or compressors are massive enough to be considered rigid

when compared to the pipe. In most cases, vessels can be considered to be rigid when local shell flexibility is not of

concern.

An anchor has the ability to restrain all translations and rotations of the attached pipe or beam element. Forces and

moments from one side of a rigid anchor are not transmitted to the other side. This property can be used to control the

movement of a pipe attached to sensitive equipment, or to divide a large piping system into two or more separate,

manageable systems.




Page 1 of 137AutoPIPE Modeling Approaches

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Example An anchor is used to model a pipe attached to a large pump which is assumed to be rigid. However, it is known that

when the pump reaches an operating temperature (400F), the pipe connection point will displace as follows due to the

thermal expansion of the pump itself:

Modeling The thermal movement of the pump can be included in the AutoPIPE system model by specifying displacement offsets

calculated for each of the defined thermal load cases at the anchor.

1. Build a system from A00 to A04 using an 8 inch, standard schedule pipe. Define an operating load case (T1) of 400 F. The global coordinates for the system points are listed below (length units are feet, and offsets are

measured from the preceding point):

2. These coordinates define the position of the piping system at ambient temperature (70F).

3. Select Insert/Anchor to open the Anchor dialog:

4. Define a rigid anchor at point A04. Move the cursor down to the Thermal anchor movements input fields for

Case 1 and specify (imposed displacement) values:

Note that the offset fields for Case 2 and 3 are closed; this is because only one operating load condition (T1) was

specified on the General Model Options dialog. In general, when a static analysis is performed, the results for each

thermal load case (T1, T2 & T3) will include the forces exerted on the piping system due to the thermal anchor

movements specified for each thermal load case respectively.

Other Anchor-related Topics

DX = 0.0 in DY = +1.25 in DZ = +0.45 in

(no rotation of the attachment point)

Anchor Releases For Hanger Selection The intent of a hanger is to insure that adjacent equipment does not support the weight of the attached pipe, or any

other vertical loads resulting from the piping system operating conditions. This is due to the fact that equipment

manufacturers allowable flange, or nozzle, loads are often minimal. If an undesigned hanger is located near a piece of

equipment (modeled as a rigid anchor), the cold load and spring rate determined by the hanger selection procedure

(Analyze/Hanger) will be very small when it is intended for the hanger to support the vertical loads. In this case, it is

necessary to release restraints at the anchor in order to design the hanger while maintaining the rigidity of the anchor

for all other purposes.

Example




Modeling The anchor at the end of the pipe run, which represents the equipment, is released for vertical shear loads. This means

that when a hanger design run is performed, the anchor will not support a vertical load. Thus, the hanger is sized

correctly (the vertical forces at the pipe-pump connection point are eliminated) while the pump itself is modeled rigidly.

1. Define the pipe system by repeating Step 1 from Flexible Anchor - Model 1.

2. Move the crosshairs to point A03.

3. Select Insert/Support to open the Support dialog, then enable the "Undesigned" option at point A03.


5. Select Insert/Anchor to open the Anchor dialog.

6. In the Release for hanger selection field, click inside the Y field to enable the vertical displacement hanger selection release option.

Note: The "Release for hanger selection" fields should not be confused with "Trans. stiff" and "Rot stiff." The latter

define DOF releases or stiffnesses which are in effect at all times, while the former release a DOF for the purpose of

designing hanger springs only.


Flexible Anchor An anchor is used at locations where the piping system ties into a wall, anchor block, foundation, or a piece of large

equipment. A flexible anchor can be defined when the flexibility of the anchored point is known (such as for modeling

equipment), or when a particular type of support is desired (e.g. roller, hinge, socket, etc.).

Most large equipment such as pumps, turbines, or compressors are massive enough to be considered rigid when

compared to the pipe. However, if the local flexibility of the equipment is known, those values may be specified. For the

special case of vessels, it is recommended that the local (shell) flexibility be modeled using the Nozzle command.

Model 1: Local Flexibility of the Attached Equipment

Model 2: Definition of a Hinge Support






Model 1: Local Flexibility of the Attached Equipment If the local flexibility of the equipment attached to a pipe is known, the stiffness values can be defined.

1. Build a system from A00 to A04 using an 8 inch standard schedule pipe. The global coordinates for the system points are listed below (length units are in feet, and offsets are measured from the preceding point):


3. Define a flexible anchor at point A04; this allows the cursor to enter the stiffness fields. Specify translational and rotational stiffnesses as follows:

The stiffness values entered correspond to a global Z translation flexibility (axial with reference to the pipe), and a

bending flexibility in the plane perpendicular to the pipe (global X-Y).


Model 2: Definition of a Hinge Support A flexible anchor is used to model a hinge support at the base of a beam member (column). Modeling specific support

types is allowed for both beams and pipes, however, this approach is probably more useful for beams. In addition, gaps

and friction cannot be specified for anchors modeled as supports. For the model that follows, it is assumed that a

framing system (which supports piping) has already been defined.

1. Move the crosshairs to the beam point that is to be anchored. For this example, the base of the column (FP1).


3. Define a flexible anchor at point FP1; this allows the cursor to enter the "Trans. stiff." and "Rot. stiff." fields. Accept the default stiffnesses (Rigid) in all fields except "Rot. stiff Z"; where 0.00 should be entered as shown:

Entering 0 stiffness for the rotational restraint about the Z axis allows the column base to rotate freely in the X-Y plane,

thus creating a hinge support.

Note: All degree of freedom (DOF) fields are for the global coordinate system.

The user is reminded to consider the overall effect on the system stability when defining a zero stiffness (a DOF

release) in any of the "Trans. stiff." or "Rot. stiff" fields.






Bends Choose from the following modeling examples:

45 Elbow

180 Elbow

Flanged Elbow

Elbow Wall thickness

Reducing Elbow

Base Supported Elbow

Miter Bends

45 Elbow A 45 elbow is a common piping component. They are used whenever a full 90 elbow is not appropriate or required.

Example

Modeling A 45 elbow is modeled as half of a 90 elbow. This is done by specifying the point following the bend (TIP) in such a

manner that the coordinates define a 45 angle.

1. Build a system from A00 to A01. The global coordinates for the system points are listed below (length units are feet, and offsets are measured from the preceding point):

2. Select Insert/Run to open the Run Point dialog.

3. Specify the coordinates for A02 as shown. These values define a 45 angle with respect to the direction of the pipe established between A00 and A01, such that the distance between A01 and A02 is 6 ft.





Display of the 45 Bend

180 Elbow A 180 elbow, or U-bend, is a common component in an expansion loop. Expansion loops are used to relieve thermal

stresses in the piping system.

Example

Modeling A 180 elbow is modeled as two 90 elbows back-to-back.

1. Build a system from A00 to A01 using a 12 inch standard schedule pipe. The global coordinates for the system points are listed below (length units are feet, and offsets are measured from the preceding point):

2. Select Insert/Bend to open the Bend Point dialog.

3. Since a bend defaults to a long radius (= 1.5 Dnom), locate A02 three feet away from A01 as shown in the offset fields. This will result in two back-to-back bends, such that A01 F coincides with A02 N.

4. Complete the bend by defining a run of pipe to A03. The global coordinates for the system point are listed below (length units are feet, and offsets are measured from the preceding point):




Display of the 180 Bend

Flanged Elbow Elbow fittings are often connected to the adjacent pipe sections with flanges. A flange may exist on one or both sides of

the bend. Flanges are important in a system model since their weight may have a significant effect on the pipe stresses.

Also, the stress intensification and flexibility factors for a given bend will decrease if one or both of its ends are flanged.

Example

Modeling First a plain elbow bend is defined, then pipe flanges are placed at the near and far tangent points.

1. Build a system from A00 to A02 using a 12 inch, standard schedule pipe. The global coordinates for the system points are listed below (length units are feet, and offsets are measured from the preceding point):




2. Move the crosshairs to point A01 N.

3. Select Insert/Flange to open the Flange dialog. Specify a SLIP-ON flange with a pressure rating of 150. The flange weight is recalled from the component library since a standard pipe flange was used. Next, select

SO (slip on) as the type of connection.

4. Repeat Step 3. A second flange should also be defined at A01 N. This provides a mating surface for the first flange, allowing the pipe and the elbow to be bolted together.

5. Move the crosshairs to point A01 F.

6. Repeat Steps 3 so that two flanges are defined at the other end of the elbow.

7. Press F3 to open the text window shown below, which displays the data related to point A01 F. The listing includes the flange data for this point. A similar display also exists for A01 N.

Display of the Flanged Elbow

Note: AutoPIPE assumes a zero thickness for the flange component. Thus, the thickness of the real flange may

require an additional point so that the inner face of the flange is at the tangent point of the bend curve.

Reducing Elbow Reducing elbows provide a means for changing the pipe size when such a change is required at a bend.

Example




Modeling AutoPIPE does not have a reducing elbow component. Therefore, the elbow is simply modeled as a section of pipe with

a diameter that is equal to the mean of the pipe diameters at each end. Such a representation is reasonably accurate

for calculation of pipe stresses as long as the reduction is not too drastic.

In this model a 12 inch pipe is connected to an 8 inch pipe by a reducing elbow. The bend is modeled with a pipe

section that is an average of the connecting pipes. Next, stress intensification factors (SIF's) are defined at each end in

order to represent the SIF's for an actual reducing elbow. Since the piping codes do not specify SIF's for reducing

elbows, this information must be provided by the user. Contact the elbow manufacturer for information on their

recommendation for SIF values.

1. Build a system from A00 to A01 using a 12 inch, standard schedule pipe named 12STD. The global coordinates for the system points are listed below (length units are feet, and offsets are measured from the

preceding point):

2. Select Insert/Bend to open the Bend Point dialog. The bend radius must be specified in inches, since a standard bend is calculated by a single pipe size. Specify the new pipe data identifier ELBOW. After accepting

this dialog, the Pipe dialog (shown in Step 3) will automatically be displayed since "ELBOW" has not yet been

defined.

3. Define the new pipe. Enter the pipe data as shown in the figure (nonstandard nominal size: NS) based on the following averages:

Do = (12.75" + 8.625") 2 = 10.69 in

t = (0.375" + 0.322") 2 = 0.349 in

4. After providing the data for the new pipe and pressing OK, the Location dialog requests the specific location on the bend where the pipe change is to take effect. Select Near for the near tangent.

5. Select Insert/Pipe Properties to open the Pipe Properties dialog. Enter 8STD as the pipe identifier and define a nominal 8 inch standard schedule pipe.

6. Again, after providing the data for the new pipe and pressing OK, a Location dialog requests the location on the bend where the pipe change is to take effect. Enter Far for the far tangent.

7. Finish the bend by defining a run of pipe to A03. The global coordinates for the system point are listed below (length units are feet, and offsets are measured from the preceding point):


9. Select Insert/Xtra Data/User SIF and Flexibility to open the User Flexibility dialog. Enter the SIF to



be used at the large end of the elbow. As stated previously, contact the manufacturer for information on the

SIF's recommended for the particular reducing elbow.


11. Repeat Step 9 for the small end of the elbow.

Elbow Wall Thickness The wall thickness of a bend can be different than the thickness of the connecting pipes. This allows specific elbow

fittings to be modeled in a continuous piping system.

Example

Two methods for modeling elbow wall thickness are provided below:

Elbow Wall Thickness (Method 1)

Elbow Wall Thickness (Method 2)

Elbow Wall Thickness: Model 1 An elbow fitting is modeled by controlling the bend radius, and the pipe wall thickness. In order to define an elbow with

a different wall thickness than the joining pipes, the pipe size can be changed for the bend and then reset to the original

pipe size.

1. Build a system from A00 to A01 using a 12 inch standard schedule pipe named 12STD. The coordinates of the system points listed below are global (length units are feet, and offsets are measured from the preceding

point):

2. Select Insert/Bend to open the Bend Point dialog. Input the tangent intersection point coordinates as shown and specify the new pipe data identifier ELBOW. After accepting this dialog, the Pipe dialog (shown in

Step 3) will automatically be displayed since the pipe named "ELBOW" has not yet been defined.

3. Define the new pipe. Enter a Nominal Pipe Size of 12.00" and a Schedule of 120. After providing the data for the new pipe, the Location dialog is automatically displayed as shown in Step 4.





4. The Location dialog requests the specific location on the bend where the pipe change is to take effect: at the near or far point of the elbow. To change the elbow thickness over the entire bend, select Near for the near

tangent.

5. Select Insert/Pipe Properties to display the Pipe Properties dialog. From the selection list, specify 12STD as the pipe identifier. A message is displayed indicating that "Previously defined pipe date will be

used."

6. Again, the Location dialog requests the specific location on the bend where the pipe change is to take effect.

This time select Far for the far tangent. This will place the pipe 12STD in effect for subsequent piping components.

7. Define a run of pipe to A03. The coordinates for the system point listed below are global (length units are feet, and offsets are measured from the preceding point):

Display of the Thick Elbow Model

See Also:

Elbow Wall Thickness: Model 2

Elbow Wall Thickness: Model 2 The entire system defined in Model 1 can be built using the same pipe identifier (i.e. 12STD). The bend can then be

modified using the Modify/Pipe Properties command.

1. Build a system from A00 to A03 using a 12 inch standard schedule pipe named 12STD. The global coordinates for the system points are listed below (length units are feet, and offsets are measured from the

preceding point):




2. Position the cursor over the outline of the elbow. After being properly selected, the elbow is highlighted (you can accomplish this same task by first selecting the near point of the elbow, A02 N, then pressing and holding

the [Shift] key while selecting the far point, A02 F).

3. Select Modify/Pipe Properties to open the Pipe Properties dialog.

4. Define the pipe ELBOW. See Step 3 of Model 1 .

Note: AutoPIPE will issue a warning for these models when the Global Consistency Check is performed. The

messages are provided to alert the user to the sudden change in pipe properties in the event that those changes

were unintentional (for our models this is not the case).

See Also:

Elbow Wall Thickness: Model 1

Base Supported Elbow A base elbow, or a dummy leg at a bend point, can be modeled in various ways depending on the location of the leg

along the bend and the orientation of the leg. The leg can be placed at either tangent point, or at a point anywhere

along the bend. The leg itself can be modeled as a support or a structural member welded to the bend.

It should be noted that supporting an elbow in this manner will greatly effect the flexibility and stress intensification

factors for the elbow. For simplicity, the following models do not address this aspect of a base supported elbow.

However, an SIF should be applied at the tangent points of the bend.

Example

Figure 1.2.6

Four methods for modeling base supported elbows are provided below:

Model 1: Supported at a tangent point (simple vstop support for fig 1.2.6 a)

Model 2: Supported at a point along the bend (simple vstop support for fig 1.2.6 b)

Model 3: Alternate method for defining a support at a midpoint

Model 4: Modeling a "dummy leg" as a structural member (fig 1.2.6 b & c)

Model 5: Modeling a "dummy leg" as a pipe (Recommended fig 1.2.6 b)

Model 1: Supported at a tangent point





In this model, a V-stop is to be placed at A02 F as shown in Figure 1.2.6 (A), above. The support acts along the

centerline of the vertical run and does not restrain the rotation of the elbow.

1. Build a system from A00 to A03. The global coordinates for the system points are listed below (length units are feet, and offsets are measured from the preceding point):


3. Select Insert/Support to open the Support dialog. Select V-stop from the "Support type" selection list.

Display of Model 1

Other Base Supported Elbow Models

Model 2: Supported at a point along the bend In this model, a V-stop is placed at a point along the bend at A02 as shown in Figure 1.2.6 (B). It is assumed that a

system exists with a bend defined, and that A02 is the current point (repeat Steps 1 and 2 from Model 1).

1. Select Modify/Bend or Modify/Point to open the Bend Point dialog. Modify the bend to include a midpoint (A02 M) halfway between A02 N and A02 F.

2. Move the crosshairs to point A02 M.

3. Select Insert/Support to open the Support dialog. Define a V-stop at this point.




Display of Model 2


Model 3: Alternate method for defining a support at a midpoint A midpoint may be added to an existing bend without using the Modify/Point or Modify/Bend command sequence.

This is particularly useful for defining supports at bend points that have been defined without a midpoint.

1. Build a pipe run from A00 to A03 (see Model 1 , Step 1).

2. Move the crosshairs to A02 (the TIP).

3. Select Insert/Support . Since A02 is not a physical point on the piping run, a support cannot be placed there. Thus, the Location dialog is displayed requesting the specific location on the bend where the support

should be placed. Select Mid from the "Location around the bend" selection list.

4. Since the midpoint was not specified when the bend point was created, the location of this point along the bend is requested in the "Enter percentage along the bend" field. Accept the default (50) and press OK. Once

the percentage along the bend is accepted, the Support dialog is automatically displayed. Define a V-stop

support.


Model 4: Modeling a "dummy leg" as a structural member In this model, a beam member is used to model the dummy leg as shown in Figure 1.2.6 (C). The leg can be placed

either at a tangent point or at a point along the bend. In order to represent a fully welded moment connection, by

taking into account the rotation of the bend, the dummy leg will be placed at the midpoint. It is assumed that a system

exists with a bend midpoint defined, and that A02 M is the current point (see Model 2 , Steps 1 and 2).





1. Select Insert/Beam to open the Beam dialog:

2. Define the dummy leg as a beam member from A02 M to a new point named BASE. Specify 2 (two) feet for the length of the leg from Point I by entering -2.0 in the "DY" field. Enter W as the "Table Name," W8X24 as the

cross "Section ID," and A36 as the "Material ID." Note that the Beta angle is 90.

Note: A pipe or any other structural shape can be used to model the leg.

3. Make "BASE" the current point.


5. Define an anchor at the base of the dummy leg. An anchor can also be defined at "BASE" without moving to it. While in the Anchor dialog, enter BASE in the "Point Name" field. This now becomes the new current point

and the anchor will be placed at this point.

Display of Model 4


Model 5: Modeling a "dummy leg" as a pipe In this recommended model, a short rigid beam member is used to connect a pipe segment to the bend, to model the

dummy leg as shown in Figure 1.2.6 (B). This model can be used to capture the radial thermal expansion of the bend

and any thermal growth of the trunnion. It is assumed that a system exists with a bend midpoint defined, and that A02

M is the current point (see Model 2 , Steps 1 and 2).

1. Select Insert/Beam to open the Beam dialog:

2. Define the dummy leg as a beam member from A02 M to a new point named B00. Specify a small length of

the leg from Point I by entering DX = 0.01, DY = -0.01' field. Select "Table Name" - Rigid.

3. Make B00 the current point.

4. Select Insert/Segment to start a new pipe segment from B00 and enter pipe identifier name = Pipe1 (same properties as the trunnion e.g. 6" standard schedule pipe.

5. Note the coordinates of B00 (using view/point properties, F3) then click on the bend tip point A02 and also note its coordinates. Subtract the two sets of coordinates to give the offsets from B00 to A02 i.e. DX =

0.2829', DY = -0.2829' using pipe identifier = Pipe1.




6. Make B00 (segment B) the current point, Insert/Run (B00 to B01) and enter offsets from step 5.

7. Insert/Run ( B01 to B02) and enter offsets to the base of the trunnion e.g DY = -2'.

8. Make B02 the current point, and select Insert/Support to open the support dialog and select V-stop (using default above gap = 100 and below gap = 0).

9. Click on the pipe between B00 and B01 to select this pipe (highlighted Red) then select Insert/Rigid Options Over Range with Include Weight = No, Include Thermal Expansion = Yes (shown as purple). [This takes account of the radial expansion of the outer wall surface of the bend assuming temperature is applied from B00 to B01].

Note:

1. If there is temperature e.g. if insulated or connected to a high temperature line, on the dummy leg B01 to

B02 then apply temperature over this range typically less than the main pressure pipe due to the heat

conduction along the non-insulated dummy leg.

2. Remember to remove any pressure from segment B since it is a non-pressure component.

3. The coordinates of Bend tip point A02 and B01 should be the same.

Display of Model 5

A close up of this trunnion connection to the bend midpoint can be seen below with pipe = transparent under

View/Transparency.




Miter Bends Miter bends are typically used where space limitations do not allow the use of elbows, or when using a miter bend is

more economical than an elbow. Miter bends are most often found in pressure vessels, steel water piping, and drain

lines.

Miter bends are classified as either closely or widely spaced. Evenly spaced miter bends, whether close or wide, are

defined by the following parameters:




The miter is considered to be closely spaced if S < Sb. Conversely, the miter is widely spaced if S Sb. Where:

Sb = Ra (1 + tan )

The effective miter radius (Re) is:

if closely spaced Re = Rb

if widely spaced Re = 0.5 Ra (1 + cot )

Close miter bends may have from 1 to 9 cuts. A 90 bend modeled with one cut has a miter angle of 45, a two cut

miter angle is 22.5, a three cut miter angle is 15, and a four cut miter angle (shown in the figure above) is 11.25.

AutoPIPE allows a closely spaced miter bend to be input on one &rsquoBend Point dialog regardless of the number of

cuts (the miter cuts are calculated automatically). However, if the miter is widely spaced, a series of one cut (single

miter) bend points must be input by the user.

Note: The user is responsible for predetermining whether the miter bend is closely or widely spaced. The current

version of AutoPIPE does not trap an incorrectly specified miter bend.

Two methods for modeling miter bends are provided below:

Model 1: 3 Cuts - Closely Spaced

Model 2: 3 Cuts - Widely Spaced





Since S < Sb, the miter is closely spaced. Therefore, the miter bend can be defined as a single bend point and AutoPIPE

will automatically calculate each miter point (these are transparent to the user).

1. Build a system from A00 to A01 using a 12 inch standard schedule pipe named 12STD. The global coordinates for the system points are listed below (length units are feet, and offsets are measured from the

preceding point):

2. Select Insert/Bend to open the Bend Point dialog. Define Bend point A02 with a Short radius, Close (miter) bend with 3 cuts. Then, input the tangent intersection point coordinates as shown.

3. Define a run of pipe to A03. The global coordinates for the system point are listed below (length units are feet, and offsets are measured from the preceding point):

AutoPIPE displays the miter bend information in the Point Data Listing sub-report (see SYSNAME.RPT; select the Edit/List

command).

Click here to view the miter data for Model 1.

See Also:


Nom. pipe size 12 in, Std. Sch.

Do 12.75 in

t 0.375 in

Bend type = Short radius, 3 cut miter

90.0

N 3

90.0 (2 3) = 15.0

Rb 1.0 12" = 12.0 in

Ra (12.75" - 0.375") 2 = 6.19 in

Sb 6.19" (1.0 + 0.2679) = 7.85 in

S 2.0 12.0" 0.2679 = 6.43 in < Sb





Let's define the same bend as in Model 1, except this time using a long radius (this will result in a wide miter bend).

The changed parameters are:

Bend type: long radius

Rb: 1.5 12" = 18.0 in

S: 2.0 18.0" 0.2679 = 9.65 in > Sb

Since S > Sb, the miter is widely spaced. Therefore, the miter bend must be defined as a series of single bend points.

1. Determine the effective miter radius Re. This value will be entered in the "Bend radius" field when defining each miter tangent intersection point (TIP).

Re = 0.5 6.19" (1 + cot 15) = 14.64 in

2. Determine the coordinates for each of the miter cuts. Since each cut must be defined as an individual bend, the coordinates will locate the tangent intersection points TP1, TP2 and TP3.

In order to establish the coordinates for each miter cut TIP it is necessary to define a reference axis from which

the point offsets can be related. This reference axis shall be along the centerline of the pipe coming into the

bend to the overall TIP (refer to the Figure above).

a. The first miter cut (TP1) is always located on the reference axis at a distance of "0.5 S" from the near tangent point (of the overall bend). Thus, TP1 is located by offsets are measured from point A01 (see

Model 1 for coordinates):

b. The coordinates for all subsequent miter cuts (regardless of the total number of cuts in the miter bend) are given by the following two equations (where, i = miter cut number):

Thus, the coordinates for the second miter cut TP2 (i = 2) measured from the first miter cut

TP1 are:



The coordinates for the third miter cut TP3 (i = 3) measured from the second miter cut TP2

are:

Note: If the bend angle () does not equal 90 or the reference axis does not coincide with a global axis, a transformation of coordinate systems must be performed in order to calculate the correct offset values.

The user should be very careful when calculating coordinate offsets.

c. Calculate the offset from the last miter cut TP3 to the next (run) point RUNP on the piping system (the coordinates of RUNP are the same as A03 in Model 1 ).

4. Define the pipe and system points up to, and including point A01 by repeating Step 1 from Model 1.

5. Select Insert/Bend to open the Bend Point dialog. Define a bend point A02 as Wide (miter) bend with a bend radius (Re) of 14.64 inches. Then, input the tangent intersection point coordinates as shown. Notice that

the Cuts field is closed as wide miters are always a single cut.

6. Repeat Step 5 for each of the remaining miter cut TIPs (TP2 and TP3). Use the offset values calculated in Step 2 for each bend TIP.

7. Define a run of pipe to A05, use the offset values calculated in Step 3. The global coordinates for the points in the completed system are listed below (length units are feet, and offsets are measured from the preceding

point):

AutoPIPE displays the miter bend information in the Point Data Listing sub-report (See SYSNAME.RPT, select the

View/Point Properties [F3] command).

Click here to view the miter data for Model 2.

See Also:




Cuts: Cold Spring A cold spring is used to reduce thermal forces on vessels, pumps, and other types of equipment connected to a piping

system. The force reduction is achieved by fabricating the pipe slightly shorter than the required dimension and then

pulling it into place during erection (at the ambient temperature). This creates a state of internal pre-stress which is

opposed to the stress that results from the (high) temperatures encountered under operating conditions.

When a cut-short is specified at a point, AutoPIPE applies the cut to the section of pipe preceding the current point.

Thus, a cut cannot be defined at the first point in the pipe system. In addition, a cut cannot be specified at a bend.

Example System

Two methods for modeling cold spring cuts are provided below:

Model 1: Cut-Short (high operating temperature)

Model 2: Cut-Long (low operating temperature)





Model 1: Cut-Short (high operating temperature) In order to counter the anticipated thermal stresses, both legs are to be fabricated 0.27" shorter than the 10'-0" leg

length. First, the system is modeled with the established dimensions. Then, a cut-short is specified for each pipe leg.

The user has the option to analyze the system with or without the cold spring effect. If included in the analysis,

the cold spring is applied to the load case in which the cut short was defined.

1. Build a system from A00 to A03 using an 8 inch, standard schedule pipe. The global coordinates for the system points are listed below (length units are feet, and offsets are measured from the preceding point):


3. Select Insert/Xtra Data/Cut Short to open the Cut Short dialog: Specify a cut of 0.27 in the GR load case. A positive value defines a shortening in the horizontal leg of the system which causes a pretension

load.

4. Add a cut-short in the vertical leg by repeating Step 3 for point A03.

5. Select Analyze/Static to open the Static Load Cases dialog. To include the effects of the cold spring, enable the Cut-short analysis option.

For proper evaluation of the results, a user combination should be defined which includes both the GR and T1 load

cases. This combination represents the total effect of the cut-short pre-stress (defined in GR) and the stress relief

induced by the operating temperature (T1).

See Also:

Model 2: Cut-Long (low operating temperature)

Model 2: Cut-Long (low operating temperature) For this model, we will use the same example system, but this time the operating temperature is -150F.

In order to counter the anticipated thermal stresses, both legs are to be fabricated 0.145" longer than the 10'-0" leg

length.

1. Build the system described in Step 1 of Model 1, in this section.


3. Select Insert/Xtra Data/Cut Short to open the Cut Short dialog. Specify a cut of -0.145 inches in the GR load case. The negative value defines a lengthening in the horizontal leg of the system which causes a pre-

compression load.

4. Add a cut-long in the vertical leg by repeating Step 3 for point A03.

5. Repeat Step 5 from Model 1 in order to include the effects of the cold spring in the analysis.

As stated for Model 1, a user combination should be defined which includes both the GR and T1 load cases. This

combination represents the total effect of the cut-long pre-stress (defined in GR) and the stress relief induced by the




operating temperature (T1).

Note: The user should be aware that the ASME codes do not allow the inclusion of the cold spring effect when cyclic

loading is a factor on the system. Refer to the specific code for details regarding this matter.

The models presented have each used a 100% cold spring. The user should be aware that this was done for

simplicity, and is not a standard practice in piping design.

See Also:

Model 1: Cut-Short (high operating temperature)

Flexible Joints Choose from the following flexible joint modeling examples:

Single Bellows Expansion Joint

Tied Bellows Expansion Joint

Tied Universal Expansion Joint

Hinged Expansion Joint

Gimbal Expansion Joint

Slip Joint

Ball and Socket Joint

Pressure Balanced Expansion Joints

Single Bellows Expansion Joint A single bellows expansion joint is used to absorb the axial and lateral movement (caused by thermal expansion or

contraction) of the pipe section in which it is installed. It is not capable of absorbing pressure thrust, which must be

restrained by the piping system itself.

Example

Modeling The primary axial growth of the piping system, due to thermal expansion, is absorbed by the single bellows acting in

compression. Since the bellows cannot absorb pressure thrust the bend near the expansion joint is anchored to support

this load.

1. Build a system from A00 to A02 using an 8 inch, standard schedule pipe. The global coordinates for these

points are listed below (length units are feet, and offsets are measured from the preceding point):

2. Select Insert/Flexible Joint to open the Flexible Joint dialog.

3. Define a flexible joint to point A03. Enter a length of 1.0 foot i.e. DX = 1.00, DY = 0.00, DZ = 0.00





Define Axial stiffness = 1000 lb/in, Y-bending stiffness = 10000 ft-lb/deg, Z-bending stiffness = 10000 ft-lb/deg, All

other stiffness values = Rigid(the default), and the component weight (user supplied) = 53 lb. Also, a pressure thrust

area of 50.03sq. in should be specified. The area shown assumes that the bellows has an internal sleeve (based on Di =

7.981").

A = pi (7.981 in)2 4 = 50.03 in2

4. Define the remainder of the piping system. The global coordinates for these points are listed below (length

units are feet, and offsets are measured from the preceding point):

5.


6. Select Insert/Support to open the Support dialog. Specify an Inclined, rigid support acting in the Global X

direction. The (directional) support restrains the pressure thrust developed in the bellows due to the internal

operating pressure of the pipe.

Display of a system that uses a single bellows to control thermal expansion

It should be noted that the flexible joint has been placed in the long leg of the piping system. This orientation enables

the joint to absorb the large (relatively speaking) thermal expansion axially. In addition, it can be seen that the small

axial expansion in the leg between A04 and A05 is absorbed by the joint in bending. The designer should always try to

minimize bending loads acting on a single bellows expansion joint.

Tied Universal Expansion Joint A universal expansion joint contains two bellows joined by a common connector. It is used for the purpose of absorbing

any combination of axial movement, lateral deflection, and angular rotation. Universal joints are usually furnished with

tie rods whose function is to distribute the movement between the two bellows, and absorb pressure thrust. A common

application of a tied universal joint is its use in a Z bend. In this case, the joint assembly absorbs the axial expansion of

the long legs as lateral deflection, and the tie rods are adjusted to prevent axial expansion in the short leg due to

pressure effects.

Example




Modeling The tie rods in a universal expansion joint can be modeled using either of two methods in AutoPIPE. The simple

approach is to use a single two-point (tie/link) support, which represents the total stiffness of the tie rods, to connect

each end of the flexible joint (refer to the approach used for Model 1 of the Tied Bellows Expansion Joint

Example ). This method neglects bending effects at the joint due to the actual orientation of the rods.

The second method (modeled below) places the tie rods in their actual position, in relation to the pipe and bellows. The

end plates are modeled as rigid beams, and the tie rods are modeled as Tie/link supports with gaps set (rods only resist

tension loads). As will be shown, the gap settings specified have an important effect on the manner in which the tied

bellows is modeled.


Note: Points A04 and A06 have been skipped intentionally.


3. Select Insert/Support to open the Support dialog. Define a Rigid planar guide by specifying a large (10 inch) gap down and gap up. This allows the upper section of pipe to move only in the X-Y plane.

4. Move the crosshairs to point A08. Define another planar guide at this point (repeat Step 3). Again, specify large values in the gap down and gap up directions in order to limit movement of the lower section of pipe to

the Y-Z plane.



7. Define a flexible joint to point A04. Enter a length of 1.0 foot i.e. DX = 0.00, DY = -1.00, DZ = 0.00

Axial stiffness = 1000 lb/in, Y-bending stiffness = 10000 ft-lb/deg, Z-bending stiffness = 10000 ft-lb/deg, All other

stiffness values = Rigid (the default), and a component weight of 53 lb. Also, a pressure thrust area of 50.03 sq.in should be

specified. The area entered assumes that the bellows has an internal sleeve (based on Di = 7.981").

A = pi (7.981") 4 = 50.03 in

8. Move the crosshairs to point A05. Define a second flex joint from A05 to A06 (repeat Steps 6 and 7). Again, the point at the far end of the joint is defined by the point name (A06), and length (1 ft) specified.

9. Move the crosshairs back to point A03. We will now begin to define the tie rod assembly for the universal joint.

10. Select Insert/Beam to open the Beam dialog.



11. Define a rigid beam (M1) from A03 to the point TB1. TB1 is located 6 inches away from A03, in the +X direction.

12. Define the remainder of the rigid beams. Add three more beams connecting A03 to TB2 through TB4. Then, add four more beams connecting A06 to TB5 through TB8. The beam point offset coordinates are as shown

in the table below (DX, DY and DZ lengths are relative to the point referenced in the "From Point I" field).

13. Select Insert/Support to open the Support dialog.

14. Specify a Tie/link from TB1 to TB5 in order to simulate the effect of a 0.5" diameter rod. Enter a spring rate of 152171 which is equal to the axial stiffness (ka) of the rod (Refer to the Note for Step 4, Model 2, in Section

1.4.2 for additional details on the purpose of the gap setting values.):

E = 27,900,000 psi L = 36.0 in A = pi (0.50") 4 = 0.1963 in

ka = 27,900,000 psi 0.1963 in 36.0 in = 152,170.9 lb/in

15. Move the crosshairs to point TB2, then repeat Step 14 (place a tie/link between TB2 and TB6). Continue defining the tie rods in this manner (there should be ties between TB3 and TB7, and between TB4 and TB8).



Hinged Expansion Joint A hinged expansion joint contains one bellows and is designed to permit angular rotation in one plane only by the use of

a pair of pins through hinge plates attached to the expansion joint ends. The hinges and hinge pins must be designed to

restrain pressure thrust and any extraneous forces, where applicable. Hinged joints should be used in sets of two or

three to function properly.

Example

Modeling A set of hinged joints are commonly used to absorb the axial (lateral) growth in a planar Z-bend piping system. Each

individual joint in this system is restricted to pure angular rotation by its hinges. However, each pair of joints, separated

by a section of pipe, will act in unison to absorb lateral deflection in much the same manner as a universal expansion

joint in a single plane application. For a given angular rotation of the individual hinges, the amount of lateral

deflection which a pair of hinges can absorb is directly proportional to the distance between the hinge pins. Thus, in

order to utilize the joints most efficiently, this distance should be made as large as possible.







3. Select Insert/Support to open the Support dialog. Define a Rigid planar guide by specifying a large (10 inch) "Gap down" and "Gap up." This allows the upper section of pipe to move only in the X-Y plane.

4. Move the crosshairs to point A08. Define another planar guide at this point (repeat Step 3). Again, specify large values in the "Gap down" and "Gap up" directions in order to limit movement of the lower section of

pipe to the X-Y plane.


6. Select Insert/Flexible Joint to open the Flexible Joint dialog. Define a flexible joint to point A04. Enter a length of 1.0 feet i.e. DX = 0.00, DY = -1.00, DZ = 0.00. Specify a zero (0) Y-bending stiffness and all

other stiffnesses = Rigid , with the component weight of 53 lb. Also, a pressure thrust area of 50.03 sq.in should

be specified. The area entered assumes that the bellows has an internal sleeve (based on Di = 7.981").

A = pi (7.981") 4 = 50.03 in

7. Move the crosshairs to point A05. Define a second flex joint from A05 to A06 (repeat Step 6). Again, the point at the far end of the joint is defined by the point name (A06), and length (1 ft) specified.



Display of Planar "Z-Bend" Model

Gimbal Expansion Joint A gimbal expansion joint is designed to permit angular rotation in any plane by the use of two pairs of hinges affixed to

a common floating gimbal ring. The gimbal ring, hinges, and pins must be designed to restrain pressure thrust and any

extraneous forces, where applicable. Gimbal expansion joints should be used in sets of two or three to function

properly.

Example

Modeling A set of gimbal joints are commonly used to absorb the axial (lateral) growth in a multiplane Z-bend piping system.

Each individual joint in this system is restricted to pure angular rotation by its hinges. However, each pair of gimbals,

separated by a section of pipe, will act in unison to absorb lateral deflection in much the same manner as a universal




expansion joint. For a given angular rotation of the individual gimbal, the amount of lateral deflection which a pair of

gimbals can absorb is directly proportional to the distance between the gimbals. Thus, in order to utilize the joints most

efficiently, this distance should be made as large as possible.




3. Select Insert/Support to open the Support dialog. Define a rigid planar guide by specifying a large (10 inch) gap down and gap up. This allows the upper section of pipe to move only in the X-Y plane.

4. Move the crosshairs to point A08. Define another planar guide at this point (repeat Step 3). Again, specify large values in the gap down and gap up directions in order to limit movement of the lower section of pipe to

the Y-Z plane.


6. Select Insert/Flexible Joint to open the Flexible Joint dialog. Define a flexible joint to point A04. Enter a length of 1.0 feet i.e. DX = 0.00, DY = -1.00, DZ = 0.00. Specify 0 Y and Z-bending stiffnesses, and all

other stiffnesses = Rigid , with a component weight of 53 lb. Also, a pressure thrust area of 50.03 sq.in should be specified. The area entered assumes that the bellows has an internal sleeve (based on Di = 7.981").

A = pi (7.981") 4 = 50.03 in

7. Move the crosshairs to point A05. Define a second flexible joint from A05 to A06 (repeat Step 6). Again, the point at the far end of the joint is defined by the point name (A06), and length (1 ft) specified.



Display of Multiplane "Z-Bend" Model

Slip Joint A slip joint allows axial expansion of a pipe section by permitting the adjacent pipes to move through a telescoping

action. Slip joints have the great advantage of being capable of absorbing relatively large amounts of axial expansion in

a single device and doing so in the most direct way possible. The slip joint can also accommodate torsional motion.

However, even small bending loads can cause binding or galling, severely reducing the capacity and effectiveness of the

joint. It should be noted that slip joints are susceptible to lateral buckling (or squirming) due to the internal pipe

pressure. Therefore, suitable guiding must be provided to assure that buckling is prevented, and that the male and

female components remain concentric at all times.

Example

Modeling The axial thermal growth of a straight run of pipe is absorbed by a slip joint. A single action slip joint is placed at the

end of the long pipe section, near the attached equipment (or anchor). Then, several guides are provided to assure that

the pipe movement is in the axial direction only.

1. Build a system from A00 to A07 using a 4 inch, standard schedule pipe. The global coordinates for the system points are listed below (length units are feet, and offsets are measured from the preceding point):




Note: Point A06 has been skipped intentionally.


3. Select Insert/Flexible Joint to open the Flexible Joint dialog. Define a flexible joint to point A06. Enter a length of 1.0 foot i.e. DX = 1.00, DY = 0.00, DZ = 0.00. Specify a small value e.g. 0.1 axial, 0.1 torsional

stiffnesses and all other stiffnesses = Rigid with and a component weight of 15 lb. Also, a pressure thrust area of 12.73 sq.in should be specified. The area entered assumes that the slip joint has an internal sleeve (based

on Di = 4.026").

A = pi (4.026") 4 = 12.73 in

Display of System Model

Note: When two slip joints are placed adjacent to each other in a piping system, the pipe between the two slip joints

is supported primarily by friction. Since AutoPIPE does not consider friction in the flexible joint component, the Axial

and Torsional stiffnesses should be specified as small values ( 0.1 ft lb and 0.1 ft lb/deg) instead of zero in order to

prevent an unstable system error.

Ball and Socket Joint A ball and socket joint allows free rotation (in any direction) of the connected pipes, but does not permit translational

movements. Since translation is fixed, pressure loads are transmitted through the joint, and axial movement cannot be

absorbed. Instead, the joint must be oriented so that movements are absorbed laterally. Thus, it can be seen that ball

and socket joints provide an alternative to other types of expansion joints when used in pairs, or in threes. It should be

noted that actual ball and socket joints are limited in their range of angular rotation. They should be placed in the

piping system so that these limits are not exceeded.

Example




Modeling A common application for a system of ball joints is a multiplane Z-bend. This model illustrates an arrangement of three

ball joints as an alternative to a universal, or gimbal expansion joint for absorbing thermal expansion laterally.

1. Build a system from A00 to A09 using a 6 inch standard schedule pipe. The global coordinates for the system points are listed below (length units are feet, and offsets are measured from the preceding point):

Note: Points A02, A05 and A07 have been skipped intentionally.


3. Select Insert/Flexible Joint to open the Flexible Joint dialog. Define a flexible joint to point A02. Enter a length of 0.75 feet i.e.DX = 0.75, DY = 0.00, DZ = 0.00. Specify 0.1 ft-lb/deg for torsional, Y-bending and Z-

bending stiffnesses, and a component weight of 30 lb. Also, a pressure thrust area of 28.89 sq.in should be specified. The area entered assumes that the ball joint has an internal sleeve (based on Di = 6.065").

A = pi (6.065") 4 = 28.89 in

4. Move the crosshairs to point A04. Define a second flexible joint from A04 to A05 (repeat Step 3). Again, the point at the far end of the joint is defined by the point name (A05), and length (0.75 ft) specified.

5. Move the crosshairs to point A06. Define a third flexible joint from A06 to A07 (repeat Step 3). However, a zero torsional stiffness cannot be used since this will result in free rotation of the pipe between A05 and A06

about the longitudinal (local x) axis. In order to prevent an unstable system error, enter a value of

0.1 ft lb/deg.

Note: The 0.1 ft lb/deg torsional stiffness could have been defined at A05 instead of A06 to prevent

instability.

In this model, the ball joints in the vertical pipe leg absorb the axial expansion of the (long) horizontal legs. The axial

expansion of the centerspool, in the vertical leg, is absorbed by the ball joint in the upper horizontal leg. If the

centerspool expansion is small enough to be absorbed by the flexibility of the horizontal pipe sections, the flexible joint

between A01 and A02 could be omitted.



Display of Multiplane "Z-Bend" Model

Tied Bellows Expansion Joint Tie rods are devices, usually in the form of rods or bars, attached to the expansion joint assembly, whose primary

function is to continuously restrain the full bellows pressure thrust during normal operation while permitting only lateral

deflection. It should be noted that when tie rods are furnished on expansion joints subject to external axial movement,

they will only restrain the pressure thrust in the event of an anchor failure. During normal operation, the adjacent

equipment would be subject to the pressure thrust forces.

Example

Two methods for modeling tied bellows expansion joints are provided below:

Model 1: Tie rods modeled as a single two-point support

Model 2: Tie rod assembly modeled as beams and two-point supports





Model 1: Tie rods modeled as a single two-point support This approach produces a simplified model of a tied bellows as bending effects at the expansion joint, due to the actual

orientation of the rods, are neglected. A (Tie/link) support with gaps is used to model tie rods that act in tension only.

The pressure thrust acting on the bellows is restrained by the tie rods and thus no external support is required.

1. Build a system from A00 to A07 using an 8 inch standard schedule pipe. The global coordinates for the system points are listed below (length units are feet, and offsets are measured from the preceding point):



3. Select Insert/Support to open the Support dialog. Define a rigid planar guide by specifying a left and right gap of 10 inches. This allows the pipe to move, due to thermal expansion, in the plane of the pipe.



6. Define a flexible joint to point A05. Enter a length of 1.5 feet i.e. DX = 0.00, DY = 0.00, DZ = 1.50. Specify axial stiffness = 100 lb/in, Y-shear and Z-shear stiffness (i.e. lateral )= 100 lb/in and torsional & bending

stiffnesses = Rigid, and the component weight of 53 lb. Also, a pressure thrust area of 50.03 sq.in must be

specified. The area entered assumes that the bellows has an internal sleeve (based on Di = 7.981").

A = pi (7.981") 4 = 50.03 in


8. Select Insert/Support to open the Support dialog:

9. Specify a Tie/link from A03 to A06 in order to simulate the effect of four 0.5" diameter rods (positioned symmetrically between A04 and A05). Enter a spring rate of 730420 equal to the axial stiffness (ka) of the four

rods combined:

E = 27,900,000 psi L = 30.0 in A = pi (0.50") 4 = 0.1963 in

ka = 4 (27,900,000 psi 0.1963 in ) 30.0 in = 730,420.3 lb/in

A large forward gap and no backward gap has been specified in order to model the rods for tension loads only (refer to

the discussion of Tie/Link Supports for details on the forward and backward directions). When a static analysis is

performed, the "Gaps/Friction/Soil" must be enabled in order to include the tension only behavior of the tie rods.

Note: Alternatively all stiffnesses (Note: torsion = 1E9 or Rigid) can be defined for the flexible joint i.e. non-zero and a

tie-link, rigid X-rotation and rigid Y-rotation connecting from A03 to A06 which maintains both ends of the tied

bellows will rotate the same i.e remain parallel.




Display of Model 1

See Also:

Model 2: Tie rod assembly modeled as beams and two-point supports

Model 2: Tie rod assembly modeled as beams and two-point supports This is a more accurate model of the tied bellows since bending effects at the expansion joint are being considered: the

actual orientation of the rods is specified. The tie rods themselves cannot restrain bending loads, but their combined

interaction does effect the bending behavior of the joint. The end plates are modeled as rigid beams, and the tie rods

are modeled as Tie/link supports with gaps set (rods can only resist tension loads). As will be shown, the gap settings

specified have an important effect on the manner in which the tied bellows is modeled.

1. Define the pipe system; repeat Steps 1 - 7 from Model 1.

2. Select Insert/Beam to open the Beam dialog. Define a Rigid beam (M1) from A03 to the point TB1. TB1 is located 6 inches above A03.

3. Define the remainder of the rigid beams as shown. Add three more beams connecting A03 to TB2 through TB4. Then, add four more beams connecting A06 to TB5 through TB8. The beam point offset coordinates are

as shown in the table below (DX, DY and DZ lengths are relative to the point referenced in the "From Point I"

field).




Note: End plate beams could probably have been defined at points A04 and A05 instead of points A03

and A06 without any significant loss of accuracy.

4. Select Insert/Support to open the Support dialog. Specify a Tie/link from TB1 to TB5 in order to simulate the effect of a 0.5" diameter rod. Enter a spring rate of 182605 which is equal to the axial stiffness (ka) of the

rod:

E = 27,900,000 psi L = 30.0 in A = pi (0.50") 4 = 0.1963 in

ka = 27,900,000 psi 0.1963 in 30.0 in = 182,605.1 lb/in

Note: A large forward gap and no backward gap has been specified in order to model the rod for

tension loads only. It should be noted that the gap settings can be used to model limit, or control,

rods by specifying meaningful gap values. For example, defining a backward gap would model a limit

rod, with the gap value being the amount of axial expansion allowed (such as the bellows design limit)

before the rods restrain the joint. When a static analysis is performed, the "Gaps/Friction/Soil" option

must be enabled in order to include the tension only behavior of the tie rods.




Single Line Display of ties linking beam members

See Also:

Model 1: Tie rods modeled as a single two-point support

Pressure Balanced Expansion Joints A pressure balanced expansion joint is designed to absorb axial movement and/or lateral deflection while restraining the

pressure thrust by means of tie rods interconnecting the flow bellows with an opposed bellows also subjected to

operating pressure. This type of expansion joint is normally used where a change of direction occurs in a run of piping

(e.g., at a bend or a tee). A tee may be used in place of the elbow where flow considerations allow its use.

The major advantage of the pressure-balanced design is its ability to absorb externally induced axial movement without

imposing pressure loading on the system. Therefore, it is often used to relieve loads acting on equipment such as

pumps, compressors, and turbines. However, in order for the expansion joint to function properly, the pressure thrust

restrained by the tie rods must exceed the axial movement forces.

When large amounts of lateral movement are required, or when the lateral force must be held to a minimum, a

pressure balanced universal expansion joint is used. In this case, the flow end of the expansion joint contains two

bellows separated by a common connector (centerspool). The lateral movement is absorbed by the flow bellows in the

same manner as a tied universal expansion joint.

Two methods for modeling pressure balanced expansion joints are provided below:

Model 1: Pressure Balanced Elbow

Model 2: Pressure Balanced Tee










4. Define a flexible joint to point A03. Enter a length of 0.50 feet i.e. DX = 0.50, DY = 0.00, DZ = 0.00.

Define Axial stiffness = 1000 lb/in, Y-bending stiffness = 10000 ft-lb/deg, Z-bending stiffness = 10000 ft-lb/deg, all

other stiffness values = Rigid(the default) with a component weight of 53 lb. Also, a pressure thrust area of 50.03 sq.in should be specified. The area entered assumes that the bellows has an internal sleeve (based on Di = 7.981").

A = pi (7.981") 4 = 50.03 in

5. Select Insert/Segment to begin a new segment: Accept the new segment name default (B). Enter A03 as the first point. Since A03 already exists, the Tee dialog is automatically displayed once the current dialog

is accepted.

6. Accept the default type of tee (Welding). All this step does is assign a stress intensification factor (SIF) at the joint. The SIF for the default tee type is 1.0. This is an acceptable value since we are not really modeling a

tee connection.

7. Select Insert/Run to open the Run Point dialog. Define point B01. Locate this point 1.33 feet from A03 (in the +X direction).

8. Define a second flexible joint from B01 to B02 (repeat Steps 3 and 4). Again, the point at the far end of the joint is defined by the point name (B02), and length (0.50 ft) specified.

9. Move the crosshairs back to point A02 to begin defining the tie rod assembly for the pressure-balanced elbow.

10. Select Insert/Beam to open the Beam dialog. Define a Rigid beam (M1) from A02 to the point TB1. TB1 is located 6 inches away from A02, in the +Y direction.

11. Define the remainder of the rigid beams. Add three more beams connecting A02 to TB2 through TB4. Then, add four more beams connecting B02 to TB5 through TB8. The beam point offset coordinates are as shown




12. Move the crosshairs to point TB1.

13. Select Insert/Support to open the Support dialog. Specify a Tie/Link from TB1 to TB5 in order to simulate the effect of a 0.5" diameter rod. Enter a spring rate which is equal to the axial stiffness (ka) of the rod

(195648):

E = 27,900,000 psi L = 28.0 in A = pi (0.50") 4 = 0.1963 in

ka = 27,900,000 psi 0.1963 in 28.0 in = 195,648.3 lb/in










Display of the Pressure Balanced Elbow Model

See Also:






3. Select Insert/Segment to open the Segment dialog. Accept the new segment name default (B), and enter A04 as the first point. Since A04 already exists, the Tee dialog is automatically displayed after closing




this dialog.

4. Accept the default Type of tee (Welding). This step assigns a stress intensification factor (SIF) at the joint. The SIF for the default tee type is 1.0.

5. Complete the tee by defining a run of pipe to B01. The global coordinates for this point are listed below (length units are feet, and offsets are measured from the preceding point):



8. Define a flexible joint to point A03. Enter a length of 0.50 feet i.e. DX = 0.50, DY = 0.00, DZ = 0.00.

Define Axial stiffness = 1000 lb/in, Y-bending stiffness = 10000 ft-lb/deg, Z-bending stiffness = 10000 ft-lb/deg, all

other stiffness values = Rigid(the default) with a component weight of 53 lb. Also, a pressure thrust area of 50.03 sq.in should be specified. The area entered assumes that the bellows has an internal sleeve (based on Di = 7.981").

A = pi (7.981") 4 = 50.03 in

9. Move the crosshairs to point A05. Define a second flex joint from A05 to A06 (repeat Steps 7 and 8). Again, the point at the far end of the joint is defined by the point name (A06), and length (0.50 ft) specified.

10. Move the crosshairs back to point A02, then select Insert/Beam to open the Beam dialog. Define a rigid beam (M1) from A02 to the point TB1. TB1 is located 6 inches away from A02, in the +Y direction.

11. Define the remainder of the rigid beams. Add three more beams connecting A02 to TB2 through TB4. Then, add four more beams connecting A06 to TB5 through TB8. The beam point offset coordinates are as shown




12. Move the crosshairs to point TB1, then select Insert/Support to open the Support dialog. Specify a Tie/link from TB1 to TB5 in order to simulate the effect of a 0.5" diameter rod. Enter a spring rate which is

equal to the axial stiffness (ka) of the rod (228256.00):

E = 27,900,000 psi L = 24.0 in A = pi (0.50")2 4 = 0.1963 in2 ka = 27,900,000 psi 0.1963 in2 24.0 in = 228,256.3 lb/in








Display of the Pressure Balanced Tee

See Also:


Frames: Pipe Rack Modeling Examples Frame structures are commonly used to support piping systems. In most cases, the structure is assumed to be much




stiffer than the piping itself and can be modeled simply as a rigid support. However, AutoPIPE also allows a supporting

frame structure, such as a pipe rack, to be included in the system model.

Example The following models depict a system of parallel pipe runs (shown in the figure) which are supported by a pipe rack

structure. The pipe-frame connection type varies with each model. The piping system is usually defined first as this

simplifies the modeling of the frame that supports the pipes.

Three methods for modeling pipe racks are provided below:

Pipe Rack (Method 1)



Pipe Rack (Method 1) Each piping point is connected to a corresponding beam point using a two-point support.

1. Build segments A (12" standard pipe) and B (6" standard pipe), which are to be supported by a pipe rack in each model. The global coordinates of the system points are listed below (length units are feet, and offsets

are measured from the preceding point):




Note: Save the system as defined at this point. Each of the three models that follow use this piping

system for the demonstration of pipe-beam connection types.

2. Select Insert/Beam to open the Beam dialog. Define beam M1 as the first frame leg (a column) from point 1 to point 2. The maximum pipe diameter and beam depth have been taken into account for the

calculation of the coordinates for point 2 (also 3, 4 and 5).

3. Define the remainder of the frame. Add a beam between each beam point listed below (e.g. beam M2 spans from point 2 to 3, M3 spans from 3 to 4, etc.). Length units are feet.

Note: Note that in Step 2, point 2 was defined as an offset from point 1. By using point 2 as the I

point for beam M2, its coordinates are recalled. Thus, only point 3 needs to be defined (again as an

offset from point 2). This is a convenient method for defining beam points.

Another convenient way to define beam points is to enter a piping point (e.g. A02) which has similar

coordinates as Point I. Then, change the point name (e.g. to 3). Finally, modify the Y coordinate in

order to position the point as required.

4. Make 1 the current point.

Note: The crosshairs do not have to be located at point 1 in order to define an anchor (see

Step 5). Entering 1 in the "Point Name" field on the Anchor dialog will automatically move the

crosshairs.

5. Select Insert/Anchor to open the Anchor dialog. Define a rigid anchor at point 1. (An anchor may be defined at point 1 without moving to it. While in the Anchor dialog, enter 1 in the "Point Name" field. This

now becomes the new current point and the anchor is placed at this point.)

6. Move the crosshairs to Point 6 and insert a second anchor at that location (repeat Step 5).

7. Make A02 the current point.

8. Connect the piping system to the structural frame with a two-point support. Select Insert/Support to open the Support dialog. Select a Tie/link support type, then enter 3 in the "Connected to" field. A support has

been used to connect A02 to point 3.

Note: In this case a large backward gap has been specified (the forward direction of the support is

defined as from the pipe to the beam) in order to model the ability of the pipe to rise off of the support.

In addition, a coefficient of friction has been specified, thus friction force effects due to the downward

force of the pipe on the support are modeled. In order to include (nonlinear) support gap and friction

effects in an analysis, enable the "Gaps/Friction/Soil" option located on the Static Load Cases dialog.

9. Repeat Step 8 for B02 (add a tie/link support between B02 and point 4).

Two point V-stops or Guides could also have been used in place of the tie/links specified in Model 1. V-

Beam

Point

Global Coordinate

X Y Z

1 0 0 0

2 0 11 0

3 5 11 0

4 7 11 0

5 12 11 0

6 12 0 0



stops are commonly used in situations similar to this model since the direction sense of the gaps is less

confusing than for ties.

Display of Model 1

Other methods for modeling pipe racks

Pipe Rack (Method 2) A pre-defined directional support at each piping point can be connected to a single beam point. This model takes

advantage of the fact that a V-stop always restricts the movement of a point in the vertical direction irrespective of the

location of the Connected to point. This simplifies the modeling of the frame itself as definition of all connection points

are not necessary. However, all of the support reactions are transferred to the one beam point rather than their actual

locations (directly beneath each piping point).

1. Define the pipe system and the first leg of the pipe rack by repeating Steps 1 and 2 from Model 1 .

2. Define the remainder of the frame. Add a beam between each beam point listed below (e.g. beam M2 spans from point 2 to 3, M3 spans from 3 to 4, etc.). Length units are feet.

3. Define an anchor at beam points 1 and 5.

4. Make A02 the current point.

5. Connect pipe segment A to the structural frame with a V-stop. Select Insert/Support to open the Support dialog. Note that point 3 has been entered in the "Connected to" field. Also, a large gap above pipe

has been specified to allow the pipe to lift off of the support.

Beam

Point

Global Coordinate

X Y Z

1 0 0 0

2 0 11 0

3 6 11 0

4 12 11 0

5 12 0 0




6. Connect pipe segment B to point 3 on the structural frame with a V-stop by repeating Step 5 for B02.

Display of Model 2


Pipe Rack (Method 3) Each piping point is connected directly to a corresponding beam point. This model represents a rigid connection

between the pipe and beam member.

1. Define the pipe system by repeating Step 1 from Model 1.

2. Select Insert/Beam to open the Beam dialog. Define beam M1 as the first frame leg (a column) from point 1 to point 2.

3. Define the remainder of the frame. Add a beam between each point listed below (e.g. beam M2 spans from point 2 to A02, M3 spans from A02 to B02, etc.). Length units are feet.

Beam

Point

Global Coordinate

X Y Z

1 0 0 0

2 0 12 0

A02 5 12 0

B02 7 12 0

3 12 12 0

4 12 0 0




4. Define an anchor at 1 and 4 by repeating Steps 4 and 5 from Model 1 for each of these beam points.

Display of Model 3


Hangers Select from the following modeling examples:

Variable and Constant Force Hangers

Two-Point Hanger

Imposed Hanger Displacements

Multiple Hanger Arrangements

Variable and Constant Force Hangers A hanger is a device which is used to suspend a section of pipe. The hanger is designed to support the weight of the

piping system, and any vertical loads imposed on the hanger due to the thermal displacement of the supported piping

point.

In AutoPIPE, spring and constant force hangers may be specified as designed or undesigned. Typically, a hanger which

is present in an existing piping system is designed (where the spring rate and the cold load, or pre-load, are known). If

the hanger is specified as undesigned, AutoPIPE will determine the cold and hot loads, the spring rate, and then make a

selection from the specified hanger manufacturer's table when a hanger run is performed. This is particularly useful if a

new hanger is to be added to a system.

Example





Modeling Both a designed and an undesigned hanger will be defined in this model, and then a hanger run will be performed.

Create a model with two operating load conditions and specify the ambient temperature as 70F. It should be noted that

the hanger run will not alter a user-designed hanger. In other words, AutoPIPE only selects springs for those hanger

supports which have been specified as undesigned by the user, or those which were previously AutoPIPE-designed.

1. Build a system from A00 to A04 using an 8 inch standard schedule pipe. Define T1 as 400F and T2 as 800F. The global coordinat

autopipe manual

Documents

large piping system

anchor block

autopipe system model

piping system ties

overall piping system

hanger selection rigid

example systems

system points