What is the spacing for HDPE pipes?

Pipe support spans play a crucial role in maintaining the longevity, efficiency, and safety of aboveground piping and pipeline systems. Pipe support span is also known as pipe support spacing. A proper pipe support span not only reduces the pipe supporting problems but also adequately supports pipes at regular intervals to reduce failures associated with improper supporting. In this comprehensive guide, we will discuss the intricacies of pipe support spans, covering design considerations, factors on which it depends, best practices, and pipe support spacing charts based on different codes and standards.

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A. What is a Pipe Support Span?

Pipe Support Span is defined as the optimum distance between two consecutive pipe supports to avoid excessive stress, sagging, bending, vibration, or failure of the piping or pipeline system in extreme cases. It ensures that the piping system remains securely in place throughout operation. Adequate pipe support spacing is synonymous with

• Structural Integrity
• Reduced Maintenance
• Safety
• Operational Efficiency

We all know that while routing aboveground piping or pipeline from one part or equipment to another we have to support the pipe at some definite spans. A properly designed pipe support span helps the piping design personnel to support pipes at regular spacings, thus reducing his work for unnecessary calculations. Pipe Support Span is also known as Pipe Support Spacing. Refer to Fig. 1 which defines the pipe support span for a pipeline system.

B. Factors on Which Pipe Support Span Depends

Various factors influence the pipe support span. In the following section, we will discuss 11 such important criteria that dictate the Pipe support spacing.

1. Pipe Material:

Pipe Support spacing varies with pipe material, For non-metallic pipes, the support span is lower than metallic pipes of the same size. Even Stainless Steel pipes have lower pipe support spacing as compared to Carbon steel pipes.

2. Nominal Diameter of Pipe & Schedule:

With the increase in pipe diameter and schedule, the pipe support span increases. That is the reason you will find that a 10-inch pipe has more support span as compared to a 4-inch pipe support spacing.

3. Type of Fluid Service:

Piping support span varies with fluid service; Pipes carrying liquid service have less support span as compared to pipes carrying gaseous fluids. This means with an increase in the density of the flow medium pipe support spacing decreases.

4. Type and Thickness of Insulation Material:

With an increase in thickness and density of the pipe insulation material, pipe support spacing reduces. An increase in insulation density and thickness imposes more load on the parent pipe which needs to be supported by increasing the number of supports which means the pipe support span reduces.

5. Piping Configuration (Straight pipe and Pipe with elbows):

Pipe support spacing is dependent on the piping routing or geometry. A straight pipe has more support span as compared to pipes with directional changes. Because of this reason, to find out the span for piping including elbows, the straight pipe span is multiplied by a factor as shown in Fig. 2.

6. Locations of Valves and Rigid Bodies:

The presence of rigid bodies in a piping or pipeline system reduces the pipe support span. It is a general engineering practice to provide at least one support near rigid bodies like valves (Preferably to provide support on both sides of the valve).

7. Structural Availability for Supporting:

Available structures are normally used for supporting the pipe. So, the pipe span chart may be reduced in those places. Also, an increase in the number of supports distributes the piping loads on supports and increases the piping stiffness. So, if a structure is available, pipe supports are usually taken from those structures.

8. Vibrating or Pulsating lines:

For vibrating or pulsating lines pipe support span is reduced to avoid vibration tendency and to increase the natural frequency of the piping system. A reduction in pipe support spacing increases the system rigidity which reduces the tendency of pipe vibration.

9. Fluid Temperature:

With an increase in fluid temperature as the pipe material's allowable stress value reduces, the pipe is supported in a nearby position, thus reducing the pipe support spacing.

10. Equipment Connection

Sometimes, the Pipe support span is determined considering various equipment connections that have the potential for vibration transfer from the equipment like reciprocating compressors and reciprocating pumps. For these pipes, the supporting span is reduced from the standard pipe support spacing.

11. Flow Induced Vibration Criteria

For lines with the flow-induced vibration susceptibility as high, the pipe support span is reduced to increase the natural frequency of the piping system so that the tendency of FIV failure is reduced.

Fig. 1: Figure showing pipe support span

C. Deciding Pipe Support Span

Pipe Support Span Length Depends On-

• Bending Stress
• Deflection
• Indentation
• Allowable Loads
• Vibration Possibility and Natural Frequency of the piping system

1. Bending Stress

Bending is caused mainly due to two reasons:

• Uniform Weight Load
• Concentrated Weight Load

1.1 Uniform Weight Load

• Own Weight Of Pipe
• Insulation Weight
• Weight of Fluid During operation
• Weight of hydrostatic fluid During Hydro Test

1.2 Concentrated Load

• Weight Of Valve, Flanges,
• Strainer, specialty items, inline items, etc.

2. Deflection

Deflection (Δ) is defined as a relative displacement of the point from its original position.

• The basic piping practice is to limit pipe deflection between supports to 1' or 1/2 the nominal pipe diameter, whichever is smaller.
• The most important reason for limiting deflection is to make the pipe stiff enough, that is, of high enough natural frequency, to avoid a large amplitude response under any slight perturbing force. As a rough rule, for average piping, a natural frequency of 4 cycles per second will be found satisfactory. The natural frequency can be calculated by

3. Indentation

Where,

• t=corroded Thickness of pipe Wall(mm)
• S=0.67Sh(N/mm^2)
• R=Radius of pipe (mm)
• d=Bearing Length(mm)
• b=Bearing width(mm)

4. Allowable Load at Support

Where,

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• Pa=Allowable Load at the Support point
• t=effective local thickness (pipe wall +Reinforced Pad If Any)
• R=outer radius of Pipe
• b=Bearing length of pipe (along the axis) on the support structure

IF THE ACTUAL LOAD AT SUPPORT IS GREATER THAN THE ALLOWABLE LOAD GIVEN BY THE ABOVE FORMULA, A REINFORCEMENT PAD WILL BE REQUIRED.

5. Vibration Possibility

The support span for vibration-prone lines is reduced to make the system stiffer such that the pipe does not easily vibrate. The natural frequency of the system is usually maintained above 4 Hz as mentioned in clause C.2 above.

D. Pipe Support Span Chart

A pipe support span chart is a table or diagram that provides information on the maximum allowable span for different types of piping and support configurations. The span is the distance between two points where a pipe is supported, such as at two adjacent pipe hangers.

The purpose of a pipe support span chart is to help engineers and designers ensure that piping systems are properly supported to prevent sagging, bending, or other types of stress that could cause damage or failure. By referring to the span chart, designers can select the appropriate type and spacing of supports for a given piping configuration, based on the materials used, the size and weight of the pipes, the fluid being transported, and other factors.

Pipe support span charts may also include information on the recommended type of support for different piping materials, such as steel, copper, or plastic, as well as information on recommended hanger spacing, temperature limits, and other design considerations. Proper use of a pipe support span chart can help ensure that piping systems are safe, reliable, and long-lasting.

Normally project-specific Support Span is provided in tabular format for straight pipes that are known as a 'Pipe Support Span Chart'. But for elbows or turns, the span is to be reduced by a factor as shown in the attached figure (Fig. 2). Readymade support spans for specific pipe diameters and thicknesses are available in the MSS code. For the Shell group of companies, the support span is provided in DEP in tabular format.

Fig. 2: Factor to reduce support span depending on layout.

1. Pipe Support Spacing Chart for Steel Piping as per MSS-SP-69

A pipe support span chart is a tabular chart giving a rough idea of supporting distance. These charts are normally mentioned in piping stress analysis project specifications. In the following image (Fig. 3) pipe support span chart from MSS SP-69 is reproduced as a sample.

Fig. 3: Sample Piping Support Span Chart (Reference: MSS SP-69)

2. Pipe Support Spacing Chart for Steel Piping Based on ASME B31.1

The pipe support span as per ASME B31.1 for Steel piping is provided below:

Pipe Support Span Based on ASME B31.1, Power Piping CodeNPS
(Inches)DN
(mm)Water/ Liquid
Service (m)Water/ Liquid
Service (ft)Steam, Gas,
Air Service (m)Steam, Gas,
Air Service (ft).172...................842Table 1: Pipe Support Spacing in ft and m as per ASME B31.1-Power Piping Code

General Notes for Table 1:

• This support span is valid for horizontal straight runs of standard and heavier steel pipe at a maximum operating temperature of 750°F (400°C).
• This support spacing chart does not apply in the presence of concentrated loads between supports, such as flanges, valves, and specialties.
• The pipe support spacing is based on a fixed beam support with a bending stress limiting to 2,300 psi (15.86 MPa) and insulated pipe filled with water or the equivalent weight of steel pipe for steam, gas, or air service, and the pitch of the line is such that a sag of 0.1 in. (2.5 mm) between supports is permissible.

3. Pipe Support Span Chart as per ASME B31.3

Process piping code ASME B31.3 does not provide any span chart for steel piping systems. Users usually develop their pipe support spacing table considering parameters like allowed stress, deflection, etc. A typical pipe support span for process piping for carbon steel and stainless steel pipe material is provided below (Reference: Shell DEP) in Table 2 and Table 3.

3.1 Pipe Support Span for Carbon Steel

Typical Support Span for carbon steel and heavy wall stainless steel Vapour serviceLiquid servicePipe sizeBareInsulatedBareInsulatedDN 15
(NPS ½)900 mm
(3 ft)800 mm
(2 ½ ft)900 mm
(3 ft)800 mm
(2 ½ ft)DN 20
(NPS ¾) mm
(4 ½ ft) mm
(3.9 ft) mm
(4 ½ ft) mm
(3.9 ft)DN 25
(NPS 1) mm
(11.8 ft) mm
(7.5 ft) mm
(11.3 ft) mm
(7.3 ft)DN 40
(NPS 1 ½) mm
(11.8 ft) mm
(9.8 ft) mm
(11.3 ft) mm
(9.1 ft)DN 50
(NPS 2) mm
(11.8 ft) mm
(11.3 ft) mm
(11.3 ft) mm
(10.8 ft)DN 80
(NPS 3) mm
(21.4 ft) mm
(15 ft) mm
(17.8 ft) mm
(13.7 ft)DN 100
(NPS 4) mm
(24.6 ft) mm
(18.2 ft) mm
(20 ft) mm
(16 ft)DN 150
(NPS 6) mm
(30 ft) mm
(22.3 ft) mm
(23.2 ft) mm
(19 ft)DN 200
(NPS 8) mm
(34.4 ft) mm (26.4 ft) mm
(26 ft) mm
(21.9 ft)DN 250
(NPS 10) mm
(38.7 ft) mm
(29.6 ft) mm
(28.5 ft) mm
(24.2 ft)DN 300
(NPS 12) mm
(42.3 ft) mm
(32.1 ft) mm
(30 ft) mm
(25.5 ft)DN 350
(NPS 14) mm
(49.7 ft) mm
(38.8 ft) mm
(35.5 ft) mm
(30.5 ft)DN 400
(NPS 16) mm
(53.3 ft) mm
(42.1 ft) mm
(36.7 ft) mm
(31.9 ft)DN 450
(NPS 18) mm
(56.5 ft) mm
(45.1 ft) mm
(37.7 ft) mm
(33.3 ft)DN 500
(NPS 20) mm
(59.7 ft) mm
(47.4 ft) mm
(38.5 ft) mm
(34.1 ft)DN 600
(NPS 24) mm
(62.1 ft) mm
(52.6 ft) mm
(39.8 ft) mm
(35.9 ft)DN 750
(NPS 30) mm
(68.9 ft) mm
(57.4 ft) mm
(43 ft) mm
(37.7 ft)DN 900
(NPS 36) mm
(74.5 ft) mm
(60.7 ft) mm
(45 ft) mm
(41 ft)DN
(NPS 42) mm
(76.8 ft) mm
(64 ft) mm
(47 ft) mm
(42.6 ft)DN
(NPS 48) mm
(82 ft) mm
(67.2 ft) mm
(48 ft) mm
(44 ft)Table 2: Pipe Support Span for Carbon Steel and Heavy Wall Stainless Steel

3.2 Pipe Support Span for Stainless Steel

Maximum spans for stainless steel, schedule 10S Vapour serviceLiquid servicePipe sizeBareInsulatedBareInsulatedDN 25
(NPS 1) mm
(7.2 ft) mm
(5.9 ft) mm
(6.8 ft) mm
(5.9 ft)DN 40
(NPS 1 ½) mm
(9.1 ft) mm
(8.2 ft) mm
(7.8 ft) mm
(8.2 ft)DN 50
(NPS 2) mm
(9.1 ft) mm
(8.5 ft) mm
(8.8 ft) mm
(8.5 ft)DN 80
(NPS 3) mm
(21 ft) mm
(13.2 ft) mm
(16.2 ft) mm
(11.4 ft)DN 100
(NPS 4) mm
(21 ft) mm
(15.7 ft) mm
(17.3 ft) mm
(13.1 ft)DN 150
(NPS 6) mm
(30.8 ft) mm
(18.8 ft) mm
(19.5 ft) mm
(15 ft)DN 200
(NPS 8) mm
(35.2 ft) mm
(22.3 ft) mm
(21.1 ft) mm
(17 ft)DN 250
(NPS 10) mm
(35.2 ft) mm
(24.9 ft) mm
(22.8 ft) mm
(18.5 ft)DN 300
(NPS 12) mm
(35.2 ft) mm
(27 ft) mm
(24.1 ft) mm
(19.8 ft)DN 350
(NPS 14) mm
(35.2 ft) mm
(28.5 ft) mm
(24.9 ft) mm
(20.6 ft)DN 400
(NPS 16) mm
(36 ft) mm
(31 ft) mm
(25.4 ft) mm
(21.4 ft)DN 450
(NPS 18) mm
(36 ft) mm
(31.8 ft) mm
(25.7 ft) mm
(22.1 ft)DN 500
(NPS 20) mm
(37.7 ft) mm
(34.5 ft) mm
(27.5 ft) mm
(23.9 ft)DN 600
(NPS 24) mm
(39.3 ft) mm
(36 ft) mm
(29.6 ft) mm
(26.4 ft)DN 750
(NPS 30) mm
(45.9 ft) mm
(42.6 ft) mm
(34.5 ft) mm
(31.2 ft)DN 900
(NPS 36) mm
(52.5 ft) mm
(49.2 ft) mm
(37.7 ft) mm
(34.5 ft)DN
(NPS 42) mm
(59 ft) mm
(54 ft) mm
(41 ft) mm
(37.7 ft)DN
(NPS 48) mm
(65.6 ft) mm
(56.8 ft) mm
(44.3 ft) mm
(41 ft)Table 3: Maximum Pipe Support Spans for Stainless Steel, Schedule 10S Pipe

E. HDPE Pipe Support Span

The maximum allowable span for HDPE pipes will depend on various factors, such as the pipe size, wall thickness, and temperature of the fluid being transported. In general, HDPE pipes require more support than steel pipes due to their flexibility and low modulus of elasticity.

The Plastics Pipe Institute (PPI) provides guidelines for designing supports for HDPE pipes, which includes recommendations for maximum allowable span. According to PPI, the maximum allowable span for HDPE pipes should not exceed the following:

• 4 feet for 1-inch diameter pipes
• 5 feet for 1.25-inch diameter pipes
• 6 feet for 1.5-inch diameter pipes
• 7 feet for 2-inch diameter pipes
• 9 feet for 3-inch diameter pipes
• 11 feet for 4-inch diameter pipes
• 13 feet for 6-inch diameter pipes
• 15 feet for 8-inch diameter pipes
• 18 feet for 10-inch diameter pipes
• 22 feet for 12-inch diameter pipes

However, it is important to note that these are general guidelines and the actual span may vary depending on the specific application and the design criteria used. It is always recommended to consult with a qualified engineer or piping designer to determine the appropriate support span for a specific HDPE piping system.

F. GRE Pipe Support Span

The maximum allowable span for Glass Reinforced Epoxy (GRE) pipes will depend on various factors, such as the pipe diameter, wall thickness, and the type of fluid being transported.

The Fiberglass Reinforced Plastic Institute (FRPI) provides guidelines for designing supports for GRE pipes, which includes recommendations for maximum allowable span. According to FRPI, the maximum allowable span for GRE pipes should not exceed the following:

• 2 feet for 1-inch diameter pipes
• 2.5 feet for 1.25-inch diameter pipes
• 3 feet for 1.5-inch diameter pipes
• 4 feet for 2-inch diameter pipes
• 6 feet for 3-inch diameter pipes
• 7 feet for 4-inch diameter pipes
• 8 feet for 6-inch diameter pipes
• 10 feet for 8-inch diameter pipes
• 12 feet for 10-inch diameter pipes
• 14 feet for 12-inch diameter pipes

It is important to note that these are general guidelines and the actual span may vary depending on the specific application and the design criteria used. It is always recommended to consult with a qualified engineer or piping designer to determine the appropriate support span for a specific GRE piping system.

ISO - also provides a typical GRE pipe support span table to be used for FRP/GRE pipes in Table 1 (The same is reproduced below in Fig. 4).

Fig. 4: GRE Pipe Support Span as per ISO -

G. ABS and PVC Pipe Support Spacing

PVC and ABS pipe support spacing is mainly based on the manufacturer. The following image (Fig. 5) provides some typical values for ABS and PVC Pipe Support Spans.

Fig. 5: Horizontal Support Spacing for PVC and ABS Pipes

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