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The Canadian Piping Flexibility Stress Analysis Standard

The Canadian Piping Flexibility Stress Analysis Standard. By Meena Rezkallah, P.Eng. Piping Stress Engineer. professional engineer in canada
The Canadian Piping Flexibility Stress Analysis Standard. By Meena Rezkallah, P.Eng.

The Canadian Piping Flexibility Stress Analysis Standard for a premium piping engineering & full-service pipe design and pipeline / pipe stress analysis services across Canada & globally. Using CAESAR II and pipe stress calculations as per API, ASME B31.3, B31.1, B31.8, B31.4, CSA Z662.



This standard prescribes the basic requirements for the engineering of piping systems and components

for thermal flexibility, support, pressure, vibration, fluid, or gas flow reactions and environmental factors,

including effects on equipment.


The publications listed below form part of this standard. Each publication shall be the latest revision and

addendum in effect on the date this standard is issued for construction unless noted otherwise. Except as modified by the requirements specified herein or the details of the drawings, work included in this

standard shall conform to the applicable provisions of these publications.

2.1 API (American Petroleum Institute)

2.2 ASME (American Society of Mechanical Engineers)

  • SM23 Part 8

2.4 NBC (National Building Code of Canada)

2.5 CSA Group


3.1 Quality Assurance

3.1.1 The practices outlined herein establish the minimum requirements to which the Piping Stress Analyst shall adhere in the performance of quality assurance activities to ensure adequate engineering review of piping systems. Pipe flexibility and stress analysis shall conform to the governing piping code. The pipe line list for the project shall be the controlling document establishing individual line parameters, with the piping drawings defining line configurations.

3.1.2 Calculations shall be retained by the Engineering Contractor or Engineering Consultant for a period of 15 years.

3.1.3 Formal computer analysis shall be performed on the following piping systems:

• Process lines to and from steam generators.

• 2 inches and larger diameter process lines to and from pumps, compressors, turbo-expanders, and blowers.

• Lines with design temperatures over 260°C.

• Piping systems that are selected by the Lead Piping Stress Engineer.

• Steam lines to and from turbines.

3.1.4 As a minimum, engineering analysis by visual inspection and short-cut manual calculations shall be performed on the following systems:

• 16 inches and larger diameter lines.

• Lines to vessels that cannot be disconnected for purging or steam out.

• 3 inches and larger diameter lines at design temperature over 150°C.

• Piping systems selected by the Lead Piping Stress Engineer, which do not require formal computer analysis.

• Relief systems, whether closed or relieving to atmosphere, with considerations for attached or detached discharge pipes.

• Vacuum lines.

• Nonmetallic piping.

• Lines subject to excessive settlement.

3.1.5 Special consideration shall be given to piping systems in the following categories:

• 3 inches and larger diameter lines subject to greater than 25 mm differential settlement of equipment, or supports.

• Lines designated as "Category M," according to ASME B31.3, shall be so identified in the line list.

• Lines subject to mixed-phase flow (liquid and vapor), and lines identified as vibrating service on the flow diagrams.

• Lines subject to external pressure by reason of vacuum or jacketing.

• Piping connected to reaction sensitive equipment.

3.1.6 Lines to be considered for analysis shall be so marked on the line list.


4.1 Piping Systems

4.1.1 Piping flexibility shall be obtained through pipe routing or expansion loops. Expansion loops, when installed in a horizontal plane, shall be offset vertically to clear adjacent piping whenever possible. Expansion Joints / Flexible connectors shall be used only when it is not feasible to provide flexibility by other means. Expansion joints / flexible connectors shall be marked on the P&IDs and approved by the project Owner.

4.1.2 The flexibility analysis shall consider the most severe operating temperature condition sustained during startup, normal operation, shutdown, or regeneration. The analysis shall be performed for the maximum temperature differential. The effect of minimum installation and solar temperatures shall be considered in determining the maximum temperature differential.

Note: Hydrocarbon lines within units, areas, and unit pipeways shall be considered subject to steam purge. Interconnecting pipeway lines shall not be considered subject to steam purge. Lines subject to steam purge shall be designed for the steam temperatures or the design temperatures of the line, whichever is higher. Consult the process engineer at the beginning of the job for the correct temperatures.

4.1.3 Lines to purged vessels that cannot be disconnected during purging shall be designed with sufficient flexibility to accommodate the thermal displacement of the vessel.

4.1.4 The mean installation temperature shall be assumed as -10°C for above ground and +10° for underground.

4.1.5 The metal temperature from the effect of solar radiation shall be assumed as 65°C for pipe stress analysis purposes.

4.1.6 If the line is a vapor line, hydrotest weight shall be considered in the analysis.

4.2 External Load Limits on Equipment

4.2.1 Rotating Equipment

Upset/design temperatures are considered transient. For allowable loads the normal operating temperature and the maximum temperature differential shall be used to check the stress in the system.

4.2.2 Vertical In-Line Pumps Piping to small vertical in-line pumps (20 horsepower or less) shall be supported immediately adjacent to suction and discharge flanges by means of conventional pipe supports. Piping loads shall be determined with the pump considered as a rigid but unanchored segment of the piping system. Piping to larger vertical pumps furnished with casing footmounts shall be supported on suitable foundations. The allowable force and moment limitations at pump nozzles shall be per API 610.

4.2.3 Centrifugal Pumps

For pumps that are single-stage, centerline mounted, 2-point support, the allowable

forces and moments published in API Standard 610 shall be used, unless higher loads

are permitted by the Supplier.

For pumps that are multistage, centerline mounted, or barrel type horizontal cases with 4-point

supports, force and moment limitations shall be per API 610, unless higher loads

are permitted by the Supplier.

4.2.4 Centrifugal Compressors

The maximum allowable forces and moments that may be applied to compressor flanges

by the piping shall be per API Standard 617 Section 2.5, unless higher loads are

permitted by the Supplier.

4.2.5 Reciprocating Equipment

Allowable forces and moments shall be as permitted by the Vendor and agreed by the

Engineering Contractor.

4.2.6 Heat Exchangers (Shell and Tube)

Allowable external forces and moments shall be limited to those that produce a limiting

stress as set by ASME B31.3, for the exchanger nozzle/shell material recognizing stress

intensification factors as determined by the applicable code.

4.2.7 Air Cooled Heat Exchangers

The maximum allowable forces and moments that may be applied to air cooler process

nozzle flanges shall be per API Standard 661, unless higher loads are permitted by the


4.2.8 Pressure Vessels and Miscellaneous

Allowable loads shall be calculated in accordance with criteria given by the API

Recommended Practices, API Standards, or ASME sponsored codes that apply to the

specific equipment or system, unless higher loads are permitted by the Supplier.

4.2.9 Fiberglass Vessels / Glass Lined Vessels

There shall be loads developed on these vessel nozzles. Allowable forces and moments

on nozzles shall be calculated in accordance with standard pipe stress analysis methods.

Allowable loads cannot be zero and shall be as agreed to by the Vessel Supplier.

4.3 Allowable Forces and Moments on Flanges

To avoid leakage in flanges, bending moments and forces on flanges shall be limited by the formulas listed in the ASME Boiler and Pressure Vessel Codes, Section VIII.

4.4.1 The effect of frictional resistance to thermal movement of the pipe shall be included in the anchor design of piping systems. Assume a coefficient of friction of 0.3 for steel-to-steel contact, 0.1 for teflon to stainless steel contact surfaces and 0.4 for steel to concrete.

4.4.2 Frictionless unrestrained movement of the piping system shall be assumed only when the entire system is supported by means of rod or spring hangers.

4.4.3 Friction shall be considered a short-term transient load. Allowable load limits on equipment may be increased by a factor of 1.5 when considering normal loading plus friction loads. Supports immediately adjacent to equipment nozzles shall be assumed frictionless.

4.5 Supporting

4.5.1 Lines shall be supported in accordance with the limitations set by the applicable codes

listed herein. Deflection between supports shall be limited to 25 mm or less if accumulation of small quantities of liquids is not acceptable.

4.5.2 NPS 20 and larger carbon steel lines and thin-wall lines (D/T ≥ 100) shall be analyzed for crushing loads at support points, and shall be reinforced as necessary.

4.5.3 Systems including tanks / vessels shall be analyzed. These tanks / vessels shall not have springs directly under equipment lugs without the approval of Lead Piping Stress

Engineer. Flexible connectors may also be considered with the approval of Lead Piping Stress Engineer and the project Owner.

Design wind pressure and height zones shall be according to NBC.

Seismic loads shall be considered for piping design according to NBC or other local building codes, as required by the project.

Dampeners, restraints, or both shall be provided for lines subject to mixed-phase flow, as required.

4.9 Existing Lines

In verifying stress levels of existing lines due consideration shall be given to requirements of API 570 ‘Piping Inspection Code’. Connections to existing lines or changes in temperatures and pressures of existing lines shall be

analyzed as follows:

4.9.1 Ultrasonic measurements shall be taken for thickness at critical points on all subject lines. This thickness shall be assumed to prevail throughout these lines.

4.9.2 Calculations shall be performed to determine the integrity of pipe wall thickness for the new design conditions or continued operation under original design conditions.

4.9.3 Field sketches shall be drawn of the entire as-built systems for existing lines, subject to a change in operating or design temperature of more than plus or minus 15°C.

4.9.4 Field sketches shall be drawn of as-built systems from new connection points, both upstream and downstream of the connection, to the nearest anchor point or logical discontinuity when anchors are not available.

4.9.5 Type of flexibility analysis required shall be determined by the Engineering Contractor and agreed to by the project Owner.



Located in Calgary, AlbertaVancouver, BCToronto, OntarioEdmonton, AlbertaHouston TexasTorrance, CaliforniaEl Segundo, CAManhattan Beach, CA; Concord, CA; We offer our engineering consultancy services across Canada and United States. Meena Rezkallah.

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