Pipeline Design & Stress Analysis

Introduction

The Pipeline Toolbox is home to many tools and calculators. The PLTB User’s Guide presents information, guidelines, and procedures for use during design, construction, operations, and integrity tasks for field or office applications.
The Steel Pipeline Design & Stress Analysis module is intended to provide adequate analysis for public safety under all conditions encountered in the gas industry. Conditions that may cause additional stress in any part of a line or its appurtenances shall be provided for, using good engineering practice. Examples of such conditions include long self-supported spans, unstable ground, mechanical or sonic vibration, weight of special attachments, outside induced stresses, stresses caused by temperature differences, and the soil and temperature conditions.

Module/Application

• Design Pressure – Steel Pipe
• Wall Thickness – Steel Pipe
• Restrained Pipeline Stress Analysis
• Unstrained Pipeline Stress Analysis
• Flume Design – Rational Method
• Buoyancy Analysis & Concrete Coating Requirements
• Buoyancy Analysis & Concrete Weights Spacing
• Pipe Anchor Force Analysis
• Maximum Impact Load & Penetration Depth
• Internal Pressure % SMYS
• Hoop and Longitudinal Stress
• Requirements to Move Unpressured Pipe
• Bending Stress and Deflection
• Maximum Allowable Pipe Span Length
• Bending Stress-Caused By Fluid Around Pipeline
• Linear Thermal Pipeline Expansion
• Thrust at Blow-Off

References

• ASME B31.8 – Gas Transmission and Distribution Piping Systems
• API 5L, API 5LS and API 5LX – Specification of Pipe Grade
• ASTM – Various – Weld Joint Factor
• CFR Code Part 192
• USDA-SCS Modified (Permissible Velocity of Water and Soil Erodibility)
• FHWA-HEC
• Pipeline Rules of Thumb Handbook
• Timoshenko, S – Theory of Elasticity Anchor Force

Appendix of Definitions

ACTUAL PIPE SIZE – The measurement is equal to the outside diameter of the pipe.

BEND RADIUS – The radius corresponding to the curvature of the bent specimen or bent area of a formed part, measured on the inside of a bend or on the centerline of the tube, as defined.

CASING – Pipe used as a structural retainer for the exterior walls of water, gas, oil well, or other application; also used as a structural interior retainer for another pipe commonly seen in oilfield applications.

COEFFICIENT OF THERMAL EXPANSION – A physical property value representing the change in length per unit length, the change in area per unit area, or the change in volume per unit volume per one-degree increase in temperature.

DIAMETER – The distance between one edge of a circle and the other as measured on a straight line through the center of the circle.

ELECTRIC RESISTANCE WELD – A method of manufacturing steel pipe in which a flat ribbon of steel is cold-formed by rolls; electrical current is then used to weld the edges together. This pipe can be normally produced in sizes from NPS 1/8 through NPS 26.

EXPANDED PIPE – Pipe which has been enlarged circumferentially by mechanical or hydraulic pressure.

FATIGUE – The tendency for a metal to break under conditions of repeated cyclic stressing;
stresses that are considerably below the ultimate tensile strength.

FRACTURE STRESS – The maximum principal true stress (fracture load divided by fracture area).

GRADE – A class of steel defining amongst others, chemistry, tensile strength, and yield strength requirements.

HYDROSTATIC TEST – A mill test that is normally required by specifications. The ends of the pipe are sealed, and high-pressure water is applied into the pipe at predetermined pressure for a specific period of time as required by the various specifications.

INSIDE DIAMETER (ID) – The distance of a straight line passing through the center of a pipe from one inside pipe wall to the opposite inside wall.

JOINT – The point in a piping system at which a connection is made; joints connect pipe, fittings, and valves to form a system. Also, a single length of pipe can be called a joint.

KIP – Unit of weight equal to 1,000 pounds dead weight.

KIS – K equals I,000, thus the term is actually K (1,000) psi. The P has been dropped, and KSI is the new term. (i.e. 50 KSI = 50,000 psi).

MODULUS OF ELASTICITY – The slope of the elastic portion of the stress-strain curve in mechanical testing. The stress is divided by the unit elongation. The tensile or compressive elastic modulus is called Young’s modulus; the torsional elastic modulus is known as the shear modulus or modulus of rigidity.

OUTSIDE DIAMETER (OD) – The distance of a straight line passing through the center of the pipe from one outside rim of the pipe to its opposite outside rim.

PSI – Pounds per Square Inch.

PSIG – Pounds per Square Inch Gauge.

RADIUS – The distance of a straight line from the center of a circle to its edge.

STRESS – The load per unit of area. Ordinarily, stress-strain curves do not show the true stress
(load divided by area at that moment), but a fictitious value obtained by always using the original area.

TENSILE STRENGTH – The value obtained by dividing the maximum load observed during tensile straining until breakage occurs by the specimen cross-sectional area before straining. Also called ultimate strength.

YIELD STRENGTH – The stress at which a material exhibits a specified limiting deviation from proportionality of stress to strain. An offset of 0.2 percent is used for many metals such as steel, aluminum base, and magnesium base alloys, while a 0.5 percent total elongation under load is frequently used for copper alloys.

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