Pipe SMYS & Hoop Stress Analysis
Specified Minimum Yield Strength (SMYS) is the anchor of every steel-pipeline design check. From the pipe’s OD, wall thickness, and grade, this calculator uses Barlow’s equation to relate internal pressure to hoop stress, express that stress as a percentage of SMYS, and solve for the maximum allowable operating pressure (MAOP) once a design factor and joint/temperature factors are applied.
It is the fast first pass engineers run when sizing wall thickness, verifying an existing line’s pressure rating, or checking that a crossing or HDD segment sits inside its allowable design factor.
Open in the Pipeline Planning Toolbox — Free 7-Day TrialWhat it computes
- Hoop stress from internal pressure (Barlow’s equation)
- Hoop stress as a percentage of SMYS
- Maximum allowable operating pressure (MAOP) for a chosen design factor
- Required wall thickness for a target pressure and %SMYS
Barlow and the design factor
Barlow’s equation, S = P·D / (2·t), links pressure P, diameter D, and wall t to hoop stress S. Design codes then limit the allowable stress to a fraction of SMYS through a design factor (and location/temperature/joint factors), so MAOP = 2·SMYS·t·F·E·T / D. The calculator applies the factor set for your governing code and location class.
Because the check is so sensitive to grade and wall, it pairs naturally with the crossing and installation-stress calculators, which all report their results back against the same %SMYS ceiling.
Frequently asked questions
What is the difference between SMYS and hoop stress?
SMYS is a fixed material property — the minimum yield strength guaranteed for the pipe grade (e.g. 52,000 psi for API 5L X52). Hoop stress is the actual circumferential stress produced by internal pressure. The design check keeps hoop stress below a set percentage of SMYS.
What design factor should I use?
The design factor depends on the governing code (ASME B31.4, B31.8, or 49 CFR) and, for gas, the location class. The calculator lets you set it so the MAOP and %SMYS results match your design basis.