Source: https://guthlabs.ai/docs/instruments/thin-wall-pressure-vessel-stress/mechanism/

instrument mechanism / verified-clean

# Thin-Wall Pressure Vessel Stress mechanism

The inspectable method record for Thin-Wall Pressure Vessel Stress, kept separate from implementation and qualification.

Status: **VERIFIED_CLEAN**Lifecycle: **verified-clean**

## Model scope

The stated equations are standard membrane-stress formulas: cylinder hoop stress pr/t, closed-end cylinder longitudinal stress pr/(2t), and spherical-vessel membrane stress pr/(2t). Review is required because pressure convention, radius-versus-diameter handling, and the closed-end assumption are not fully specified.

- The cylinder longitudinal-stress formula is valid for a closed-ended cylinder under internal pressure; the specification does not state the closed-end assumption.

- The inputs allow r or d, but the specification does not define the required conversion d=2r before applying the formulas.

- The pressure convention is unspecified; these membrane-stress formulas normally use internal gauge pressure, not absolute pressure.

## Units and conventions

- p, r, d, and t must use mutually consistent units; stress has the same pressure units as p.

- If diameter d is supplied, use r=d/2 before calculation.

- p is assumed to be internal gauge pressure; signed pressure may represent external pressure if the sign convention is explicitly defined.

- The thin-wall validity condition is t/r<0.1, using the mean radius and uniform wall thickness.

## Inspectable vector

One of 4 source-bound review vectors:

````
{
  "inputs": {
    "p": 200000,
    "r": 0.5,
    "t": 0.01,
    "vessel_type": "cylinder",
    "units": "p in Pa; r and t in m"
  },
  "expected_outputs": {
    "sigma_hoop": 10000000,
    "sigma_long": 5000000,
    "stress_units": "Pa"
  },
  "working": "t/r = 0.01/0.5 = 0.02, which is less than 0.1. σ_hoop = pr/t = (200000 Pa × 0.5 m)/0.01 m = 100000/0.01 = 10000000 Pa. σ_long = pr/(2t) = (200000 × 0.5)/(2 × 0.01) = 100000/0.02 = 5000000 Pa."
}
````

## Failure boundary

**BREAK_CLAIMED** · SELF_FLAGGED

The instrument should reject t=0 because both formulas divide by zero, and it should flag or reject t/r=0.1 because the thin-wall assumption is valid only for t/r<0.1. Signed-versus-magnitude pressure conventions can also reverse the reported stress signs.

## Other records

[01**Overview**](<https://guthlabs.ai/docs/instruments/thin-wall-pressure-vessel-stress/>)[03**Implementation**](<https://guthlabs.ai/docs/instruments/thin-wall-pressure-vessel-stress/implementation/>)[04**Qualification**](<https://guthlabs.ai/docs/instruments/thin-wall-pressure-vessel-stress/qualification/>)

## Sources and evidence

These pointers bind the page to evidence. They do not grant authority or collapse verification into deployment.

- `VERIFIED_LEDGER.json`

- `evidence-tranche4/tranche4-results.json`

- `BOUNDARY_HAZARD_CATALOG.json`