Reference
Proper Pigging · HydroTech Testing Services
Reference
Formulas, constants, and definitions
Appendix B and Appendix D, published openly, with calculators that carry the same arithmetic.
B.1Core relations
- Hoop stress
- S = P D / 2t → P = 2 S t / D
- Internal area
- A = π (D − 2t)² / 4
- Fill volume
- V = L × A, field form V ≈ 0.0408 d² L in gallons
- Hydrostatic gradient
- ΔP = 0.433 × SG × Δh, fresh water SG = 1.0
- Pressurisation volume
- ΔV = V ΔP [ (D/(Et))(1 − ν²) + C ]
- Pressure-temperature
- ΔP = ΔT [ γ − 2(1 + ν)α ] ÷ [ (D/(Et))(1 − ν²) + C ]
- Real-gas law
- PV = ZnRT, R = 10.7316 psia·ft³/(lb-mol·°R)
- Elastic PV slope
- dP/dV = 1 ÷ ( V [ (D/(Et))(1 − ν²) + C ] )
B.2Constants
| Quantity | Symbol | Value | Note |
|---|---|---|---|
| Young’s modulus, steel | E | 29 × 10⁶ psi | constant |
| Poisson’s ratio, steel | ν | 0.3 | constant |
| Linear expansion, steel | α | 6.5 × 10⁻⁶ /°F | = 1.17 × 10⁻⁵ /°C |
| Compressibility of water | C | ≈ 3 × 10⁻⁶ /psi | temperature dependent |
| Volumetric expansion, water | γ | ≈ 1.3 × 10⁻⁴ /°F | near 68 °F; near zero at 39 °F |
| Fresh water gradient | — | 0.433 psi/ft | multiply by SG |
| Molecular weight, nitrogen | MW | 28.01 lb/lb-mol | N₂ |
| Standard conditions | — | 14.7 psia, 60 °F | 14.73 psia also in tariff use |
B.3Regulatory anchors
Verify against the current text of the Code of Federal Regulations before use.
- 49 CFR 195.304
- Liquid test at not less than 125 percent of MOP for four continuous hours, plus four hours at not less than 110 percent if the line is not visually inspectable.
- 49 CFR 192.505
- Gas strength test held at least eight hours where operating stress is 30 percent SMYS or more, at the class-location test factor.
- 49 CFR 192.503
- Maximum hoop stress permitted during gas-medium testing, by class: natural gas 80/30/30/30; air or inert gas 80/75/50/40.
- 49 CFR 192.506
- Spike hydrostatic pressure test, added by the 2019 gas transmission rule.
- 49 CFR 195.306
- Conditions under which alternative test media are permitted on liquid lines.
- 192.517 & 195.310
- Test records, retained for the life of the pipeline.
Glossary and calculators
Thirty-five terms, from air lock to tracer gas, defined as a test crew uses them. The calculators carry the relations above, and the same arithmetic is available offline in the HydroTech Pocket Engineer application.