Pipeline Hydrostatic Testing – Liquid

Introduction

Hydrostatic testing is a method to determine strength, expose defects, expose leak & validate integrity of the vessel. Typically, tests are conducted at 125% of MAOP.

These tests are limited to defects that are ready for failure such as cracks. The test pressure must be adjusted for the related allowable stress at the design temperature. This requires adjustments during the testing phase due to ambient temperature conditions.

Volume of Water required to Fill Test Section

V=0.0408d^2L

V=0.0408d^2L

Where:
𝑉 − Volume of Water to Fill Test Section (gal)
𝑑 − Inside Pipe Diameter (in)
𝐿 − Length of the Test Section (ft)

Volume of Water required at Test Pressure

V_{tp}=VF_{wp}F_{pp}F_{pwt}

V_{tp}=VF_{wp}F_{pp}F_{pwt}

Where:
𝑉_𝑡𝑝 − Volume of Water at Test Pressure and Test Temperature (gal)
𝐹_𝑤𝑝 − Correction Factor for the Compressibility of Water due to Inc of Pressure from 0 psi to Test Pressure
𝐹_𝑝𝑝 − Correction Factor for Volume Change in Pipeline due to Increase of Pressure
𝐹_𝑝𝑤𝑡 − Correction Factor for the Change of Pipe and Water Volume due to Temperature Change from Base to Test Temperature

F_{wp} = \frac{1}{1 – \left(4.5 \times 10^{-5}\right) \left(\frac{P}{14.73}\right)}

F_{wp} = \frac{1}{1 - \left(4.5 \times 10^{-5}\right) \left(\frac{P}{14.73}\right)}

𝑃 − Test Pressure (psi)

F_{pp} = 1 + \left[ \left(\frac{D}{\left(Wt\right)}\right) \left(\frac{0.91P}{30 \times 10^6} \right)\right] + \left[(3.68 \times 10^{-6} )(T_1 – 60)\right]

F_{pp} = 1 + \left[ \left(\frac{D}{\left(Wt\right)}\right) \left(\frac{0.91P}{30 \times 10^6} \right)\right] + \left[(3.68 \times 10^{-6} )(T_1 - 60)\right]

𝐷 − Pipe Outside Diameter (in)
𝑊𝑡 − Pipe Wall Thickness (in)
𝑃 − Test Pressure (psi)
𝑇1 − Test Temperature (°F)

F_{pt} = 1 + (18.2 \times 10^{-6})(T_1- 60 ) \~\ F_{pwt} = \frac{F_{pt}}{F_{wt}}

F_{pt} = 1 + (18.2 \times 10^{-6})(T_1- 60 )  \\~\\  F_{pwt} = \frac{F_{pt}}{F_{wt}}

𝐹_𝑤𝑡 − Correction Factor for Thermal Change in Specific Water Volume from 60℉ to Test Water Temperature

\Delta P = \frac{(B – 2a)}{\frac{D(1 – \nu^2)}{Et} + C} \~\ B \times 10^6 = -64.268 + 17.0105T – 0.20369T^2 + 0.0016048^3

\Delta P = \frac{(B - 2a)}{\frac{D(1 - \nu^2)}{Et} + C} \\~\\ B \times 10^6 = -64.268 + 17.0105T - 0.20369T^2 + 0.0016048^3

Δ𝑃 − Pressure Change (psi/℃)
𝐵 − Coefficient of Expansion of Water
𝐷 − Pipe Outside Diameter (in)
𝐸 − Modulus of Elasticity for Steel 30×106 (psi)
𝑣 − Poisson′s Ratio
𝐶 − Compressibility Factor for Water
𝑎 − Coefficient of Expansion for Steel 1.116×10−5/℃
𝑡 − Pipe Wall Thickness (in)
𝑇 − Temperature (℃)

Case Guide

Part 1: Create Case

Input Parameters

• Nominal Pipe Size (in) : (0.625” – 48”)
• Outside Diameter (in)
• Wall Thickness (in) : (0.068”- >2”)
• Pipe Grade
• Internal Diameter (in)
• Pipeline Length (miles)
• Test Temperature (°F)
• Test Pressure (psig)

Part 2: Outputs/Reports

Results

• Water Compressibility due to Increase of Pressure
• Volume Change due to Increase of Pressure
• Volume Change due to Temperature Change
• Volume Change Ratio Pipe/Water
• Pipeline Fill Volume (gal)
• Volume Required for Hydrotesting (gal)
• Incremental Volume Required for Hydrotesting (gal)
• Compressibility Factor for Water (3rd Degree Poly fit) (in³/in³/psig) x10-6
• Compressibility Factor for Water (5th Degree Poly fit) (in³/in³/psig) x10-6
• Pressure Change (3rd Degree Poly fit) (psi/°F)
• Pressure Change (5th Degree Poly fit) (psi/°F).

References

• Pipeline Design for Hydrocarbons Gases and Liquids, Committee of pipeline planning, American Association of Civil Engineers, 1975
• Engineering Data Book, Volume II, Gas Processor Association, Revised Tenth Edition, 1994
• Pipeline Design & Construction, A Practical Approach, American Society of Mechanical Engineers, 2000

FAQ