Pipeline Hydrostatic Testing – Gas

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.

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)}

Where:
𝑃 − Test Pressure (psi
𝐹_𝑤𝑝 − Water Compressibility due to Increase of Pressure

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

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

𝐹_𝑝𝑝 − Volume Change due to Increase of Pressure
𝐷 − Pipe Diameter (in)
𝑊𝑡 − Pipe Wall Thickness (in)
𝑃 − Test Pressure (psi)
𝑇₁ − Test Temperature (°F)

F_{pt}=1+(18.2\times10^{-6})(T_1-60)

F_{pt}=1+(18.2\times10^{-6})(T_1-60)

𝐹_𝑝𝑡 −Volume Change due to Temperature Change

F_{pwt} = \frac{F_{pt}}{F_{wt}}

F_{pwt} = \frac{F_{pt}}{F_{wt}}

𝐹_𝑝𝑤𝑡 − Volume Change Ratio Pipe/Water
𝐹_𝑤𝑡 − 𝑤𝑡 Factor Lookup Table

v=0.0408(D-2Wt)^2L

v=0.0408(D-2Wt)^2L

𝑣 − Pipe Fill Volume (gal)
𝐿 − Pipe Length (mi)

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

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

𝑉_𝑡𝑝 − Volume Required for Hydro Testing (gal)
𝑉_𝑖 − Incremental Volume Required for Hydro Testing (gal)

V_i = V_{tp} – v \~\ t = \left(\frac{5}{9}\right)(T_1 + 40) – 40 \~\ Dp_1 = \frac{(B – 2A)}{\bigg(\frac{D(1 – ni^2)}{EWt} +{C_1}\bigg)} \quad Dp_2 = \frac{(B – 2A)}{\bigg(\frac{D(1 – ni^2)}{EWt} +{C_2}\bigg)} \~\ dp_1 = \frac{Dp_1}{\left(\frac{9}{5}\right)(1 + 40) – 40} \quad dp_2 = \frac{Dp_2}{\left(\frac{9}{5}\right)(1 + 40) – 40}

V_i = V_{tp} - v \\~\\ t = \left(\frac{5}{9}\right)(T_1 + 40) - 40 \\~\\ Dp_1 = \frac{(B - 2A)}{\bigg(\frac{D(1 - ni^2)}{EWt} +{C_1}\bigg)} \quad Dp_2 = \frac{(B - 2A)}{\bigg(\frac{D(1 - ni^2)}{EWt} +{C_2}\bigg)} \\~\\ dp_1 = \frac{Dp_1}{\left(\frac{9}{5}\right)(1 + 40) - 40} \quad dp_2 = \frac{Dp_2}{\left(\frac{9}{5}\right)(1 + 40) - 40}

𝐶₁ − Compressibility Factor for Water (3rd degree poly fit)(in³/in³/gal)
𝐶₂ − Compressibility Factor for Water (5th degree poly fit)(in³/in³/gal)
𝑑_𝑝1 − Pressure Change (3rd degree poly fit)(psi/℉)
𝑑_𝑝2 − Pressure Change (5th degree poly fit)(psi/℉)
𝐸 − Modulus of Elasticity
𝑡 − Test Temperature (℉)
𝑛𝑖 − Poisson′s Ratio (ni = 0.3)
𝐴 − Coefficient of Thermal Expansion of Pipe Material (1/℉)

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