pressure test objectives and acceptance...
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Pressure Test Objectives and Acceptance Criteria
Sheri Baucom
Director, Integrity Services
RCP Inc.
What’s a “good” pressure test?
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“ILI will detect any anomaly that would fail a hydrotest.”
- an ILI vendor who shall remain anonymous
Case Study 1
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Case Study #1
• Pipe specs: • 8-inch, Grade B, 0.188 wt. • Seam type: LF-ERW• 1950s vintage
• Goal: Re-establish MAOP at 400 psig; incomplete material records
• Test Details:• 8 hour test planned • Target test pressure: 765 • 26% SMYS• 113 feet of elevation change • ~1.55 miles, all 8-inch • Part of a much larger hydrotest project
Pressure Temperature
On Test 766 psig 66˚F
End Test 754 psig 68˚F
2 injects = 3.6 gallons
Calculated Loss 9.3 gallons
Allowable Loss 1.9 gallons
Case Study 1:PT Attempt #1
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Lost ~45 psi
Pressure Temperature
On Test 765 psig 65˚
End Test 762 psig 64˚
5 injects = 8.9 gallons
Calculated Loss 7.6 gallons
Allowable Loss 1.8 gallons
Case Study 2:PT Attempt #2
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Lost ~75 psi1˚F = 15 psi
Leaking manufacturing defect in long seam =A potentially hazardous leak
Strength Test
Leak Test
Leaking Defect ID’dBy Hydrotest
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Lessons Learned(from the Operator)
1. A pressure test may ID defects that are not ID’dby ILI.
2. Verifying the absence of leaks is required to meet the test objectives.
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• The objective: 1. Reestablish MAOP (incomplete material records) per
CFR requirement
2. Assess manufacturing defects i.e ensure there are no defects present that could leak or rupture in-service.
192.503: No person may operate a new segment of pipeline, or return to service a segment of pipeline that has been relocated or replaced, until…
Desired MAOP 400 psig
Design Pressure 1098 psig
Test Pressure 1.9*MAOP (70% SMYS)
Test Plan:
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192.503: Each potentially hazardous leak has been located and eliminated.
Test Plan:
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Establish MAOP
Meet CFR Leak
Requirement
Strength & Leak
Test
ID defects that may rupture
ID defects that may
leak
Strength & Leak
Test
Test Plan
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Test Parameters
Objective: Reestablish MAOP; Assess ERW-LF
Test Type Strength & Leak
Test Duration 8 hours
Strength Pressure ≥ 765 psig
Leak Calculated loss ≤ 2 gallons
Allowable Loss = Temperature Measurement Accuracy = 1˚F
If calculated loss < allowable loss, no potentially hazardous leaks.
API 1110
Disclaimer
• This is not to say hydrotesting is “better” than ILI or vice versa.
• (I <3 ILI. Plug for my talk tomorrow.)
• The point is… if you’re not analyzing your pressure test data (like you analyze your ILI data), you risk wasting all that time and $$.
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1 mile = $1 million
Pressure TestsCost $$$$
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1. Objective (establish MAOP, satisfy IMP, asses SCC)2. Test Subject (what are you testing?)3. Test Type (strength, leak, spike)4. Acceptance Criteria5. Test Parameters
Pressure Test Design
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Test Objective Test Subject Test Type Test Pressures1. (Re)Establish MAOP
MAOP ≥ 30% SMYS
Strength & Leak Test, 8 hours
CL TF*MAOP
2. (Re)Establish MAOP
Fabrication, MAOP ≥ 30% SMYS
Strength & Leak Test, 4 hours
CL TF*MAOP
1. Category 1 allows above-ground leak survey to assess for leaks2. CL TF = Class Location Test Factor
Every Code-required test requires proving the absence of leaks.
Test Parameters for Steel Gas Pipelines
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Test Objective Test Subject Test Type Test Pressures3. (Re)Establish MAOP
100 psi ≤ MAOP ≤ 30% SMYS
Strength & Leak1 ≥ 1 hour
2CL TF*MAOP
4. (Re)Establish MAOP
1 psi ≤ MAOP ≤100 psig
Leak test, duration TBD3
90 psig
5. (Re)Establish MAOP
MAOP ≤ 1 psig Leak test, duration TBD3
10 psig
1. If NG, inert gas or air is the TM AND TP>20% SMYS, a leak survey must occur during the PT
2. CL TF = Class Location Test Factor3. Duration defined by GPTC guide material
The test procedure used must ensure discovery of all potentially hazardous leaks in the segment being tested.
Test Parameters forSteel Gas Pipelines
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Test Parameters for Plastic Gas Pipelines
1. Duration defined by GPTC guide material
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Test Objective Test Subject Test Type Test Pressures6. (Re)Establish MAOP
Plastic Gas Pipeline
Leak test, duration TBD1
1.5*MAOP OR 50 PSI (whichever is greater)
The test procedure used must ensure discovery of all potentially hazardous leaks in the segment being tested.
Code-Required Test Types
Liquid Pipelines: A Strength & Leak test
• Strength Test (& Leak Survey)• Strength & Leak Test • Leak Test
Gas Pipelines:
Notice that every PT req’d by Code requires a leak
test…
• No ruptures or significant leaks occur that prevent the pressure from being maintained above the minimum
• Minimum usually defined by desired MAOP
Easy!
Time Pressure
SuccessfulStrength Test?
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1. Visual Inspection• If all pipe is visible
2. Leak survey • Only allowed for Cat. 1
and sometimes Cat. 3
3. Engineering Analysis• Prove any loss <
allowable loss
Time Pressure Temp. Volume
I repeat: Every Code-required test requires proving the absence of leaks.
SuccessfulLeak Test?
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• IMP Pressure Test = MAOP PT • Impending Gas Mega Rule
• Spike @100% SMYS or 1.5*MAOP + MAOP PT
• Cracking due to SCC or mfg: Spike + Strength + Leak
• Metal Loss: Strength + Leak
Integrity PressureTests
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“I just know it’s a good test.”- every testing contractor I’ve ever encountered
Case Study 2
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Bad Temp. Data
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Pressure Temperature
On Test 2023 psig 69˚F
End Test 2026 psig 85˚F
Calculated Loss = 500+ gallons
Increasing pressure doesn’t mean there aren’t any leaks!
1˚F = 25 psi (400 psi)
“I don’t have a good feeling about this one.”- person responsible for signing their name on the test when
they see appreciable pressure loss
Case Study 3
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• Pressure loss is acceptable • as long as it correlates with temperature loss
• is equivalent to a loss that is less than the allowable loss.
• We can prove this with scientific principles.
Temperature goes down, pressure goes down…
Pressure Temperature
On Test 100 psig 72˚F
End Test 85 psig 71˚F
Calculated Loss = 0.5 gal
Allowable Loss = 1 gal
Pressure-Temp. Correlation
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“Looks good!”- California State Fire Marshal Model
Case Study 4
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Not all modelswork well…
CSFM*ALLOWABLE LOSS
RCP MODEL ALLOWABLE LOSS
PREDICTED LOSS PREDICTED LEAK SIZE
PREDICTED LEAK RATE
10.47 GALLONS 0.30 GALLONS 0.54 GALLONS 0.0025 IN DIAMETER
0.23 GAL/HR
* CSFM = CALIFORNIA STATE FIRE MARSHAL
Time 0 hours 409 psig Pipe Temp 64oFTime 8 hours 327 psig Pipe Temp 63.5oF
“I certify that no leaks exist on this meter station.”- Licensed PE working with an engineering firm that shall not
be named…
Case Study 5
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How was thiscertified?
Pressure Temperature
On Test 1820 psig 79˚
End Test 1814 psig 82˚
Found multiple leaks!!
• “The P-V plot proves there aren’t any leaks.”
• P-V plots can:• Indicate yielding of
pipe• % of air entrapped• Correct P-V ratio• Pump efficiency…
Pressure-Volume Plots
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“The test is deemed acceptable if there is no evidence of leaks.”
• What about when the pipe is buried?
• What about when the pipe is laying on the ground?
Ineffective Acceptance Criteria
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“If the pressure drops below minimum specified, the test segment shall be re-pressurized and the test duration requirement be restarted.”
• So if you have a leak, as long as you keep re-injecting to keep the pressure above minimum, the test is acceptable?
Ineffective AcceptanceCriteria
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“It’s okay to have some leaks, right?”- ….
Engineering Analysis
Consequence of Not
$<1% $100k+++
What is your risk tolerance? What constitutes a failure?
Define “Hazardous”
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If we can show calculated loss is less than allowable, we can
prove there are no “potentially hazardous leaks.”
Summary
Engineering Standard• Objective• Acceptance Criteria
• If pipe is buried• If all pipe exposed
Confirm (in real time)• Test meets Acceptance Criteria• Otherwise, repair/adjust and repeat the test.
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Questions for you!
• What’s a “good” pressure test?
• One that meets the acceptance criteria!
• What’s your company’s acceptance criteria?
• Ensure you have a leak requirement!
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