Field Verification Practices for Gas Pipeline Emergency Isolation Valves

Seat

Pipeline emergency isolation valves rely on internal mechanical barriers to establish total fluid containment during unexpected system ruptures. In high-pressure natural gas transmission lines operating above fifty bar, these valves must hold full line pressure with absolute shutoff to prevent catastrophe downstream. How the sealing interface is configured determines how the valve behaves when closed against full differential pressure.

Emergency isolation valves ~ typically deployed as main line block valves or station entrance isolation units ~ use either elastomeric soft inserts or fine-lapped metal-to-metal seating faces. Soft-seated ball valves incorporate materials like polyether ether ketone or Devlon set into heavy stainless steel seat rings. Under low differential conditions, these inserts deform plastically against the polished chrome or tungsten carbide ball surface to seal off gas micro-passages.

Metal-to-metal seats rely on hard-faced coatings applied via high-velocity oxygen fuel spraying, ground to mirror finishes to withstand particulate abrasion and severe thermal loads.

Isolation configurations follow distinct mechanical classifications defined in API 6D and ISO 14313. Double Block and Bleed (DBB) arrangements use two seating surfaces, each sealing against pressure from its respective end of the valve when closed. A central cavity vent lets operators bleed trapped fluid between the seats to confirm complete isolation.

Double Isolation and Bleed (DIB) designs feature seats that seal independently against differential pressure from either the pipeline or the internal body space. DIB-1 designs use two double-piston-effect seats, which require an external cavity relief valve to vent pressure spikes caused by thermal expansion of trapped fluid. DIB-2 designs combine a single-piston-effect upstream seat with a double-piston-effect downstream seat, offering auto-relieving capability back into the upstream line while maintaining a secondary barrier.

Field verification procedures must account for these topographies; testing a DIB valve with DBB procedures leads directly to false leakage diagnoses.

Mechanical Isolation Topologies in High Pressure Gas Pipelines

Upstream seat rings in trunnion-mounted ball valves take heavy mechanical loads during emergency shutdowns. When a valve closes against an active gas column, line pressure drives the floating seat ring against the ball face. The net sealing force depends entirely on the effective piston area behind the seat ring.

Single-piston-effect rings rely on line pressure acting on the outer circumference to push the ring inward toward the ball. Cavity pressure works in opposition, unseating the ring if body cavity pressure exceeds line pressure. Double-piston-effect seats reverse this balance: cavity pressure acts on a larger annular area than line pressure does, forcing the seat ring tighter against the ball regardless of where the pressure originates.

Consistent diagnostic signatures appear across double block and bleed installations operating above sixty bar. Field technicians often misinterpret seat ring behavior during routine cavity venting. When an operator opens the body bleed on a closed DBB valve, line pressure behind the upstream seat forces it against the ball to form a seal, while gas in the body cavity vents to atmosphere.

If the bleed valve continues to vent steadily without pressure decaying, one or both seat faces are passing gas. Isolating which seat is leaking requires sequential differential testing using dedicated cavity isolation techniques.

API 6D Annex B mandates that operational seat integrity testing for gas service valves operating above ASME Class 600 extends to a minimum thirty-minute duration under full differential pressure to accurately capture subtle seal bypass.

Soft insert material selection dictates both field verification frequency and long-term sealing reliability. Elastomeric inserts deliver zero-leakage performance during factory hydrostatic acceptance tests, but they degrade in active service. Rapid gas decompression events tear soft materials when high-pressure gas absorbed into the polymer matrix expands faster than it can diffuse out.

The resulting decompression blisters ruin the seal geometry, creating leak paths that seat sealant injection cannot fix. In raw gas streams, particulates such as mill scale, sand, and hydrates score soft inserts during closure. Metal-to-metal seats eliminate decompression blistering and resist particulate erosion, though they demand higher seat contact stress to achieve tight isolation.

Verification routines must evaluate seal face condition without inducing unnecessary seat wear.

Soft Insert Degradation and Seat Ring Mechanics

Emergency isolation valves in sour or wet gas service face chemical attack alongside mechanical wear. Hydrogen sulfide and carbon dioxide degrade elastomeric elements, causing swelling, hardening, or loss of resilience. Swollen inserts increase breakaway torque during emergency closing and prevent seat rings from floating freely.

When seat springs cannot hold the ring flat against the ball face, low-pressure sealing fails completely. Field inspectors verify seat ring mobility by tracking cavity pressure buildup rates during controlled baseline venting.

Seat injection systems supply heavy synthetic grease directly to the seating interface through internal ports. Operators often inject emergency sealant to temporarily stop seat leakage during field compliance audits. Heavy grease seals over scored inserts and masks damaged metal faces long enough to pass a differential pressure test, but this compromises safety function.

Active gas flow flushes sealant out of the interface within hours of returning the valve to service, leaving the underlying defect unaddressed. Standard verification protocols require that all seat integrity tests occur prior to any sealant injection, or after thoroughly flushing the seat cavity.

Double Block and Bleed versus Double Isolation Dynamics

Field verification procedures must reflect the mechanical differences between double block and double isolation configurations. Testing a DIB-1 valve requires applying differential pressure from both directions independently while monitoring the body cavity vent. Because both seats use double-piston mechanics, line pressure from either side seals the valve against the body cavity.

A leak in a DIB-1 valve indicates failure of both seating faces or damaged seat ring O-rings. Testing a DIB-2 valve requires pressurizing the upstream side to test the single-piston seat, followed by body cavity pressurization to verify the secondary double-piston downstream seat.

The performance of these seating systems largely dictates ongoing maintenance overhead on pipeline emergency isolation systems. Soft-seated valves carry lower initial purchase costs but require frequent field validation due to insert wear. Hard-faced metal seats require tighter precision during testing but preserve baseline isolation over thousands of cycles.

Table 1 details the operational trade-offs and verification requirements across standard API 6D seating configurations.

Procurement specifications for emergency isolation valve seats must state exact contractual acceptance criteria. Leaving seating topologies loosely defined leaves operators vulnerable to improper installation. Specifying API 6D Annex B clause 3 shifts field acceptance from simple factory hydrostatic tests to mandatory thirty-minute operational seat integrity validation under actual line gas pressure, preventing premature field failures.

Torque

Mechanical energy transferred from an actuator to a valve stem must overcome static friction, packing drag, and dynamic hydrodynamic loads. Emergency isolation valves frequently remain fully open for months or years without cycling. During this static dormancy, stem packing consolidates, seat rings bed into ball coatings, and particulate settles into stem journals.

As a result, break-out forces required to start movement can reach two to three times the factory baseline. Field verification of these valves requires measuring dynamic force profiles during travel routines to ensure actuator torque preserves an adequate margin over required seating forces.

Scotch-yoke actuators, whether pneumatic or gas-over-oil, deliver variable torque across their stroke. Output peaks at breakaway (zero degrees rotation), drops to a minimum at mid-stroke (forty-five degrees), and rises again at full closure (ninety degrees). This profile mirrors the torque demand of a trunnion-mounted ball valve, which requires maximum force at break-out to unseat the ball and at closure to seat against full differential pressure.

Testing routines must assess dynamic force generation across the entire stroke to catch mechanical binding before a valve seizes entirely.

Dynamic Stem Force Profiles and Diagnostic Curve Analysis

Automated partial stroke testing (PST) provides non-disruptive field verification of emergency isolation valve movement. By cycling the stem through five to fifteen percent of its stroke, operators confirm that the actuator, stem connection, and internal trim move freely. High-speed electronic sensors track pneumatic cylinder pressure while optical encoders log stem position.

The resulting data produces a dynamic force profile of applied force against travel percentage. Deviations from the baseline factory signature highlight developing mechanical faults within the assembly.

Dynamic force profiles expose mechanical anomalies well before complete actuator failure. A sudden step-change in required break-out force points to packing consolidation or dry stem threads, whereas a gradual rise in running torque over the first five percent of travel indicates scale buildup within the seat ring clearance gap. Diagnostic comparisons must be normalized against current line differential pressure, since fluid loading directly increases stem thrust through trunnion friction.

A twenty percent increase in breakaway stem force during partial stroke verification signals severe seat binding before gross acoustic leakage develops.

Gathering diagnostic signatures from automated or manual emergency isolation valve actuators requires calibrated instrumentation and strict adherence to test sequence steps.

1. Connect transient pressure transducers to actuator power ports while mounting an optical position encoder directly to the valve stem extension.
2. Trigger a controlled five-to-ten percent stem displacement command via the digital valve controller using steady supply pressure.
3. Log differential cylinder pressure and real-time stem angular position at a sampling frequency of at least one hundred Hertz.
4. Calculate dynamic torque by multiplying differential pressure across the actuator piston area by the scotch-yoke moment arm length.
5. Compare the calculated breakaway and running values against baseline commissioning signatures stored in the field registry.

Partial Stroke Testing Bounds and Field Verification Frequency

Partial stroke testing on active gas transmission lines must remain strictly bounded to avoid operational upsets. Cycling an emergency isolation valve beyond fifteen percent stroke creates flow restriction and pressure waves that can trip downstream compressor stations. Restricting travel to between five and eight percent proves mechanical mobility, checks position transmitter calibration, and confirms solenoid air discharge without choking gas flow.

Verification intervals typically run quarterly or semi-annually, based on process criticality and regulatory requirements.

Actuator sizing calculations must apply safety margins that account for operational degradation. Standard engineering specifications call for an actuator torque margin of at least one point five times the valve’s maximum required break-out torque under worst-case differential pressure. In severe operating environments, including high-temperature or sour service, this margin rises to two point zero.

If diagnostics show the available actuator margin dropping below one point two, maintenance is required immediately ~ whether packing adjustment, stem lubrication, or actuator seal replacement.

Actuator Output Margins under Asymmetric Differential

Asymmetric pressure across a closed emergency valve substantially increases the force needed to reopen it. When full line pressure bears on one side of a closed ball while the downstream side sits at atmospheric pressure, the ball is thrust hard against the downstream trunnion bearing. This increases journal bearing friction, demanding higher break-out torque from the actuator during reopening.

Diagnostic evaluations must account for line differential pressure so that differential friction is not misdiagnosed as mechanical failure.

Dynamic force curves are evaluated by overlaying real-time diagnostic traces onto factory acceptance baseline data. Shifts in curve shape help field engineers separate stem packing friction from internal seat ring galling. Packing friction produces a continuous offset across the entire travel arc, while seat binding causes sharp spikes at break-out and at the closing limits.

Cataloging these variations systematically supports predictive maintenance scheduling ahead of mandatory shutdown windows.

Elevated breakaway forces measured during partial stroke testing are sometimes attributed to temporary packing relaxation or ambient temperature swings to defer physical inspections when diagnostic curves show abnormal friction spikes. However, unverified torque increases remain reliable precursors to total valve seizure during emergency shutdowns.

Acoustics

High-frequency elastic wave detection provides a non-invasive way to detect internal gas bypass across closed valve seats. When high-pressure gas forces its way through micro-gaps between a damaged seat insert and the ball, the resulting pressure drop and rapid expansion generate turbulent jet noise across a broad frequency spectrum. Low-frequency signals disperse into the fluid column, but high-frequency structure-borne ultrasonic waves travel directly through the metal body walls.

Acoustic emission monitoring captures these waves using external piezoelectric sensors mounted on the valve body.

Acoustic verification operates in the ultrasonic band between thirty kilohertz and five hundred kilohertz. Working above the audible range filters out background pipeline noise, including compressor vibration, line turbulence, and mechanical impacts. Because structure-borne acoustic energy attenuates rapidly across metal interfaces, heavy wall castings, and bolted flanges, transducers must be placed directly on the valve body casting near the internal seat rings for reliable signal acquisition and leak rate estimation.

High Frequency Structure Borne Ultrasonic Signal Paths

Piezoelectric sensors mounted on the outer valve body convert elastic stress waves into electrical signals. Field amplifiers filter the raw input, using root-mean-square processing to calculate mean signal strength in decibels acoustic emission (dB AE). Peak detection algorithms record transient spikes caused by particulate impacts or seat shifting.

An intact, tight valve seat generates a steady baseline signal near ambient electronic noise ~ typically below twenty-five decibels acoustic emission. An active leak elevates baseline energy into the forty-to-eighty decibel range, scaling with leak size and differential pressure.

Signal attenuation depends on body wall thickness, material density, and sensor placement. A transducer mounted ten centimeters from the seat ring records clear, high-amplitude leak signatures. Moving that sensor fifty centimeters away onto adjacent pipe spools drops signal amplitude by up to twenty decibels from geometric spreading and material damping.

Inspectors rely on acoustic couplants and magnetic clamps to ensure consistent, low-loss coupling between the sensor face and the prepared valve body surface.

When Does Acoustic Emission Measurement Outperform Pressure Decay?

Acoustic emission monitoring holds clear advantages over differential pressure decay testing under specific field conditions. On large-diameter, high-pressure gas lines, filling or venting large cavities for pressure-hold tests takes hours and vents methane. Acoustic verification requires no cavity venting, delivering real-time leak detection on fully pressurized, online valves within minutes of mounting sensors.

The technique readily identifies small micro-leaks that sit below the resolution threshold of pressure decay gauges in large body cavities.

Thermal swings introduce significant error into pressure decay calculations. Solar heating of an exposed valve body raises cavity gas temperature, causing pressure to rise and masking a slow leak. Acoustic emission sensors measure turbulent fluid kinetic energy directly, remaining unaffected by ambient temperature changes or slow thermal equalization through heavy steel bodies.

In double-seated valves, acoustic monitoring can also isolate which seat is passing by placing sensors adjacent to both upstream and downstream seats simultaneously.

Acoustic processing algorithms use empirical correlations to translate measured sound intensity into volumetric gas leak rates. Table 2 details the relationship between measured structure-borne decibels, differential pressure, and calculated standard gas leakage rates across typical pipeline valve sizes.

Operational background noise can contaminate acoustic field data. Upstream control valves, pressure regulators, and internal line pigging generate broadband noise that propagates along the pipe wall to the test valve. Field engineers filter out this interference using differential acoustic mapping.

By placing reference sensors on adjacent spools upstream and downstream of the valve and subtracting those readings from the valve body signal, they isolate internal seat leakage from external line noise.

Direct contact between the piezoelectric transducer and the valve body casting ensures clean high-frequency transmission, whereas isolated flange bolts attenuate critical leak frequencies.

Because acoustic signal attenuation climbs steeply above one hundred kilohertz, keeping sensors close to the internal seat faces remains the critical factor in diagnostic accuracy.

Pressure

Field verification of emergency isolation barriers relies heavily on tracking fluid accumulation or loss within isolated cavities over time. Differential pressure decay testing is the standard field validation method for isolation integrity. A valid pressure hold test requires isolating the body cavity, venting pressure down to a safe baseline, closing the vent, and recording cavity pressure with high-accuracy digital loggers.

The resulting pressure-versus-time trace determines compliance with standards such as ISO 5208 and API 598.

Thermal stability inside the test cavity directly affects measurement accuracy. Natural gas behaves as a compressible gas where pressure tracks temperature. In heavy-walled steel valve castings, thermal equilibrium among line gas, the valve body, and ambient air can take hours.

A small drop in ambient temperature cools the cavity gas, producing a pressure drop that mimics seat leakage. Conversely, direct sun on an exposed valve body warms the cavity, causing pressure to rise and masking an active leak. Reliable testing protocols require continuous ambient and valve skin temperature logging so compensation factors can be applied to raw decay curves.

Thermally Induced Variances in Closed Cavity Hold Tests

Calculating thermally corrected pressure decay requires high-frequency temperature logging throughout the hold period. Thermodynamically, a temperature shift of one degree Celsius changes cavity pressure by roughly zero point three percent at seventy bar line pressure in a static volume. In a fifty-liter body cavity, a temperature drop of half a degree Celsius lowers pressure by more than one hundred millibar, easily exceeding standard allowable leakage limits.

Field testing must allow sufficient thermal stabilization time before starting the official hold clock.

Non-intrusive ultrasonic screening is recommended before venting the body cavity. Venting high-pressure gas creates localized cooling through Joule-Thomson expansion. Depressurizing a body cavity quickly can drop internal gas temperature by tens of degrees Celsius, causing severe thermal instability.

Starting a pressure decay test immediately after rapid depressurization generates invalid data driven by thermal recovery rather than seat performance.

Differential Bleed Verification for Double Isolation

Bleed-off test procedures must align with the seating mechanics of the valve assembly. For double block and bleed valves, testing requires closing the main valve, venting cavity pressure to zero, and monitoring for pressure buildup over the test interval. If cavity pressure stays at zero, both seats are holding.

If pressure climbs, at least one seat is leaking line gas into the cavity. Isolating the passing seat requires pressurizing the cavity, closing the bleed valve, and observing whether pressure climbs toward upstream line pressure or bleeds down toward downstream pressure.

For double isolation and bleed (DIB-1) valves, verifying both seats requires pressurizing the body cavity through an external test port above line pressure. Technicians monitor cavity pressure decay over a thirty-minute hold. A pressure drop indicates fluid escaping past either the upstream or downstream double-piston seat ring into the line.

DIB verification protocols require digital deadweight testers sensitive enough to detect pressure changes as small as one millibar at full test pressure.

Field inspectors frequently encounter several common failure modes during differential pressure evaluations:

• Thermal transient confusion occurs when ambient temperature drops collapse cavity gas volume and mimic seat bypass during hold intervals.
• Body vent line clogging creates false positive seal verification readings by trapping gas inside the bleed manifold during differential testing routines.
• Incomplete cavity depressurization leaves compressed gas behind the upstream seat ring, masking downstream seal failure during double block testing routines.
• Grease packing masking temporarily stops seat leakage during field testing while operational gas flow flushes emergency sealant out during active service.

Low Pressure Gas Bubble Testing versus High Pressure Differential Decay

Low-pressure gas bubble testing offers a sensitive visual method for checking seat leakage on depressurized lines during plant turnarounds. Technicians apply low pressure ~ typically four to seven bar of air or nitrogen ~ to one side of the closed valve while monitoring the opposite side or body bleed with a bubble film or liquid displacement manometer. Measuring the bubble rate or displaced fluid volume gives leak rate resolution down to fractions of a milliliter per minute.

This low-pressure check detects micro-paths that high line pressure might temporarily squeeze shut against soft inserts.

High-pressure differential decay testing remains necessary for operational validation because soft inserts and metal seats behave differently under full line loads. A seat that holds tight at five bar can suffer structural ring deflection at eighty bar, opening a leak path past the outer O-ring. Thorough field verification tests across both low and maximum operating differentials to confirm sealing across the entire operating envelope.

Table 3 outlines ISO 5208 leakage classes and their field equivalents.

Failing to meet ISO 5208 Rate A leakage acceptance criteria during field acceptance testing invalidates safety integrity level verification calculations for the entire isolation loop.

Misinterpreting thermal pressure decay as seat bypass triggers unnecessary pipeline depressurization, eroding operating margins and causing substantial unrecoverable venting losses.

Proof

Functional safety compliance in natural gas transmission relies on validating safety instrumented functions under realistic field conditions. Emergency isolation valves serve as final elements in pipeline loops designed to shut off gas during line breaks, overpressure events, or facility fires. Regulators like the U.S. Department of Transportation Pipeline and Hazardous Materials Safety Administration require documented proof that these systems will operate on demand.

Achieving compliance involves physical field testing paired with probabilistic safety analysis under IEC 61508 and IEC 61511.

Safety calculations quantify system reliability through average Probability of Failure on Demand (PFDavg). A valve’s PFDavg depends on its dangerous undetected failure rate, proof test coverage, and the test interval. An emergency valve left unexercised in a line for years accumulates a high failure probability from mechanical binding, stem galling, or seat deterioration.

Periodic field verification resets this failure probability, keeping the safety loop within its certified Safety Integrity Level (SIL) rating.

Safety Integrity Level Calculations and Field Verification Frequency

Calculating the SIL rating of an emergency isolation loop requires accurate data on proof test thoroughness. Full-stroke proof testing, where the valve closes completely against full differential pressure, provides one hundred percent test coverage by verifying break-out force, full travel, and tight shutoff. However, full-stroke testing requires shutting down or bypassing the line, introducing major operational costs.

Partial stroke testing delivers partial coverage ~ typically sixty to seventy percent ~ by verifying mechanical movement without disrupting gas flow.

Automated partial stroke testing routines on scotch-yoke pneumatic actuators yield an average diagnostic coverage factor of seventy percent. Combining regular partial stroke testing with extended full-stroke proof test intervals lets operators maintain required SIL 2 or SIL 3 ratings while stretching full shutdown test intervals from annually to once every three to five years. The allowable extension depends directly on diagnostic coverage and field data quality.

Diagnostic Coverage Metrics for Automated Emergency Isolation

Verification records must stand up to regulatory scrutiny. Missing diagnostic logs, uncalibrated test gauges, or incomplete partial stroke records routinely lead to audit findings and mandatory operating pressure reductions. A compliant verification dossier contains structured engineering data collected during factory acceptance, site commissioning, and routine operations.

Pipeline compliance teams retain specific historical operational records to satisfy audit mandates:

• Baseline torque signatures recorded during initial factory hydrostatic testing and field site commissioning routines.
• Calibration certificates for digital pressure transducers, acoustic emission sensors, and deadweight testers used during logging.
• Partial stroke event logs detailing automated execution dates, stem travel percentages, and dynamic pressure profiles.
• Body cavity vent logs recording fluid discharge volumes, liquid hydrocarbon presence, and acoustic emission levels.

Regulatory Compliance Dossiers and Audit Trails

Modern proof testing relies on digital valve controllers mounted directly to the actuator manifold. These microprocessor-based units run automated partial stroke tests, capture high-frequency pressure and position data, and compute dynamic break-out torque. Built-in diagnostics track pneumatic pressure decay, solenoid coil health, and valve travel hysteresis, flagging developing faults over HART or Modbus before a failure occurs on demand.

Linking smart valve controllers to enterprise asset management platforms establishes an automated compliance audit trail. Digital records eliminate manual transcription errors and provide verifiable evidence of safety system testing. When diagnostics reveal abnormal torque spikes or seat leakage, the system flags the valve for targeted maintenance during the next scheduled outage, heading off unexpected failures.

Whether automated partial stroke testing can eventually replace full-stroke hydrostatic isolation tests under evolving international standards remains an open question across the pipeline industry.

Margin

Financial risk management across gas transmission infrastructure hinges on balancing diagnostic capital expenditures against the severe cost of unplanned downtime. An unscheduled line shutdown caused by a stuck emergency isolation valve or passing seat costs operators millions of dollars per day in lost throughput, supply penalties, and emergency call-out fees. Structured field verification protects operating margins by shifting emergency repairs into planned maintenance events.

Capital invested in non-intrusive diagnostic tools pays for itself quickly by eliminating unnecessary line depressurizations. A single blowdown on a thirty-six-inch transmission line vents hundreds of thousands of dollars in gas while creating major carbon regulatory liabilities. Acoustic emission testing and automated partial stroke testing verify seat integrity and mechanical health without venting gas, protecting operating revenue while meeting environmental targets.

Commercial Exposure of Unscheduled Pipeline Shutdowns

Evaluating total cost of ownership for isolation assets requires looking at upfront purchase price alongside lifetime verification costs. Inexpensive valves fitted with soft inserts and basic manual actuators look economical during project buildout, but they generate high life-cycle costs through frequent seat failures, high packing friction, and labor-heavy manual testing. High-spec valves with hard-faced metal seats, redundant stem packing, and smart diagnostic controllers cost more initially but deliver significantly lower operating expense across a thirty-year service life.

Advanced diagnostic testing extends service life by identifying worn components before major structural castings suffer damage. Catching insert degradation early lets technicians replace inexpensive seat rings during scheduled turnarounds, protecting the mirror-polished ball. Deferring verification to hit short-term budget targets leads directly to accelerated valve wear and emergency capital replacements.

Capital Allocation for Non Intrusive Online Diagnostics

Gas transmission contracts contain strict delivery commitments backed by heavy non-performance penalties. If a leaking emergency valve prevents isolating a downstream pipe section during maintenance, operators must either delay the work or blow down upstream segments, triggering supply penalties. Confirming valve isolation with proven field methods prior to starting line work protects both maintenance safety and commercial obligations.

Capital allocation for field diagnostics should reflect the risk-weighted failure probability of each isolation loop. Permanently mounting acoustic sensors and smart positioners on critical, remote station entrance valves mitigates severe environmental, safety, and financial risks. Operating margins benefit when empirical diagnostic data drives maintenance, replacing arbitrary calendar-based overhauls with targeted interventions.

Field verification costs pale in comparison to the financial losses incurred during an un-programmed pipeline shutdown caused by a stuck emergency isolation valve.

Risk-weighted capital models weigh diagnostic hardware costs against expected downtime losses. Equipping critical emergency block valves with non-intrusive ultrasonic arrays and automated partial stroke controllers cuts unexpected isolation failure rates by over eighty percent, protecting long-term pipeline operating margins.