A gas transmission operator reported minor passing on two 12 inch ball bypass valves. Line pressure was 82 kg/cm², so both valves were serviced online in one mobilisation. Gas transmission continued without interruption, and the operator returned the service report signed.
Case study
12 inch ball valves serviced on a live gas trunk line at 82 kg/cm²
Two passing ball valves serviced in one visit, with gas flowing throughout.
The valves and their duty
A gas transmission operator reported minor passing on two 12 inch ball valves. Both worked as bypass valves at a sectionalising station.
The station sits on a live natural gas trunk line. Sectionalising stations divide a long pipeline into sections that can be isolated.
A passing bypass valve weakens the isolation that the station provides. Minor passing often shows first as noise or a downstream pressure change.
Signs like these indicate a problem, but they do not prove one. An approved seat test confirms the diagnosis before any treatment plan.
Site conditions
Line pressure was 82 kg/cm² at the time of the work.
The trunk line stayed in service, so every task ran online. Both valves were treated under full line pressure throughout.
Bypass pipework lets a station route gas around a closed mainline valve. The bypass valves must therefore seal as dependably as the mainline valve itself.
The intervention
The client supplied the full valve datasheet before mobilisation, down to station coordinates. Our engineer then serviced both valves in a single mobilisation. Live service of this kind follows a controlled routine, not a single injection.
- Confirm the valve type, its duty and the condition of the injection fittings.
- Inject controlled amounts of product within the equipment and fitting ratings.
- Watch the pressure response and stop work if it behaves abnormally.
- Record what each valve received and how it responded.
In-service treatment is not possible on every valve. The fittings, the valve design and operations approval must all permit it. Where a gate fails, the right answer is an assessment, not a forced injection.
One mobilisation covered both valves, so the station was visited only once.
The outcome and the record
Gas transmission continued without interruption throughout the work.
The operator reviewed the service report in detail and returned it signed. It checked closely enough to correct one recorded detail before signing. The signed report closed the visit as the client's own record.
Our gas transmission valve guide explains sectionalising valve duty in more depth. Browse more field results from live valve work.
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A documented before and after
Our post-job report recorded no passing under observation, and the operator accepted and paid.
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