Instrumentation for Pipelines |
(返回上一页) |
By far the main risk to pipelines is from landslides. These sudden, short-lived
geomorphic events that involve the rapid-to-slow descent of soil or rock
in sloping terrains occur worldwide, often in conjunction with natural hazards
like earthquakes, floods, or volcanic eruptions. Landslides can also be
caused by excessive precipitation or human activities, such as deforestation
or development, that disturb natural slope stability.
Historically, most pipeline operators have responded to landslide hazards
only after a failure occurs or a potential failure is imminent. Given the
relatively infrequent occurrence of landslide-induced pipe ruptures, this
is understandable. But the financial, political, environmental, social and
legal costs of pipe failures are skyrocketing. A landslide hazard assessment
of a pipeline corridor is quite cost effective in view of the huge costs
associated with a spill response.
A landslide hazard assessment can occur in two or more phases and involves
close coordination with the pipeline operator. In general, the evaluation
includes the following:
- Review of general pipeline geology and topography.
- Interviews with pipeline operators to identify known areas of landslide
activity or past pipe repair.
- Aerial examination of the pipeline alignment by a trained geologist.
This often can be done in conjunction with the pilot who normally conducts
the surveillance over-flights.
- Helicopter reconnaissance is recommended for heavily forested terrain.
- Interpretation of stereographic aerial photographs of potential hazard
areas.
- Detailed field examination of identified hazard features.
- Hazard ranking and prioritisation of future actions.
- Training of operator field personnel in the recognition and understanding
of landslide hazards.
Monitoring System
Once a landslide hazard assessment has been conducted it is recommended
that a monitoring system is implemented to keep track of the forces acting
on the pipeline so that failure can be avoided by putting into place remedial
works.
This monitoring system would be a combination of various sensors that
would take into account each of the parameters under investigation. Experience
has shown that for the best possible system a combination of sensors should
be used. These include Vibrating Wire Strain Gauges
to monitor the actual stresses in the pipeline itself, In-place
Inclinometers to monitor the rate of movement of the landslide, Vibrating
Wire Piezometers to measure any changes in the pore water pressure
which may pre-empt a possible failure and Rain Gauges
to monitor the relationship between rainfall, pore pressure changes, the
movement of the landslide and the subsequent effect on the pipeline itself.
These instruments should be linked to a datalogging system with communication
via telemetry, fibreoptic cable or other means.
At the central monitoring system a comprehensive near-real time software
package should be utilized, that allows alarms to be generated should
a parameter exceed preset parameters.
Vibrating Wire Spot Weldable Strain Gauges
VW strain gauges are used to monitor strain in the pipe. At each monitored
location, three strain gauges are mounted at 120 degree-intervals around
the pipe and oriented to measure strain in the longitudinal axis. The
gauges report on the tensile and compressive strains to which the pipe
is subjected and these reveal how the pipe is being deformed.
Strain gauges should be installed on new pipe or pipe that has been stress-relieved
by trenching or cutting, thus providing baseline readings for later calculations
of stress in the pipe. The maximum strain in the pipe is calculated from
the three measurements and can be substantially higher than the individual
strain readings.
Trigger levels for stress relief or other mitigation measures are based
on allowable longitudinal stress. This provides a safety margin to account
for such uncertainties as initial stress condition, future deformation
of the pipe, corrosion effects, and the fact that the strain gauges may
not be located at the point of maximum strain.
Photographs courtesy of Weir-Jones Engineering Consultants
Ltd. - Vancouver, Canada
Strain gauges are ideal for situations where pipelines are affected by
slow-moving landslides, and also for monitoring the effectiveness of mitigation
measures. They are not appropriate for monitoring fast-moving hazards
such as mudflows or rock falls.
(返回顶部)
In-place Inclinometers
The In-Place Inclinometer (IPI) sensor produced by Soil Instruments utilises
a solid state  accelerometer.
The solid-state device has no moving parts and is almost completely shock
proof.
The sensor itself, a small discrete device which measures in g (gravity),.can
be combined with gauge lengths and wheel assemblies to build up a concatenated
string of sensors to be positioned into the borehole. The sensors are
powered and data recorded by a datalogger. (IPI sensors are not designed
for manual monitoring.)
To assist in the long term monitoring the In-Place Inclinometer should
be very low power, low EMC device which conform to the specifications
laid down under EN50121 1.
(IPI Product page)
(返回顶部)
标准振弦渗压计
设计用于精确量测完全饱和或不完全饱和岩土中的孔隙水压力，包括：
- 抽水井、观测井以及水库堤坝的降压与恢复试验.
- 基础、填筑体、挡土墙和小型大坝里的孔隙水压力监测.
- 隧洞、矿井、管线以及其他地下工程的稳定调查研究.
The piezometer tip comprises a porous element integral with a diaphragm
type vibrating wire pressure transducer, installed in boreholes or placed
in fill materials. A cable connects the transducer to a read-out, terminal
unit or datalogger.
(Standard VW Piezometer product
page)
(返回顶部)
Rain Gauge
The tipping bucket rain gauge is ideal for measuring rainfall. Two specially
designed buckets tip when the weight of 1 millimetre of rain falls into
them. As can be seen in the graphic below, when one bucket tips, the other
bucket quickly moves into place to catch the rain. Each time a bucket
tips, an electronic signal is sent to the datalogger. To calculate the
rainfall for a certain time period, simply multiply the number of marks
on the recorder by 1 millimetre. The tipping bucket rain gauge is especially
good at measuring drizzle and very light rainfall events. The datalogger
can determine how much rain fell during certain time periods.
|
