regarding the physics of pipeline failures.
This is a work in progress...
Link to this: TinyURL.com/PipelineFailureFAQ
- What was the pipeline MAOP?
What was the operating pressure at time of failure?
Every pipeline will have a
Maximum Allowable Operating Pressure (MAOP)
This is determined by physics (Barlow's Formula)
and also a "safety factor" which is determined politically.
If the operating pressure exceeds the MAOP,
either due to an impulse, or for an extended period,
the pipeline runs the chance of failure.
- History of Earthquakes, Construction, and Flooding in the area?
These are external stressors which can damage pipelines.
- Barlow's Formula
P = (2 ST) / (DF)
where P= pressure, S=yield strength of pipeline material,
T=thickness, D=diameter, F=Safety Factor
- Age of Pipeline?
As a pipeline ages, the chance of failures increase due to corrosion, external damage, sustained operating pressure over the MAOP, or impulses due to cavitation, or fluid hammer.
- Was there Cathodic Protection?
Cathodic Protection is a system to help prevent pipeline corrosion.
These systems must be inspected at regular intervals.
- Thickness at point of failure vs. Design Pipeline Thickness
Due to corrosion, or damage, pipeline thickness may be reduced.
This will reduce the maximum operating pressure as determined by
- Yield pressure of Steel used?
This can only be determined from manufacturer specifications
or though metallurgical analysis.
- Corrosion is a fact of life. It cannot be avoided.
Due to this and other factors, a pipeline can handle less pressure as a pipline ages.
HOWEVER, due to economic reasons,
there are economic "pressures" to increase capacity and flow of pipelines over time.
These two factors work against each other and is a major
contributing cause of pipeline failures.
- Smart Pig? When was it last inspected?
In-line devices "smart pigs" are used to inspect pipelines, They are required by regulations to be run at certain intervals. If the pipeline is corroding or has sustained other damage, this damage should be discovered by inspection.
Remember that the economic "pressures" on the operator is for them to keep pressures UP, despite that pipelines will be able to handle LESS pressure over time as they age.
- Who is Lead Agency handling the Investigation?
Could be PHMSA/DOT, or it could be NTSB.
RED FLAG: If the pipeline operator is in charge
-- mostly this is what happens.
Gulf/Transocean: BP was in charge.
Mayflower: It's ExxonMobil.
This is a really bad idea.
- Alternate MAOP?
Was this pipeline using the DOT/PHMSA "Alternate MAOP" formula?
This is a complex forumula, but basically this sets a lower safety factor
in order to allow pipelines to use a higher MAOP. This is a BAD IDEA,
since pipelines can handle LESS pressure as they age.
- Timeline of the incident?
When was the leak detected? When was the pipeline shut down?The timeline from when the rupture first occurred to when the pipeline was shut down is critical.
Remember, it is the job of pipeline operators to KEEP THE PRESSURE UP! However, when there is a leak, this causes a pressure drop.
So it may be the instinct of an operator to increase pressure in response to a drop, rather then shut the pipeline down. It is definitely counter-intuitive to shut the pipeline down.
There are supposedly automated systems in place to detect leaks and shut the line down, but such a symptom could fool an automated system as well as a human.
- What is the viscosity of the material being transported?
Most "crude oil" these days are really synthetic products, dilbits (Diluted Bitumen) or "syn-dilbits". They take materials with high carbon content (bitumen, pitch, tar, etc), and add lighter oils and distillates (generally in the BTEX range, sometimes called "condensate" or Natural Gas Liquids, NGLs) to allow this material to be transported in a pipeline.
They have very high specific gravity, high density, high viscosity (stickiness), and high corrosivity.
(Don't be confused by the API gravity number, which is an inverse function... the number DROPS as the actual mass increases)
Pipelines which transport material which is high-mass / high-viscosity are especially prone to failure due to impulse shocks caused by cavitation and fluid hammer. These shocks can cause weld failures or pipeline ruptures.
High viscosity pipelines also generally must run at higher pressure. Dilbit pipeline pressures can run in the range of 1300-1450 psi.
Higher sustained operating pressure can cause failures due to age, corrosion.
- Were there any reports of strange sounds prior to failure?
Stephen Kohlhase has a theory that pipelines emit low frequency (LF) radiation which can be heard of felt. This can be observed with ~1mi of pipelines. This can manifest as a pattern of waves on swimming pools. The source of this acoustic radiation could be from compressor stations, or resonances from internal friction and the physics of pipelines. Kohlhase suggests that these vibrations or oscillations can cause pipeline failures over time. I call this the "Kohlhase Effect".