- Locating Missing Manhole Covers
- Locating Missing Manhole Covers - Part 2
- Urban Gas Pipeline Defects and Gas Leaks
- Finding Pipe Joints in Cast Iron Gas Pipes
- Pinpointing Small Pipeline Faults
- Locating Deep Sewers
- Water Leaks From Plastic Pipes
- Internal Water Leaks and Pipe Bursts
- Using A Pipe and Cable Locator
- Cable Sheath Fault Location
- Avoiding Site Stupidity
- Cable Fault Location
Barney’s Blog no 5 - Pinpointing Small Pipeline Faults
The Russian pipeline company security man was wearing just what a Russian security man should wear. Dark Glasses, even though the weather did not require them. A ¾ length black leather jacket, it might not have actually been leather but who cares, as it hid most of the bulge of the weapon under his left shoulder, and shoes more appropriate for walking in city streets than across recently tilled fields where we were walking the pipeline.
The trip to Volgograd (formerly Stalingrad) had been interesting. The Air Volgograd plane was a recently refurbished YAK 50, a small jet passenger plane with 50 seats and 3 small jet engines at the rear. From the outside its fresh white sprayed paint looked quite smart. The wings stuck straight out rather than being swept back, and with its big oval windows it reminded me of the Playskool toy plane that the children can install their brightly coloured legless cylindrical passengers into their round holes through the windows. As we boarded the plane up the rear steps between the engines, the interior was quite dark and quiet as there was no auxiliary power unit. The interior had fold forward seats for ease of boarding either side of the aisle, and the interior panelling was something like a 1960's Formica kitchen surface. The windows had curtains that could be drawn across on a simple plastic curtain rail. There was an overhead rack, but it was without any lids just like in a train, and the only security for the contents was an elasticised net, brown coloured and slightly sticky from over use. Apart from the chemical smell of the toilet that reduced the further up towards the front of the plane, there was the smell of wet animal/wet dog probably coming from the fur hats drying out after getting wet in the rain and placed in the overhead rack.
As we sat down and the doors were closed the plane was completely silent. There was then an odd creaky grinding noise from under the floor, sounding like cables running over pulleys, and I noticed that the wing ailerons were moving – obviously Russian fly-by-wire. The flight was very smooth and the landing perfect, arriving in Volgograd.
The next part of the journey, travelling in a bouncy Toyota people carrier along undulating rough roads to the pipeline co, took as long as the flight.
The pipeline company supervised 8500Km of coated steel pipeline, mostly greater than 50cm dia. Most of the time these pipes carry unrefined crude to the refineries. Different sets of pipelines carry refined products, petrol, diesel, kerosene or whatever.
Our task was to develop a method to pinpoint the positions where the pipes were tapped into and the crude or product stolen, as this was causing severe problems, not only due to the financial loss of product, but main concern was the ground pollution and consequent environmental damage caused by the poor connections leaking product into the ground. The pipeline company wanted to check 18KM of pipeline.
Various methods of pipeline surveying are used to find defects in the coating of the steel pipeline. The pipeline is coated to prevent corrosion and cathodic protection current is additional protection, to reverse the possible effects of electrolytic corrosion.
The intensive method of pipeline surveying uses DC from the rectifier as the measuring medium. This traditional ground contact method is slow as it required the whole section length of pipeline to be surveyed by walking it, and the instruments usually have a cable reel and a long trailing wire back to the rectifier system. It the pipeline runs through forested area, there are practical difficulties dealing with the trailing wire.
Current measurement needs to use alternating current, and this has some advantages because the equipment used is light, portable and quick to use. With a signal transmitter connected at the rectifier or a test point, the measurement process uses the locator's detection coils not spikes or electrodes touching the ground, the equipment can be used over any ground surface. The locator software compensates for changes in depth and displays the current from the pipeline as a current measurement in mA or dB.
Audio frequency AC signals frequency of about 1kHz are in common use, and the current measurement method relies on faults losing sufficient current over a section, so that the operator sees a greater rate of loss (current gradient) in one section than the previous one. For small faults that loose little AC current there is so little change in current measurement that the small fault will not be distinguished from the general capacitative signal loss over the pipe section, so the best method is to use a ground contact method using an A frame to pinpoint the fault.
Reducing the AC frequency to about 500Hz improves the current measurement resolution and also the response and sensitivity of the A frame (see blog no 3)
Using much lower frequency AC and near DC transmitted signals onto a pipeline has some advantages over usual audio frequency AC. Signal losses due to capacitance are almost eliminated; So if there are no faults the current measurement remains steady as measurements are taken along the pipeline. So any loss of current is attributable to a fault. Large faults resulting in a large current loss in any pipe section are immediately obvious; Small faults obviously have less loss of current and if the operator recalls the present and previous measurements, change is easy to display.
On earlier pipeline current mapping locators, the operator could recall the mA current measurement reading to see a change of say 10mA and realise that there was a fault to be investigated. Generally the next stage would be to attach an A frame to locate the fault using the voltage gradient.
On the new Vloc Defect Mapper the current measurement is also displayed as a graph, and aided by GPS the operator can walk back to the fault position, use the A frame and pinpoint the fault.
More interesting is the method that we worked out to pinpoint faults that were not meant to be found. In early tests with the pipeline current mapping locators it was noticed that sometimes current measurements would reduce by relatively small amount, perhaps as small as 5mA , then almost recover to the same value or maybe just 1mA from the previous section measurement, so the 1mA change may not be considered interesting by the operator, unless they saw the 5mA change. The fact that the current reading diminished and recovered required explanation.
The obvious first test is measure current at closer intervals than the usual 100 or 50M distances. It was found that the current changed but the pipe depth did not change so much. Next was to use the A frame to see if this change of current also indicates a fault. More often that not there was the direction arrows changing very precisely, indicating a small (electrically) fault of a small size. Finally the only method to prove if the pipe had a small coating defect or an illegal tapping was to dig and inspect.
So following us across the freshly tilled and sown fields was a travelling circus of several vehicles from 3 small Lada Niva 4 X 4 with the security man and his driver, chief pipeline corrosion engineer with assistant and driver, assistants to both of those and driver, one of the survey crew's company's trucks, and a very large 6 wheeler with 8 man digging crew, followed by the creaking tracks of a long reach Hymac digger.
Half way through the morning we had covered 5 KM, one possible place proved to be a coating fault. 500M further on the pipe crossed into a lightly wooded copse area between 2 fields. Strangely there was the characteristic signal dip on the current measurement, and also someone had left a small mound of earth, now self seeded with weeds exactly on the pipeline route. The A frame indicated a reasonable size fault close to the mound of earth, and even more oddly someone had burned some rubbish exactly on this spot. Pipeline following crews gathered round us, and the leather jacketed security man, who walked over to our fault position, cleared away the ashes of the fire with his rather clean shoes, almost tripping up when his toe caught in what definitely was a metal handle. He looked quite excitable. It seemed that some of the pipeline crew were quite nervous. We wanted to get out of the way rather quickly. Security man raised himself on tiptoe and brought his heels down to a satisfying hollow boom. Digging crew quickly revealed a second handle and a well built metal cover. When this was lifted it revealed a nicely welded spigot and valve with a threaded top to take a pipe to a tanker that could easily be concealed on the copse area. There was quite a lot of shouting into telephones and radios, diggers and welders set to work, and I was hoping that we could leave now and have a nice lunch somewhere. Not just yet. We covered another 8KM found 4 more connections.
Next day another 8 KM stretch and 3 illegal connections.
Then we had lunch. Even the security man was pleasant. The pipeline company chief made a nice speech with several toasts and presented us with a large frozen fish caught in his nearby river. So we wrapped it well in a local newspaper and it became a flying fish as it joined the damp fur hats in the overhead rack for the flight back to Moscow!
Email firstname.lastname@example.org for more info on this subject.