Posted at 11.28.2018
Petronet, a local company that transports gas through underground pipelines across South Africa, got approached MA2K Evaluation Labs to conduct an investigation over a leakage on the pipeline, which was found throughout a random drip inspection. The Pipeline manages from Johannesburg to Potchefstroom. Upon inspection a joint was designated as being a major source of leakage. The influenced area was joined up with using a butt weld and reinforced with a clamp. This section was dissected and inspection revealed that the leakage was anticipated to imperfect fusion in the weld which initiated the formation of hook splits and cavities in the welded materials directly adjacent to the weld. External stresses from the surroundings may have accelerated the progress of the cavities and splits yet the clamp increased the effectiveness of the joint aiding in preventing any accelerated growths of the flaws.
As a brief term solution it is preferred to replace the destroyed section with a fresh pipe. It must be properly welded of the same material and as an added precaution to weld an additional sleeve above the newly became a member of and welded section.
Petronet, a respected company in South Africa which transports gas through underground pipelines conducted a random leak inspection review on one with their pipelines operating from Johannesburg to Potchefstroom, and it was discovered that there was a gas leak at the precise joint. The pipe carries gas which is important that the drip should be set, because of the volatile dynamics of gas as well as the loss of resource, subsequently profits. The systems made up of numerous smooth pipes and connected using a butt weld; these bones were strengthened by clamps bolted on.
MA2K Evaluating Labs have been approached by Petronet, to examine the leakage and was utilized to identify the real cause of failure and as well as make many suited recommendations for the repair and elimination of breakdown of the joint. The pipeline was effective since the 20th Feb 1995; this put the pipeline age in the region of 15 years.
Figure 2. 1 (Below) was used on site
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Figure 1. 1: Pipeline on Site
The defective section of the pipe, like the clamp was then proclaimed, trim out and removed from the site for even more inspection and analysis. The inspection and research was carried out in MA2K Screening Labs in Durban.
Two grade A 106 GR. B SCH40 seamless pipes with exterior diameters of 168. 3mm and wall width of 9mm were butt welded end to end. A butt weld contains the two pipes warmed to an effective fusion temperatures then joined by means of push. The joint was further guaranteed with a clamp. The working inside gas pressure was 2620 kPa (380 psi).
Figure 2. 1: Tube Inspection
0. 291. 06
Penetration is poor in the beginning of welding
Ensure the levels of pipes are frequent to boost bonding strength
Poor quality welds caused by
Incorrect pressure applied
Failure anticipated to exhaustion (welding lowers tiredness strength)
Fusion did not arise between weld metallic and fusion encounters.
Weld metal does not stretch through the joint thickness
Exposed to H2O and foreign material in the gas, such as CO2, H2S, O2, or chlorides.
Under some operating conditions gases created may cause corrosion
Oxygen content (oxidizing salts)
Passing through soils of different mineral content
Contact of different metals, specifically at valves (galvanic corrosion)
Normally includes gouges and dents.
Generally occurs during removal or incorrect handling of equipment during set up.
Results from cyclic tensions that are below the best tensile stress, or even the yield stress of the materials.
Material defects are credited to pollutants that combine with the material during the melting of metallic, the forming of steel or through the heat dealing with process.
Faults can occur by incorrect storage space or control.
Material defects can occur in various ways.
Example of various defects talked about below :
Refers to fracture of weld brought on as a result of poor parts fit-up, speedy cooling, and localized strains exceed the ultimate strength of the metallic etc.
Examples of weld cracks :
When metals absorb hydrogen at inside defects, e. g. Laminations and inclusions, Blisters form and eventually forms cracks.
The clamp was removed for even more inspection of the weld be a part of. Removing the clamp was done under guidance by Country wide Energy Regulator of South Africa (NERSA).
The pipe surface was necessary to be washed. An acetone solution was used. Water Penetrant exam was performed on the weld area of the pipe. Surface discontinuities were obvious on the bottom of the pipe. All examinations and examination was completed by MA2K Tests Labs. Through inspection it was deduced that a Butt weld was used to join the pipe collection and macrostructure images uncovered that there were problems on the welded area. Particularly weld cracks, poor penetration and imperfect fusion. Cavities were uncovered near/adjacent to the welded portion of the pipe material.
Figure 4. 1: Inspection WITH THE Pipe Weld
Surface discontinuities were made noticeable by the Water Penetrant assessment. These results further justify the suspicion that there was an poor weld process conducted on the joins of the pipeline and so the cause of the gas drip. Cavities are noticeable in the tube walls. This can be induced by vacancies in the material join in the weld.
Figure 4. 2: Analysis Of The Pipe Weld
The extracted test was looked into by approach to etching. A Nital solution was used to etch the tube materials. Nital, a mixture of alcoholic beverages and nitric acidity is utilized for etching of metals. It really is ideal for displaying the microstructure of carbon steels. The alcoholic beverages used can be either Ethanol, M or methanol. By taking a look at the etched test under a Scanning Electron Microscope it was uncovered that there was an overlap of materials and for that reason, it was learned that there is an irregularity or there's a non-uniform overlap or join of material. This could result in a weakness in the be a part of due to variants in material or condition of the materials. The non-uniform joint of material gives weak spot on the composition of the pipeline and so resulted in a drip.
Arrows on shape 5. 3 clearly indicate all the weld areas, heat affected areas and the pipe material.
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Figure 4. 3: Etched Material
Before the tube was sectioned for thorough examination, a radiographic examination was performed on the premises of MA2K Trials Labs. The following image was exposed on the radiographic film. The radiograph picture shows the microstructure of the materials and identifies the weld overlap with the welded materials. There are clear signs of variant materials or says which cause weakness in the sign up for when added stress is applied. A couple of cut out root cavities visible in the radiograph which could be the reason for leakage in the offing.
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Figure 5. 1: Radiograph Of Material
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Figure 5. 2: Radiograph Of Material
In shape 6. 3 below: The longitudinal cross portion of the pipe exhibited the weld framework inside the pipeline. This unveiled flaws in the weld framework and cavities in the wall membrane of the pipeline and a definite indicator of the split and fracture lines that could cause a leak in the offing. These defects happened in the getting started with of the pipe and as well as possible external stresses that act on it due to the environment, no corrosion possessed occurred and pipe was made to endure pressure of the gas within the pipe.
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Figure 5. 3: Part Section: Inside Of The Pipe
Longitudinal samples were taken from the extracted part. Slices were made across the weld lines, to explain the differences in the material found in the weld and the welded materials.
The two cross portions through the wall thickness of the tube was refined and etched with Nital. The main one macroscopic image (Shape 6. 4) discovered a clear leakage journey through the wall thickness of the pipe. This shows that there is a weakness in the join between the weld materials and the welded materials. Further fracture and stress brought on the weld to break up at the join between the weld material and the welded materials. Shape 6. 5 implies that there was too little side wall fusion in the tube and that there is another weld bead on the left, this have been made to make an effort to complete the vacancies created from the lack of fusion.
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Figure 5. 4: Part Section: Tube Wall
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Figure 5. 5: WAY TO OBTAIN Leakage
After thorough analysis of the faulty area of the pipe it was found that the leakage was scheduled to inappropriate weld process and lack of fusion, insufficient fusion causes cavities. Cavities form splits over a period. Due to this hook cracks were made and leakage possessed occurred. Therefore, the components used contain no post installation defects as there was no internal or external corrosion to the materials. The look of the materials is suited to the environment as it was able to withstand cyclic launching, fatigue stresses no indications of hydrogen blistering was present on the materials. Mechanical destruction may have aided or accelerated the development of the crack size. The clamp made discovering the source of the leak more difficult and could have helped in the reduction or retarded the speed where the cracks had grown. The condition of the tube or clamp platform material compositions or microstructures was as expected for the working life of the system. No softening was found from the weld and tube Heat Affected Area.
As a brief term solution it is preferred to replace the ruined section with a new pipe. It must be properly welded of the same materials and as an added precaution to weld an additional sleeve in the newly became a member of and welded section. This may suffice for another 10 years
As a long-term solution it is advised to replace the complete pipeline with a new combination of materials according to Petroleum Bulk Storage area Regulations, the requirement is that all new underground pipelines be as follows:
Pipes must be either made of a non-corrodible materials such as fiberglass reinforced clear plastic, nylon or designed thermo-plastic, or material such as material with a cathodic safety system designed to protect it for 30 years.
Pipes may be in one or double-walled construction
Access slots must be installed allowing tightness tests;
Installation must maintain accordance with regarded engineering practices
Pipes and joints must be tightness tested before being covered and placed in.
To reduce downtime and loss of revenue, the new pipeline may be installed next to the existing pipeline and until conclusion will be inadequate. Thereafter the new pipeline will replace the old with reduced downtime. That is another good thing about laying down a fresh pipeline.
Surface should be machined/surface easy to avoid tiny discontinuities.
Ensure welding current is enough.
Weld arcs should not be much longer than the pipe diameter
The "V" perspective should not go over 7 degrees
The remove width should be appropriate and steady for the diameter of the pipe