- +27 (0) 10 446 5706
- gp@orsco.co.za
- Plot 13, RD 5, Brentwoood Park, Gauteng, 1501
Pipeline Condition Assessment is not a single activity but rather a process whereby multiple technologies and skills need to be applied selectively and sequentially, resulting in an informed conclusion being reached as to the condition of a pipeline and its components.
A holistic and multi-disciplinary approach is required to ensure that relevant and appropriate information is gathered to enable an accurate assessment of a pipeline’s condition.
The following pipeline condition assessment services are available:
Relevant information, including original design details and specifications, as-built drawings, failure and leak history and previous investigation reports and drawings will be required. There will also be discussions with the project team and operational personnel to gather undocumented ‘institutional’ and historical information on the system.
Soil resistivity is widely considered to be the most comprehensive indicator of a soil’s corrosivity. Lower soil resistivities typically indicate environments of higher corrosivity while a value larger than 100 Ω-m is generally accepted as a non-corrosive environment. Soil resistivity is typically assessed utilizing the Wenner four electrode technique, according to the ASTM G57 Standard. A soil resistivity survey will be conducted to identify areas with a greater potential for external corrosion.
Stray current may be defined as current flowing on a structure that is not part of the intended electrical circuit. Stray currents flow at random in and through the soil and for corrosion to occur there must be an exchange of current between a metallic structure and an electrolytic environment (soil). On a Power Station site there could be complex stray current conditions present. Stray currents (or the absence thereof) on existing infrastructure will be surveyed by logging both AC and DC pipe-to- soil potentials over the entire length of the respective pipelines. The DC pipe-to-soil potentials gathered from this survey will also provide an indication of the likelihood of the pipeline to corrode, with a higher pipe-to-soil measurement indicating a higher risk of pipeline corrosion.
Coating defects will be detected by means of a Pipeline Current Mapping (PCM) and Alternating Current Voltage Gradient (ACVG) surveys. These methods utilise a sensitive instrument to track voltage gradients that exist around coating defects when an external current is applied from the earth to the pipeline, thereby identifying the major coating defects on a pipeline, which provide a representation of the overall coating condition and provides preferred locations for the excavation sites to complete the direct assessments. Interference from adjacent infrastructure could affect these surveys and the efficacy will first be assessed as part of the investigation. The efficacy of the approach within such a congested environment will be assessed before proceeding.
The purpose of the current drainage test is to determine the current required to provide cathodic protection to a pipeline and can provide an indication on the quality/condition of the pipeline’s coating, where a high-quality coating requires a low current and a poor-quality coating will require a higher current. The current drainage test is a small-scale cathodic protection system which utilises a temporary groundbed, such as earth spikes, a fence or other buried steel structures.
If present along the sections of pipe to be assessed, a detailed review of the status of the current cathodic protection system (if any) will be conducted to assess its status and efficacy of protecting the buried pipeline. The impressed current rectifier(s) will be inspected with regards to cable connections, power output, operating voltages, ground bed resistance, etc. This inspection will be conducted with the purpose to identify the potential requirement for maintenance, refurbishment or upgrading the installation to extend its useful life. A pre-inspection site visit is recommended to assess the condition of the existing system and determine the requirements for the field surveys.
The need for physical soil sampling and laboratory testing will be assessed during this stage of the investigation. If deemed necessary, soil samples at the level of the pipe installation will be collected and the following lab tests will be performed:
Physical excavation to the required level to collect the sample will be the responsibility of the client.
Relevant information, including original design details and specifications, as-built drawings, failure and leak history and previous investigation reports and drawings will be required. There will also be discussions with the project team and operational personnel to gather undocumented ‘institutional’ and historical information on the system.
Soil resistivity is widely considered to be the most comprehensive indicator of a soil’s corrosivity. Lower soil resistivities typically indicate environments of higher corrosivity while a value larger than 100 Ω-m is generally accepted as a non-corrosive environment. Soil resistivity is typically assessed utilizing the Wenner four electrode technique, according to the ASTM G57 Standard. A soil resistivity survey will be conducted to identify areas with a greater potential for external corrosion.
Stray current may be defined as current flowing on a structure that is not part of the intended electrical circuit. Stray currents flow at random in and through the soil and for corrosion to occur there must be an exchange of current between a metallic structure and an electrolytic environment (soil). On a Power Station site there could be complex stray current conditions present. Stray currents (or the absence thereof) on existing infrastructure will be surveyed by logging both AC and DC pipe-to- soil potentials over the entire length of the respective pipelines. The DC pipe-to-soil potentials gathered from this survey will also provide an indication of the likelihood of the pipeline to corrode, with a higher pipe-to-soil measurement indicating a higher risk of pipeline corrosion.
Coating defects will be detected by means of a Pipeline Current Mapping (PCM) and Alternating Current Voltage Gradient (ACVG) surveys. These methods utilise a sensitive instrument to track voltage gradients that exist around coating defects when an external current is applied from the earth to the pipeline, thereby identifying the major coating defects on a pipeline, which provide a representation of the overall coating condition and provides preferred locations for the excavation sites to complete the direct assessments. Interference from adjacent infrastructure could affect these surveys and the efficacy will first be assessed as part of the investigation. The efficacy of the approach within such a congested environment will be assessed before proceeding.
The purpose of the current drainage test is to determine the current required to provide cathodic protection to a pipeline and can provide an indication on the quality/condition of the pipeline’s coating, where a high-quality coating requires a low current and a poor-quality coating will require a higher current. The current drainage test is a small-scale cathodic protection system which utilises a temporary groundbed, such as earth spikes, a fence or other buried steel structures.
TRU and Groundbed Inspections. If present along the sections of pipe to be assessed, a detailed review of the status of the current cathodic protection system (if any) will be conducted to assess its status and efficacy of protecting the buried pipeline. The impressed current rectifier(s) will be inspected with regards to cable connections, power output, operating voltages, ground bed resistance, etc. This inspection will be conducted with the purpose to identify the potential requirement for maintenance, refurbishment or upgrading the installation to extend its useful life. A pre-inspection site visit is recommended to assess the condition of the existing system and determine the requirements for the field surveys.
The need for physical soil sampling and laboratory testing will be assessed during this stage of the investigation. If deemed necessary, soil samples at the level of the pipe installation will be collected and the following lab tests will be performed:
Physical excavation to the required level to collect the sample will be the responsibility of the client.
Water samples will be collected and analysed. It is noted that this analysis will be focused on corrosion-related parameters, which typically differs from analyses completed for compliance purposes.
The failure mechanism of internal linings depends on the type of lining, operating conditions that the pipeline experienced (i.e. excessive surges or cavitation), characteristics of the product conveyed, application quality, installation practice, age etc. Inspection of the internal surface of a pipeline by means of CCTV provides qualitative information with respect to the condition of the pipe lining and the steel substrate and can be performed by Orsco. The technique provides accurate information with respect to the position of any internal corrosion or defects.
Ideally, a man entry inspection should be conducted. During this inspection, the nature of corrosion product and pitting depth can be assessed, and a more accurate assessment of coating condition and failure mode can be made. The integrity of the internal lining can be assessed by means of visual, dry-film thickness (DFT) and pull- off adhesion testing while steel pipe thickness can also be measured using ultrasonic thickness measurement equipment.
Draining and safe lockout of the pipeline must be performed by the client before man-entry inspections will be considered.
In order to evaluate the pipeline’s capacity to withstand internal pressures (i.e. the pipeline’s integrity), an accurate representation of the pipeline’s wall thickness is required. A combination of ultrasonic non-destructive test technologies, namely: B-Scan or corrosion mapping and A-Scan or discrete/traditional ultrasonic measurements, is proposed for the Pipe Wall Assessments. The B-
Scan measurements provide a high-frequency scan of a pipeline section, from which the remaining pipe wall can confidently be measured.
The sites for assessment will be selected based on practical considerations where access is possible. If external exposure of the pipe is not possible, then metal loss assessments can be conducted from the inside only. This will be assessed in collaboration with the client.
The client or his appointed representative shall be responsible for exposing the pipeline (full circumferential exposure) and coating removal and reinstatement which is required to complete the assessment. The results will give an indication of the level of external pipe degradation/corrosion and will be compared to existing records/previous assessments to develop an understanding of the pipeline corrosion rates. Pipeline pits will be measured using a pit gauge.
Actual pressure and transient behavior will be measured by high-frequency pressure logging devices. The outcome of the field verification will confirm if the system is subject to significant pressure surges and whether the pipeline presents any anomalous hydraulic behavior. These surveys generally lead to a greatly improved understanding of the operation and behavior of a pipeline. It also yields invaluable information on the actual impact that operational changes have on a system.
If required, additional assessments can be performed typically including discrete pipe wall thickness measurements of pipe specials, visual inspection of mechanical and civil components, and coating and lining assessments, including DFT and adhesion measurements. 3D scanning of the chambers can also be completed to provide an accurate as-built model of the chambers. It is noted that the chambers will be required to be drained and thoroughly cleaned prior to these inspections.
The condition assessment data collated from the fieldwork and desktop investigations will be compiled to assess the overall pipeline risk profile, from which an accurate pipeline condition can be defined. All the data and associated assessment methodologies will be presented in a detailed condition assessment report. The report will include fitness for purpose assessment and recommendations for refurbishment or replacement as required. The components assessed (valve chambers, chamber accessories, couplings, and valves) will have a basic functionality assessment and evaluation, i.e. the item is either functional or not functional and requires refurbishment or replacement. A set of functional criteria will be defined for each item type and will be scored accordingly.
Nontoxic smoke will be pumped into the pipe and where it escapes will easily show anomalies. Smoke detection is by far the most cost-effective solution for detecting defects on long lengths quickly but is not always the most practical so context is king when using this tech.
Dye testing is great as a fluorescent luminous dye is pumped or simply poured into the pipes and can be traced in surrounding soil as well as in areas where it would never be expected to show up. Dye residue is almost invisible to the naked eye as soil acts as a filter but cannot filter out the Fluoresceine visible with a black light at night or Shon down a dark pothole that was vacuum excavated in the area of the suspected voids.
The low-pressure hydraulic test can be done on the pipeline, This will prove if the pipe still has integrity. This is simply plugging the line with an inflatable plug.
If the pipeline is concrete we will do Pundit and other tests on the substrate – probably would be spigot and socket and these would need to be closely inspected.
If it is steel we will use Magnetic flux or other NDT depending. Regardless wall thickness tests should be done no matter what.
If the pipeline will be Polyethylene or Poly Vinyl Chloride the joints should be checked.
Concrete GPR can be used to look into the wall of the pipe to determine if there are voids in the wall of the pipe. Steel rebar or mesh can also be assessed for corrosion if the pipe is re-enforced.
We manufacture our own vacuum excavators potholing and geotechnical partners would be called in to assess the area once we start potholing. Potholing is an elegant way of a vacuum sucking down 2-4 meters with a 150mm neat vertical hole in the ground we agitate the soil and vacuum as we go down (as a dentist’s assistant would vacuum in your mouth as the dentist works).
Soil tests should be done we can take samples and deliver them to the lab, we have our own lab but it is limited to our polymers so it would need to be outsourced.
Inflow, infiltration, and exfiltration can be verified as the potholing will reveal strata content as samples are extracted all over the area.
With the use of drones using Thermal imagers can locate anomalies showing us where to start looking especially in uncongested areas where thermal radiation can show temp changes of the ground.
A Local environmental survey will reveal external influences such as:
