Pipeline cleanliness and black powder: an increasing issue for gas pipelines
IT SEEMS A PARADOX: 10-15 years ago, as intelligent inspection was developing and the science was coming into its own, a major point of discussion among all involved was to do with the technology itself. The big question was “high resolution or low resolution?”, relating to the capacity of the equipment to detect pipewall features. Putting this another way, did the operator want a ‘quick-and-dirty’ (and therefore cheap) inspection, or was the Full Monty required? The issue revolved around the capacity of the intelligent inspection tools to inspect, and the cleanliness of the pipeline that the tool was to inspect was sometimes considered of less significance.
Now, however, intelligent-inspection tools are of an undreamt-of greater sophistication, and the general question being asked is no longer to do with their capacity accurately and precisely to detect features, but it’s to do with how clean the pipeline is – a far more basic issue, and one that does not take advanced equipment to resolve. A pipeline’s internal cleanliness has, quite properly, become a question of great significance: nevertheless, there are no published standards of ‘cleanliness’ and although there are many ways in which deposits can be removed from a pipe wall, ensuring a pipeline is clean enough for an inspection to be carried out remains very much a subjective process. It has often been said that the best cleaning tool is a magnetic-flux leakage intelligent pig, and this remains true, although it is also the most expensive. While it is clear that each pipeline is different, and its internal cleanliness is very much dependant on the physical conditions of the fluid or gas that it is transmitting, it seems surprising that the industry as a whole has not found it possible to establish some basic guidelines for achieving cleanliness. Under normal operating conditions, minimization of pipewall deposits will obviously improve the flow conditions as well as the pipeline’s overall efficiency and cost-effectiveness, to say nothing of the effect on reducing the potential for corrosion. When it’s time for an inspection, deposits and other debris must be removed, both to ensure that the tool’s sensors can have unimpeded access to the pipe wall, and to remove the possibility of debris clogging-up the tool, and even causing it to become stuck.
The question of ‘how clean is clean?’ is not unfamiliar and, in fairness, is being asked increasingly more frequently nowadays. At three recent pipeline-industry events that the Journal of Pipeline Engineering has attended (in Ostend, Pittsburgh, and Aberdeen), the question was once again raised, although once again there were no particular answers other the general advice of establishing and maintaining a regular cleaning-pig programme, which would be enhanced prior to an inspection run.
One of the most pernicious cleaning problems for gas pipelines is the formation and accumulation of so-called ‘black powder’. This material, which is as fine as flour although far more dangerous because it is pyrophoric, is one of the least understood but most prominent contamination problems in gas pipelines. Black powder is the name given to the mixture of iron oxides, carbonates, and sulphides found in gas lines; it can also incorporate salt, sand, clay, mineral scales such as calcium carbonates and gypsum, strontium and barium sulphates, metal powder, welding flux, and stubs of welding rods. The sources of black powder include millscale, corrosion products, salts and scales from gas wells and wet gas gathering systems, and atmospheric corrosion, and the variability of its composition is illustrated by reports of the powder ranging from being completely iron sulphide to completely iron oxide.
Black powder can cause product quality problems and excessive wear and erosion on internal pipe walls and many other pipeline components including compressors, turbines, and valves. The accumulated solids can plug small orifices and consequently affect measurement equipment and, as the particles settle out of the gas stream, they can fill-in surface pits and other internal pipe-wall anomalies, preventing accurate inspection; in sag bends, these build-ups can harbour corrosive bacteria.
Although difficult to deal with, the problems cased by accumulations of this material can be overcome, as can most pipeline problems, by careful planning and attention to detail. Dr John Smart points out that the problem of black powder is as much one of powder movement as one of the presence of the material in the first place. Oil and gas pipeline cleaning chemistries have been developed that have superior cleaning characteristics that can dissolve the oil, glycol, or paraffin matrices that can hold black powder particles to pipe walls. After being dispersed, the particles can be pigged out of the pipeline, and frequent pigging and chemical treatments with biocides and corrosion inhibitors can control internal corrosion caused by solids’ deposition.
Removal of the black powder from the pipeline is not the end of the affair: as the material is hazardous, necessary arrangements for its disposal must be made, and obviously these should be in place before any pigging operations begin.
A special session on this problem is being organized at the Pipeline Pigging and Integrity Management (PPIM) conference being held in Houston on 17-18 February, and organized by our sister publication Pipelines International and Clarion Technical Conferences (see www.clarion.org), and other papers at the event will also address the issue. The more the subject of ‘how clean is clean?’ can be discussed, the more likely it is that shared experiences can lead to a shared solution; at the very least, ‘clean’ needs to be kept in the spotlight of pipeline integrity management and operations.
Funding announced for pipeline research
THE PIPELINE Research Council International (PRCI) 2010 research programme has been approved by its Board of Directors at a meeting in Banff, Alberta, Canada. Just over $8 million in funding has been allocated to the 2010 programme, which includes research into pipeline corrosion, integrity, operations, design, materials, construction, facilities, and underground storage. PRCI Chairman Paul MacGregor said “This commitment of the PRCI membership in the face of challenging financial constraints in all sectors of the global economy, demonstrates how industry leadership and collaboration can meet the challenges facing the energy pipeline industry.
“The projects selected by our members reflect their commitment to the safe, efficient, and reliable operation of energy pipelines worldwide,” Mr MacGregor continued. In addition to core programmes, the PRCI will also undertake a range of initiatives in 2010, many in conjunction with its European and Australian research partners. Some of the initiatives include:
The development of a co-ordinated research plan to address the specific technical issues associated with carbon dioxide transport
The development of guidelines to assist operators in evaluating damage to subsea pipelines
The development of a comprehensive approach for the management of unpiggable pipelines will be expanded to include a ‘Base Resource’ document to provide guidance for inspection and assessment of unpiggable pipelines – a keynote paper on this project will be given at the Pipeline Pigging and Integrity Management conference (see above).
Improving the understanding of data produced by pipeline inspection technologies, with an emphasis on determining the effects of uncertainty in the data
The re-examination of standard emissions factors for compressor station fugitive emissions, and the development of improved fugitives measurement methods and reporting procedures
Improving compressor and pump station facility integrity to evaluate the effects of vibration on station piping components, and improve the methods and practices used for bolted joints.
As many readers will know, the PRCI is a non-profit corporation comprised of 34 energy pipeline operating companies located in the United States, Europe, Canada, South America, and the Middle East. The Council has recently moved its US-based administration headquarters from Arlington to Falls Church – see www.pric.org.