The ingredients required for the production of line pipe steels come from all corners of Australia, with iron ore from Western Australia and South Australia, coal from the Illawarra and limestone from Marulan in New South Wales all brought to BlueScope Steel’s Port Kembla operation.
Before the production of steel can begin, high-quality iron – the basic ingredient for steelmaking – needs to be produced. The iron-making process is carefully controlled by blending various grades of iron ore to produce a mix which is exact in its content. Fines of iron ore and coal are also mixed and fused together in a sintering process to form a lumpy feed for charging into the blast furnace, and constitute approximately 60 per cent of the charge.
The last components of the reduction process are coke and limestone. Coke, a strong porous product, is formed by burning coal in ovens and is charged into the blast furnace to support the iron ore and sinter. It is coke which provides the carbon necessary for reducing the iron ore to iron. Limestone is used as a flux or cleaning agent in the reduction process.
These products are charged into either one of two blast furnaces, which are as tall as a 27 storey building and heated by the injection of air and gas to a temperature of 2,300 degrees Celsius. As the charge melts, the molten material makes its way to the bottom of the furnace where it is taken off and stored in refractory-lined ladles awaiting transfer to the next stage of production, where the liquid iron will be converted into steel at a production facility called the BOS or basic oxygen steelmaking.
Prior to this, there is one more important step which is key to the production of high-quality pipeline steel grades – the process of desulphurising the molten steel iron. Sulphur is an undesirable element in pipe steels as it reduces the cleanliness of the steel, decreases the ductility and restricts the weld properties of the final pipe. Once desulphurised, the molten iron is ready for conversion into steel.
In the BOS, iron is converted to steel around 50 times a day, and the Port Kembla operation produces in excess of 5 MMt/a of steel. In the process, the iron, which has a carbon content of around 4 per cent, is refined to levels of less than 1 per cent. It is this process that differentiates iron from steel. A vessel containing a mixture of approximately 300 t of charge, made up of 50 t of scrap and 250 t of iron from the blast furnace, is converted to steel by injection of pure oxygen, which creates a chemical reaction and increases the temperature to 1,700 degrees Celsius. Fluxes are added to absorb the impurities, the scrap melts and the carbon content is lowered to form steel.
The molten steel then moves to the vacuum degassing station where precise additions of the necessary alloys such as niobium, manganese, aluminium and titanium are made to meet the tight specification limits of pipe steels. Then, to further enhance the cleanliness of the steel, the molten steel is injected with a calcium silicide powder, which combines with some of the last remaining impurities and removes them from the molten steel. At this point the final chemical composition of the pipe steel grade is set and the molten steel is transferred to the slab casting facility.
In the slab caster, the steel is poured into a water-cooled mould and drawn through a series of segments, which chill the outer surface and slowly solidify the steel to a stage where it is fully hardened. The continuous strand of steel is then cut to length by automated gas torches to individually designed lengths or slabs. At this stage, the slab is approximately 12 m long and 230 mm thick.
After cooling, the slabs are inspected for any defects that may have been induced during the casting operation. Once the slabs have passed this quality assessment they move onto the final major processing stage where they are converted to a hot rolled strip to the exact dimensional and mechanical property requirements of the customer.
The purpose of rolling the cast slab is two-fold; firstly to achieve the final product dimensions and secondly to produce a finer grain structure; thereby giving the steel greater toughness and strength. In the Hot Strip Mill the slabs are reheated prior to rolling the steel down to its final desired thickness by passing it through a number of rolling stands. BlueScope Steel’s Port Kembla Hot Strip Mill uses six finishing stands to achieve the final desired strip thickness. The strip is then water-cooled on a long “˜run-out’ table prior to coiling. Precise control of slab reheating and rolling temperatures, scale removal, width and thickness ensure that the final strip meets all the dimensional, strength and toughness requirements of the ordered steel grade.
The steel coils are now allowed to cool before being strapped and labelled for despatch to the pipe manufacturing mills.
Before steel is released from the steel mill, it is required by pipe manufacturers Orrcon Steel and OneSteel to have passed various quality tests, including: composition, strength, toughness, surface condition, and coil shape. When steel is despatched from the steel mill, a test certificate is also sent from the steel mill’s data system. When each coil arrives at these plants, checks are performed to ensure there has been no transport damage and that the identity of the coil matches its paperwork, markings and labels. Each coil is then unloaded into the warehouse, and its identity carefully recorded at OneSteel using a barcode process, or at Orrcon Steel using a traceability system called OrrTrace. The coil is then ready to be loaded onto a mill to make pipe.
After identifying the coil, the key stages involved in the pipe making process include:
- Loading the coil into the mill;
- Hydrostatic testing;
- Ultrasonic inspection; and,
According to OneSteel Piping Systems Quality Assurance Manager Dr John Piper these are merely the manufacturing processes and much of the company’s effort is spent verifying the quality of each pipe as it is made via a multitude of test and inspection processes. These include visual inspection of the coils, weld visual monitoring, cooling process control, preliminary inspection of dimensions and surface quality, mill control ultrasonic testing, sampling for strength, composition and toughness testing, flattening and hydrostatic testing, and the final inspection process. This final process consists of ultrasonic testing, length and mass measurement, visual and dimensional inspection of the weld and body, and the bevel inspection. The outcome against the unique identity of each pipe is recorded to ensure that all pipe has passed all tests before being placed to order.
Orrcon Steel employs approximately 100 people at its Wollongong API Pipe Mill. This includes technical and quality, operations, administrative, maintenance, laboratory, logistics and other support staff. At OneSteel, the number of employees required at the plant is dependent on market demand and whether the company is running one, two or three shifts.
According to Mr Piper, the number of man hours required to make a pipe depends on the section and diameter, which range from 6-18 m in length and 168.3-508 mm in diameter. A production crew at the plant typically produces between 100 and 400 pipes per shift depending on the diameter, thickness, length and grade of the product being produced. Large diameter heavy wall pipe is produced at a slower rate than small diameter light wall pipe, however large diameter heavy wall pipe delivers a much higher output on a tonne per shift basis.
Orrcon Steel Technical Manager – Pipelines and Infrastructure Dr Cameron Dinnis says “Depending on the pipe size, the welding speed will be anywhere from 14-21m per minute. The pipe spends 10seconds at pressure during the hydrostatic test and will spend about one minute being ultrasonically tested. All of this means that the total man hours that go into a pipe can range between 1.5 and 5 hours.”
Welding the seam
As an electric resistance welded (ERW) pipe manufacturer, Orrcon Steel is essentially a manufacturer of weld seams.
To make the seam, the company uses a precise machine to trim the edges of the steel coil in a process known as edge milling, then heats the edges using high frequency electrical current and pushes them together to form the weld. The external and internal weld bead, which is the material that is ejected from the weld area when the strip edges are forced together, is then trimmed off by carbide cutting tools, leaving the weld seam flush with the surface of the pipe. The weld seam is then immediately subjected to an initial ultrasonic inspection. The seam is then heat-treated to ensure the microstructure is suitable for service. Following this, the pipe is tested to ensure that the weld seam and the pipe body have structural integrity and are within dimensional tolerances.
Specifically, the seam is subjected to a hydrostatic test and the full length of the weld seam is subjected to an ultrasonic inspection from both sides by 36 differently angled beams. The inspection frequency is such that a 0.5 mm long defect will be detected five times by each of the 36 angles in the time the ultrasonic probes traverse across it.
OneSteel achieves the weld seam using a similar process. “The integrity of the weld seam is of course, critical to the end use of the pipe so we are very careful in both process control and inspection,” says Mr Piper.
Ensuring a quality product
At OneSteel and Orrcon Steel, quality assurance is a high priority and is addressed on a number of levels. Both companies have third-party accreditation of their quality management systems, product and laboratory practices. They are accredited to ISO 9001 and API Q1, with API Monogramming privileges. Both companies have been accredited by NATA for conducting mechanical tests and chemical analyses.
Orrcon Steel ensures quality at a fundamental level through process control, product inspection and testing regimes. At OneSteel, employees apply the principles of quality, test and inspection systems to ensure that no substandard pipe is placed to order.
Innovation at the mills
In the past decade, Orrcon Steel and OneSteel have introduced and successfully implemented numerous technical innovations at their pipe manufacturing plants.
Orrcon Steel has introduced the following methods at its Wollongong Pipe Mill:
- Edge milling, which involves machining the edge of the coil to provide clean and sound surfaces to weld together, resulting in higher weld integrity;
- Cage-forming: an automated pipe-forming technology that is designed to cradle the coil as it is deformed into a pipe, resulting in lower forming strains;
- On-line monitoring of welding parameters and heat treatment parameters;
- Phased array ultrasonic technology, which allows the generation of various ultrasonic beams from the one transducer;
- Integration of pipe mill data with construction management systems using OrrTrace;
- Long-lengths, with the capability to produce pipe up to 24 m in length; and,
- Testing and examination: computer-controlled Ring Expansion yield strength determination.
In the past ten years, OneSteel has:
- Rebuilt its Ultrasonic Inspection systems;
- Increased mill capability to 508 mm diameter in both X70 and X80 grades;
- Upgraded mill drives and pipe handling capability to cope with heavier sections;
- Implemented weld line accelerated cooling capability to enhance weld line toughness;
- Developed improved steel compositions in conjunction with steel manufacturers; and,
- Upgraded the plant’s computerised factory control, test and inspection data management systems.
There are a number of challenges facing the pipeline industry today. Dr Dinnis of Orrcon Steel says that one of the main challenges is “ensuring that the pipeline industry recognises the value provided by local manufacturers, versus foreign economies, in terms of compliance with and understanding of local design specifications”.
Dr Dinnis adds “The intermittent nature of pipeline projects, particularly from a pipemaking perspective, ensures that the companies that make up the Australian pipeline industry must be able to operate very flexibly and allocate resources appropriately.”
Meanwhile, OneSteel is pleased that the pipeline and other industry segments are improving following the global financial crisis. “There are continuing demands on the pipemaker to increase the range of sections available and improve the mechanical properties of line pipe while maintaining competitive pricing,” says Mr Piper.
Before the pipe is coated…
Pipe is extensively tested before it moves onto being coated. It is measured, pressurised and probed by ultrasound. Key physical dimensions are checked to ensure compliance with specifications including length, mass, gauge, diameter, and bevel dimensions. Samples are also taken for destructive testing to ensure that the chemistry, strength and fracture toughness of the pipe comply with the specification and that the strength, fracture toughness, hardness and microstructure of the weld seam comply with the specification.
Coating the pipe
Bredero Shaw Technical Services Manager Peter Mayes says that the first order of business when pipe arrives for coating involves the collection of data. Generally this will include pipe size, wall thickness, manufacturer and steel heat number. This information is immediately uploaded into Bredero’s pipe tracking system, PipeTrak, to provide reference and checking ability. The pipe is given a cursory inspection for damage or obvious steel defects on arrival and then stockpiled in the company’s yard.
Nine steps to a successful coat
1. The first stage in the application of coatings is to wash away surface dirt then dry the pipe with a heater before blasting the pipe clean with a mixture of round shot and angular grit. The shot removes mill scale and the grit provides a consistently rough surface profile. The blasting process assists in reducing the potential for stress corrosion cracking in service.
2. The pipe is acid washed to remove any other surface contaminants and rinsed using a high-pressure water spray utilising low-conductivity water.
3. The pipe is heated using high-frequency induction coils to the required application temperature.
4. Epoxy powder is conveyed by clean-chilled compressed air, which is electrostatically-charged, then spray-applied to the rotating pipe. If pipe is to be fusion-bonded epoxy (FBE) coated only, then at this stage, it would be quenched and inspected. However, in the case of a three-layer coating, the adhesion powder or second-layer is then spray-applied by multi-heads while the FBE layer is still liquid and forms a chemical link.
5. The final third-layer or top coat of polypropylene (PP) or polyethylene (PE) is then extruded and spirally applied to the pipe with the molten material combining with the adhesive.
6. The coated pipe progresses to a water quench where it is cooled. Both external quenching and internal quenching may be utilised.
7. The pipe then rolls onto the final inspection racks. Here the coating thickness is measured, and an electrical inspection is conducted to locate pinhole defects – which are commonly called holidays – and the pipes are tallied. The tally station records the raw material batches against the pipe number. Barcode labels are automatically positioned on the pipe ends and a centre line marking may be applied to assist in identifying the mid-point of the pipe during subsequent pipe handling and laying at the right-of-way. An integral non-conformance database controls integrity of the product.
8. The ends are brushed clean and the coating chamfered to facilitate the field joint coating.
9. The finished pipe is removed and transported to the yard for stockpiling.
The coating process is defined by what system and thickness the client has requested. On average, normal production speeds range from 3,500-4,500 m/d. These rates are calculated for a nine-hour shift.
According to Mr Mayes, presently the most popular coating systems in Australia are either single or dual-layer FBE and three-layer PE, with smaller quantities of Yellow Jacket. Internal epoxy lining is provided for gas flow enhancement or for corrosion protection.
This popularity is due to the exceptional corrosion properties of the provided products, which are suitable for Australian operating conditions and temperatures. This is enhanced by its excellent mechanical properties, suitable for all modes of transportation in Australia.
At Bredero, all coatings are applied in accordance with relevant Australian standards or as otherwise specified by the client. The company’s quality assurance team reviews all customer specifications and ensures bilateral agreement in the development of an encompassing Quality Plan. Bredero utilises a fully-equipped quality control laboratory to ensure all coatings meet specification.
Experienced supervisors and team leaders at key stations throughout the process take responsibility for the quality control of their product. When requested, full detailed manufacturer’s data records are available to the customer, which cover the history of pipe during the coating process.
Mr Mayes says that quality control and quality assurance are important elements at every stage of the coating process. Customers’ free-issue material is checked on receipt and the many thousands of individual pipes are logged into the PipeTrak system to maintain traceability and status. Barcodes can also be applied to suit specific project requirements.
Coating quality is assured through the use of audited operating procedures and verified by inspection and testing in the factory and in the laboratory. Depending on the type of coating and the relevant Quality Plan, testing may include: thickness of coating (DFT), holiday testing, adhesion, differential scanning calorimetry, flexibility, resistance to hot water soak, resistance to cathodic disbondment, cross section and interfacial porosity, interface contamination, impact resistance, peel testing, yield strength, per cent elongation, and residual magnetism. Finally, before any pipe leaves the site, one last visual check is always performed.
Throughout the past decade, Mr Mayes says that a number of technological innovations have been successfully integrated at Bredero’s pipe coating facilities. These include:
- Newer coatings for higher operating temperatures;
- New coatings to assist in gouge resistance and to enhance flexibility and impact resistance;
- Other coatings available for use where existing coatings may be considered “˜overkill’;
- Real-time entry of quality control date to touch-screens, providing data for analysis and reporting;
- Automatic barcode application and pipe centre line marking;
- Introduction of low VOC paint products for flow lining;
- Phosphoric acid pre-treatment for all FBE coatings;
- Automated high voltage holiday detector; and,
- The ongoing investigation of applying FBE coatings at lower temperatures with similar desirable properties, thus saving energy cost
In addition, PipeTrak, in conjunction with the company’s automated barcode application, provides clients with assurance that processes will maintain their unique numbering system as supplied by the pipe manufacturers.
According to Bredero Business Development Manager Dean Bennett, the competitive challenge from overseas companies is always prevalent. “However, through advances in coating technology, continuous improvement of the coating process, training and enabling our workforce, working with our customers to ensure their pipeline’s corrosion protection works with repeatable manufacturing processes, and liaising with our suppliers to get the best raw materials has placed Bredero in a competitive position in the Australian marketplace.”
With the ever-changing nature of requirements for gas transmission pipelines, all contributors to the manufacture and supply chain are committed to maintaining their technical and manufacturing excellence and providing solutions to new challenges.