Issue 10 2011
Reaching new depths
Tata Steel is part of the Tata Group, a diversified global company with operations in every major world market.
Established in 1907, Tata Steel Group is among the top ten global steel companies with an annual crude steel capacity of over 28 million tonnes per annum. Tata Steel, formerly known as Corus, is also one of Europe’s largest steel producers. It serves many different and demanding markets worldwide, including aerospace, automotive, construction, packaging and energy and power.
Tata Steel manufactures a wide range of products for the oil and gas industry including offshore line pipe. The offshore industry as a whole is extremely demanding in terms of quality and performance of products, but achieving this within the requirements placed on offshore line pipe is a particular challenge.
Offshore line pipe covers a multitude of different activities, with design requirements determined by the purpose of the pipe, however Tata Steel is particularly focused on the challenges of deepwater applications: “One of the biggest concerns about operating in the very deepest waters is whether the pipe is going to be crushed due to the external pressure,” begins Martin Connelly, technical manager (Energy) of Tata Steel. “In the industry this is known as collapse resistance. With these pipes transferring resources like oil and gas it is vital that this doesn’t happen, so collapse resistance has to be incorporated into the design of the pipeline. The use of smaller diameters and/or greater wall thicknesses is one solution to this design challenge. In each case though, this is determined by the volume of product you are transporting, and the selected route for the pipeline.”
It is technically more challenging to control the manufacturing process of a thick wall, small diameter pipe, than a large, thinner wall product. Excellent process control is vital. Tata Steel has one of the world’s most powerful ‘U’ and crimp press combinations. This is utilised within the company’s preferred method of manufacture – the UOE process. First a steel plate is pressed into a U, then an O shape and then welded internally and externally. Finally, the pipe is mechanically expanded to ensure consistency of shape and strength. A small crimp along the length of the pipe is also applied prior to the U pressing stage, which helps deliver the optimum shape for welding. Each step is critical to the manufacture of a quality product with excellent dimensional tolerances, and significant research and investment has been undertaken by Tata Steel to optimise this manufacturing process.
In the eyes of customers though, it is often the weld that is of greatest concern, not only because it has to meet all the properties required by demanding deep-water applications, but also because completing high quality welds in such small diameter pipes is a challenge in itself. Therefore the final processing step is full nondestructive testing (NDT) utilising techniques such as ultrasonics and radiography to check for any defects in the weld.
For many operators and manufacturers the answer to collapse resistance is to increase the wall thickness of the pipe – however this is not always practical, especially with smaller diameter pipes. By increasing the amount of steel used in construction, this also sees a rise in the cost to the end customer. The collapse resistance capabilities of the pipeline manufactured by Tata Steel offers significant customer benefits in this area: “If you can prove that the steel used is more resistant to collapse than the international codes assume it to be, then you can present an opportunity for cost saving, or increased safety, to the market,” explains Martin.
“Through our manufacturing process at Tata Steel we are able to characterise our products in such a way as to challenge the accepted norms for deepwater line pipe design. Over the last ten years we have carried out extensive research and development to prove that you don’t necessarily need to derate your pipe strength by 15 per cent each time (and hence increase wall thickness) – that you may only need five or ten per cent. Having focused our strategy on deepwater applications, this is just one of the advantages we can offer,” he continues.
Another key benefit is the speed of installation afforded by Tata Steel’s highest quality formation process. Although an end client such as BP, Shell, or Chevron may purchase the line pipes an engineering contractor typically lays them. With lay vessels commanding high day rates, there is a palpable need to minimise installation times. One of the biggest threats to this schedule is poor pipe shape, which makes it difficult to closely match and satisfactorily weld the pipes into lengths making them more sensitive to fatigue. If after welding the join doesn’t meet the necessary standards it has to be cut-out, which is time prohibitive.
“Tata Steel’s powerful forming process and shape control means that industry leaders routinely report very fast lay rates with our products,” enthuses Martin. “This rate not only equates to the number of kilometres covered per day, but also the number of cut-outs that have to be performed. In one particular project, Tata Steel supplied approximately 24,000 pipes with just one cut-out during the entire installation process. This is the type of performance that can be expected when you have a deep understanding of manufacturing process.”
It is therefore of no surprise that Tata Steel is involved in some of the most demanding upcoming offshore projects around the globe; recently, Tata Steel’s 42” Mill has successfully manufactured pipes with the complex dimensions of 26-inch diameter, 37.1 mm wall thickness and grade X70 material. This size presented unique challenges to Tata Steel that were addressed through new understanding in tooling design, plate formability and finite element modelling. These advancements resulted in an astounding level of shape control; <2mm out of roundness and <1mm local out-ofroundness were consistently achieved.
Whilst the company’s ever-increasing standards of performance come from its own in-house desire to be world class, it also benefits from its relationship with the European Pipe Research Group (EPRG) in terms of industry engagement. As an entity, EPRG has primarily been focused with onshore line pipes but as hydrocarbon resources become more difficult to source, it is following the market into offshore agendas.
Despite its clear reputation in deep-water practices, Tata Steel is not taking the easy route as it recognises that the energy industry still has a number of challenges to face: “In terms of real long term projection, we can’t look too far in the future because we are dealing with an industry where there is a finite amount of resource available. But certainly for the foreseeable future hydrocarbons are going to be a major part of every countries energy policy. Therefore we continue to push the accepted limits, whilst extending our capabilities into new avenues such as renewable energy,” concludes Martin.
Products: Welded steel tubes and coatings