To keep the world’s supply of oil and gas flowing, many of today’s sub-sea carbon steel pipelines are dosed with chemical inhibitors to control corrosion caused by ever more aggressive fluid conditions. As inhibitors are expensive, engineers need to measure the rate at which pipelines are corroding, in order to introduce chemicals at the right time and in optimum quantities.
An innovative solution to measuring corrosion rates 3,000 m below the sea is manufactured by West Sussex-based Cormon Limited, a leading provider of corrosion monitoring packages for the oil and gas industry. The company’s Ring Pair Corrosion Monitor (RPCM) is a high-resolution pipeline corrosion monitor developed for deepwater, high-pressure, high-temperature applications. The piggable device, which is designed for lay barge installation, is butt welded into the pipeline making it ideal for use in subsea oil and gas developments that have long pipelines tying them back to existing platforms or shore facilities.
Weld overlay cladding specialist Arc Energy Resources is Cormon’s preferred supplier of welding and fabrication services, particularly for the RPCM spool, so when a recent order for 10 units was placed for a major offshore gas infrastructure project in India, the two companies began a collaboration that produced one unit every week in a schedule that was only interrupted by a two-week break at Christmas 2007.
The order, the largest ever for RPCMs, was placed by Reliance Industries Limited (RIL), one of the first private sector companies in India’s exploration and production sector to have discovered large gas reserves. This new field is expected to provide natural gas for a vast number of India’s burgeoning industries.
 Because the pipeline is linked directly to a shore facility it is subjected to multi-phase flows containing media such as water, oil and carbon dioxide, which is why RIL specified the latest high-resolution, dual redundant, RPCMs featuring remotely operated vehicle (ROV) retrievable electronics. They provide real-time measurement to less than a micron; a level of accuracy that allows the pipeline operator to respond more quickly to corrosion problems in order to reduce chemical usage and extend the life of the pipeline.
As RPCMs are designed to be part of the pipeline, they must have the same performance characteristics as the pipeline itself, which is why Arc Energy’s input is an essential element of Cormon’s production planning, as Bob Davies of Cormon explains.
“The electronics package in each RPCM includes a fixed instrument pod, ROV retrievable pod and an inner spool assembly. The sets were prefabricated by Cormon and delivered to Arc Energy with the main forgings and pipe sections. Arc Energy applied weld overlay cladding to the inside of the forgings, carried out the machine finishing and welded on sections of pipe, known as pup joints, to the forgings.
“Our engineers then installed the electronics and assembled the RPCM, at which stage Arc Energy performed the high specification girth welds to join the halves together and then added end domes to prepare the unit for pressure testing. This stage, together with NDT testing and factory acceptance testing with our customer, was carried out at Arc Energy’s Gloucestershire factory. The final stage was removal of the domes and preparation of the pipe for welding on the lay barge,” Davies said.
The steels used are high-strength X65 (65,000 lb yield), which means that welding procedures are critical and have to be meticulously qualified. Davies believes that in welding circles this contract would be recognised as an exceptional challenge. He also acknowledges that Arc Energy responded very well to the challenge. 
Explaining the significance of the project and the collaboration, he says: “This is the first time we have needed to produce one unit a week, and for an eight week period leading up to Christmas 2007 we actually completed one a week. It required a considerable amount of planning and teamwork between our two companies, which resulted in our engineers being onsite at Arc Energy for around 14 weeks in all.
“Meticulous planning was vital due to the volume of work and the timescales, as was the ability to repeat the production process week after week. But that’s exactly what we achieved and if Christmas hadn’t been in the way, we would have produced all 10 in 10 weeks. As it was, the delivery schedule was maintained throughout the project!”
Commenting for Arc Energy Resources, technical and quality director Neil Cook says: “The project was a major undertaking for Arc Energy, and was a good test of our all round ability. It was also a useful learning curve and we are sure the experience gained would enable us to produce one RPCM a week throughout the year.”
Summing up the relationship, Davies says Arc Energy is much more than Cormon’s welding services supplier: “They are our fabrication partner. They do our cladding, all our weld qualification, machine finishing and NDT testing as well as providing facilities for our engineers to carry out pressure testing and client acceptance testing. They work well with our people and our clients which gives everybody confidence in the quality of the product we produce together.”