Tight deadlines to meet? It's a steel
Barnard explores the many advantages of choosing fabricated steel over ductile ironGiven the large number of senior engineers that have been lost to the water industry in the past decade, have the advantages of installing steel pipes and fittings been under-valued and even overlooked in recent years? The pressure of today's tight deadlines, which often see consulting engineers and contractors designing and installing on-site, has arguably led to the most obvious route-one consideration - that of standard-sized ductile iron - or has it?
Ductile iron is always going to have its place but with so many current water treatment projects on sites that are as confined for space as they are tight on deadlines, the 'flexibility' of fabricated steel is proving very important. To get round the problem of non-standard shapes and angles in WTWs and WwTWs, carbon steel is forever going to offer more options than ductile.
This is particularly true in the refitting of existing WTWs and WwTWs, where bespoke steel can be shaped and sized to suit almost any twist or turn. "For larger diameters, especially greater than 600mm, carbon steel also has significant cost-savings over other materials", said Ian Tindell, sales and marketing manager at Birmingham-based fabricator Barnard. "Sometimes the benefits of using fabricated carbon steel are not as recognised as they should be", he added. "For example, the price of ductile iron and MDPE and HDPE rises steeply for larger diameters but because we can combine steel fittings, cost-savings are made, and with fewer joints, the likelihood of leakage is also greatly reduced." thrust blocks The use of welded steel pipe also does away with the need for large concrete thrust blocks. This is especially important in remote areas where the supply of ready-mixed concrete may be difficult or in urban areas where there are utility services in close proximity.
On-site welding usually results in damage to the internal coating that may appreciably speed up corrosion. However, this can be eliminated by using line-welded joints, which ensures 100% internal coverage is maintained, without any damage to the coating. These joints are particularly suitable where future maintenance may be difficult or impractical, such as tunnels under river or rail crossings, and will eliminate any concerns about potential leaks at joints.
Standard ductile iron pipes may be mass-produced and therefore easy to obtain in volume, but a growing number of contractors have reported that delivery of ductile fittings is often way behind that of the pipes. Precious time can be lost, tight deadlines compromised and in the worst cases a risk of fines for work not completed on time.potential headaches
Tindell continued: "It is fair to say producing non-standard ductile iron fittings will create headaches for manufacturers and, subsequently, their customers, especially if they are being imported from as far away as China or India, for example, and it should be remembered too that because steel fabrication means less fittings, installation can be significantly quicker, offering a potential reduction in labour costs." Few can disagree there is also the question of weight. Far lighter than ductile iron, carbon steel is much easier to transport and lift into position on-site.
Recognised for its experience, Barnard has been supplying the water and wastewater industry for 30 years and was one of the first companies to have been approved by the Drinking Water Inspectorate (DWI) under 25 (1)(a) for factory coating of potable water pipes using Scotchkote 206N fusion bonded epoxy, as well as BS EN ISO 9001 (2000) quality assurance. Tindell said: "It goes without saying that water quality is imperative. But engineers should not shy away from asking about the suitability of any coating material, which will provide the long-term durability required to protect their assets. They should certainly ask if it fully complies with the WIS 4:52:01 (Water Industry Standard) polymeric anti-corrosion barrier coatings. It is especially important such coatings can resist cathodic disbondment."
Unlike some steel fabricators, Barnard's DWI 25 (1)(a) approval is in its own name, with the coating application carried out in-house rather than sub-contracting to a separate coatings specialist - and with the largest fluidised bed in the UK, Barnard can produce bigger pipe sections than most companies in the UK