Spiral welded pipes ideal for municipal works

The issue of water security for South Africa not only circumscribes the entire water sector, but also has far-reaching consequences across the entire economy of South Africa. In the context of the Department of Water and Sanitation’s master plan, water security touches on many facets, including identifying future water sources for our growing population, the operation and maintenance of water and sanitation infrastructure, and the proper management of our water quality. It affects the growth and development of all sectors of our economy.

The roll-out of water and sanitation civil infrastructure is a key step towards the realisation of ensuring water security and availability in our communities. It also has a plethora of value-added opportunities addressing employment, industrialisation, manufacturing localisation and designation of materials.

Spiral welded pipe is a 100% designated product as per Treasury Designated Sector Circular No.4 of 2017/2018 and a product that is suitably applicable in municipal piping applications for the conveyance of water. It has been used extensively by many municipalities and metros in their water infrastructure projects with great success, sustainability and suitability.

Locally, we have three proudly South African companies manufacturing spirally welded, large-bore steel pipes, ranging from 500 mm up to 3 500 mm in diameter – these are Africa Pipe Industries, Hall Longmore and LB Pipes (formerly Group Five Pipe). They have been servicing and supplying pipeline infrastructure for water projects for many years and on various notable projects. Examples of a few municipal projects are:
• TCTA – Vaal River Eastern Subsection (VRESAP) where Eskom and Sasol were key strategic end-users: 125 km water pipeline. OD: 1 930 mm; steel grade: API X42, X52 and X65; Sintakote coating and bitumen fibre wrap.
• eThekwini Water and Sanitation: 70 km Western Aqueduct. OD: 610 mm to 1 600 mm; Sintakote coating.
• Komati Water Supply Augmentation Scheme: 70 km water pipeline. OD: 813 mm and 1 118 mm; steel grade: API X42 and X52.
• Contermanskloof Reservoir for City of Cape Town: 2.2 km pipeline. OD: 914 mm to 1 016 mm; steel grade: API X42. Cement mortar lining; rigid polyurethane coating. • Booysens Ext 4 for City of Tshwane: 4.9 km pipeline. OD: 800 mm to 1 100 mm; solvent-free epoxy lining; rigid polyurethane coating.
• Various pipelines for Rand Water augmentation projects, and upgrades of various diameters, mainly using X42 grade steel. Solvent-free epoxy lining; polymer modified bitumen coating. Spiral welded pipe is designated because it is readily manufactured in South Africa, sufficiently meeting all local demand needs. It is in many ways superior to imported products designed to serve similar purposes.

Fully engineered system
The versatility and strength of spiral welded steel pipes allow for customised performancebased designs to meet the criteria specified. Unlike other imported products that have been used by some municipalities, the type of steel can be selected to meet the specific strength and other physical/mechanical properties needed for a given application. The imported products can only be regarded as commodities, as they limit the ability of a designer to engineer to specific needs. The ability to fully engineer a steel pipe system with a wall thickness ranging from 4.5 mm to 25 mm, to the type of integral jointing system needed, to the specific type of lining and coating (based on the nature of the soils in which it is buried and the fluid it transports), and to the inside diameter required makes it one of the most versatile products available for use in municipal applications. The availability of spiral welded steel pipes in diameter sizes of 500 mm up to 3 500 mm makes them ideal for critical water transmission projects. And, of course, the ability to fully engineer a system results in significant cost savings.

Tensile, yield and elongation
Imported commodity products typically have a standard tensile: yield: elongation www.astpm.com ratio that is representative of all such products used in water and sanitation applications. The ratio for steel can be adjusted as needed. For example, tensile strength can be varied from 50 ksi to 70 ksi; yield strength can be varied from 33 ksi to 55 ksi; and elongation can be varied from 18% to 30% or more. The ability to vary the elongation of steel pipes allows it to withstand stresses and strains without fracturing under shocks from surge, water hammer, earthquakes, cave-ins, washouts, extreme temperature changes, traffic vibrations, unstable foundations, and blasting.

Corrosion control
The reason for the wide use of steel pipe is directly related to the steel pipe industry’s efforts to control the effects of corrosion when metal pipes are buried, resulting in a minimum service life of 50 to 100 years.

In order to prolong the lifespan of the pipelines, a variety of linings and coatings, which are adapted to suit South African conditions and challenges, are offered. Corrosion protection on pipelines is critical, as corrosion can reduce pipe service life drastically, makes water unfit for use, and also exposes the environment to harmful materials.

The steel pipe industry offers very effective lining and coating systems. Linings such as cement mortar significantly improve the longterm hydraulic capabilities of steel pipe by preventing internal corrosion or tuberculation. On the coatings side, both cement mortar and polyurethane are products of choice. Other dielectric coatings are also specified throughout South Africa for both water and wastewater applications.

Keitumetse Moumakoe is the executive director at the Steel Tube Export Association of South Africa.