We at Chemipetro supply flanges and pipe fittings made of extremely resistant alloys, such as super duplex, to the process industries. The development of these alloys is the result of many hundreds of hours of research. This research is on-going, because even today cracking in petrochemical pipelines, flanges and pumps is a problem – and it isn’t restricted to low-nobility alloys like carbon steel.

When selecting pipe flanges for the petrochemical industry, corrosion resistance is the thing that is usually given highest consideration. However, not all of the accidents that occur in plants today are attributable to corroded pipe fittings alone. Petrochemical pipelines operate under extremes of pressure and temperature. The volatile and corrosive chemicals they contain can leak out in a number of ways, often suddenly and with great force.

NACE (the National Association of Corrosion Engineers) is an internationally recognised organisation that actively researches corrosion control. As recently as 2001, a NACE white paper reported problems of early cracking in pipes and pipe fittings fabricated from alloys selected for their corrosion resistant properties. Failure was observed in the welded areas of stabilised austenitic stainless steel charge heater pipes, in a petrochemical plant where working temperatures in excess of 650 degrees were recorded.

Using detailed FEA (finite elemental analysis) and other techniques, the study showed that a combination of thermal pipe movement, internal pressure and bolt movement at the flanges all contributed to cracking. When choosing pipe flanges, therefore, operators should never depend on the corrosion factor alone. How the flanges are supported to minimise vibrational, thermal and pressure stresses is just as important.