An Experimental Investigation on Welding of 5Cr- 0.5Mo Material for Heat Exchanger Application

Abstract

Chromium-Molybdenum (Cr-Mo) steels are widely used in oil refineries, petrochemical industries and power plants for
various applications, including heat exchangers, pressure vessels and piping. The main advantage of these steels are the
improved creep strength due to addition of Molybdenum and enhanced corrosion resistance imparted by chromium.
5Cr-0.5Mo steels are extensively used in seamless tubing in petroleum industry because of their corrosion resistance
against oils and crude containing hydrogen sulphides and other corrosive agents. The main advantage of 5Cr-0.5Mo steels
is the improved oxidation resistance because of increased Chromium content. In modern refineries, a more recent and
common application of this steel grade is in the fabrication of desulphurization plants used for the production of clean
low Sulphur petrol and diesel fuels.
In recent past, L&T heavy engineering received a challenging project for manufacturing of 2 nos.of high-pressure exchangers
involving 5Cr-0.5Mo material having a wall thickness of 85 mm. The severe operating conditions also demanded a stainless
steel347 weld overlay on inner surface of the vessel. Producing crack-free weldments in 5Cr-0.5Mo which are adequate for
a given service would conventionally entail correct choice of filler metal, stringent welding conditions including preheat,
proper welding technique and post-weld heat treatment (PWHT). This paper describes about development of welding
procedures for this material and our experience in successful fabrication of high pressure exchangers with 5Cr-0.5Mo as
the material of construction.