Recent rupture of syngas 10 " bypass line in ammonia unit caused shut down of plant .the investigation showed severe internal corrosion in upper part of the line in which the thickness decreased from 9.2 mm to less than 3mm( from position 9 oclock to 3). In process of ammonia to increase the temperature of outlet gas from absorber tower (from 70 C to 270 C) before intering the methanator the gas go through two exchanger . The bypass line located in the line before syngass intering first exchanger .In normal operation and during the years the control valve in bypass line and the block valves before and after and in the bypass of this control valve were in closed position.The temperature of gas after first exchanger and near the bypass line is 215 C .After failure the valve in bypass of the control valve tested and found that has leakage.The material of pipe is low alloy Cr-Mo steel and no indication of hydrogen attack found in the ruptured zone.The plant use benfiled solution for absorbing CO2.Analyse of the gas is : CO 0.3 CO2 0.2 H2 74.5 N2 24.1 CH4 0.5 AR 0.5 with presure 28.5 Kg/Cm2 and 160000 Nm3/Hr flow. Any comment to hel;p us find the cause of corrosion would be appreciated. masoud

Masoud 10" by pass line at the down stream of CO2 absorber tower - low alloy steel material - might have failed due to higher velocity erosion -corrosion. Low alloy steel at this temp 270 deg cent with partial hydrogen gas pressure being low will not fail from hydrogen related damages. By pass line failure when main line valves are kept in closed condition or if main line control valve kept half throttled or leaking conditions will allow less fluid and more velocity in the by pass line. If flow in the line is less with more velocity than design will contribute to erosion corrosion and this will contribute to reduced thickness with the leaky control valve positioning. Your reduced thickness from 9.0 mm to 3.0 mm partially at the bends or sides of straight is a result of this erosion corrosion impact corrosion due to high velocity CO2-CO-H2 gas impact. Hope this helps C.V.Srinivasan Nishi Engineers Pvt Ltd India April 13, 2010 E-mail: nishi@vsnl.com >Recent rupture of syngas 10 " bypass line in ammonia unit >caused shut down of plant .the investigation showed severe >internal corrosion in upper part of the line in which the >thickness decreased from 9.2 mm to less than 3mm( from >position 9 oclock to 3). In process of ammonia to increase >the temperature of outlet gas from absorber tower (from 70 >C to 270 C) before intering the methanator the gas go >through two exchanger . The bypass line located in the line > before syngass intering first exchanger .In normal >operation and during the years the control valve in bypass >line and the block valves before and after and in the >bypass of this control valve were in closed position.The >temperature of gas after first exchanger and near the bypass >line is 215 C .After failure the valve in bypass of the >control valve tested and found that has leakage.The material >of pipe is low alloy Cr-Mo steel and no indication of >hydrogen attack found in the ruptured zone.The plant use >benfiled solution for absorbing CO2.Analyse of the gas is : >CO 0.3 CO2 0.2 H2 74.5 N2 24.1 CH4 0.5 AR 0.5 with presure >28.5 Kg/Cm2 and 160000 Nm3/Hr flow. >Any comment to hel;p us find the cause of corrosion would be >appreciated. >masoud