Luis For Carbon Steel piping in refinery service, a typical C.A. assumed and given will be = 1.5 mm (1/16") . In some extreme cases, a C.A. of 1/8" or 3.2 mm is given (but not as a general rule). Piping designer adds this C.A over the calculated design / discard thickness and choose the next commercially available schedule of piping for service use. For other materials - Low Alloy, S.S., Duplex, Ti, Brass, Cu-Ni it varies. Trust this help you C.V.Srinivasan Nishi Engineers Pvt Ltd India July 13, 2006 E-mail: nishi@vsnl.com >Typical corrosion allowances. > >Piping designer, based on service corrosivity, adds >corrosion allowances to the calculated pipe thickness. In a >new oil refinery construction project, which would be >typical corrosion allowances? > >Is there any rule to be followed? > >Thanks > >Luis

Luis You are talking on the one hand of RBI approach for a new refinery - which gives a predictable C.R for a material for a particular refiniing service / temp. When RBI concepts are built -in at the design and pre-ordering and pre-monitoring stage, where is the question of C.A of 6.35 mm coming for an equipment or piping? On the second hand, you are asking for a C.A of 6.35 mm - which with r current day plant design and usage with RBI approach / new materials advancement / new proecess advancements, no licensor or designer would even think or agree to implemetn today ( i guess). Basically, you should remember that providing a known C.A of 6.35 mm for a service - will tremendously increase cost of the project, increase in weight for equipment (tonnage) and difficulties in fabrication, operational problmes. It is partly true there could be no empirical or code guided rule to specify C.A other than the 50-60 years of refining practice and corrosion effects to more or less standardize the parameters of C.A of 1.5 mm and in the extreme case to 3.2 mm. That is why a little corrosion allowance is given for unknown factors in design stage to avoid future problems. A licnesor, piping designers or equipment manufacturers have to go be accepted industry standards and accepted code guided rules for designing. It is a universal prctice in the refining industry for the last 60 years. Please go by code guided parameters and industry standards for an existing plant or for a new plant as well. Trust this answeres yoru querry C.V.Srinivasan Nishi Engineers Pvt Ltd India July 13, 2006 E-mail: nishi@vsnl.com >Thank you very much Srinivasan > >For high temperature services on bottom cuts of corrosive >hydrocarbon services should we use 6.35mm corrosion >allowances? >From my search on this subject I suppose that there is no >rule or recommended practice and the things are a little bit >established ad hoc empirical based on licensors experience. >I think that actually in a new refinery construction a RBI >approach should be made to define expectable corrosion rates >then based on those expectable corrosion rates designer >should add corrosion allowances with the following criteria: >high corrosion rates high corrosion allowance, medium >corrosion rates medium corrosion allowance, low corrosion >rates low corrosion allowances. > >Thanks for you sharing > >Luis