Selection of pipe flange grades and types for concentrated sulfuric acid?
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According to the standards HG 20660-2000, sulfuric acid is classified as a medium-hazardous medium. Per clause 7.2.3 of HG/T 20583-2011, the nominal pressure class of the flanges used for connections to storage tanks holding concentrated sulfuric acid should be no less than 1.6 MPa. Appendix B of HG/T 20583-2011 specifies that for sulfuric acid with a concentration of 79%–98%, the nominal pressure class of the flanges should be 0.6 MPa, with the flange type being flat weld. According to Appendix B of standard HG/T 20583-2020, for sulfuric acid with a concentration of 79%–98%, the nominal pressure class of the flanges is still 0.6 MPa, but the flange type is butt weld. Question: 1. Should the nominal pressure of the flanges used for connections to storage tanks holding concentrated sulfuric acid be set at 0.6 MPa as specified in Appendix B, or should it be no less than 1.6 MPa? 2: Was the change in flange type from butt welding to socket welding in HG/T 20583-2020 due to the upgrade of the hazard level of sulfuric acid from moderate to extreme hazard in HG/T 20660-2017? If it is due to extreme hazards, should the nominal pressure class of the connection flanges for concentrated acid storage tanks be selected at no less than 2.0 MPa in accordance with the provisions of 4.2.3 of HG/T 20583-2020?
It’s a bit inappropriate according to the rules; those who are well-informed should speak up
According to the new version, sulfuric acid 20660 is highly hazardous; the pressure rating should be increased to PN25
According to the latest standards, the scope of application for butt-welded flanges is becoming increasingly limited
There seem to be some issues with the table contents in HG/T20583-2020. Standard HG/T20592-2009 does not specify welded flanges for pressure class PN6; sulfuric acid is considered a highly hazardous medium, and the pressure class for pipe flanges should be at least 2.0 MPa.
HG/T20660-2017 classifies sulfuric acid as a highly hazardous medium, but the regulations on fixed containers still refer to HG/T20660-2000; in that version, it is classified as a moderately hazardous medium. The choice depends on the designer, who must take into account all relevant factors related to the conditions of use of the container.
Still follow Version 2000 of the Fixed Capacity Regulations, classified as moderate hazard.
Is this important? What matters is the material; it’s better to choose a flange with a higher grade. The price difference among the 0.6, 1.0, and 1.6 specifications isn’t significant
Based on our experience, using flanges with a pressure rating of 1.0 MPa for concentrated sulfuric acid is no problem.
Is it a plate-type butt weld flange, or a necked weld flange?