ASME Section VIII, Division

American Society of Mechanical Engineers, ASME Section VIII, Division 1, Pressure Vessels, 1995. 

These recent tests were conducted at applied stress levels similar to those that might be experienced by ASME Section VIII, Division 2 vessels. Test exposure times exceeded 50,000 hours depending on applied stress and temperature. The test specimens were from weldments of thick section plates and represented base metal, weld metal, and heat-affected zone. Detrimental effects of hydrogen were found down to the Figure 1 limit of 850°F (454°C) at 2000 pounds per square inch absolute (14 megapascals) and 3000 pounds per square inch absolute (21 megapascals) hydrogen partial pressure. 

The confusion is due to a number of reasons. First is the way ASME does not relate the maximum allowable pressure (MAP) limits to SRV capacity. Throughout the entire document, ASME, Section VIII, Division 1, refers to MAWP when talking about SRV set pressure and allowable overpressure. 

However, when ASME talks about certifying the capacity of a relief device, MAWP is never mentioned. ASME Section VIII, Division 1, clearly states in paragraph UG-131 (c)(1) that ... 

ASME Section VIII Division 1, 1992 Edition Pressure Relief Devices. Ug-136 Minimum Requirements of Pressure Relief Valves specifies the following regarding springs ... 

The most common pressure vessel codes that include the evaluation of fatigue are the North-American "ASME Section VIII Division 2" [1] and the German "AD-Merkblatt S2" [2], the latter being the most detailed fatigue analysis currently available in pressure vessel codes. 

Impact testing of Grade B7 studs (but not Grade 2H nuts) is required by ASME Section VIII, Division 1 for temperatures below -40 F (-40° C). by ASME VIII, Division 2 for temperatures below -20aF (-30 C), but not by ANSI 831.3 above -50CF (-46 C) if the material Is quenched and tempered. 

B, Impact tests of aluminum are required only under ASME B31.3 for ervfce below -452° F (-2706Q. Notched tensile teats to prove ductility are required for service below -452 F (-270BC) by ASME Section VIII, Division 1... 

The Division 2 code implied from the beginning that the safety factor was being lowered from 4 1, as required by the ASME Section VIII, Division 1 code, to the 3 1 permitted by the Division 2 code. At first it seems that a vessel built to the Division 2 code will be less expensive than a Division 1 code vessel. This conclusion is correct if only the materials and welding used in the manufacture of any such vessel are considered. 

ASME Section VIII, Division 1 requirements to prevent brittle fracture are 15 ft. -lb. Charpy Keyhole applied only below -20°F. Until recently, these requirements were thought to protect against brittle fracture. In the past few years, however, a considerable number of catastrophic brittle fractures in thick-wall pressure vessels have occurred throughout all industry. In each instance, the code impact values seemed to have been met or exceeded. 

Note European codes and ASME Section VIII, Division 2 base the allowable stress, f, on 2/3 yield strength instead of 1/4 the ultimate strength. 

Figure 4-18 compares maximum permissible design stresses for British, German and U.S. carbon-manganese steels about 70 psi ultimate strength. The disparity that existed a few years ago has disappeared. It must be remembered, however, that BS 1515 and ASME Section VIII Division 2 are more exacting and costly than the AD-Merk-blatter Code. 

Second, material costs become dominant only for large values of pressure multiplied by diameter — LPG spheres, for example. For reactors, one of the more notable applications of carbon steel is in cat crackers, where the operating temperature is such that ASME Section VIII Division 1 provides the most economic design stress. 

Spheres are built according to ASME, Section VIII, Division 1 or 2, API 620 or BS 5500. In the United States, ASME, Section Mil, Division I is the most commonly used code of construction. Internationally spheres are often designed to a higher stress basis upon agreement between the u.ser and the jurisdictional authorities. Spheres below I5psig design pressure are designed and built to API 620. 

Figure J-1. Allowable stresses per ASME, Section VIII, Division 1 and Section II, Part D...

Appendix A Guide to ASME Section VIII, Division 1, 443 Appendix B Design Data Sheet for Vessels, 444 Appendix C Joint Efficiencies (ASME Code), 445 Appendix D Properties of Heads, 447... 

The user of this book should be advised that any code formulas or references should always be checked against the latest editions of codes, i.e., ASME Section VIII, Division 1, Uniform Building Code, and ASCE 7-95. These codes are continually updated and revised to incoiporate the latest available data. 

The new ASME Section VIII, Division 2, Part 5 utilizes the distortion energy theory to establish the equivalent stress in an elastic analysis where in the pre-2007 edition this was done with the maximum shear stress theory. 

Some vessels are subjected to periodic repetitions of mechanical and thermal loads and the resulting stresses during their service life. When a vessel is subject to repeated loading that could cause failure by the development of progressive fracture, the vessel is considered to be in cyclic service. The ASME Code, Section VIII, Division 1, does not specifically provide details for the design of vessels in cyclic service. However ASME Section VIII, Division 2 has detailed procedures for determining if a vessel in cyclic service requires a detailed fatigue analysis or not, and how to conduct the analysis. 

Compare the total number of cycles, Nj = Nafp + Napo + Nate + NATa with the criteria listed in Table 5.9 of ASME Section VIII, Division 2, shown in Table 1-3. 

Fatigue curves are used to determine the number of allowable cycles. The fatigue curve is also known as the S - N diagram, because one axis represents stress, S, and the other axis represent number of cycles, N. Each material group has their own fatigue curve based on test results and are shown in ASME Section VIII, Division 2, Annex 3-F. 

Occasionally a vessel shell will sustain damage or be overground in a local area such that the thickness in the damaged area is below the minimum wall thickness. This is known as a Local Thin Area or LTA . ASME VIII-1 has allowance for such a case as long as certain proportions and guidelines are followed. These guidelines are taken from ASME Section VIII, Division 1, Mandatory Appendix 32 and are presented here. 

High pressure vessels can be built to ASME Section VIII, Divisions 1, 2 or 3. People tend to discount Division... 

Thick walled cylinders can be designed to either ASME Section VIII, Divisions 1, 2 or 3. However, what is different in each of the Divisions is the allowable stress. Using the same allowable stress in the equations for the three divisions will yield approximately the same results. An example has been provided to illustrate this. 

There are advantages to using Divisions 2 or 3 from a purely economic cost standpoint, since these two Divisions will yield lesser wall thickness, and therefore cost less to produce. However, this may not be the only consideration for choosing which Division to use. ASME Section VIII, Division 1 can be used economically up to about 10,000 PSI. However, if the designer wishes to reduce the wall thickness to the maximum extent possible, then there are advanced techniques in Division 2 and 3 that may be utilized. These advanced techniques are not covered in this book at this time. 

ASME Section VIII, Division I requires that the minimum metal temperature during hydrostatic test shall be at least 30°F above the MDMT of the vessel that is stamped on the nameplate but not greater than 120°F. 

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