He then worked as a power ascension test engineer for General Electric Co. In this capacity he had to oversee installation and startup of Westinghouse mechanical equipment at the Callaway Nuclear site in Missouri. Be Connected and Informed. Krrao Flashcards Grammar checker. Brian Gray is a Registered Professional Engineer with over thirteen 13 years experience in the design, analysis, and construction of nuclear and conventional power facilities and asem throughout the United States. He has authored and coauthored more than one-hundred journal publications, conference papers and research reports.
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The service history on these vessels is good, resulting in an attitude that the current code rules are too restrictive. However, there is an alternate way to understand these vessels: many are in service conditions like propane storage where the pressure at lower temperatures can never get very high.
Many of these vessels can never experience situations of combined high pressure and low temperature. Propane Pressure Temperature Curve: A propane storage vessel typically has a pressure rating of psi.
The pressure temperature curve for Propane is shown Fig-1 below. Some data points have been highlighted on the propane P-T curve. Once the contents of the vessel reach this temperature, a psig relief valve will open allowing the release of some gas reducing the temperature of the remaining contents through boiling heat transfer. Fig 1 — Propane pressure vs temperature curve. Data source A Typical Vessel Design: We designed a sample vessel with a minimum wall thickness to just pass psi service.
A crude generalization is that Curve A represents coarse grained materials with poor low temperature impact toughness properties like some SA materials. Curve D materials have the best properties obtained through methods like normalization or quench and tempering. Curve B and C are intermediate materials. The program reported the allowed minimum temperature for the design as the pressure was changed Fig 2. But for all material groups, by lowering the design pressure, lower minimum temperatures resulted.
The Curve A material can be seen to have the poorest pressure rating at low temperature, and the Curve D the best. This is recorded according to the rules of UG a 5 footnote 37 which does not restrict the number of minimum temperature pressure combinations used. One full calculation set is required for each P-T combination. As an alternative to using these curves, it is possible to impact test materials and welds.
In general it does not pay to be optimistic about coarse grained materials and welds passing impact tests prior to seeing the actual test results. More on SA material: Source: www. There were two grades in S A and B, each with two different minimum tensile strength requirements controlled by carbon content.
In … it was required in SA that plates intended for low-temperature service must meet the impact requirements in SA SA could be purchased to a fine-grain-melting practice-and subsequently normalized and tempered-for low temperature service, or purchased to a coarse grain-melting practice; the single specification permitted the manufacture of both plate grades.
The SA Specification continued up to as the carbon steel plate material of choice for low-temperature service for boiler drums and pressure vessels. They continue to be used today as the carbon steel plate materials of choice for boiler and pressure-vessel applications. SA in older vessels being recalculated could be either coarse or fine grain. Either Curve A or a better curve.
Proving that it was built to fine grain practice and impact tested to SA could be difficult for an old vessel. Sometimes it is only possible to assume that it was made to Curve A. There are also some concerns that special care is required for hydrotesting coarse grained pressure vessels. The CRN calculations are based on the inspected wall thickness. Three possible calculation methods are used: 1 calculations to be based on current code rules see note from ABSA below ; 2 Calculations based on code rules at time of construction or; 3 Calculations based on both the time of construction and the current code rules, the most conservative to be applied.
Some of our customers place reserve bids on used vessels and do not complete the transactions until the CRN has been obtained. It is important to get this sorted out before moving the vessel! More info from ABSA : 1. Is it permissible to bring into and operate a used pressure vessel that was manufactured of SA Grade B steel? The vessel was not impact tested when it was manufactured.
A used pressure vessel made of SA Grade B steel may be brought into and registered for operation in provided that its proposed design conditions meet the intent of the current ASME Pressure Vessel Code.
It is assumed that it is not feasible to impact test all the shell and head plates and weld joints to support an MDMT lower than that without impact testing.
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Dual Certified Vessels for Low Temperature Service