ASME HPS:2003 pdf download HIM PRESSURE SYSTEMS
2100 GENERAL
The objective of Section 2000 is to describe “hazards’which may be present in high pressure systems. Theword “hazard”implies the potential to do damage.
Particular emphasis is placed on hazards which aresignificantly enhanced by the presence of high pressureSome of the more probable hazards are discussed inthis Section, but one should recognize that all hazardscan not always be anticipated from past experience. Aspecific listing and quantification of hazards shall bedeveloped very early in the planning, siting, and designof any new high pressure facility. The intent of sucha review is to enable the owners and operators of highpressure systems to take positive action for a safesystem.[2] [4] [11]
2101 Leak Before Break Mode
Gcnerally,containment of highpressure demandshigh stress in structural materials.This requires aDesigner to sclect higher strength materials, to usesmaller design factors, or to use heavy wall construction.Hazards resulting from the failure of high strengthmaterials under high stress often give little warningprior to their occurrence. For example, subcritical crackgrowth in high strength alloys under cyclic, high stressamplitudes，and/or in the presence of corrosive orembrittling environments,is extremely hazardous.Growth of such cracks to critical dimensions can leadto sudden and catastrophic release of the containedenergy in the system. A“leak-before-break” mode offailure is preferred in the design, and the use of materialshaving low fracture toughness should be avoided[2] [4] [10] [16] [20]
Engineering or designing “preferential failure modesinto high pressure systems is extremely important.Among these concepts are: the inherent leak-beforebreak material response mode, placement of pressurerelief devices or structures at crucial locations in thesystem, and the design of joints such as flanges and)or bolts to yield. Careful attention shall be given to volume rate of release and safe paths for exhaustingsuch releases.
2200 HAZARDS RELATED TO RELEASE OFCONTAINED ENERGY
The sudden brittle-like fracture of a highly pressurizedvessel, pipe, or component may result in the accelerationof fragments,vessel components and contents, andadjacent structures to high velocity. Contained energyis often expressed as an equivalent weight of TNTexplosive in order to describe this hazard. [S] [6] [8]
2201 Type of Energy Release
The released energy may consist of pressurized fluidenergy of expansion, the strain energy stored in thestructural containment system, and any chemical orthermal energy which might simultaneously participatein the release. The magnitude of contained energyis strongly dependent on the pressure, volumme, andtemperature of contained material. The rate of vesselrupture increases with high stress that may be presentin high pressure systems. Under certain fast releaserates, blast-like shock waves may result and the shockfront pressure may be sufficient to injure personneland damage property and/or control systems. Releaseof a large amount of contained energy in a closedroom may result in a significant overall pressure rise.Small diarheter jet releases of fuids from high pressuresystems may penetrate the skin and other vulnerableparts of the body. If the contained material is hot orcorrosive,someone may get burned. An evaluation ofthe energy contained in a high pressure system shallbe conducted early in the design phase of the system.[4] [8] [12] [21]