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Quick guide to api 570 4 131 terminology api and asme

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Quick Guide to API 5704
1.3.1TerminologyAPI and ASME documents use terminology that occasion-ally differs from that used in European and other codes.Non-destructive examination (NDE), for example, is nor-mally referred to as non-destructive testing (NDT) in Europeand the API work on the concept that an operative whoperforms NDE is known as theexaminerrather than the termtechnicianused in other countries. Most of the differences arenot particularly significant in a technical sense – they justtake a little getting used to.In some cases, meanings can differbetweenASME andAPI codes (pressure and leak testing are two examples). APIcodes benefit from their principle of having a separate section(seeAPI570section3)containingdefinitions.Thesedefinitions are selective rather than complete (try and findan explanation of the difference between the termsapproveandauthorize, for example).Questions from the ICP examination papers are basedsolely on the terminology and definitions understood by thereferenced codes. That is the end of the matter.1.3.2CalculationsHistorically, both API and ASME codes were based on theUnited States Customary System (USCS) family of units.TherearepracticaldifferencesbetweenthisandtheEuropean SI system of units.SI is a consistent system of units, in which equations areexpressed using a combination ofbaseunits. For example:StressSð Þ ¼pressurepð Þ ±diameterdð Þ2±thicknesstð ÞIn SI units all the parameters would be stated in their baseunits, i.e.Stress:N/m2(Pa)Pressure:N/m2(Pa)Diameter:mThickness: mInterpreting ASME and API Codes5
Compare this with the USCS system in which parametersmay be expressed in several different ‘base’ units, combinedwith a multiplying factor. For example, the equation fordetermining the minimum allowable corroded shell thicknessof storage tanks istmin¼2:6ðH²1ÞDGSEwheretminis in inches, fill height (H) is in feet, tank diameter(D) is in feet,Gis specific gravity,Sis allowable stress in psiandEis joint efficiency.Note how, instead of stating dimensions in a single baseunit (e.g. inches) the dimensions are stated in the mostconvenient dimension for measurement, i.e. shell thickness ininches and tank diameter and fill height in feet. Rememberthat:.This gives the same answer; the difference is simply in themethod of expression..In many cases this can be easier to use than the morerigorous SI system – it avoids awkward exponential (106,10-6,etc.)factorsthathavetobewritteninandsubsequently cancelled out..The written terms tend to be smaller and more convenient.1.3.3Trends in code unitsUntil fairly recently, ASME and API codes were writtenexclusively in USCS units. The trend is increasing to expressall units in dual terms USCS(SI), i.e. the USCS term followedby the SI term in brackets. Note the results of this trend:.Not all codes have been converted at once; there is aninevitable process of progressive change.

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Term
Fall
Professor
NoProfessor
Tags
Passing, Nondestructive testing

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