Pressure Ve Vessel Dimension D imension Inspection The Pressure Vessel Dimension Inspection article provides you with information about the dimens dimension ional al requir requireme ements nts in pressu pressure re vessel vessel constr construct uction ion and press pressure ure vessel vessel inspection. You may know some fabrication tolerances have not been addressed in A!" #ode ection VIII. o you need to refer to other sources for inspection. This article provides you the most important dimensional inspection requirements. The dimensional check of a pressure vessel consists of the followin$ items%
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!ill &ndertolerance of Plates and Pipes
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Tolerances for 'ormed (eads
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)ut of *oundness of shell
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+o,,les and attachments attachments )rientation )rientation
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+o,,les and attachments attachments Pro-ection Pro-ection
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+o,,les and attachments attachments elevation elevation
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+o,,les and attachments attachments levelness levelness
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eld mismatch
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eld reinforcement
Mill Undertolerance of Plates and Pipes Pressure Vessel Dimension Inspection - Plate:
Your pressure vessel plates with /./0 inch or 12 undertolerance3 whichever is smaller3 may be used for full desi$n pressure3 instead of at the $iven desi$n thickness specified. (owever3 if the material specification allows $reater undertolerance3 then the ordered thickness for the material should be sufficiently $reater. 'or e4ample3 if you have A 501 6r.7/ plate with a /.185 inch nominal thickness3 and the actual thickness is /.1053 it is acceptable3 and you may use this plate without any specific desi$n consideration. Global TPI Services e Provide Pre9hipment Inspection3 Vendor Inspection and #ommodity Inspection er vices. #lick (ere for !ore Information
:ut if the same plate has an actual thickness of /.5;5 inches3 you need to consider mill undertolarence in your desi$n calculation. This plate thickness is acceptable based on the material specification inches in your desi$n calculation% e.$. Thickness ? !in Thickness @ #orrosion Allowance @ !ill &ndertolrance Pressure Vessel Dimension Inspection - Pipe:
#ontrary to the plate material3 your pipe and tube mill undertolrances need to be taken into account for desi$n consideration. Pipe and tube undertolrances are almost 908.5 2 of the nominal wall thickness3 but sometimes there are differences for different materials3 so for any specific material3 it shall be referred to the su$$ested pipe or tube material specification to obtain the e4act amount of mill undertolrances. 'or e4ample3 if there is a pressure vessel with nominal shell thickness of /.5 inch3 it needs a 1 A 0/1 6r.: no,,le to be attached to the shell plate. Assume that e4ternal loadin$ is not a desi$n controllin$ factor
o with a consideration of 908.523 the calculation will be% /.5 B /.C75 ? /.570 inches. o when we refer to A!" :>1.0/ and select our pipe schedule it will be A 0/1 6r.: chedule 01/.
Pressure Vessel Dimension Inspection - Tolerances for Formed Head:
You may know that there is a specific rule for dimensional checkin$ of formed heads3 based the fact that the &69C0 inner surface shall not deviate outside of the specified shape more than 00E2 of D and inside the shape more than 5C2. You can use sweep boards3 which are made by cuttin$ a thin steel sheet or piece of wood for checkin$ your crown and knuckle radius. 'or your skirt3 the difference between the ma4imum and minimum inside diameter3 should not be more than 023 and you can use a tape measure or laser measure for dimensional control of the skirt. o to fully understand3 letFs check the followin$ head to$ether%
(ead ID ? >>1E mm (ead Type% Torispherical Gimit for )utside of specified hape ? >>1E 4 0 H2 ? E8./5 mm Gimit for Inside of specified hape ? >>1E 4 5BC 2 ? 80./85 mm o we check the depth3 and the drawin$ is 151.> mm and the actual is 178 mm3 so it is outside of the shape. e need to check if it is in the ran$e of tolerance3 so the ma4imum outside of the shape will be E8./5 @ 151.> ? 1;C.>5 so our actual value is 178 mm. 1781;C.>53 so it is )J. e cut a sweep board equal to the head drawin$ crown radius <>E// mm= and other one for the knuckle radius equal to 8/E mm3 so we try to fit the sweep boards in the heads for the above e4ample of the sweep boards. The ed$e distance to the head surface should not be deviate from the above limited values. kirt ma4 and min ID should not be more than 02 of the ID3 which is >>.1E mm. o3 in the above e4ample skirt is also is )J. )ur nominal thickness is 8/ mm3 so up to 0;.7E1 is acceptable then for the above e4ample. The thickness dimension is also )J. o the above head dimensions are ok Pressure Vessel Dimension Inspection - ut of !oundness of S"ell:
&69C/ deals with out of roundness of shell. The ma4imum permitted ovality tolerance
The out of roundness $enerally is measured in two directions with a normal measurin$ tape or laser measure3 so one direction would be the D ma4 and other one would be the D min. The followin$ picture shows an out of roundness measurement% e Provide TPI Inspection ervices in !ost Industrial Areas Around the 6lobe. #lick (ere for !ore Information
Pressure Vessel Dimension Inspection - #o$$les and %ttac"ments rientation:
A!" #ode "# VIII Div 0 has not specified the orientation tolerances for no,,les and attachments3 so you need refer to the pressure vessel handbook. It is almost @B9 0 de$ree. The orientation check can be done by a simple calculation by usin$ a measurin$ tape in the actual measurement work on the vessel. 'or e4ample3 we want to check +> orientation in followin$ drawin$.
+> is located at 08/ de$rees in the drawin$. The manufacturer has located this point in the vessel with a marker3 and we want to check the location3 and if it is )J3 then we can allow the manufacturer to cut. o we run this simple calculation% Vessel )D ? ;7.C75 hell outside #ircumference len$th ? N 4 )D ? >.0E 4 ;7.C75 ? >/7.>875 >/7.>875 distributed to >1/ de$rees so each de$ree represents >/7.>875B >1/ ?/.C5>1 +> is located at the 08/ de$ree position3 so if we use a measurin$ tape and keep / at the ,ero reference point in the vessel and pull the tape3 the no,,le center should be located at 08/ 4 /.C5>1 ? 0/8.EE85 inches. This 0/8.EE85 is a perfect case so our tolerance is O0 de$rees. o if the tape shows in followin$ ran$e3 it will be )J. 0/8.EE85 K /.C5>1 ?0/0.5CC; 0/8.EE85 @ /.C5>1 ?0/>.8;10 Pressure Vessel Dimension Inspection - #o$$les and %ttac"ments Pro&ection:
+o,,le and attachment pro-ection is the len$th from the no,,le or the attachment face to the vessel shell centerline.
Pro-ection dimensions are addressed in $eneral assembly drawin$s. The pro-ection tolerances are not addressed in A!" #ode "# VIII Div 03 but if you refer to the pressure vessel handbook3 almost O /.85 of an inch is permissible. In followin$ fi$ure3 we need to check the :D no,,le pro-ection. It should be 11/ mm in distance from shell centerline to the flan$e face.
In practical measurement3 you may use a measurin$ tape to measure the distance between the shell outside circumference to the no,,le face. Then the measured value is summed with the shell thickness and the inside radius. o for the above e4ample3 the followin$ ran$e is acceptable%
11/ K 1.>5 ? 15>.15 11/ @ 1.>5 ?111.>5 Pressure Vessel Dimension Inspection - #o$$les and %ttac"ments 'levation:
Your +o,,les and attachments elevation is the len$th between the no,,les or the attachments centerline and the bottom or top head tan$ent line. The elevation dimension is addressed directly in the $eneral assembly drawin$. The elevation tolerances are not addressed in A!" #ode "# VIII Div 03 but if you refer to the pressure vessel handbook3 almost O/.85 inch is permissible. In followin$ fi$ure3 we need to check +o,,le ": elevation. As you see in the drawin$3 the distance between the no,,le centerline to the bottom head tan$ent line is 7// mm.
In actual measurement3 the measurin$ tape or laser measure is used to measure from the no,,le neck center line to the tan$ent line. In this e4ample3 the followin$ ran$e is acceptable% 7// K 1.>5 ? 1;>.15 7// @ 1.>5 ? 7/1.>5 Pressure Vessel Dimension Inspection - #o$$les and %ttac"ments (evelness:
The no,,les and attachments levelness tolerances are not addressed in A!" #ode "# VIII Div 03 but in the pressure vessel handbook3 a Q deflection is permissible.
'or levelness checkin$3 a level $a$e is used. If the bubble is in the middle of the desi$nated lines3 the no,,le is level. :ut if the bubble intersects the desi$nated limit lines3 you need to run a simple calculation and see if your deflection is within the tolerance limit.
You need to move one end of the level $a$e up to the bubble to be placed in middle. Then measure the distance between the level $a$e end and the flan$e face. The measured value is the R in the fi$ure. Then obtain S3 if S is less than /.5Q3 the deflection falls within the tolerances. And it is )J otherwise it will require cuttin$ out and re9weldin$. Pressure Vessel Dimension Inspection - )eld Mismatc":
A!" #ode "# VIII Div. 0 specified tolerances for weld mismatch in &9>>. It is important to know that the limit for weld mismatch is strin$ent for a cate$ory A weld inch mismatch in one lon$itudinal and one circumferential -oint. o you look to the &9>> table%
The permissible weld mismatch in the lon$itudinal -oint for your case is /.085 of an inch3 and for the circumferential -oint3 it is /.0C75 of an inch. Your weld mismatches for both lon$itudinal and circumferential -oints are /.0E>3 so your circumferential -oint is )J3 but your lon$itudinal -oint should be repaired. Pressure Vessel Dimension Inspection - )eld !einforcement:
The same concept for weld mismatch e4ists for weld reinforcement tolerances. The lon$itudinal -oint weld reinforcement limit is more strin$ent than that for circumferential -oints. This is because lon$itudinal -oint bears double stress3 and it is required that the stress concentration is minimi,ed.
In the same e4ample3 assume that there are /.05/ of an inch welds reinforcement for both cate$ory A and : welds. Do you want to review your weld acceptance #ate$ory A allowances ? /./;> inch #ate$ory : allowances ? /.0C75 o our circumferential -oint is )J3 but the lon$itudinal is not )J and should be repaired by removin$ the e4cess weld reinforcement. 9 ee more at% http%BBwww.inspection9for9industry.comBpressure9vessel9dimension9 inspection.htmlUsthash.avyG$kf.dpuf
