Fatigue Control
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DET NORSKE VERITAS Recommended Practice DNV-RP-F108, January 2006 Page 21 APPENDIX B DETERMINATION OF WALL THICKNESS AND MEMBRANE STRESS FOR ANALYSES OF PIPES WITH COUNTER BORE B.1 Determination of wall thickness and membrane stress for analyses of pipes with counter bore Counter boring, in order to improve the alignment of the inter- nal pipe diameter, will reduce the wall thickness locally in the weld. The wall thickness and membrane stress for such cases may conservatively be assessed as shown below. The weld cap shall not be included in the wall thickness determination. For surface defects in the root, the depth of the counter bore shall be regarded as part of the crack i.e. the actual defect depth in the pipe is equal to the crack depth established from the ECA less the depth of the counter bore, see. Figure B-1. For long surface defects in the root, this method becomes over- ly conservative. Therefore an assessment shall also be per- formed for a surface crack at the root going around the whole circumference of the pipe. In this assessment the wall thick- ness and membrane stress shall not be adjusted due to the counter bore, but the counter bore shall be regarded as part of the crack depth, see Figure B-2. This method gives a lower bound defect depth for all defect lengths. The defect depth as a function of defect lengths shall be plotted for the two ap- proaches, and the curve that gives the deepest defect depth for a certain defect length may be used as the critical value, see Figure B-3. Similarly, the assessments for defects at the weld cap and for embedded defects shall be in accordance with Figures B-4 and B-5 respectively. Figure B-1 Internal circumferential surface defects WT ECA = WT PIPE – CB a ECA = a PIPE +CB 2c ECA = 2c PIPE Membrane stress ECA = Membrane stress PIPE × WT PIPE /WT ECA PIPE, crack in WM ECA WT PIPE CB a PIPE Cap B a ECA WT ECA PIPE, crack in HAZ FL ECA WT PIPE CB a PIPE Cap B a ECA WT ECA
description
DETERMINATION OF WALL THICKNESS AND MEMBRANE STRESS FORANALYSES OF PIPES WITH COUNTER BORE
Transcript of Fatigue Control
DET NORSKE VERITAS
Recommended Practice DNV-RP-F108, January 2006Page 21
APPENDIX B DETERMINATION OF WALL THICKNESS AND MEMBRANE STRESS FOR
ANALYSES OF PIPES WITH COUNTER BORE
B.1 Determination of wall thickness and membrane stress for analyses of pipes with counter boreCounter boring, in order to improve the alignment of the inter-nal pipe diameter, will reduce the wall thickness locally in theweld. The wall thickness and membrane stress for such casesmay conservatively be assessed as shown below. The weld capshall not be included in the wall thickness determination. For surface defects in the root, the depth of the counter boreshall be regarded as part of the crack i.e. the actual defect depthin the pipe is equal to the crack depth established from the ECAless the depth of the counter bore, see. Figure B-1.For long surface defects in the root, this method becomes over-ly conservative. Therefore an assessment shall also be per-
formed for a surface crack at the root going around the wholecircumference of the pipe. In this assessment the wall thick-ness and membrane stress shall not be adjusted due to thecounter bore, but the counter bore shall be regarded as part ofthe crack depth, see Figure B-2. This method gives a lowerbound defect depth for all defect lengths. The defect depth as afunction of defect lengths shall be plotted for the two ap-proaches, and the curve that gives the deepest defect depth fora certain defect length may be used as the critical value, seeFigure B-3.Similarly, the assessments for defects at the weld cap and forembedded defects shall be in accordance with Figures B-4 andB-5 respectively.
Figure B-1 Internal circumferential surface defects
WTECA = WTPIPE – CBaECA = aPIPE+CB2cECA = 2cPIPE
Membrane stressECA = Membrane stressPIPE × WTPIPE /WTECA
PIPE, crack in WM ECA
WTPIPE
CBaPIPE
CapB
aECA
WTECA
PIPE, crack in HAZFL
ECA
WTPIPE
CBaPIPE
CapB
aECA
WTECA
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Figure B-2Internal circumferential surface defect that goes around the whole circumference of the pipe
Figure B-3Critical circumferential surface defect, combination of the assessment method described in Figs. B-1 and B-2
WTECA = WTPIPE
aECA = aPIPE+CBMembrane stressECA = Membrane stressPIPE
PIPE, crack in WM ECA
WTPIPE
CBaPIPE
CapB
aECA
WTECA
x
Internal circumferentialsurface defect that goesaround the wholecircumference of the pipe,see Figure B-2
Internal circumferential surfacedefect, Figure B-1
Critical defect sizes
a
2c
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Recommended Practice DNV-RP-F108, January 2006Page 23
Figure B-4 Embedded defects
Figure B-5 Outer circumferential surface defect
WTECA = WTPIPE – CB2aECA = 2aPIPE+CB2cECA = 2cPIPE
Membrane stressECA = Membrane stressPIPE × WTPIPE /WTECA
PIPE, crack in WM or HAZ
CB
CapB
WTEWTPIPE
ECA
WTECA
2aPIPE 2aECA
WTECA = WTPIPE – CBaECA = aPIPE
2cECA = 2cPIPE
Membrane stressECA = Membrane stressPIPE × WTPIPE /WTECA
PIPE, crack in WM or HAZ ECA
CB
CapB
aPIPE aECA
WTPIPE WTECA
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