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ML00149 - Dec.2018

Vibration Induced Fatigue in a Gas Piping

Micrography of a transverse section of the seamless pipe, presenting a ferritic-pearlitic structure.

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70
of a of the , presenting a - .
M

Material

Low Carbon Steel
  • ASTM A 106 Grade B
Ds

Description

After 10 years in operation, the horizontal 8” line of a gas has suffered at the main , seamless, associated to the margin of the weld between the pipe and a lateral branching with a . The system evidenced vibration, more recently. The cracks initiated at the margin of the , in the upper part of the branch, propagating into the pipe thickness.

C

Chemistry (% in weight)

Pipe analysis

0.22C; 0.24Si; 1.06Mn; 0.009P; 0.006S; 0.03Cr; 0.01Mo; 0.02Cu.

Weld metal analysis

0.10C; 0.48Si; 1.24Mn; 0.012P; 0.013S; 0.05Cr; 0.01Ni; 0.02Mo; 0.08Cu; 0.007V.

Associated Images
Gas piping. Aspect of a branching line 2" ND, lateral to a horizontal main pipe ND 8", welded using a weldolet. The cracking started at the margin of the weld in the upper part of the pipe, where the weld crossed the longitudinal direction of the pipe, perpendicular to the branch.
932
VIEW
ML00149 / Dec.2018
Vibration Induced Fatigue in a Gas Piping
M - Low Carbon SteelP - Piping spoolAp - FPSOCd - Vibration Induced Fatigue
Cm - Aspect Before AnalysisDf - Cracking
Gas piping. Aspect of a branching line 2" ND with a flange, lateral to a main pipe ND 8", welded using a weldolet. The cracking is at the margin of the weld.
115
VIEW
ML00149 / Dec.2018
Vibration Induced Fatigue in a Gas Piping
M - Low Carbon SteelP - Piping spoolAp - FPSOCd - Vibration Induced Fatigue
Cm - Aspect Before AnalysisDf - General View
Micrography of a transverse section of the seamless pipe, presenting a ferritic-pearlitic structure.
84
VIEW
ML00149 / Dec.2018
Vibration Induced Fatigue in a Gas Piping
M - Low Carbon SteelP - Piping spoolAp - FPSOCd - Vibration Induced Fatigue
Cm - Nital Etched Micrography by OMDf - Ferrite and Pearlite
Micrography of a transverse section of the seamless pipe, presenting a ferritic-pearlitic structure.
70
VIEW
ML00149 / Dec.2018
Vibration Induced Fatigue in a Gas Piping
M - Low Carbon SteelP - Piping spoolAp - FPSOCd - Vibration Induced Fatigue
Cm - Nital Etched Micrography by OMDf - Ferrite and Pearlite
Gas piping. Aspect of a branching line 2" ND, lateral to a horizontal main pipe ND 8", welded using a weldolet. In the lower part of the branch there are no cracks.
61
VIEW
ML00149 / Dec.2018
Vibration Induced Fatigue in a Gas Piping
M - Low Carbon SteelP - Piping spoolAp - FPSOCd - Vibration Induced Fatigue
Cm - Aspect Before AnalysisDf - Welded Joint
Aspect of the brach line viewed from the internal side of the main pipe, after cuting. It is possible to see that the pipe was perforated by a thermal cutting (looking the finishing aspect of the edge of the hole). The weldolet was welded only from the external side of the pipe.
62
VIEW
ML00149 / Dec.2018
Vibration Induced Fatigue in a Gas Piping
M - Low Carbon SteelP - Piping spoolAp - FPSOCd - Vibration Induced Fatigue
Cm - Aspect Before AnalysisDf - Internal Surface
Aspect by dye check of the upper side of the pipe, at the margin of the weld between the main pipe and the lateral branch, presenting a fatigue cracking initiated at the external side, probably induced by vibration.
68
VIEW
ML00149 / Dec.2018
Vibration Induced Fatigue in a Gas Piping
M - Low Carbon SteelP - Piping spoolAp - FPSOCd - Vibration Induced Fatigue
Cm - Aspect by NDTDf - Cracking
Aspect by dye check of the internal side of the 8" pipe, at the hole of the 2" lateral branch line, presenting the through thickness cracking initiated by fatigue at the external side, probably induced by vibration.
57
VIEW
ML00149 / Dec.2018
Vibration Induced Fatigue in a Gas Piping
M - Low Carbon SteelP - Piping spoolAp - FPSOCd - Vibration Induced Fatigue
Cm - Aspect by NDTDf - Through Wall Cracking
Aspect by dye check of the upper side of the pipe, external, at the weld between the 8" main pipe and the 2" lateral branch, presenting a fatigue cracking initiated at the weld margin and propagating into the base metal in a longitudinal direction.
55
VIEW
ML00149 / Dec.2018
Vibration Induced Fatigue in a Gas Piping
M - Low Carbon SteelP - Piping spoolAp - FPSOCd - Vibration Induced Fatigue
Cm - Aspect by NDTDf - Cracks
Macrography of a transverse section of the 8" pipe, cut exactly in the middle of the lateral 2" branch line, showing the through thickness crack initiated at the margin of the weld, in the upper part of the pipe.
64
VIEW
ML00149 / Dec.2018
Vibration Induced Fatigue in a Gas Piping
M - Low Carbon SteelP - Piping spoolAp - FPSOCd - Vibration Induced Fatigue
Cm - NItal Etched MacroDf - Welded Joint
Macrography of the 8" pipe, welded to a 2" fitting (weldolet), welded to a 2" flange. The branch line was operating in this position (horizontal line with a lateral branch) and the through thickness fatigue crack is associated to the margin of the weld in the upper part of the pipe.
50
VIEW
ML00149 / Dec.2018
Vibration Induced Fatigue in a Gas Piping
M - Low Carbon SteelP - Piping spoolAp - FPSOCd - Vibration Induced Fatigue
Cm - NItal Etched MacroDf - Cracking
Macrography of a section tranverse to the pipe and to the weld between the 8"pipe and the 2" fitting weldolet. The crack starts exactly at the margin of the weld, in a geometric stress concentration raiser, in a position where it growths in the pipe longitudinal direction, and propagates in a straight line, not related to any metallurgical aspect.
41
VIEW
ML00149 / Dec.2018
Vibration Induced Fatigue in a Gas Piping
M - Low Carbon SteelP - Piping spoolAp - FPSOCd - Vibration Induced Fatigue
Cm - NItal Etched MacroDf - Margin of the Weld Crack
Macrography of a section tranverse to the pipe and to the weld between the 8"pipe and the 2" fitting weldolet. The crack starts exactly at the margin of the weld, in a geometric stress concentration raiser, in a position where it growths in the pipe longitudinal direction, and propagates in a straight line, not related to any metallurgical aspect.
33
VIEW
ML00149 / Dec.2018
Vibration Induced Fatigue in a Gas Piping
M - Low Carbon SteelP - Piping spoolAp - FPSOCd - Vibration Induced Fatigue
Cm - NItal Etched MacroDf - Fatigue Crack
Micrography showing the cracking starting point, in the pipe, exactly at the margin of the weld.
292
VIEW
ML00149 / Dec.2018
Vibration Induced Fatigue in a Gas Piping
M - Low Carbon SteelP - Piping spoolAp - FPSOCd - Vibration Induced Fatigue
Cm - Nital Etched Micrography by OMDf - Margin of the Weld Crack
Micrographic detail of the cracking starting point, in the pipe, exactly at the margin of the weld.
33
VIEW
ML00149 / Dec.2018
Vibration Induced Fatigue in a Gas Piping
M - Low Carbon SteelP - Piping spoolAp - FPSOCd - Vibration Induced Fatigue
Cm - Nital Etched Micrography by OMDf - Fatigue Crack
Micrography of a section tranverse to the pipe and to the weld between the 8"pipe and the 2" fitting weldolet. The crack starts exactly at the margin of the weld and propagates in the pipe longitudinal direction, in a straight line, not related to any metallurgical aspect.
30
VIEW
ML00149 / Dec.2018
Vibration Induced Fatigue in a Gas Piping
M - Low Carbon SteelP - Piping spoolAp - FPSOCd - Vibration Induced Fatigue
Cm - Micrography by OMDf - Cracking
Micrographic detail of the fatigue crack propagation in the pipe longitudinal direction, in a straight line, not related to any metallurgical aspect.
29
VIEW
ML00149 / Dec.2018
Vibration Induced Fatigue in a Gas Piping
M - Low Carbon SteelP - Piping spoolAp - FPSOCd - Vibration Induced Fatigue
Cm - Micrography by OMDf - Fatigue Crack
Micrography of a section tranverse to the pipe and to the weld between the 8"pipe and the 2" fitting weldolet. The crack starts exactly at the margin of the weld and propagates in the pipe longitudinal direction, in a straight line until it reaches the condition of overloading and through wall final rupture, with strong plastic deformation as can be seen around the crack.
25
VIEW
ML00149 / Dec.2018
Vibration Induced Fatigue in a Gas Piping
M - Low Carbon SteelP - Piping spoolAp - FPSOCd - Vibration Induced Fatigue
Cm - Nital Etched Micrography by OMDf - Plastic Deformation
Micrographic detail of the final fracture by overloading after the fatigue crack propagated almost through the wall thickness. The microstructure presents strong plastic deformation around the crack, in a ferritic pearlitic structure.
29
VIEW
ML00149 / Dec.2018
Vibration Induced Fatigue in a Gas Piping
M - Low Carbon SteelP - Piping spoolAp - FPSOCd - Vibration Induced Fatigue
Cm - Nital Etched Micrography by OMDf - Ductile Fracture