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ML00140 - May.2019

Preferential Corrosion of Pipe Seam Weld

Macrography of a transverse section of the pipe, 8 mm thick, presenting localized dissolution at the longitudinal autogenous seam weld.

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of a of the , 8 mm thick, presenting localized dissolution at the longitudinal autogenous weld.
M

Material

Low Carbon Steel
  • API 5L grade B
Ds

Description

After some years in service, the 4” has suffered in the longitudinal autogenous weld, causing pipe in a straight line. The showed biological growth and the presence of barnacles that probably affected the flowing capacity, and operational conditions as well as created environmental changes under deposits, being responsible for the preferential dissolution of the centerline, which hardness level is higher than the pipe .

C

Chemistry (% in weight)

Pipe Analysis

0.17C; 0.02Si; 0.83Mn; 0.014P; 0.010S; 0.02Cr; 0.01Ni; 0.01Mo; 0.001V.

Associated Images
Aspect of a transverse section of the 4" pipe showing the barnacles adhered to the internal pipe surface, and the leakage position (in the top of the figure). It is possible to see that the deposits are attached all throught the internal pipe perimeter but the damage is localized. The damage morphology suggests it is a crack, or a welding defect, but the microstructural analysis indicated that the damage is a galvanic effect at the autogenous seam weld.
1135
VIEW
ML00140 / May.2019
Preferential Corrosion of Pipe Seam Weld
M - Low Carbon SteelP - Longitudinal Seam Welded PipeAp - ShipCd - Preferential Dissolution
Cm - Longitudinal Section AspectDf - Localized Corrosion
Micrography of the pipe transverse section presenting a granular microstructure.
147
VIEW
ML00140 / May.2019
Preferential Corrosion of Pipe Seam Weld
M - Low Carbon SteelP - Longitudinal Seam Welded PipeAp - ShipCd - Preferential Dissolution
Cm - Nital Etched Micrography by OMDf - Transverse Section
Micrography of the pipe transverse section presenting a predominatly ferritic-perlitic microstructure.
132
VIEW
ML00140 / May.2019
Preferential Corrosion of Pipe Seam Weld
M - Low Carbon SteelP - Longitudinal Seam Welded PipeAp - ShipCd - Preferential Dissolution
Cm - Nital Etched Micrography by OMDf - Ferrite and Pearlite
Micrographic detail of the predominatly ferritic-perlitic microstructure. Pipe transverse section.
95
VIEW
ML00140 / May.2019
Preferential Corrosion of Pipe Seam Weld
M - Low Carbon SteelP - Longitudinal Seam Welded PipeAp - ShipCd - Preferential Dissolution
Cm - Nital Etched Micrography by OMDf - Ferrite and Pearlite
Aspect of the 4" pipe that was in seawater service for 8 years and leaked in a longitudinal line that corresponds to the seam weld. The internal surface presented thick deposits. Although the pipe was cut with a thermal process, the analysis was conducted after mechanical cutting.
100
VIEW
ML00140 / May.2019
Preferential Corrosion of Pipe Seam Weld
M - Low Carbon SteelP - Longitudinal Seam Welded PipeAp - ShipCd - Preferential Dissolution
Cm - Aspect Before AnalysisDf - General View
Detail of the transverse section of the 4" pipe at the longitudinal seam weld evidencing the leakage position. The damage appears as a through wall opening. The pipe thickness is 8 mm and there are no evidences of general corrosion (the SCH 80 corresponds to 8.6 mm) or pitting at the internal surface.
99
VIEW
ML00140 / May.2019
Preferential Corrosion of Pipe Seam Weld
M - Low Carbon SteelP - Longitudinal Seam Welded PipeAp - ShipCd - Preferential Dissolution
Cm - Transverse Section AspectDf - Leakage
Detail of the transverse section of the 4" pipe 90° from the seam weld. The thickness of the pipe is 8 mm. No evidences of general corrosion or pitting were identified.
77
VIEW
ML00140 / May.2019
Preferential Corrosion of Pipe Seam Weld
M - Low Carbon SteelP - Longitudinal Seam Welded PipeAp - ShipCd - Preferential Dissolution
Cm - Transverse Section AspectDf - Transverse Section
Detail of the transverse section of the 4" pipe 90° from the seam weld. The thickness of the pipe is 8 mm. No evidences of general corrosion or pitting were identified.
70
VIEW
ML00140 / May.2019
Preferential Corrosion of Pipe Seam Weld
M - Low Carbon SteelP - Longitudinal Seam Welded PipeAp - ShipCd - Preferential Dissolution
Cm - Transverse Section AspectDf - Transverse Section
Detail of the transverse section of the 4" pipe 180° from the seam weld. The thickness of the pipe is 8 mm. No evidences of general corrosion or pitting were identified.
64
VIEW
ML00140 / May.2019
Preferential Corrosion of Pipe Seam Weld
M - Low Carbon SteelP - Longitudinal Seam Welded PipeAp - ShipCd - Preferential Dissolution
Cm - Transverse Section AspectDf - Transverse Section
Aspect of the internal surface of the pipe after cutting, showing the colors of the internal deposits and the leaking line associated to the pipe seam.
288
VIEW
ML00140 / May.2019
Preferential Corrosion of Pipe Seam Weld
M - Low Carbon SteelP - Longitudinal Seam Welded PipeAp - ShipCd - Preferential Dissolution
Cm - Aspect Before AnalysisDf - Leakage
Aspect of the internal surface of the pipe after cleaning, showing the leakage line.
67
VIEW
ML00140 / May.2019
Preferential Corrosion of Pipe Seam Weld
M - Low Carbon SteelP - Longitudinal Seam Welded PipeAp - ShipCd - Preferential Dissolution
Cm - Aspect Before AnalysisDf - Internal Surface
Detailed aspect of the internal surface of the pipe after cleaning, in a region where the pipe was leaking.
62
VIEW
ML00140 / May.2019
Preferential Corrosion of Pipe Seam Weld
M - Low Carbon SteelP - Longitudinal Seam Welded PipeAp - ShipCd - Preferential Dissolution
Cm - Aspect Before AnalysisDf - Leakage
Detail of the transverse section of the 4" pipe at the longitudinal seam weld where it is not leaking yet, showing that the damage is not a crack but a localized dissolution, or localized corrosion or preferential dissolution at the autogenous seam weld. The thickness of the pipe is 8 mm and there are no evidences of general corrosion or pitting.
63
VIEW
ML00140 / May.2019
Preferential Corrosion of Pipe Seam Weld
M - Low Carbon SteelP - Longitudinal Seam Welded PipeAp - ShipCd - Preferential Dissolution
Cm - Transverse Section AspectDf - Localized Corrosion
Macrography of a transverse section of the pipe, 8 mm thick, presenting localized dissolution at the longitudinal autogenous seam weld.
65
VIEW
ML00140 / May.2019
Preferential Corrosion of Pipe Seam Weld
M - Low Carbon SteelP - Longitudinal Seam Welded PipeAp - ShipCd - Preferential Dissolution
Cm - NItal Etched MacroDf - Preferential Dissolution
Micrography of the pipe in the leakage area, showing the preferential corrosion in the center of the autogenous weld and oxides inside the crevice, that appearas as a cracking but that is only a localized anodic process.
65
VIEW
ML00140 / May.2019
Preferential Corrosion of Pipe Seam Weld
M - Low Carbon SteelP - Longitudinal Seam Welded PipeAp - ShipCd - Preferential Dissolution
Cm - Nital Etched Micrography by OMDf - Localized Corrosion
Micrography of the seam welded joint, autogenous. The localized dissolution occurrs exactly at the weld metal that presents a bainitic structure and Vickers (100g) microhardness values about 230HV, compared to the heat affected zone presenting average of 202 HV and the base metal presenting average of 180HV.
59
VIEW
ML00140 / May.2019
Preferential Corrosion of Pipe Seam Weld
M - Low Carbon SteelP - Longitudinal Seam Welded PipeAp - ShipCd - Preferential Dissolution
Cm - Nital Etched Micrography by SEMDf - Welded Joint
Micrographic detail of the autogenous seam weld. The localized dissolution occurrs exactly at the weld metal that presents a bainitic structure of average hardness about 230HV, compared to the heat affected zone presenting average of 202 HV and the base metal presenting average of 180HV.
56
VIEW
ML00140 / May.2019
Preferential Corrosion of Pipe Seam Weld
M - Low Carbon SteelP - Longitudinal Seam Welded PipeAp - ShipCd - Preferential Dissolution
Cm - Nital Etched Micrography by OMDf - Localized Corrosion
Micrographic detail presenting the slighltly decarburized ferritic structure, with inclusions, in the center of the weld, surrounded by a bainitic structure and the preferential corrosion in the weld.
51
VIEW
ML00140 / May.2019
Preferential Corrosion of Pipe Seam Weld
M - Low Carbon SteelP - Longitudinal Seam Welded PipeAp - ShipCd - Preferential Dissolution
Cm - Nital Etched Micrography by OMDf - Localized Corrosion
Micrography of the pipe in the leakage area, at the internal pipe surface, showing the preferential corrosion in the center of the autogenous weld and oxides inside the crevice. The morphology of the corrosion is similar to a cracking but the analysis show that it is a localized anodic process.
45
VIEW
ML00140 / May.2019
Preferential Corrosion of Pipe Seam Weld
M - Low Carbon SteelP - Longitudinal Seam Welded PipeAp - ShipCd - Preferential Dissolution
Cm - Nital Etched Micrography by OMDf - Preferential Dissolution
Micrography of the pipe at the leakage position showing an oxide layer inside the crevice. The corrosion occurred exactly at the weld metal and the region at the margin of the damage shows the heat affected zone of the autogenous weld, with a refined grain size.
41
VIEW
ML00140 / May.2019
Preferential Corrosion of Pipe Seam Weld
M - Low Carbon SteelP - Longitudinal Seam Welded PipeAp - ShipCd - Preferential Dissolution
Cm - Nital Etched Micrography by OMDf - Preferential Dissolution
Micrography of the internal pipe surface at the leakage position showing an oxide layer inside the crevice. The corrosion occurred exactly at the weld metal and the region at the margin of the damage shows the heat affected zone of the autogenous weld, with a refined grain size.
40
VIEW
ML00140 / May.2019
Preferential Corrosion of Pipe Seam Weld
M - Low Carbon SteelP - Longitudinal Seam Welded PipeAp - ShipCd - Preferential Dissolution
Cm - Nital Etched Micrography by OMDf - Preferential Dissolution
Micrographic detail of the microstructure at the margin of the corroded area showing the heat affected zone of the autogenous weld, with a refined grain size.
37
VIEW
ML00140 / May.2019
Preferential Corrosion of Pipe Seam Weld
M - Low Carbon SteelP - Longitudinal Seam Welded PipeAp - ShipCd - Preferential Dissolution
Cm - Nital Etched Micrography by OMDf - Preferential Dissolution
Micrographic detail of the microstructure close to the corroded area showing the heat affected zone of the autogenous weld, with a refined grain size. The hardness level here is 202HV average, compared to the base metal that is 180HV average.
37
VIEW
ML00140 / May.2019
Preferential Corrosion of Pipe Seam Weld
M - Low Carbon SteelP - Longitudinal Seam Welded PipeAp - ShipCd - Preferential Dissolution
Cm - Nital Etched Micrography by OMDf - Heat Affected Zone
Macrography of a transverse section of the pipe presenting localized dissolution at the longitudinal autogenous seam weld.
45
VIEW
ML00140 / May.2019
Preferential Corrosion of Pipe Seam Weld
M - Low Carbon SteelP - Longitudinal Seam Welded PipeAp - ShipCd - Preferential Dissolution
Cm - NItal Etched MacroDf - Localized Corrosion
Micrography at the scanning electron microscopy showing the deposits inside the crevice. The microanalysis by EDS revealed the presence of Fe, O, as well as Cl and S.
35
VIEW
ML00140 / May.2019
Preferential Corrosion of Pipe Seam Weld
M - Low Carbon SteelP - Longitudinal Seam Welded PipeAp - ShipCd - Preferential Dissolution
Cm - Micrography by SEMDf - Corrosion