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ML00171 - Feb.2021

Corrosion Fatigue of U Bolt Pipe Clamp

Detail by scanning electron microscop of the clamp surface showing several cracks, parallel. In this image the cracks appear horizontal, but the photo was taken with the axis of the clamp in the vertical direction which means that the cracks are transverse to the axis.

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Description

Several heavy U clamps broke when operating in the bottom of a cargo oil tank, after several years in service. The metallurgical analysis of one broken clamp showed multiple surface , parallel, transverse to the clamp axis, with a brittle appearance. The protection was clearly not effective since it was detached, mainly where there was a polimeric insert, leading to of the substrate, with propagation of cracks by .

Associated Images

Aspect before cleaning of the heavy U bolt pipe clamp, 38 mm diameter wire, at the fractured position. It is possible to see that it broke in a region where the clamp was no longer coated and there is no insert in the groove (at the internal clamp diameter). The fracture is transverse to the clamp axis.

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ML00171 / Feb.2021

Corrosion Fatigue of U Bolt Pipe Clamp

M - Low Carbon SteelP - BoltAp - ShipCd - Corrosion Fatigue

Cm - Aspect Before AnalysisDf - General View

Aspect of the U bolt clamp with partial detachment of the coating (white brown) in a region where the polimeric insert (dirty white) is still in the wire groove at the internal clamp diameter (ID).

91

ML00171 / Feb.2021

Corrosion Fatigue of U Bolt Pipe Clamp

M - Low Carbon SteelP - BoltAp - ShipCd - Corrosion Fatigue

Cm - Aspect Before AnalysisDf - General View

Detailed aspect of the fractured position, in a region where the clamp was no longer coated and there is no insert in the groove (at the internal clamp diameter). The fracture is transverse to the clamp axis.

86

ML00171 / Feb.2021

Corrosion Fatigue of U Bolt Pipe Clamp

M - Low Carbon SteelP - BoltAp - ShipCd - Corrosion Fatigue

Cm - Aspect Before AnalysisDf - Fracture

Same aspect of the previous image after cleaning, showing a subcritical propagation aspect (fatigue), starting at the groove (ID) and also at the clamp surface in the OD.

75

ML00171 / Feb.2021

Corrosion Fatigue of U Bolt Pipe Clamp

M - Low Carbon SteelP - BoltAp - ShipCd - Corrosion Fatigue

Cm - Aspect Before AnalysisDf - Fracture

In the region where the polimeric insert was loose, the protective coating of the clamp has suffered detachment.

69

ML00171 / Feb.2021

Corrosion Fatigue of U Bolt Pipe Clamp

M - Low Carbon SteelP - BoltAp - ShipCd - Corrosion Fatigue

Cm - Aspect Before AnalysisDf - Layer Detachment

Close to the ID of the clamp, at the groove position, there are cracks in the coating (white brown) and also at the substrate.

63

ML00171 / Feb.2021

Corrosion Fatigue of U Bolt Pipe Clamp

M - Low Carbon SteelP - BoltAp - ShipCd - Corrosion Fatigue

Cm - Aspect Before AnalysisDf - Cracks

Detailed aspect of the cracks at the clamp substrate and at the coating.

59

ML00171 / Feb.2021

Corrosion Fatigue of U Bolt Pipe Clamp

M - Low Carbon SteelP - BoltAp - ShipCd - Corrosion Fatigue

Cm - Aspect Before AnalysisDf - Cracks

Dye check at the groove in the clamp ID, showing several parallel cracks, transverse to the clamp axis.

51

ML00171 / Feb.2021

Corrosion Fatigue of U Bolt Pipe Clamp

M - Low Carbon SteelP - BoltAp - ShipCd - Corrosion Fatigue

Cm - Aspect by NDTDf - Cracks

Aspect of the clamp fracture, before cleaning, looking from the outer diameter (OD). The fracture is in a position where there is no coating anymore.

48

ML00171 / Feb.2021

Corrosion Fatigue of U Bolt Pipe Clamp

M - Low Carbon SteelP - BoltAp - ShipCd - Corrosion Fatigue

Cm - Aspect Before AnalysisDf - Fracture

Fracture surface aspect at the scanning electron microscopy (SEM) of the clamp OD, showing different planes of propagation of the fracture.

42

ML00171 / Feb.2021

Corrosion Fatigue of U Bolt Pipe Clamp

M - Low Carbon SteelP - BoltAp - ShipCd - Corrosion Fatigue

Cm - Fractography by SEMDf - Fracture

Aspect of the clamp surface showing several parallel cracks, transverse to the wire surface, with a brittle aspect.

42

ML00171 / Feb.2021

Corrosion Fatigue of U Bolt Pipe Clamp

M - Low Carbon SteelP - BoltAp - ShipCd - Corrosion Fatigue

Cm - Aspect Before AnalysisDf - Multiple cracks

Detail by scanning electron microscop of the clamp surface showing several cracks, parallel. In this image the cracks appear horizontal, but the photo was taken with the axis of the clamp in the vertical direction which means that the cracks are transverse to the axis.

41

ML00171 / Feb.2021

Corrosion Fatigue of U Bolt Pipe Clamp

M - Low Carbon SteelP - BoltAp - ShipCd - Corrosion Fatigue

Cm - Surface Aspect by SEMDf - Multiple cracks

Detailed aspect of the previous figure showing the parallel cracks, transverse to the axis.

37

ML00171 / Feb.2021

Corrosion Fatigue of U Bolt Pipe Clamp

M - Low Carbon SteelP - BoltAp - ShipCd - Corrosion Fatigue

Cm - Surface Aspect by SEMDf - Multiple cracks

Metallographic image of a longitudinal section of the clamp (axis in the vertical direction), showing a refined ferritic perlitic structure.

34

ML00171 / Feb.2021

Corrosion Fatigue of U Bolt Pipe Clamp

M - Low Carbon SteelP - BoltAp - ShipCd - Corrosion Fatigue

Cm - Nital Etched Micrography by OMDf - Longitudinal Section

Metallographic detail of the longitudinal section of the clamp with a ferritic pearlitic structure.

32

ML00171 / Feb.2021

Corrosion Fatigue of U Bolt Pipe Clamp

M - Low Carbon SteelP - BoltAp - ShipCd - Corrosion Fatigue

Cm - Nital Etched Micrography by OMDf - Ferrite and Pearlite

Metallographic detail of the ferritic perlitic structure.

31

ML00171 / Feb.2021

Corrosion Fatigue of U Bolt Pipe Clamp

M - Low Carbon SteelP - BoltAp - ShipCd - Corrosion Fatigue

Cm - Nital Etched Micrography by OMDf - Ferrite and Pearlite

Metallographic aspect of a longitudinal section of the clamp, at the surface (left side of the image) showing a region where there are corrosion pits in the carbon steel clamp, due to the lack of protection by the coating, and the propagation of small transgranular cracks from to the surface.

30

ML00171 / Feb.2021

Corrosion Fatigue of U Bolt Pipe Clamp

M - Low Carbon SteelP - BoltAp - ShipCd - Corrosion Fatigue

Cm - Micrography by OMDf - Crack

Detail by scanning electron microscopy of the pits in the metallographic longitudinal section of the clamp, at the surface (left side of the image). There are cracks emanating from the pits.

27

ML00171 / Feb.2021

Corrosion Fatigue of U Bolt Pipe Clamp

M - Low Carbon SteelP - BoltAp - ShipCd - Corrosion Fatigue

Cm - Nital Etched Micrography by SEMDf - Crack

Detail by scanning electron microscopy of the cracks emanating from the pits in the metallographic longitudinal section of the clamp, at the surface (left side of the image).

25

ML00171 / Feb.2021

Corrosion Fatigue of U Bolt Pipe Clamp

M - Low Carbon SteelP - BoltAp - ShipCd - Corrosion Fatigue

Cm - Micrography by SEMDf - Crack

The clamp presented several cracks, parallel, transverse to the axis. The appearance of the cracks in the metallographic section shows that some cracks propagate and growth with a irregular path.

24

ML00171 / Feb.2021

Corrosion Fatigue of U Bolt Pipe Clamp

M - Low Carbon SteelP - BoltAp - ShipCd - Corrosion Fatigue

Cm - Nital Etched Micrography by OMDf - Longitudinal Section

Metallographic aspect of the cracks showing that several microcracks join from different pits and growth through the section, in a transgranular morphologyy.

26

ML00171 / Feb.2021

Corrosion Fatigue of U Bolt Pipe Clamp

M - Low Carbon SteelP - BoltAp - ShipCd - Corrosion Fatigue

Cm - Nital Etched Micrography by OMDf - Transgranular Cracking

Metallographic aspect of one secondary cracking, paralell to the fracture surface, growthing with an irregular path and transgranular morphologyy.

28

ML00171 / Feb.2021

Corrosion Fatigue of U Bolt Pipe Clamp

M - Low Carbon SteelP - BoltAp - ShipCd - Corrosion Fatigue

Cm - Nital Etched Micrography by OMDf - Transgranular Cracking

Metallographic aspect by scanning electron microscopy of one secondary cracking, paralell to the fracture surface, growthing with an irregular path and transgranular morphologyy.

28

ML00171 / Feb.2021

Corrosion Fatigue of U Bolt Pipe Clamp

M - Low Carbon SteelP - BoltAp - ShipCd - Corrosion Fatigue

Cm - Micrography by SEMDf - Corrosion Cracking

Metallographic aspect of one secondary cracking, paralell to the fracture surface, growthing with an irregular path and transgranular morphologyy.
The main crack presents small branching and cleavage propagation with a clear influence of corrosion (hydrogen evoution) .

27

ML00171 / Feb.2021

Corrosion Fatigue of U Bolt Pipe Clamp

M - Low Carbon SteelP - BoltAp - ShipCd - Corrosion Fatigue

Cm - Micrography by SEMDf - Corrosion Cracking

Metallographic aspect of one secondary cracking, paralell to the fracture surface, growthing with an irregular path and transgranular morphologyy.
The main crack presents small branching and cleavage propagation with a clear influence of corrosion (hydrogen evoution) .

27

ML00171 / Feb.2021

Corrosion Fatigue of U Bolt Pipe Clamp

M - Low Carbon SteelP - BoltAp - ShipCd - Corrosion Fatigue

Cm - Nital Etched Micrography by SEMDf - Corrosion Cracking

Etched micrograph showing a transgranular crack running across equiaxed ferrite grains with dark grain-boundary carbides.

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ML00171 / Feb.2021

Corrosion Fatigue of U Bolt Pipe Clamp

M - Low Carbon SteelP - BoltAp - ShipCd - Corrosion Fatigue

Cm - As polishedDf - Acicular Alpha

Corrosion Fatigue of U Bolt Pipe Clamp

4

ML00171 / Feb.2021

Corrosion Fatigue of U Bolt Pipe Clamp

M - Low Carbon SteelP - BoltAp - ShipCd - Corrosion Fatigue

Cm - Nital Etched Micrography by OMDf - Crack

Corrosion Fatigue of U Bolt Pipe Clamp

4

ML00171 / Feb.2021

Corrosion Fatigue of U Bolt Pipe Clamp

M - Low Carbon SteelP - BoltAp - ShipCd - Corrosion Fatigue

Cm - Micrography by SEMDf - Crack