Metallographic examination and hardness testing [4 MB PDF]

EMAIL

X:/102274.09 Report Issued 2 April 2012 of 11

Quest Integrity NZL Limited

69 Gracefield Road

PO Box 38-096

Lower Hutt : New Zealand 5045

T +64 4 978 6630

F +64 4 978 9930

E [email protected]

1. Introduction

Quest Integrity NZL Limited (Quest Integrity) have been asked to provide Vector Gas Limited

(Vector) with expert advice concerning a linepipe which failed in service, in particular the

metallurgical properties of the linepipe, in order that Vector can assess the cause of the damage to

the pipeline. This work forms part of information being gathered by Vector and Maui Development

Limited (MDL).

Three samples of pipeline were supplied by Vector on 21 December 2011 for examination. The

three sections supplied were part of the samples removed from the failure of the Maui pipeline at

White Cliffs.

Reference: 102274.09 Vector document 1167

Attention: A. Woodger

M. Webb

G. Wilson

Organisation: Vector Gas Limited

Private Bag

New Plymouth

Confidentiality: Confidential to Vector

E-Mail Address: Andrew Woodger [[email protected]]

Mark Webb [[email protected]]

Grant Wilson [[email protected]]

From: Stephen Rowbotham

Checked by: David Firth

Date: 2 April 2012

Subject: Metallographic Examination and Hardness Testing on samples removed

from Maui pipeline failure at White Cliffs

Metallographic Examination and Hardness Testing


The pipe was reported to have been purchased in accordance with API 5LX for Grade X65 (19th

Edition) with the additional requirements of Ministry of Works and Development (MWD)

specification “Maui Project Oaonui to Auckland pipeline supply of High test line pipe”.

A series of inspection and test plans were agreed, see Vector Document 1147.

This report covers the metallographic and hardness testing of the pipe and longitudinal weld.

Section 8.5 (d and e) API 5LX (20th Edition) requires the following for the weld:

(d) The height of the outside weld bead shall not extend above the prolongation of the

original surface of the pipe more than the amount listed below:

Up to 12.70 mm thick pipe maximum height of weld bead 3.18 mm.

Over 12.70 mm thick pipe maximum height of weld bead 4.76 mm.

(e) The height of the internal weld bead shall not extend above the prolongation of the

original inside surface of the pipe more than 1.52 mm.

The MWD specification (Vector document 1149) Section A.620 specifies a maximum hardness of

the weld or heat affected zone shall be less than HRC22 measured directly or by conversion from

a specified alternative measuring system. HRC22 is equivalent to HV 248 (Converted using Table

1 in ASTM E140).

2. Metallographic Examination

The following sections were removed from the pipe samples:

One transverse section (#1) was removed from the pipe through the central region of the

fracture, see Figure 1.

One longitudinal (#2) and one transverse section (#3) were removed from the pipe in the

vicinity of the cracking as shown in Figure 1.

One transverse section (#4) removed from the longitudinal weld as shown in Figure 2.

All samples were metallographically prepared on 12 March 2012.

The metallographic sections were initially examined using a metallurgical microscope (Olympus

BH50) in the as polished condition. This revealed the sections to be clear of any significant

inclusions such as sulphides or silicates. The cleanliness compares favourably with relatively low

sulphur, phosphorus and silicon content in the chemical analysis results detailed in 102274.06

Chemical Analysis Report.



The metallographic sections were then etched in a solution of 3 % nitric acid in ethanol (nital) and

re-examined using a metallurgical microscope. This revealed the microstructures of the pipe

longitudinal and transverse sections to consist of fine equiaxed grains of ferrite and pearlite, see

Figures 3 and 4. The grain size was assessed visually using charts (ASTM E112) and found to be

finer than grain size 8. The sections did exhibit a slightly banded structure which is considered

typical of a product of this type and manufacturing route (hot rolled product).

Examination of the sections from the pipe sample revealed the presence of localised areas of

corrosion pitting on both the outer and inner diameters. The depth was found to be less than 0.1

mm, see Figure 5. This level of corrosion could have occurred after the failure prior to storage.

Examination of the section through the fracture revealed the presence of a small area of the heat

affected zone on the outer surface of the pipe. However, the majority of the fracture occurred in the

base material. Examination of the section through the fracture also revealed in the area of the

fracture deformation and a rough surface profile typical of a ductile overload, see Figure 6.

A macroscopic section through the longitudinal weld is shown in Figure 7. The section through the

weld revealed a satisfactory appearance with no evidence of any inherent or welding defects such

as gas porosity, undercuts, lack of side wall fusion. The weld, heat affected zone and pipe

microstructures were found to be as expected with no abnormal metallurgical features or phases

observed see Figures 7 and 8.

The weld bead was assessed and found to exhibit the following dimensions (Section 8.5 (d and e)

API 5LX (20th Edition):

Outside weld bead height 2.0 mm.

Inside weld bead height 1.5 mm.

The weld bead height found complied with the requirements specified in API 5LX (20th Edition).

3 Vickers Hardness Testing

3.1 Pipe Sections

Vickers hardness (HV) readings using a 30 kg load were obtained and the results shown in Table

1.



Table 1. Vickers Hardness Readings Obtained on Pipe Sections.

Section Readings HV Average HV Estimated Tensile Strength N/mm2

(formula in BS7448)

Longitudinal Section Remote from Fracture

219, 218, 218 218 719

Transverse Section Remote from Fracture

214, 215, 214 214 706

Transverse Section Through Fracture

226, 221, 216 221 729

The hardness values obtained are consistent with the microstructures observed. The hardness

values were all <HV 248 (<HRC 22)

3.2 Weld Section

A Vickers hardness survey was undertaken similar to that shown in API 5L (44th Edition) Annex J.

The results are shown schematically in Figure 7 and summaries in Table 2.

Table 2. Vickers Hardness Results for Survey across Longitudinal Weld. Location Readings HV Average HV

Pipe Material 212, 207, 205, 208 208

Heat Affected zone 216, 216, 214, 212, 211, 186, 204, 190, 216, 216

208

Weld Metal 212, 212, 210, 207, 217 212

All the results were found to be below the specified maximum of HV 248 (HRC 22). The results

obtained are typical for a weld of this type and manufacturer. The results indicate that the weld filler

metal was well matched to the pipe material.

4. Conclusions

The pipe material was found to exhibit:

Aa fine grained equiaxed microstructure of ferrite and pearlite (normalised).

A banded microstructure (typical for a hot rolled product).

No abnormal phases or deleterious inclusions were found in the sections examined.

The hardness values detected in the base material were all less than HV 248 (HRC 22)

specified in the MWD specification



The longitudinal weld was found to exhibit:

A satisfactory profile to the requirements of API 5LX (20th Edition).

A satisfactory general microstructure in the heat affected zone and weld metal.

No evidence of any weld defects such as undercut, lack of side wall fusion, gas porosity,

etc.

The hardness values detected in the weld, HAZ and base material were all less than HV

248 (HRC 22) specified in the MWD specification



Figures

Figure 1. Location of metallographic sections from fracture sample located at position 1800 mm.

Figure 2. Location of metallographic section through longitudinal weld. Location 4400 mm.

Section 1

Transverse Fracture

Section 2

Longitudinal

Section 3

Transverse

Section 4

Transverse

through

longitudinal

weld

Fracture

Surface



Longitudinal section #2

Transverse section #3.

Figure 3. Typical microstructure observed. (Sections removed near to fracture from pipe sample 1800 mm).



Figure 4. Typical microstructure adjacent to fracture. Transverse section.



External Surface

Internal surface

Figure 5. Corrosion pitting found on sections near fracture. Sections from pipe sample 1800 mm. In all instances the corrosion pitting was found to be less than 100 µm in depth.

External Coating

Internal Coating



Figure 6. Section (#1) through fracture deformation next to the fracture and a rough fracture surface.

Figure 7. Macro section through longitudinal weld. Weld exhibited a satisfactory profile with no evidence of any detriment weld defects observed in the section examined. The hardness test locations and readings obtained are shown schematically.

216HV

207 HV

212 HV

216 HV

217 HV 210 HV

216 HV

216 HV

207 HV

214 HV

212 HV 212 HV 212 HV

204 HV

190 HV

190 HV

186 HV

205 HV

211 HV



Heat Affected Zone. Evidence of grain growth from left to right in photomicrograph.

Fusion boundary.

Figure 8. General microstructures associated with longitudinal weld.

Fusion boundary

Weld

Heat Affected Zone

Weld Pipe

Metallographic examination and hardness testing [4 MB PDF]

Documents

Transcript of Metallographic examination and hardness testing [4 MB PDF]