Case Study of Steam Pipe Failure

& Microscopic Examination

Mosbah Ali akrim

Industrial Research Center -Libya

makreem@yahoo.com

Abstract This paper is concerning with the state of corrosion caused the failure of carrier pipe elbow of three

steam boilers where one of them run periodically to one of the production line units & it is evaluated by

microscopic examination. The steps and actions that have been taken to study the document related to

operating line and the date, duration and time for failure occur, where samples taken from the failure part and

analysed for water input and output of boiler examined as well. The analysis of microscopic examination

indicates that the corrosion caused by the dissolved oxygen in steam, which caused an intergranualr corrosion&

stress corrosion cracking as well as.

Description

This case represented in a failure apart of the steam pipe line (elbow) connects the

boiler(1)with three steam boilers that would be one boiler operation periodically and tube

metal is a carbon steel diameter of 150mm and a thickness of 5 mm and operating pressure20

atmospheric pressure and at a temperature of 200 ° C and failure occur on04/08/1997and

Figure(1) illustrates a diagram for failure part in the steam line.

Fig (1) shows the failure position

Visual Examination

the crack exists in the left side of the elbow in the form of a fish's mouth and there is a bulge

in place of the crack is not regular. And after cutting the elbow section we find pitting

corrosion near the open crack and some of them are deep and there are some crack sin the end

of the open crack, as shown in Figure (2).

Fig (2) shows the shape of failure

Measurements & laboratory tests

Measurements

Measurement Object

Diameter elbow 150 mm

Thickness of elbow 5 mm

Length of rift 140 mm

Showing rift 30 mm

Section thickness was measured by ultrasound and the results were as shown in Figure (3). And Figure

(4) shows the length of the crack

Fig (3)

Figure (4) shows the length of the crack

Chemical analysis

Sample was taken it from the elbow part and analysis by metals spectrometer analyser and

the results are shown in Table (2).

ElementCSiMnPSNiCrCuTiMOFe

Percenta

ge

0.10

02

0.00

44

0.51

4

0.013

6

0.04

46

0.02

3

0.01

41

0.06

52

0.0

10.0028

99.2

1

Table (2)

Microscopic Examination

Samples were taken from the elbow sections shown in Figure No. (5) it was next to the crack

samples and gradually away to note how spread the crack. Microscopic examination of the

samples show that the structure of the metal is a ferrite and perlite.

the petting corrosion effect on the internal structure of the metal and found that there is an

extension of the petting Deol attack Perlite body was extend to ferrite as on fig (6).

Corrosion caused by the dissolved oxygen in steam, which caused an intergranualr

Corrosion& Stress Corrosion Cracking as well as.

Fig (5)

Fig (6)a Fig(6)b

Discussion of Results

Through field visits and examination of the place of the failure it is close to the boiler No(1).

It is out of work since the three years and this indicates there is no flow of steam in this part

and there is valve control for the passage of steam from the boiler (1) to the main line and the

crack on the side of the elbow and this causes the failure is not from erosion.

It is by measuring the thickness of the sample in several different locations next to the crack

away from it showing that there is a difference in the readings at many locations ranging from

(4.1 to 5.3mm) the originally thickness 5mm increase Statistics of a layer of oxidation on the

sample. When cutting the sample and make chemical analyses and microscopic examination

to study the micro structure Of the metal and determine the cause of the failure also we

noted that there the pitting corrosion in deferent places. Within this segment making a

difference readings the thickness found in some places the depth of petting to (0.9 mm) as

noted the presence of petting in the centre of the crack and this shows it does not reduce the

thickness of the sample resulted in the failure. At study of the micro structure of some of the

samples taken from the failure part shows that the micro structure of metal is a perlite the

base of ferrite with no difference on grain size. It was noted that corrosion petting extends to

the perlite phase then ferrite corrosion caused by the dissolved oxygen in steam, which

caused an intergranualr corrosion& stress corrosion cracking as well as. Through chemical

analysis that the metal low-carbon steel to be considered on the metal caused by the presence

of dissolved oxygen in the steam which cause the corrosion.

Conclusion

The failure of part of the main steam pipe line from boilers to production unite

Is a present of the oxygen gas has resulted in the presence of petting which the reason for the

weakness in the metal with an increase in temperature and pressure resulted in this failure.

There is no change in the thickness of the metal, except at the point of petting. No change on

microstructure of the metal. Through chemical analysis of the sample the pipes used in steam

lines according the specification standard.

REFERENCES

1. Aman company Document for steam unite .

2. Metallography and Microstructures, Vol 9, ASM Handbook, 2004

3. ASM Handbook, Volume 13, Corrosion 2006.

4. Corrosion grope , " case study for failure analysis for boiler and steam pipes on Libya

tobacte company"