cracking furnace tube metallurgy part 1 a

7/23/2019 Cracking Furnace Tube Metallurgy Part 1 A

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Ethylene Furnace TrainingEthylene Furnace Training

PEQUIVENPEQUIVEN OlefinasOlefinas IIII

23 rd to 27th March 200923 rd to 27th March 2009

Cracking Furnace Tube MetallurgyCracking Furnace Tube Metallurgy

Part I: Materials and Failure MechanismsPart I: Materials and Failure Mechanisms

LE TAW Pullach

Dr. Hubert Kpf


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Cracking Furnace Tube Metallurgy

Agenda:

Part I:

Materials and Failure Mechanisms

Part II:

Inspection and Evaluation/Failure analysis

Part III:

Troubleshooting and Repair Methods

Window rupture

of a Catalyst

Tube

Cracked CatalystTube


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1. Tube Materials


Part I: Materials and Failure Mechanisms

Ceramics / GraphiteGraphite

C / C

Refractory MetalsODS-Superalloys

PM 1000 / PM 2000

Adv anced

Titanium Allo ys

Temperature [C]

500 1000 1500

Oxidation Stability Oxidation Protective Coatings Required

Directionally Solidified Eutectics

Rapid Quenched MetalsTitanium

Composites

Alumin ium All oysAlumin ium

Composites

Conventional

TitaniumAll oys

Single

Crystals

Superalloys

-Titanium

Aluminide

based Alloys

Usablestrength

2000

In Ethylene Cracking metal surface temperatures up to 1100C in combination with

carburization and oxidation stability have to be managed by the tube materials. The

materials shall be weldable and economic. This requirements are fulfilled by high Ni,Cr austenics (superalloys).


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1. Tube Materials

Centrifugally cast tubes of these alloys are selected due to their enhanced high

temperature strength compared to wrought alloys


Part I: Materials and Failure Mechanismus

However, the ductility properties of the cast materials at ambient

temperatures are reduced compared to the wrought alloys.


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1. Tube Materials

The table below shows typical cast alloys used by LINDE in Ethylene Cracking Furnaces



Its important that Si is high to improve the carburization resistance.

Impurities such as As, Sn, Zn, Sb and Pb shall be low; these elements

are indications for the amount of scrap used in the tube production

process


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1. Tube Materials

The design of Tubes follows the general rules for all equipment in high temperature

service (example for power stations acc. to VGB)



Operation in creep rangeOperation in range of yield strength

at elevated temperature

stress

= stress

Rp0.2/ = yield strength at temperature

Rm/time/ = rupture strength at time and temperature


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1. Tube Materials




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2. Failure Mechanisms for Radiant Tubes




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Creep damage: Time-dependent strain occurring under stress. The creep strain

occurring at a diminishing rate is called primary creep; that occurring at a minimum

and almost constant rate, secondary creep; and that occurring at an acceleratingrate, tertiary creep. Below please find a principle Master curve for creep damage.



= Elongation

Au= Creep elongation at fracture

t= time

tm= time to fracture


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At temperatures above approximately 50% of the reformer tube alloy melting

(approx. 1350 C) creep is determined by relocation of micropores and lattice

defects (dislocations) towards the grain boundary.




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Cracks resulting from this mechanism are intergranular / interdendrit ic

(Example: X5NiCrTi 26-15, 1.4980)




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Stage 2(Magnification X 200)

Stage 3 - 4(Magnification X 200)


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cracking furnace tube metallurgy part 1 a

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