The Flixborough disaster occurred on June 1, 1974, caused by an explosion at the Nypro chemical plant resulting from a ruptured temporary bypass system leaking cyclohexane, which ignited and led to a massive vapor explosion. The document explains the mechanisms behind stress corrosion cracking (SCC) that contributed to the failure, detailing the stages of crack initiation, propagation, and brittle fracture, alongside the environmental factors and worker negligence involved. Recommendations for preventing similar incidents include careful steel selection, fabrication practices, surface treatments, stress design considerations, and protective coatings.

1. FLIXBOROUGH DISASTER:
EXPLOSION OF CHEMICAL PLANT
NUR AMIRA BINTI AZMI
(SA14052)
NURUL ATIRAH BINTI ABDUL RAZAK
(SA15055)

2. INTRODUCTION
•On Saturday 1 June 1974 at 4:53 p.m.,
Nypro (UK) site at Flixborough was
severely damaged by a large explosion
•Before the explosion: vertical crack on
reactor no 5 was leaking cyclohexane on
27 March 1974

4. • The temporary bypass assembly which was the bellow pipe was
installed to connect reactor no.4 and no.6 and also to further the
chemical production.

5. • Cause of the explosion:
-The bypass system ruptured due to slight rise in
pressure that strong enough to tear the bellows
-Ruptured due to shear stress
-Great amount of cyclohexane escaped from the holes
in the bellows and formed a cloud of cyclohexane
vapor
-The fire started when the cyclohexane formed a
flammable mixture and found source of ignition and
lead to massive vapor cloud explosion

6. TYPE OF
CORROSION…

7. •An environmentally well-known as a failure
caused by exposure to a corroding while under
a sustained tensile stress. (M.E. SAMIR, 2013)
•SCC is a cracking process that requires the
simultaneous action of a corrodent and
sustained tensile stress. (WebCorr website)
•Most rapid and unpredictable
STRESS CORROSION CRACKING (SCC)

8. •The process of SCC consist of 3 stages:
1. Crack initiation
2.Crack propagation
3.Brittle fracture
MECHANISM..

9. •SCC is initiated by stress concentrations at
defects on the material surface. The defect
may also be a result of pitting corrosion,
crevice corrosion, intergranular corrosion
or local galvanic corrosion.
CRACK INITIATION..

10. CRACK PROPAGATION..
• The passivation film at the tip of the crack is broken due to
plastic deformation. Pure and normally very active metal is
exposed and will be attacked by corrosion.
• Growth rate will be a combination of corrosion and cracking. The
crack start to growth when the stress concentration at the end of
te crack (KI) exceeds the threshold stress intensity factor for SCC

11. BRITTLE FRACTURE..
• When the stress concentration at the end of the crack exceeds the critical
stress intensity factor (KI > KIC), there will be a rapid, unstable brittle
fracture.

12. •NO UNIFIED MECHANISM in literature.
•Various model that have been proposed:
1. Adsorption model
2.Film rupture model
3.Pre-existing active path model
4.Embrittlement model

13. WHAT CAUSES SCC??

14. •Sources of tensile stress:
1. Assembly stress
2.Residual stress
3.Concentration of stress at the root of pre-
existing cracks or notches.

15. FACTOR : FLIXBOROUGH
• Presence of nitrates that had contaminated with
river water.
• Intergranular crack.
• Conjoint action of stress of an appropriate
magnitude and a corrosive environment, of a
specific composition, upon steel having a wide
range of composition of structures.

16. CASE DETAILS (COMMENT)
•Carelessness and less knowledge of the
workers/engineers.
• No references in designed the pipe.
• The only calculations made were of the capacity of the assembly
needed to carry the required flow.
• Nitrate treated cooling water be sprayed on the top of the reactor

17. SUGGESTION FOR PREVENTION
• - STEEL SELECTION
•- FABRICATION
•- SURFACE TREATMENT
•- DESIGN STRESSES
•- PROTECTIVE COATING

18. • STEEL SELECTION :
• -used in corrosive environment likely to cause SCC
• - steel more resistant to SCC
• FABRICATION
• - useful with careful fit-up in welding to avoid sharp notches, crevices,
rough finishes, galvanic couples between dissimilar metals and limit the
hardness
• SURFACE TREATMENT
• - shot peening/surface burnishing produces compressive stress but still
need to use steel with corrosion resistant

19. • DESIGNED STRESSES
• - designed with limit stresses below 50% yield stress
• PROTECTIVE COATING
• - organic coatings because adherent and nonporous

20. SIMILAR CASES IN THE WORLD
• 1) December 1967 : Catastrophic collapse of the
Silver Bridge
• Cause: Rust and high level of residual stress in the
eyebar joint and the main chain joint failed result of
high bridge loading and low temperature

21. • 2) 9 May 1985: Rooftop and ceiling collapsed of swimming
pool in Uster, Switzerland
• Cause: environmental cracking of metal fastening
components made of stainless steel elements in the roof
construction

22. • 3) 1 June 2001: fatal accident in Dutch Swimming pool in Netherlands
• Cause: environmental cracking of stainless steel threaded bars

23. • 4) 13 December 2003: Williams 26-inch pipeline ruptured near
Toledo Washington
• Cause: due to high pressure

24. • 5) 7 December 2009: Quartz manufacturing crystal
plant accident
• Cause: Corrosive environment that led to cracks in a
high pressure vessel’s steel walls resulting in its failure