Failure Analysis

Metals and alloys are used in almost all fields such as Life science, defense, dairy food, medical / pharma, material handling, transport including submarine, road aviation, etc. Manufacturing fields of all kinds, oil exploration, refining, petrochemical, fertilizers, electronic, electrical power plants to name a few. Material failures in above said arena occur and reasons are varied.

Therefore true root cause failure analysis (RCFA) are tailor made. We have carried out RCFA in various Organizations / industry and a partial list of our clients is given below:

1.> M/s. Samsara Shipping Pvt. Ltd, Mumbai.

2.> M/s. Allcargo Shipping Co. Pvt. Ltd, Mumbai

3.> M/s. Coromandel International Limited, Vizag Plant.

4.> M/s. Reliance Industries Limited,Hazira, Manufacturing Division, Hazira.

5.> M/s. Raj Engineering Pvt. Ltd,Thane.

6.> M/s. Coromandel International Ltd, Kakinada Plant.

7.> M/s. Sanjana Storage Tank, Tata Chemicals Ltd, Haldia.

8.> M/s.Tata Chemicals Ltd,Haldia.

9.> M/s. First Oil & Gas Services Pvt. Ltd, Trvandrum.

10.> M/s. Deepak Fertilisers & Petrochemicals Ltd.,Taloja.

11.> PTA-3 Plant, Reliance Industries Ltd. Manufacturing Division, Hazira

12.> M/s. Haldex India Pvt. Ltd, Nashik.

13.> M/s. Deepak Fertilisers & Petrochemicals Ltd.,Taloja.

14.> M/s. IMA-PG India Pvt. Ltd, Rabale, Navi Mumbai.

15.>M/s. IRC Agrochemicals Ltd.Haldia,West Bengal.

16.>M/s. JSW Steel Ltd,Dolvi

Why Failure Analysis?

Any engineering material can fail in any number of ways, including inadequate design allowances, improper manufacturing techniques, or service conditions that exceed design margins. Failures are generally costly, not only in terms of repair, but also in terms of downtime and the increased engineering support required to prevent future failures.

However, once a part has failed, it makes sense to carry out a thorough investigation to understand the root cause and to develop strategies that prevent a recurrence. A well thought out, systematic and carefully executed failure analysis at Subodh provides the Knowledge required to help prevent future problems.

The visual examination of failed components can often quickly answer questions such as:

  • What Was The Mode Of Failure?
  • Did It Crack, Or Was There A Uniform Or Pitting Corrosion Failure?
  • Did The Protective Oxide Film Break Down?
  • Were The Welds Visibly Contaminated

Typical Metallurgical Failure Mechanisms

  • Fatigue Failures
  • Corrosion Failures
  • Stress Corrosion Cracking
  • Ductile And Brittle Fractures
  • Hydrogen Embrittlement
  • Liquid Metal Embrittlement
  • Creep And Stress Rupture

Failure Analysis--Example Case Study 1

Some Excerpts from a failure analysis / case study of cracking of automotive worm gear and CI housing on endurance tests.

A broke Worm gear and its CI housing received from lab's client; this system failed prematurely during in-house endurance testing and failure analysis studies have been carried at M/s Subodh Technologists Lab at Navi Mumbai. Various studies such as visual examination, optical stereo and Scanning electron microscope (SEM), microstructural studies, chemical analyses, micro hardness measurements etc have been carried out. Visual examination indicated that about 8-10 teeth of the worm gear have been rubbed on one side only near the visible crack. The remaining teeth have grey /blackish appearances on both sides. The rubbed area got polished / burnished----indicative that worm and worm gear may have some mismatch –perhaps at later stage during endurance tests of 1.6 lac cycles. The corresponding worm needs to be inspected. It is opined that, later stage of endurance tests, the worm gear might get displaced /unbalanced slightly resulting burnishing only one side of the worm gear teeth. The cracking, that visible in naked eye is thru & thru, has initiated from valley formed by two adjoining teeth with branching. Fracture surfaces seems to be covered with (even electron) impervious scale, formed at high temperatures during some stages of heat treatments. In additions, there are number of additional cracks /fissures found during microscopic examination which are too fine—hair line type, sharp, discontinuous and step wise, some of them have encircled prior austenite grain boundaries.

Microscopic examination revealed presence of spherical inclusions of sulphide and oxide types, which are later identified as manganese sulphide and or aluminium oxide in SEM-EDS. General microstructures consists of tempered martensite within ferrite matrix having grain sizes of ASTM 8-9—which is satisfactory minus inclusions. The gear materials is in quench and temper heat treatment conditions---no decarburization or carburization found on worm gear edges.

In conclusion (worm gear), it is cracked due to presence of quench cracks present within gear but remained undetected. There are number of reasons to develop quench cracks in SAE 4140, including hydrogen absorption and not properly de-sorption during tempering. To pin point at what stages quench cracks are being formed required total review of the making, shaping and treating cum inspection of the gear manufacturing process.

As regards to CI housing, it conforms to SAEJ434 grade in chemical compositions, microstructures and other metallurgical properties. It is opined that the housing failure is of mechanical overload type from a site which had short of casting defects coincides with small lubrication /blending groove at shoulder of worm spindle thread regions. May be more safety factor required. It is finally concluded that, while the endurance testing, the housing first become loosen /broken at low thickness region, making the worm spindle slightly off balance; this phenomenon provided strong rubbing on one side of the worm gear (shining), resulting increased stress intensity and fatigue loading. As some quench cracks are already present, the gear failed by fatigue phenomenon.

It is suggested & recommended to inspect the worm gear using on-line magnetic flaw detection

technique to detect quench crack formation and segregate the defective one.

Some techniques and images taken for the Failure Analysis are shown below: