Stress Corrosion Cracking – Two Cases in a Row

The engineers at Reksolindo have an interesting inquiries for failure analysis suffered by different parts of equipment lately. Quitely different operation condition (high temperature and ambient temperature, medium and low carbon steel, marine atmosphere versus caustic feed water).  We are really satisfied for microscopy works that can catch the clear picture of lightning type-branched  small crack surrounding opening tip of main cracks below. The lightning  type and branched of small cracks which are believed in many literature [1,2,3]as the finger-print of stress corrosion cracking mode. And it was very clueful which made us more easier to find the contributing causes .

1. Chloride-SCC in an uncoated medium carbon steel bolt in marine atmosphere

2. HAZ – Caustic SCC at 100-250 °C

Erosion Corrosion – Learning from Humber Estuary

Muhammad Abduh (abduh@reksolindo.co.id)

On 16 April 2001 a fire and explosion occurred at Humber Refinery following the catastrophic failure of an overhead gas pipe. Investigation was carried by The Competent Authority and the plant operator company by legislative mechanism under Control of Major Hazard (COMAH) Regulation 1999. Humber refinery was one of approximately 1000 major hazard site under this regulation. The competent authority consisted of Health and Safety Executive (HSE) UK and Environment Agency (EA).

The cause of the piping system failure was the erosion corrosion
of the 6-inches diameter pipe, known P4363, which carried the overhead line from the De-ethanizer (W413) to the heat exchanger (X452) in saturate gas plant (SGP) unit. The failure occurred down stream of a closely water injection point. Examination to thefailed elbow recovered from the damage site showed wall thickness thinning from 7-8 mm to a minimum 0.3 mm. When the pipe failed it burst open catastrophically causing a full bore type of release the pipe contents.

The water injection point was not the original design of the piping system. Water injection to the vapor stream between the top de-ethanizer column and the heat exchanger was addressed to solve the previous problem of salts or hydrates fouling in heat exchanger X452/3. An injection point was created in P4363 by piping water to an existing 1 inches vent point on the pipe without injection quill or dispersal device and made the water entering the pipe as a free jet.

Erosion-Corrosion
There are studies that noted the synergistic effect ofmechanical impingement and electrochemical corrosion result in greater rate of metal loss than the sum of the two mechanism ( S. Zhuo, N. Stack & R.C Newman)

The highest rate of erosion-corrosion occurred in stagnant region, immediately beneath the jet, where the particles impacted the surface at an angle of 90°, This critical erosion-corrosion region in a piping system are found at the outer side of elbow where the fluid impinges the wall directly at an angle 90°.

NACE 34101: Refinery Injection & Process Mixing
Points
One of the generic guidance to overcome the problem of erosion corrosion in refinery process is NACE 34101 which gas already published as recommended practice for the design consideration of  injection system.

RBI Regime was not Effective
This accident also has shown the effect of in-effective implementation of RBI for inspection management. RBI as a comprehensive method shall be supported with complete and adequate data. The ignorance of the operator company for the significant risk contribution of the injection system to the piping were resulted in the failure.

Similar Accidents:

1. Wilmington California United States – October 8,1992
2. North Rhine West Phalia Germany-  December 10,1991
3. Yokkaichi Mie Japan – May 2, 1997
4. Mina Al-Ahmadi Kuwait-  June 25, 2000

Heat Exchanger In- Service Damages

1. Excessive mineral deposits on the cooling water side of ammonia reactor effluent gas cooler.

2. Ice and fouling in a condenser tube.

3. Shell-side bacteria growth in cooling water heat exchanger

4. Fin Cooler tubes severly corroded

5. Deposits build-up on the inside of a heat exchanger tube

6. Plugged exchanger tube

7. Scaling on the inside diameter of a cooler tube

8. Deep Pitting in Exchanger Tubes

9. Cluster Pitting from Sour Glycol

10. Shell-side Pitting

11. Cooler Tube Rupture

12. Tube Failure Due to Thinning

13. Shell-side ruptured tube

14. Wall thinning led to this catastrophic failure of an exchanger tube

Image Source: Maverick Inspection

Book on Heat Exchanger Fouling: Heat Exchanger Fouling: Mitigation and Cleaning Techniques