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AN INVESTIGATION INTO STORAGE TANK IMPLOSION

posted on April 12, 2021 / IN Fire and Explosion Investigation /

Used widely across many industries, storage tanks are durable and long-lasting. However, many run the risk of damage if proper care is not practised. An imploded tank can cause your business valuable time and finances, so read on to discover one of the common causes of this equipment failure and what to look out for.

On 19 June 2019, a storage tank (R1) in a local facility imploded followed by a loud noise during an unloading operation to a road tanker. All operations were stopped immediately after the incident.

Imploded north-east section of R1

AGI was requested to conduct an onsite investigation to identify the cause of the storage tank implosion. The investigation included interviews conducted with relevant parties who were present during the incident as well as photos and sketches of observations seen onsite followed by a detailed analysis.

Below are the findings and results of the investigation and examination of the origin and cause of the storage tank implosion.

Upon establishing the chronology of incidents leading up to the storage tank implosion, it was identified that to fulfil the requirements to cater methanol storage, in January, the goose neck of R1 was to be replaced with a blank flange, while a breather valve was required to be connected on another spare flange. However, as a blank flange was unavailable, the goose neck was blanked by inserting a metal sheet between it and the connecting flange. A breather valve was then fixed on the connecting spare flange. Methanol was unloaded somewhere in the mid of March, following that the R1 was loaded with palm stearin.

In May,  another storage tank required the breather valve, hence the breather valve from R1 with palm stearin in it was transferred to the other tank.. The following month during the unloading of the tank R1, the implosion occurred prompting a cease in operation.

Based on the damage assessment carried out by the team, several observations such as minor oxidation on the exterior valves, flanges and bolts, heavily corroded condensate pipeline, modified branch pipelines were noted.

Oxidation
Oxidation
Modified pipeline connected to the tank inlet
R1 inlet pipeline modified

R1 had imploded across its top and middle segments, however it did not suffer any significant damage. Paint coatings remained intact on the surface of dented areas inside the tank.

Imploded south-west section of R1
Imploded south-west section of R1

AGI identified four possible causes of the implosion, namely:

  • Failure due to Overflow Entering Ventilation System – our findings prove that the normal venting system of a storage tank should not be combined with liquid overflow as this could cause improper operations of one or both systems. As seen in Figure 1, when a tank is shut off with overflow in its system, the product must be siphoned out of the ventilation which can cause the air inside the tank to be removed as well. This could result in the sides of the tank curving in and implosion to occur. However, as R1’s ventilation and overflow lines are separate, this possible cause was ruled out.
  • Failure due to Equipment Malfunction – although R1 had a number of devices fixed on it, the only ones that could directly contribute to the implosion were its ventilation devices which included pressure reliver or its breather (pressure and volume stabiliser). However, during the after accident internal inspection, once the metal sheet in R1 was removed, its ventilation was able to be re-activated barring further implosion ruling out equipment malfunction as a possible cause.
  • Failure due to Rapid Cooling of Product – a reduction in temperature will cause a reduction in volume which brought the probability that when the product stored in R1 undergoes rapid cooling without proper ventilation to control condensation, it could have led to an implosion. However, conditions recorded via statements proved that no rapid cooling was taking place during the time of incident. Furthermore, the breather valve would have been able to cater the ventilation required if R1’s heating system was interrupted. Hence, this too was ruled out as a possible cause of the tank’s implosion.
  • Failure due to Inadequate Ventilation – There can be many contributing factors to over pressure or negative pressure inside a tank. These include liquid movement in or out of the tank, temperature or weather changes, fire exposure and other circumstances caused by operational errors and equipment failures. As AGI had analysed and ruled out the first three, this left unforeseen human errors to be the most likely cause. The documentations provided to the team showed that proper procedure was not followed on the R1’s ventilation valve shift. Papers show that the installation of the breather valve is recorded with no details on R1’s gooseneck being blanked with a metal sheet. With the breather valve from R1 being transferred to another tank and the gooseneck still being blanked, air intake to accommodate the void space left by pumped out palm stearin was not being establish. The condition led to an enormous negative pressure formation within R1. Further investigation proved that no checks were conducted on R1 prior to the loading operation leading to the conclusion that if it had been done, the implosion of the tank could have been prevented.

The cause of R1’s implosion was due to inadequate ventilation. As storage tanks undergo enormous amount of stresses due to pressure, temperature and volume changes, AGI recommends an addition of analogue pressure gauge to be introduced to them. This allows the tank pressure to be constantly observed during operation.

AGI uses investigational techniques to identify the proximate and root cause of failures such as this. Our findings are then compiled into a comprehensive report that will withstand scrutiny in a court of law. Need our assistance? Get in touch with us now!

 

By Approved Group International (AGI)

Our mission is to provide scientific approach to forensic investigation, failure analysis and non-destructive testing; professional and economical disaster restoration.

AN INVESTIGATION INTO STORAGE TANK IMPLOSION

posted on April 12, 2021 / IN
By Approved Group International (AGI)

Our mission is to provide scientific approach to forensic investigation, failure analysis and non-destructive testing; professional and economical disaster restoration.