PRECAUTIONS FOR TANKS WITH INBUILT HEATING COILS

 PRECAUTIONS FOR TANKS WITH INBUILT HEATING COILS:

Design of facilities: 

Three interacting elements need to be taken into account when designing installations, particularly in terms of their compatibility with the operating conditions: - the nature of the products stored: flammable or non-flammable, likely to generate decomposition products that are themselves flammable or even explosive, requiring or not requiring temperature control; - the materials used for the storage tanks: flammable or non-flammable, and must be resistant to the products stored; - the heating elements: essential or non-essential, electric or using a thermal fluid (steam, hot water, heat transfer fluid, etc.), sized for a specific heating power. 

Reliable control equipment: - products are present in the tanks to prevent heating if tanks are empty (level and weighing sensors, etc.) - temperature of the thermal fluids used, the products contained in the tank, the atmosphere in the tank, etc. (appropriately positioned probes and sensors); - heating is controlled by the presence of product and by temperature control; - no contact between the heating elements and the tank’s walls; - monitoring of all of the installation’s operating and safety parameters. 

Regulated operating conditions: - preventive maintenance of facilities and equipment to prevent failures; - operating and intervention instructions (concerning the start-up of facilities in manual or automatic mode, shut-down of heating systems before intervention requiring tank emptying, after all interventions, etc.) - training of personnel in procedures and operating instructions; - monitoring and supervision of the installations during operations (the night prior, at night, early in the morning); - verification that all instrumentation and control channels are operating correctly, that the servocontrol and command logic is functioning correctly, and verification of automatic operation programmers.

Source:Aria database

ARE YOUR INTERLOCKS TESTED?

A fire broke out in a chemical warehouse that was inactive at the time. The flames had spread through the area used to store acids, bases and peroxides and included 28 storage tanks. This area is separate from the flammable products area. The site's Internal emergency Plan (IOP) was initiated. 

Six tanks containing hydrochloric acid, potash, flocculant, alkaline solutions and soda were destroyed, and the flames damaged five others. Overheating of a heating element in an empty soda tank over several hours caused the incident, as the product low-level detector had not switched off its power supply. The energy produced melted and then ignited the tank filled with HDPE (high-density polyethene). The material of which tank is made of then also fuelled the fire. The operator implemented the following preventive measures: - no heating device on product storage tanks not requiring it; - preference is given to steel or stainless steel tanks with electric or hot water heating; - the new plastic tanks are heated by hot water only; - the heating power must not allow a tank to ignite, - the reliability of the controller used to regulate the tank heating systems must be improved.

Source:Aria database

ARE YOUR TEMPERATURE SENSORS MEASURING PROPERLY?

 An explosion occurred in a metal bitumen tank (15 m high) in a company that manufactures, stores and distributes bitumen emulsion. The top of the tank was blown off and landed more than 45 m away on the grounds of the neighbouring facility. Upon arriving at the site, the operator switched off the electricity to the entire facility. The site was shut down. The tank in question was destroyed, and two other tanks were damaged in the explosion. The amount of bitumen in the tank was less than indicated by the sensor (10 tonnes) and insufficient to cover the resistors completely. The system began heating the fluid and caused the temperature in the tank to rise because the temperature sensor was not immersed in the bitumen. The heating system thus operated at its maximum level. The temperature rise caused a fire to break out, which ignited the combustion gases. The course of the accident implies that the level sensor had failed.

Source:Aria database

FAULTY ELECTRICAL COMPONENT TRIGGERS FIRE IN PLASTIC TANK

 A fire broke out on a tank containing 0.3 t of a mixed acid solution feeding a phosphating production line. The security guard raised the alarm. The tank eventually ruptured, spilling product into a retention basin. The fire resulted in an economic loss of €40,000. The fire is believed to have been caused by a faulty electrical component on the level sensor and the combustible nature of the tank (PE plastic). The line involved had been out of operation for maintenance since 20/12/2018. On 28/12/2018, the preventive maintenance was completed after 4 hours of testing. The line had been in preheating mode just 6 minutes before the fire broke out. Following the fire, a variety of actions were implemented: . modification of the tank’s materials (stainless steel); . replacement of the control relays (as a preventive measure); . modification of technology used to measure bath level; . installation of a preventive maintenance system with a thermal camera.

Source: Aria database

EMPTY SULPHURIC ACID TANK EXPLODES DURING HOT WORK AT TOP OF TANK

An empty 100-m³ tank sulphuric acid (H2SO4) exploded at 9:15 am at a chemical site. The tank was projected and fell nearby, toppling the scaffolding set up for reservoir maintenance and causing 3 workers (2 subcontracted personnel) to fall. Two of the three were seriously hurt: the plant employee sustained cranial trauma after falling some ten metres; and a subcontractor was pinned between the tank and the scaffolding, injured to the face by the grinder he had been using. The internal emergency plan was activated, bringing both internal and external responders to the site. The injured were taken to hospital. 

The tank had been temporarily plugged on 18th July using a sealant box after discovering a leak on 17th July. Scheduled for repair at the beginning of August following its drainage, the tank was rinsed with water throughout the weekend of 2nd August, then a subcontractor installed the scaffolding for the specific intervention: reservoir access, process insulation plating, etc. A plant employee, accompanied by 2 subcontractors, then climbed up the tank in order to open the top manway when the explosion occurred.

The accident appears to have followed a hydrogen (H2) accumulation at the top of the tank due to ignition of the inflammable mixture formed with air when cutting corroded bolts from the manway with a grinder. The tank was torn over half the circumference of the shell/bottom junction, and its anchorages were stripped. 
Insufficient rinsing of the tank (just a single rinsing cycle was performed) combined with the presence of a low concentration of sulphuric acid caused an acid attack of the metal, leading to the formation and accumulation of hydrogen at the top of the tank (dome-shaped tank roof). The explosion occurred by means of igniting the flammable mix created with air at the time of splitting the corroded bolts on the dome manhole with a grinder. The metallurgical assessment performed on this tank indicated the presence of extensive internal corrosion over the lower part of the structure. This observation confirmed the sudden onset of corrosion at the tank sidewall due to diluted acid, thus generating a source of hydrogen production.

Source:Aria database