Leak found at the bottom of steam generator lower drum

Location: Prince George

Regulated industry sector: Boilers, PV & refrigeration - Boiler and pressure vessel system

Impact

Injury

Qty injuries: 0

Injury description: None

Injury rating: None

Damage

Damage description: Small hole on one Blow Down Mud drum pipe

Damage rating: Minor

Incident rating: Minor

Incident overview

Operators found water and mud had tripped a conveyor. They also saw that a mud and water had leaked above the generating bank hopper. As the precise location of the leak was unknown, an emergency shut down of Recovery Boiler was employed.

Investigation Conclusions

Site, system and components

This industrial site utilizes the KRAFT Pulp manufacturing process. The “Recovery Boiler” is a high pressure steam boiler used in the KRAFT process. The intense heat in the boiler furnace fuses the inorganic elements of black liquor (mainly sodium carbonate and sodium sulphide) to form what is known as smelt. One of the main hazards in operation of recovery boilers is the smelt-water explosion. This can happen if even a small amount of water is mixed with the solids in high temperature.

Failure scenario(s)

The leak location was found at the bottom of the steam generator lower drum. The area of the leak is exposed to a corrosive atmosphere. A small hole developed and water/steam was released.

Facts and evidence

A small leak in 1-¼” drain pipe resulted in mud forming on a conveyor and stopping it. When a leak was identified the operators shut down the boiler via an Emergency Shutdown Procedure (ESP). The identified leak location was not in proximity of the smelt bed. The age of Recovery boiler is 38 years, the equipment is nearing end of life. This section of the boiler is subject to periodic “water washes” and contributes to corrosion.

Causes and contributing factors

It is highly likely that external corrosion of the pipe from water washes and the age of the equipment contributed to development of the leak.