Putting a Stop to Steam Kettle Failure
Chief Boiler Inspector, State of Hawaii
Summary: The following article is a part of National Board Classic Series and it was published in the National Board BULLETIN. (3 printed pages)
No one wants to experience the effects of a boiler or pressure vessel-related incident. With this in mind, one goal is apparent to every inspector: find a way to prevent the destruction of property, and more importantly, the loss of lives.
Unfortunately a variety of injuries, and even deaths, continue to encumber the boiler and pressure vessel industry, not only in Hawaii but around the world.
For instance, eight years ago a steam kettle exploded in a Hawaii school cafeteria kitchen, injuring one cook. The incident occurred at a time when the cafeteria was not filled with school children.
The investigation revealed that the cook had turned the kettle on and was standing on a step next to the unit, when 10 minutes later, its lid blew off and struck her face. The entire kettle was blown 30 to 40 inches above its footing before falling to the floor. Steam and debris blew about in the immediate vicinity following the accident. No other employees, nor any children, were injured.
It was discovered that the jacketed steam kettle had been losing water for some time and that the water had to be replenished on a regular basis. The school administration had ordered a replacement, but prior to its arrival, the original kettle failed. Surprisingly, the kettle had been in service for only five years.
Following the incident, the remaining four kettles were inspected for corrosion. Serious corrosion was found and the kettles were immediately taken out of service.
After some investigation, it was found that the failed vessel had suffered excessive corrosion in the skirt area and the lower head, therefore causing the failure at a very low pressure. In addition, the vessel failed at the circumference of the head skirt.
Upon this conclusion, the investigation team suggested that the failure may have occurred because of the presence of a silicone-like substance between the decorative vessel skirt and the lower head. The substance may have caused cleansing agents and moisture to collect between the head and skirt. This possibly led to localized corrosion of the carbon steel head, resulting in the kettle?s failure.
The National Board issued an alert after the incident and suggested the following inspection guidelines to help prevent further incidents.
Jacketed Steam Kettle Inspection Guidelines:
- If the lower head and all pressure parts are fully exposed, external inspection should reveal any apparent problems.
- If the lower head is concealed by a skirt and is fabricated of carbon steel, inspect for corrosion in the following manner:
- Check the bottom of the unit. If there is a splash shield covering the lower end, have the shield removed.
- Examine the lower head. If there is evidence of staining or moisture, there is an excellent chance of corrosion in the skirt area.
- If there appears to be a seal between the skirt and head, remove a portion and determine if corrosion or debris exists. (This area is very tight and will be difficult to observe. A strong light and mirror are necessary.)
- If water is added to the jacket manually, check with maintenance to find out how much water is being added and determine the path the liquid follows inside the kettle.
Obviously, no pressure-retaining item is immune from the possibilities and dangers of a failure. However, the guidelines mentioned above are designed to greatly reduce the chance of another jacketed steam kettle failure.
Editor's note: Some ASME Boiler and Pressure Vessel Code requirements may have changed because of advances in material technology and/or actual experience. The reader is cautioned to refer to the latest edition of the ASME Boiler and Pressure Vessel Code for current requirements.