SPECIAL INSULATED
EXPANSION JOINTS

Belman has designed, manufactured and supplied four special hot combustion airline Expansion Joints for installation at a producer of carbon black in Italy. These Special Insulated Expansion Joints are designed to operate at extremely high temperatures (950°C).

Client requirements
As carbon black is produced at elevated temperatures the Special Insulated Expansion Joints required a unique design in order to maintain the low skin temperature of the bellows while the inside temperature of the media was very high. The high temperature of the media also placed special considerations for the material selection for the bellows and inner sleeve. Due to safety grounds, the client was very concerned about the materials ability to withstand the operating temperature, while at the same time, maintain a low bellow skin temperature and provide a smooth and trouble free operation.

The client returns to Belman
The Special Insulated Expansion Joints were required to replace some of the existing special hot combustion airline Expansion Joints that were engineered and supplied by Belman back in 2011. After many years of successful operation, the existing Expansion Joints had reached the end of their service life and needed replacing. As the client was highly satisfied with the previous solution, they requested Belman to manufacture again the replacement Expansion Joints with the same specifications.

The Belman solution
With the client’s requests in mind, Belman examined the previous design of the Special Insulated Expansion Joints and confirmed to the client that the design, combined with the previously specified steel grades and insulation type could withstand a design temperature of +950°C. As Carbon black is produced at extremely elevated temperatures the media can easily reach +900°C during operation. Insulation of the Expansion Joints would play a key role in ensuring that the prevailing safety factors could be met and at the same time, keep the bellows skin temperature at an acceptable low level. The design of the bellows incorporated a 200 mm ceramic wool (Superwool, thermal ceramics) insulation, which is placed between the inner sleeves and the bellow plus pipe ends. The material 1.4828 (AISI 309) selected for the bellows and the inner sleeves is a heat resistant steel grade designed for use at temperatures above 550°C. This is in the temperature range where creep strengths are the dimensioning factor and high-temperature corrosion occurs. Due to the design code being both ASME and EN 13445, all materials used were double certified as per PED and ASME.

The Expansion Joint insulation required significant expertise
Expansion Joints can be insulated in many different ways to mitigate the prevailing conditions. An Expansion Joint can be insulated internally as well as externally. In the specific case of this carbon black producing client it is done for safety reasons, in order to protect the outer surroundings from an Expansion Joint surface temperature that is too high. Additionally, it also protects the bellows from hazardous media or to ensure the operating temperature is kept at an acceptable level. Irrespective of which insulation type is chosen, it is important to consider the characteristics of the insulating material. With certain insulating materials there is a risk of packing up, for this reason they must not be placed between the convolutions of the bellows as this impairs their functionality. In such cases it is important to prevent the insulating material from settling between the convolutions, for example by placing the insulating material around a shell mounted around the bellows. Belman has a vast experience in the insulation of Expansion Joints, using brick refractory linings as well as ceramic wools. For this reason, Belman is happy to outline the full range of insulation possibilities that exist and provide expert advice on the best options for the client’s project.