Fluids always have vibration and it can cause metal fatigue. Eventually it causes serious damages on steel products, structure of buildings or facilities. Any structures, especially pipe lines are exposed to vibration. And we have been trying to prevent it. Technically, it can’t be prevent so we decide to let it happen by using device, such as Spring Hangers.
Without Spring Hangers, structure could be broken by continuous vibration. Also welding process increases hardness on HAZ area. Increasing hardness means that the area is weaken to impact. Pipe lines carries natural gas, and the gas itself has low temperature. Pipe lines can be installed in cold weather in Siberia or a country has four seasons, for example 35˚C in summer, -20˚C in winter. Such a streng environment makes steel structure vulnerable. The problem is that broken can be happened in any time even in stable temperature and we can prevent an acccident if use the divice. Original Picture from http://www.sme.org/MEMagazine/Article.aspx?id=49508&taxid=1424
The pictures left are the sample how easly steel can be broken after welding. The numbers 10, 11, and 12 are the area where mostly heat affected on base metal. Area 7, 8, and 9 are where welding rod is melt. Once any steel is melt and cooled down, hardness increases. It must be reheated or have PWHT process to reduce hardness and prevent any accident. The reason of broken when hardness increased is because steel structure changes and it makes solidarity of molecular weak. But in case we use Spring Hangers, PWHT on welded area is still necessary. So, PWHT and using Spring Hangers can prevent metal fatigue while fluids go through pipe lines. Checking hardness value on welded area by portable hardness checking device before useing is recommendable.
The Original Posted by Jethro