Pressurized DA tank inspection

[Jazzerman]

Can anyone help me with requirements vs recommendations on DA tank inspection? Hospital client with central steam plant, with pressurized DA tank operating at 5 psi. I assume relief valves set at 15 psi but have not checked. I would figure an annual inspection inside the tank is smart, but is it required by code (ASME or other)?

 

[metengr]

For a DA tank, it would be wise to perform an internal inspection. In states or cities which regulate pressure vessels, these could be considered as corrosive service which would require access to the internal surface as part of a 3 year Jurisdictional inspection. Each State or city has their own rules for what is required for inspection to obtain an Operating certificate.

 

[MJCronin]

Some relevant DA inspection/failure information here:

http://www.eng-tips.com/viewthread.cfm?qid=209396

http://www.steamforum.com/steamforum_tree.asp?master=4926

http://www.heatexchange.org/

http://www.eng-tips.com/viewthread.cfm?qid=388455

It is important to recognize a few features about deaerators:

1) They are usually (fairly) large vessels designed for low pressures and therefore somewhat fragile. As they age, there is little or no margin in the design. For any vessel designed to a design pressure of less than 15 psig, the ASME rules on quality, testing and inspection DO NOT apply. There have been catastrophic DA failures in the past that have killed people.

2) In the 1990s, the heat exchange institute and NACE recognized this significant hazard and issued recommended guidelines for design,inspection and construction.

3) Deaerators are somewhat unique as they are commonly subject to internal impact forces during normal operation and therefore experience an accelerated degree of cracking and failure. Many, many internal trays have become loose and caused internal damage...

My opinions only

-MJC




MJCronin
Sr. Process Engineer