[Query] Criteria Of Piping Steaming-Out

[Oildreaming]

Nice to meet professional engineers in Eng-tips. I am now working in refinery of South Korea. It is second year as a operation engineer so there are a lot of query to deal with about refinery.

As one of them, I got a question about a criteria of Piping steaming-out

As far as I know, There are two main purpose of piping steaming-out.
1. O2 freeing 2. Hydrocarbon stripping

In the case of O2 freeing criteria, it is commonly known as a rule of thumbs that O2 freeing is applied about 5-6 times of system volume. Do you know the criteria for hydro-carbon stripping? Any reference or rule of thumbs would be appreciated. Thank you in advance for your answers.

 

[mk3223]

My understanding is to use LP steam to heat up the pipe to 275 deg-F to burn off hydrocarbon inside the pipe. And then, the Operator will sniff the pipe to make sure the hydrocarbon level is low and safe for the maintenance work.

 

[MJCronin]

Steam-out of piping systems comes with its own set of hazards ....

Make sure that if the steam-out can generate a vacuum in the piping system, the system can structurally withstand the vacuum generated by condensation without piping damage or collapse.

I have worked on the repair of several "thin-walled" systems that had collapsed because field test people didn't understand the dangers of steamout.

IMHO Generally speaking you should be concerned with:

- Schedule 10S piping larger than 14 inches
- Schedule 40 piping larger than 20 inches
- All expansion joints

Anybody else have rules of thumb ????


MJCronin
Sr. Process Engineer

 

[MJCronin]

http://www.eng-tips.com/viewthread.cfm?qid=208133

MJCronin
Sr. Process Engineer

 

[georgeverghese]

Dont have these thumb rules for hydrocarbon stripping, but I can tell you this has always been a major hazard in offshore facilites with separator / other vessel walls covered in a thick layer of heavy hydrocarbons, where light hydrocarbons are trapped within this layer. You can keep purging with LP steam for forever on these vessels, and you'll still get a high reading on the flammable gas portable monitor after a while. The only way to get the reading down to acceptable levels is to vaporise this thick layer of hydrocarbons completely off the walls with higher temperature steam.

 

[EdStainless]

George, this probably explains why I have seen people cycling the temp in a steam out, going higher to break down heavy stuff, but not for long enough to get the whole system too hot.
The end point is determined by explosive gas content at the outlet.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

 

[shvet]

4 Inert gases ...
The most commonly used inert gases are:
...
c) Steam
Steam with pressures over 3 bar might be used as an inert gas, as its oxygen content is usually negligible. Condensation has to be taken into account and might lead to a pressure drop which supports air ingress into the plant or create a vacuum. When using steam for fire fighting in dust plants the condensation can be an advantage as the dust becomes wet, preventing a dust dispersion and extinguishing smoulders. However, there can be a risk of increased mass, chemical reaction due to the water, or microbial activity

7.3.2 Possible sources of purge gas shall include, but shall not be limited to, the following sources:
(4)*Steam, if it can be supplied at a rate that raises and maintains the protected vessel or system at a temperature high enough to prevent condensation of the steam.
...
A.7.3.2(4) The rate of application for steam inerting should be sufficient to maintain a steam concentration of at least 1.13 kg/min · 2.83 m3 (2.5 lb/min · 100 ft3).
A.7.5.5 This requirement is intended to provide for a sufficient number of isolation points to facilitate maintenance, while holding the number of isolation valves to a manageable number so that accidental shutoff is minimized.

As per my experience steam is the best way really to clean pipes and vessel from chemicals, water soluble inorganics and hydrocarbons. Steam is much better than N2 even in cleaning pipes and vessel from H2S in sour weater service. We seek to provide steam utility connection for every pipe and permanent blinded steam-out connection for a vessel. We provide steam utility connection even for cooling water headers is there exists a risk of hydrocarbon contamination caused by HX internal leakage.