materials for condensate piping system

[sunshine419]

We have a 3” and 4” condensate piping system from a flare drum to an oil settling tank. These lines pump condensate to an elevated oil settling tank via an intermittent pump which leads to liquid condensate remaining stagnant in low lying areas of the piping leading to corrosion with resultant pin holes. We are in the process of replacing these corroded sections and I would appreciate if members can advise on how we can eliminate these low lying areas and also what suitable materials to use as replacement. At the moment the lines have been carbon steel.

 

[metengr]

Re-plumb the line to improve drainage and provide several low point drains, if necessary. There is no reason to change material without going down this path, first.

 

[sunshine419]

thanks Metengr, but won't the drain points be a source of dead legs and therefore susceptible to corrosion and potential leak source?

 

[metengr]

Not if the drain lines are open periodically to drain them. It is easier to replace leaking drains with isolation versus main piping.

 

[weldstan]

One must ask, "That else is in the condensate besides water?"

 

[MJCronin]

One must also ask about the schedule of the piping.

For boiler condensate piping,(which is subject to carbonic acid corrosion) it is recommended to use schedule 80 CS piping.

https://www.swagelok.com/~/media/Di...ices/ES - Condensate System Piping_BP_14.ashx

Would schedule 10S stainless piping be worth the investment ?

How high are the chlorides ?

MJCronin
Sr. Process Engineer

 

[weldstan]

Correction: "What else..."

Recently cracking was found at welds near the drip leg of carbon steel pipe in steam service. Failure was due to caustic cracking. Apparently the Owner preferred to remake and re-install the affected spools every few months rather than stress relieve the welds.

 

[sunshine419]

@weldstan, H2S, CO2 and remainder are compounds of alkanes. the ratio of H2S to CO2 is about 5.

 

[weldstan]

Not enough info to recommend a metallurgy change; however, you know that pitting is occurring and you know the current pitting rate and should know the replacement rate and costs thereof. You may try as metengr proposed but it is highly likely that pitting will occur in the drip legs based on the H2S & CO2 + other constituent's contents that are present in the condensate. The drip legs may be the only item requiring a metallurgy change (possibly with stainless cladding or solid stainless - 12% Cr min.)

 

[11echo]

Ever though of internally coating the pipe? "Tuboscope" is the one I've seen used here in the oil field I work in. There are some limitations, spools can only be so long (don't remember limits, but probably based on shipping length), also spools can only have two axis of the piping configuration required (this is to allow the spray nozzle down into the piping leg(s), so "IF" a Z configuration it couldn't get to the center section), lastly you can't weld on this piping after-the-fact, you'd burn off the coating! So you'd have to flange the connection points, so it's just a bolt-up operation. OR maybe Victaulic couplings ...if the piping is supported well.