Problem with pickling of pipes

[phex]

Hi fellows.

I've got a problem with some pipelines. while pickling some lines (on site) we encountered a black coating on the inside of the pipes. these pipes were new, no process fluid ever touched them. the coating seems to be some kind of plastic, it is inflammable and highly resistant to the acid (HCl).
is it possible that it is some kind of polymere that results from a reaction between the pickling acid and leftover grease? i'm talking at large now cause we don't have a clue what that can be. any suggestions are welcome, even crazy ones

thanks for your help,
chris

 

[phex]

FYI, we narrowed it down to two possible sources. First one - and most probable one - is simple plastic foil which has been used to cover the pipes while storage (the workers here did not have the normal covers, so they needed to improvise). Sadly, they didn't remove this foil for assembly and after the annealing we got a nice, resistant and shrink-fitted black coating on the insides.
Second possibility would be that the heat transfer increasing agent which is used during annealing to guarantee sufficient heat removal has somehow degraded into this stuff. This one is not as likely, but - according to one of our senior piping inspectors - possible.

So, whats to be learned from this? Never underestimate the stupidity of workers. Sorry, this might sound a little belligerent, but the consequences are dire. We probably need to sandblast the complete piping.

Read you later,
chris

 

[saxon]

phex, Before you condemn the tradesman, where were the Engineers in charge?

saxon

 

[phex]

You are certainly right, the supervisors have made a mistake on that. There should have been someone who stopped them. What I wanted to express is that I didn't think - at least before this incident - that you have to be told to remove a clearly noticeable black plastic foil BEFORE you start welding these pipes together. I thought this would be common sense. The fact that this plastic foil was then fused to the pipes while annealing is of course something which is not the fault of the workers. This couldn't be prevented after the foil has been inside, how so, one can't look through the steel, of course. I was a little vague in my rant above, that's certainly true, and I'd like to apologize, if I offended anyone.
And btw, I haven't been on the construction site when this happened. I'm here for commissioning, not for construction, and I'm really not the guy who tries to make others look bad when I'm the one responsible.

chris

 

[StoneCold]

phex
What kind of pipe would you "pickle" with HCl?
And why?

Just Curious.
StoneCold

 

[saxon]

phrex, I didn't mean to flog you on this one. When it comes to common sense, I have an old saying, "If common sense were a common commodity, the world would be a utopia". With that said, you've gained some valuable experince and the value of clear, detailed, and specific specifications and procedures. Not too mention, the need for good supervision at the lowest levels. Even if common sense should have prevailed.

saxon

 

[phex]

StoneCold: The lines we are talking about are suction side lines of a compressor for hydrogen-rich gas for a deep desulphurization. The reason we have to pickle/passivate these lines is that the recycle gas is designed to allow minimum H2S contamination. The MoC of the pipes is ordinary carbon steel (don't ask... this was a prerequisite from our client).

Saxon: I realized myself that the post in question wasn't verbalized the way it should have been. So the clarification post as well as your initial criticism was well deserved. No harm done, and you are right: I learned my lesson

chris

 

[jay165]

"ordinary carbon steel" in H2S service? I hope you're follwong NACE MR0175 and/or other practices to prevent H2 embrittlement, otherwise you're going to have a much bigger problem than melted plastic in your lines.

 

[phex]

Yes, we have. "ordinary" is kind of exaggerated, it is carbon steel with very low phosphor and sulphur content, designed to withstand hydrogen embrittlement. I sincerely hope that our designing engineers have kept that in mind

chris

 

[steveen]

There use to be a way to sandblast piping using a company called UNISCO??? they used high pressure nitrogen from a liquid truck and injected special sand in the high pressure gas stream to scour the sides of the pipe. The sand was carried out with the process, so no worry about leaving material behind in the compressor suction lines...
Which brings up the question -- What are the vanes or valves of the compressor going to look like when the remains of the foil make their way to the compressor... That is why you pickle the lines, to remove all traces of particulates and construction scale. Don't forget the reason for the procedure.

Blame is easy, the answer is difficult, a safe efficient process.
Last dealings I had with plastic problems was melting plastic packing while steaming out the vessel. Plastic shards ended up everywhere after the vessel was returned to service..... Seems no one thought to report the packing was missing when they openned the vessel....

 

[phex]

Yes, we came to the same conclusion. By now, we tried to remove the foil with HCl, with a stong NaOH solution and with citric acid. None of these measures gave us a satisfying result, so we decided to install an additional strainer directly before the pulsation dampers. This way we can insure that even in case some particles of the foil come of the piping, they won't be reaching the compressors. Sandblasting was no option because of the complex piping system.
Even the specialists from the compressor manufacturer found our solution acceptable, so this is the way with the shortest time loss.

chris

 

[steveen]

Don't know the system, but get your specialists to comment on the pressure loss across the screen. Is it a permanent installation or just a "start up" screen?.
Recommend a procedure be written and reviewed with the specialists. Inquire as to what experience other locations have had with screens.

be sure to calculate pressure loss across screen and design load.

If the screen works as intended it will quickly have a high pressure loss.
also will the cone be towards flow or away from flow? I can't recall which is preferred in a compressor suction line. For recip compressors I would think cone points upstream to give more open crossectional area as debris is collected.

 

[phex]

the orientation of the screens is not yet fixed. I thank you for this valuable hint, I will suggest doing it this way during test run.
There are some specialists from the manufacturer on site for the test run. We will have plenty of time discussing the problem with them.

thanks,
chris

 

[steveen]

Chris,

For the possible salvation of your career, get something in writting from your specialists before the test run. Smoking ruins cause everyone to clam up....
VOE (Voice of experience -- and how I came to be an expert)

HAVE A PLAN FOR THE SCREEN... Either it is a permanent fixture with routine checks or it is a start up device TO BE REMOVED... Write a letter to the operator...

I use to lead unusual happening investigations. I was called out Friday night 10 pm for a large seal fire for a large hydrocarbon pump. Being one of the first on the scene, after the fire was put out, I carefully checked the inlet line for screens. There was one in the line, but the tab had been broken off long ago. Within an hour, David, the unit foreman (10+years in the job 30+ years on the unit) commented the pump always had problems pumping as much as the spare. When I asked him (IN PRIVATE) when the last time they cleaned the screen was, he laughed and said there wasn't a screen there because they had checked the year prior due to a fire on another unit caused by a plugged suction strainer. He changed his tune when we walked out to the site and I showed him the screen. When they pulled it out, there were 20+ years of material plugging up the screen. The pump ran a lot better, too.... Never found the check off sheet to determine who signed off on this particular pump.... Seemed to have disappeared. Vibrational records showed a persistent vibration for the life of the vibration monitoring program. Fire damage was only $85,000 but it screwed up one weekend of my youth...

Steve

 

[phex]

Thanks for your concern Steve.

Let me describe in detail, what has been done concerning the problem.

First, the pickling procedure has been repeated 5 times all together. 3 times with above mentioned HCl. Then we used 40% NaOH to flush the system. Then we used citric acid in a final cleaning step. Due to this, the inspection with an endoscope showed an almost clean pipe. We also used a different passivation solution and this with "warm" water (60 °C) and got a perfect surface with very few leftover spots of the black coating.
The compressor supplier then sent a specialist to evaluate the situation (the video of the endoscopic inspection was shown to him), who was asked to design the above mentioned additional strainers based on the amount of coating he saw. As such, we are definitely on the safe side in this case. All in all, it cost us about 3 weeks delay, almost 10000 euro for the inspection service with the endoscope, and the not yet fixed cost for design and supply of the strainers. But we finally conquered this problem.

bye for now,
chris