13 replies to this topic

[J_Leo]

Hello Fellow Engineers,

 

I just started to work on a detailed engineering project for a sulfuric acid alkylation unit. Since I joined the project, my lead has been pushing to delete PSVs to minimized total PSVs in the unit. The FEED was done by another EPC company. He worked on the operations side as a process engineer before he works as a process design engineer on the job. So, his point is the less PSVs, the better.

 

The attached diagram shows the Settler and reactor system with PSVs. The settler is sitting on a platform directly above the reactor which is liquid full. He proposed to delete PSV-02, so the settler can be protected by PSV-01 on the reactor by adding CSO on the block valve between. Since the settler is sitting directly above the reactor, I guess the 25 ft fire height is not valid. The flame can go beyond 25ft. Can PSV-01 provide enough protection for the fire case for the settler? 

 

Similarly, he proposed to delete PSV-3, so the fire case on the tube side will be protected by PSV-04. I feel this might be ok, but I don't feel it is necessary to do it as a process designer, especially the HAZOP has been done already.

 

Any advice? Any safety concerns if these PSVs are deleted. I feel pretty confused about the deleting activities. These are expensive vessels made of Alloy 20.

 

Thank you.

Regards,

_Loe

 

Attached Files

•  Acid Settler and Contactor.PDF   70.21KB   25 downloads

[Bobby Strain]

I think I would not change anything. Right or wrong, when you make such changes your company is assuming liability unnecessarily.

 

Bobby

[fallah]

J_Leo,

 

Because it's a safety issue, it should be conducted through a HAZOP by relevant MOG (Management of Change).

[J_Leo]

Hi Bobby and Fallah,

 

I totally agree with you. That is why I am against deleting the PSVs, but the lead won't listen. He is asking me to write a request to the client to delete the PSVs. I feel frustrated and don't know what to do.

 

Thanks,

Leo

[Bobby Strain]

This is not unusual. When faced with an obstinate lead for such things I simply refused. You might want to be more diplomatic.

 

Bobby

[J_Leo]

Bobby,

 

Thank you. I trying to make a summary of my concerns in written.

One concern is the 3% rule, per API 520 II, the pressure drop starts from the protected vessel to the psv. So, if deleting PSV-03, the inlet pressure drop has to start from the reactor to PSV-04. During fire, we cannot assume there is no normal flow in this line. I think it is impossible to meet the 3% rule at all. If I am wrong, please correct me. 

 

Thank you,

-LEO

[fallah]

 

One concern is the 3% rule, per API 520 II, the pressure drop starts from the protected vessel to the psv. So, if deleting PSV-03, the inlet pressure drop has to start from the reactor to PSV-04. During fire, we cannot assume there is no normal flow in this line. I think it is impossible to meet the 3% rule at all. If I am wrong, please correct me. 

 

Leo,

 

It could be a real concern, provided that to be supported by proper calculation...

[Bobby Strain]

Leo,

     Your reasoning does not seem sound to me. The real problem is that by eliminating safety valves you are assuming risk to your company. A lead engineer should never do as yours is doing. But it happens all the time. There is nothing wrong with the PSVs as they are. Hopefully your client will insist on a formal review and HAZOP to make any changes. And you should suggest this. Simply claim your lack of experience with such equipment. And maybe you can ask your lead for P&IDs your company might have. Or ask your lead to provide some. If he has none, he may relent and leave the design as it is. I'm sure if you express your concern about liability the request will disappear. You can always profess to have more pressing matters and simply delay any response. Your lead is an idiot and will not listen to reason from you. Maybe someone here can give you their experience. But, I would not remove any PSV from a design provided by others.

 

    There is usually a licensor for the technology and they provide P&IDs as part of the licensing package. These were probably provided to the FEED engineer. If the licensor is still involved, suggest to your lead that he talk to your client about his wishes, and get an approval from the licensor. I am almost certain that the licensor placed the PSVs as they are. And they won't agree to eliminating them.

 

Good luck.

Bobby

[Saml]

As an elder said  "It is never wrong to do the right thing". The problem here is that it is not clear what is right.

 

Your boss might be right about the valves, but at the wrong time in the project. Those sulfuric acid valves are a maintainance problem. BUT....you are doing detailed engineering. It is not your job to be the custodian of your client's operability and mantainability, unless there is something egregiously wrong and you could be held liable for negligence. This is not the case. Your job is to do complete the details of the basic design and build it.

 

I disagree about your boss being stupid. He seems a plant engineer without project culture. I've met a few. They want to change the design for something "better" even at commisioning time. They are a pain in a project environment.

 

But now you have to make up your mind about what is your main objective here: it is to keep those valves because you think they are absolutely neccesary? You don't want to be blamed for delays and confusion that this request will cause? Or you don't want to sign something you are not conviced about?

 

If it is the first case. Just say no, and face the "or else". Going to your boss's boss is usually worse.

 

If it is the second or third, you aim is that the person that make the decision (your boss) is the one who take the responsibility for the results.

 

So one option is to say: " I'll write the request as you asked for, but you sign it and send it to the client, I am not convinced that we should do this at this time in the project as this may expose our company to liabilities, but you are the boss".  Just eat your professional pride.

 

Plain "No" is an option. You may keep your professional pride, but not the bonus, the good performance review (or the job)

 

Another line of defense is: "Put that instruction in writing and I wil comply". See, there is nothing wrong with analyzing an scenario with fewer valves. The problem is the timing. This is not something to address during detailed engineering specially if it was specifically adressed during FEED. But if the client agree, appropriate change management is used, the Hazop node is reviewed, the client determine that the risk is acceptable to them,  and all the code calculations are met, I see no issues. If he writes it, keep a copy of that memo. The most likely outcome after the request is sent, is that your client's representative will call for a brief meeting and decide that you should keep the original FEED design, that it is not the time to make changes. 

 

If he does not want to put it in writing, and eventually takes a threathening stance,  it is a big screaming flashing sign that you should say no.

[J_Leo]

Fallah and Bobby,

 

Thank you for your support! I assume we are all on the process design side. I already talk about the liability issue with him. He said no liability issue. Also, I might have to stamp on the PSVs because I am a PE.

 

Saml, thank you for looking at it from a different angle.

 

I will definitely consider all of you advices.

 

Now come to the technical part, are there any problem doing the way my lead suggested. I have objection, not only because of the liability issue, also if the proposed system will provide adequate protection. If so, I don't have problems to follow his lead.

 

To remove the one on the top settler and keep the one on the reactor for fire relief. Because these are the liquid full vessels, is there a open pass for vapor relief from the contactor during fire? How do you consider the pressure drop for the 3% rule?

 

For the one on the tube side of the reactor, the PSV is on the downstream vessel, should we start the inlet from the reactor or the down stream vessel where the psv located. Based on my understanding, it should start from the reactor. The lead and the client insist it start from the down stream vessel. Also, do you consider it a open pass for vapor to go through the line mostly liquid. The second vessel is elevated like 20 ft above the reactor.

 

I need technical support from you. I never had experience dealing with the same situation before.

 

Thank you.

Happy thanksgivings!

_Leo 

Edited by J_Leo, 22 November 2017 - 01:22 PM.

[Bobby Strain]

It sounds like neither you, your lead, or your client representative have any experience in the area. I won't lead you through something that you should not do. Again, your client should rely on his licensor for advice. Your client rep may be a fool, too.

 

Bobby

[J_Leo]

Bobby,

 

In fact, the client is pretty knowledgeable on the operational side of alky unit, but he didn't work on the process design side. It is true though I have sized many PSVs before, but not particularly in this unit.

 

The client has agreed to check with the licenser though the lead was not happy. My lead is trying really hard to delete as many PSVs as possible, which is beyond my imagination. I will try to get myself away from the deleting activities.

 

Thank you all.

_Leo

[Bobby Strain]

Congratulations! Now be looking for a new project with a different lead. Make sure the lead is a process engineer, not an operator, if possible.

Where are you located?

Bobby

[J_Leo]

Hope for the best.

Edited by J_Leo, 15 February 2018 - 07:35 AM.