Derating of process piping designed to ASME B31.3 2

[deepu78]

Hi
Derating of process piping
I want to know whether derating can be applied in the below scenario.
This is a modification of existing syngas line which is 15 years old. The current piping is designed to 550 deg C and pressure to 52 bar
But there is an alarm in the system at 285 deg C.
My query is derating of the existing line can be to a made to 350 deg C and Pressure of 35 bar which is the operating pressure? This is for compliance of pipe stress analysis of the for the modification piping.

Is derating can be only be appiled to ASME B31.8 gas transmission and distribution piping ? or derating can be made for ASME B31.3 process piping?
Also how to approach derating of process piping in a safe manner?
What is the definition of derating of piping? IS this done during the piping design of a new process plant? Is re-rating same as de-rating?
DV

 

[1503-44]

You can derate any pipe system and should do so, if it cannot be operated at its current rated temperature.

See your company procedures and/or talk to your engineering manager about this.

--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

 

[mk3223]

Not like the pressure vessel may required to be certified per ASME BPV Code, if there is nothing wrong with the 15 years old piping, such as corrosion, the Engineer may determine once the pipe material is suitable and new process conditions, P&T don’t exceed the original design parameters.

 

[NovaStark]

Also how to approach derating of process piping in a safe manner?

The first thing to do is to properly define the problem to ensure that the correct engineering solution is being applied - or at the very least, to understand the root causes of the issue(s) being faced. If de-rating is necessary, you should have a comprehensive assessment with your process, operations, maintenance, engineering teams, etc. to fully understand the new limits that will be imposed onto the system. As a result of de-rating, you might need to alter the alarm limits, relief set points, etc.

I want to know whether derating can be applied in the below scenario.
This is a modification of existing syngas line which is 15 years old. The current piping is designed to 550 deg C and pressure to 52 bar
But there is an alarm in the system at 285 deg C.

What is the modification being done ? It sounds like the piping alyout is being altered which requires more flexibility.
For the alarm at 285 degC, do your operating manuals (or design documents) say what the purpose of this alarm is ?

My query is derating of the existing line can be to a made to 350 deg C and Pressure of 35 bar which is the operating pressure? This is for compliance of pipe stress analysis of the for the modification piping.

As 1503-44 says, you can de-rate as required for safe operation. (A re-rate is the same thing as a de-rate. De-rate is just implying that you are lowering the conditions essentially).

Do you have in your design basis the reason for these design conditions ?

 

[LittleInch]

You need to run this through an appropriate Management of Change or MOC procedure including probably a mini HAZOP.

For me an "alarm" is insufficient protection if the fluid can reach higher than 350C or 35 bar?

So ignoring the de-rating / re rating thing, it all boils down to how do you as a company manage change to the design parameters with the required checks and approvals of senior and experienced personnel and a review of protection, alamrs and trips (LOPA study).

Just be aware that over time, too many MOCs can result in a change to the overall plant operations and then you really need, IMHO, to do a complete plant revalidation and HAZOP to pick up things missed or not realised which has an impact on other systems and processes.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[GD2]

OP,
You need to clarify more why do you want to de-rate the piping? Have the process conditions changed or piping material degraded over time?
Getting a temperature alarm doesn't indicate anything. What's the alarm for? if the design conditions were at 550C, you shouldn't be getting the alarm at 285C.
To do de-rating, you need to do a FFS. If our new process conditions are under the design conditions, you don't have to de-rate the piping unless the pipe walls have thinned and/or influenced by other damage mechanisms.
FFS is expensive and you will need to engage a third party.

GDD
Canada

 

[georgeverghese]

If your operating pressure is 35barg, what is PSHH trip setting and what is PSV setting ? The PSV setting is the pressure value relevant for derating.
While that for temp, it is the TSHH setting +10degC as advised in the previous post on this same subject.
If you are unsure about these and procedures, speak to plant process engineer. Any derating should be documented, calcs checked and signed off, and HAZOP may be called for.