Brittle fracture risk of leaking bleeder 3

[ENG-RAY]

Hi all,
For high pressure Ethylene piping, how you solve problem of auto refrigeration if bleeder leaks?

 

[LittleInch]

You ensure all the materials and fixtures are suitable for the temperature if this occurs.

"Bleeder" is very vague. Can you elaborate a bit.

More than one line gets better answers....

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

 

[ENG-RAY]

we have a high pressure ethylene piping. Pressure is about 80 barg. Material is carbon steel. There is two possibilities which we may face auto refrigeration/brittle fracture:

1- There are some bleeders on piping which in case of leaking may cause auto refrigeration ( pressure drops from 80barg to atmospheric pressure and consequently temperature can decrease to -100 deg C)

2- If there is a need to repair piece of the pipe, it needs to be depressurised to our flare system. There is a piping which connectes high pressure ethylene piping to flare system. This piece of piping is made of CS as well and is separated from main Ethylene pipe by a manual valve which is normally closed. On this pipe a restricted orifice has been installed to drop the pressure when depressing to flare system.Down stream of RO the piping is made of stainless steel.
If the manual valve leaks we will have again problem of brittle fracture.


we are looking for Solutions for above problems.

 

[LittleInch]

ENG-RAY,

I repeat myself. Your pipework material and valves etc therefore need to be able to withstand -100C without becoming brittle and loosing strength and more importantly toughness.
Your pipework design also needs to allow for contraction to -100 or similar and should also be protected from personnel injury (cold temp) if this event occurs with them close by.

Is this system in operation or in design?

These things should normally be considered by the designer in a HAZOP or design review and suitable mitigations made.

The lowest risk option is to use materials able to withstand -100C.

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

 

[ENG-RAY]

system is in operation.
I understand what you say but then all high pressure Ethylene piping should be stainless steel. But normally it is Carbon steel. The pipeline from which we receive Ethylene is also carbon steel.

 

[LittleInch]

Then you really need to find out how the designers considered this.

The usual way for a pipeline is to say that depressurisation is a controlled operation and temperature is monitored and controlled to not exceed the min design temp of the C Stl. In terms of a leak or rupture the rationale used is that you don't get low temps and high pressure at the same time so the risk of escalation from leak to rupture is low. Personally I don't agree with that but I accept that's what tends to happen.

On a plant however, you are in a different place. Depressurisation occurs much faster and hence cools down faster. You can get much more concentrated locally low temperature and the impact of low temperature on pipe stress and things like nozzles and tees can be sufficient to cause failure. Do some research into the Longford Gas plant explosion to see the impact of a piece of plant failing as a result of brittle fracture.

So you seem to have identified that this is a "problem". This though should have been considered in the design so you need to look at the design documentation, including HAZOP and process description etc to find out how they justify using material which has a higher min design temp than the pipe can actually see in service.

For de-pressurisation you may need to accept that this takes longer and temperature is controlled when it occurs as apart of a planned or automatic operation.





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

 

[MJCronin]

I beleive that there may be a problem with the NEWBIE OP and his definition of "carbon steel" in piping systems

There are "carbon steel" piping materials that are suitable for -100C service (commonly called "Low Carbon Steels") and there are those that are not (commonly called mild carbon steels)

-- Low temperature carbon steel pipes are covered by B31.3 in ASTM A333 (an example)
-- Mild Carbon steel piping system are covered by B31.3 in ASTM A53, A106 (as examples)

Low Carbon Steels -75° to -100° Celsius temperatures are cold enough that low carbon steels are typically the most reliable choice. Low carbon steel containing 3.5% nickel or higher is an ideal choice.

Perhaps DEL-RAY could actually go out to the plant to determine exactly which materials that his piping system is constructed from..... His "problem" is a contrived one because he is a new engineer and becaause he works for an MBA who somehow wants to cover his ass in some way

The next thing that will happen is that DEL-RAY never post on this thread again ...

MJCronin
Sr. Process Engineer

 

[LittleInch]

True - There are low temperature carbon steels - ENG-RAY needs to define what material it actually is and what its Min Design temp is.

Haven't seen you for a while MJC, but good to know your deep hatred of MBA's is undimmed with time...

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

 

[hacksaw]

What is the size of the "bleeder valves" and the main piping in the original post? You might also provide a measure of the piping insulation.

 

[ENG-RAY]

minimum design temperature of piping is -30 deg C and it has been tested for -50 deg C.
bleeder is 3/4''.Main pipe is 8''.The pipe is not insulated.
I talked to our third party inspector and he confirmed that we do not need to consider leakage of bleeder. It will be considered as permanently technically leak-proof.
But for second scenario, we need to either install a doble block and bleed or we need to change the piping material.

 

[mk3223]

The "permanently technically leak-proof" sound a "magnic" word...

I talked to our third party inspector and he confirmed that we do not need to consider leakage of bleeder. It will be considered as permanently technically leak-proof.

The questions are:
Was the leak of any bleeder happened in the past?
If happened, why and how?
what's the proper action needed to prevent it?

 

[georgeverghese]

If it has been tested to -50degC, then it could be low temp carbon steel A333 Gr 6 ??. This would have been charpy impact tested at the pipe mill at -50degC.

 

[LittleInch]

Charpy tests are usually done 20C below the design temp. That sounds like bog standard A106

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

 

[MJCronin]

I have a wild idea here. MAN-RAY, ...

What do you think about going into the plant, removing some insulation (if necessary) and READING THE MOC FROM THE PIPING ITSELF !!... I have done material verification countless times in the past, I do not understand why this is not already done ....

- If you find a type of "carbon steel" suitable for your low temperatures, then you are home free !!!

- If you find another, non-suitable type of "carbon steel" ... we can talk some more

Why do you refuse to find out more ?

Why do you refuse to post any pictures of these "bleeders" and their SPECIFIC materials of construction?

Are you afraid to go into the plant and investigate ?

MJCronin
Sr. Process Engineer

 

[georgeverghese]

Typically, we dont use high point vent and low point drain bleeders to depressure large sections of piping. These should be blinded off so there is no leak, and no possibility of unsupervised mis operation. Check that this cautionary statement is in the Operating Manual. For depressurisation from 80barg to 1-2barg, use the dedicated depressure facility you have described :

"2- If there is a need to repair piece of the pipe, it needs to be depressurised to our flare system. There is a piping which connects high pressure ethylene piping to flare system. This piece of piping is made of CS as well and is separated from main Ethylene pipe by a manual valve which is normally closed. On this pipe a restricted orifice has been installed to drop the pressure when depressing to flare system.Down stream of RO the piping is made of stainless steel."

This entire section needs to be in stainless steel, as you say, so repair would be to install an 8inch A333 Gr 6 to SS316L transition flange, then replace everything downstream currently made out of A333 Gr 6 with SS316. Otherwise, ask the process design engineers for this plant for depressuring dynamic simulation results which show that this section in A333 Gr 6 is adequate.

 

[LittleInch]

I talked to our third party inspector...

err Sorry, but what has the TPI got to do with a design and operational risk issue? He or she just inspects things.

If they are reviewing the design and have passed this off using what is frankly a ridiculous reason then they will be taking responsibility here, but I really doubt it.

What did you mean by "tested at -50"? Tests are often dune below the design temp, but this doesn't mean that it has been accepted or approved for use at that lower temperature.

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

 

[hacksaw]

Apparently a leaking bleeder valve is being described, so the reported fix is to put a second block valve downstream, and shut it.