Bypass Valve for Equipment in Piping

You need your own copy:List of NFPA codes and standards

I'm not sure this is really what you are after...............................

NFPA code would vary depend on what the pipe line carries. That info was not given. I'm sure if the pipe line carries water for fire suppression they would cover it in depth. Not so much sanitary waste water.

RAKESH REDDY,

You have not given enough information for anyone out here to give you any real help. Information such as:

• the type of Facility
• the commodity
• the type of equipment
• the governing Piping Code
• the location of this facility
  
• etc

You also need to look at the link that "Lyn" posted for you. That is a list of NFPA Documents. Only a very few of them are "Codes". The vast majority of the NFPA Documents are "Standards" that normally cover only a narrow subject. The balance of the documents are "Guidelines" and "Practices". You also need to understand that none of the NFPA Documents are mandatory for a given project unless the Client specifically states so in the Project Basic Engineering Design Document (BEDD).

Dear All,

Sorry for providing incomplete information and thank you for your immediate response.

In Fuel OIl Line (HFO and LDO ) we have provided a bypass line for flow meter considering continous running of system during maintainance of Flow meter.

C&I has informed us that the measurement from Flow meter is the major control for Boiler operation. Hence bypaassing the flow at the time of maintaince wil not provide any inputs for controlling. Hence bypass in acceptable.

I heard that if system is designed as per NFPA then bypass for every equipment is complusary. I search NFPA standard but i didnt get proper information.

Hence kindly let me know whether Bypass is complusary for Equipments in fuel oil Pipe line as per NFPA ??

Regards,

Rakesh

You need to get someone who is qualified just to read the standards, long before attempting to implement them.

"Compulsory"

Some good advice. Get the right info and get suitably qualified technical people. Then use the good old Hazop Study to identify all sorts of other technical issues in your process that you may have overlooked. The one you mentioned (By-pass valve) is a fairly simple one. The Hazop Study should bring out more such flaws in your process. As Tornado and Lyn insisted you need to get suitably qualified people and enough of the technical information before embarking on such ventures. The Hazop Study will require a multi-disciplined team of between 5 - 12 technical people.

For start-up and commissioning purposes alone you will need a by-pass valve or two just to make sure that you can revert back to your old process in case the new plant addition does not work straight away. By pass valves are handy. They will provide you with more operating options in many different ways. Looks like you might even need isolation valves as well - to shut off and isolated units of equipment eg for maintenance purposes.

From the description of the plant it sounds as though the use of a bypass valve could potentially lead to overfeeding of fuel oil to the boiler resulting in an explosive situation. A hazop analyses (see reply 6, (good answer BJ)) will confirm if this is the case.

If it is, you then have two options.

Option 1

If the boiler is crucial to operation of the plant and cannot be out of service, add a second flow meter in parallel with the first with upstream and downstream isolation on both and switch between the two when maintenance is required. This is standard practice for things like filters that have to be serviced at frequent intervals.

Option 2

Don' install a bypass, and generate at written report to inform the management that the plant will be unavailable for H hours every X period (based on flow meter supplier's recommendations for routine maintenance) and there will be an outage an average of every Y period (based on MTBFs for the flow meter) while the flow meter is exchanged. Add to the report the time needed to install the replacement, delivery delay for a new unit, and price of a flow meter, so that management can assess if it is economic to keep a spare flow meter in your maintenance stores. If they decide that it is economic, then Option 1 is the obvious way to proceed.

The relevant NFPA code is 85. Section 1if you only have one burner, Section 2 for multiple burners. If you bypass the flow meter during operation and you have a simple control system, you will over feed the fuel into the boiler. This could result in an explosion. If you have a cross limiting system then loss of flow signal will reduce the air flow. Whatever, bypassing this unit is dangerous with very serious results. A simple check is to relate the flow to the control valve position. Build a look up table in the logic so that if there s a deviation of more than say 5% it will alarm. Bottom line, - bypasses around the control valves is normal. Bypass around a flow meter is unacceptable and dangerous. NFPA 85 is a good base but has some weaknesses in relation to safety standards. Try the Australian AS 3814. It complies with the safety standards 61508 and 61511

By the way, if a bypass line is to be installed around a flow meter, wouldn't be a good idea to include an additional flow meter in the bypass line, so you could continue to monitor the flow, while the bypassed flow meter is being repaired?...

Mr G, this is not necessary at all. He should simply install the flow meter before the by-pass valve. i.e. install the by pass option after the flow meter. Then there is no need for 2 flow meters. What is needed in addition to a by-pass valve is usually a shut off valve. The two usually go together. A short by-pass line would usually be used in applications such as a pressure meter or when flow has to go through a filter device. [This type would require two isolation valves]. Our application in this example would be a long by-pass as the user is considering the option of using a plant or sub-section or not using it at all. With the use of shut off valve together with by-pass valve, the flip from old to new plant (or the other way around) is usually simple in practical plant terms. It is the computer control system that can give headaches during commissioning.

Yes, but doesn't the type of fuel doing the bypassing, under what other hazardous conditions, at the same time and place of the installation also require some further consideration?...

Otherwise, why was it so important that the flow be continuously monitored in the first place?...

Rakesh, Your C & I have already told you it is an essential measurement for the boiler control. A number of comments on this forum have also advised of the danger of bypassing this instrument. The NFPA code does not mention it probably because the panel never thought anybody would even dream of doing it. Forget the bypass, isolating valves and all that other stuff. Run your boiler safely please!!

Think of the scenario of when a unit blows up and you have to go to court. What are you going to tell them when asked what did you do to prevent hazards? Are you going to say you installed a by-pass around an essential control instrument? In Court, the Hazop Study Report s will usually play a good role in showing that one has made some effort in hazard & safety analysis. But any good Hazop will show easily highlight a bad practice such as eliminating an essentail instrument fromm your process. If anything, hazops usually add items to your system as they demand additional safety features. Raskesh, from your practical example and reasoning, it gives one the impressions that you are not following many of the standard engineering practices. We mention a few of the basic ones (Codes, Hazops, Qualified people, Manuals). Just as an after-thought : What does your Boiler Manual say ?

Well, isn't the cost of a little (functional redundancy) significantly less than the price tag of serious (and avoidable?) accident?...

I wonder what British Petroleum would say now, after the Deepwater Horizon accident, etc.?...