Allowable Wall Thickness in Process Piping 2

[ak1965]

Dear Fellow Members,

What should be the criteria for replacing a process piping with respect to reduction in piping wall thickness?

How much remaining wall thickness can be allowed?

To be very specific,we have a process gas receiving header that services at high temperature say around 800 Deg C at inlet positions & pressure is around 3 Kg/Cm^2. The header material is A335 P 22 & nominal wall thickness is 21.44 mm.

The header receives hot ethylene gases from furnace and located at the top of Furnace. It may be appreciated that all inlet points in the header are subjected to Erosion & in 12 years of operation, we have observed 3 mm reduction in wall thickness.

Can some one may guide, as how mcuh reduction in wall thickness is allowed before replacemnt or repair of this header?

Also is there any standard formula available to calculate max allowbale reduction in wall thickness of process piping?

 

[SANJCALG]

Please refer to API 579 appropriate parts and appendices to assess the fitness for service for the header. You will find all necessary information to take a decision.

 

[etsen]

And BS 7910 is also a good choice.

 

[dave5599]

The straight answer is API 570 (PIPING INSPECTION CODE—INSPECTION, REPAIR, ALTERATION, AND RERATING OF IN-SERVICE PIPING SYSTEMS)I am attaching an extract from the same code...Hope it will be useful.

 

[DSB123]

ak1965,
A335 P22 at 800 Deg C -Are you sure?? ASME B31.1 only lists this material for use up to 1100 Deg F (593Deg C)

At that sort of temperature I would have thought another alloy would have been used.

Remember it's not only the pressure wall thickness you need to consider but also the structural strength of the pipe.

What you do not state is the diameter of the pipe.

 

[ak1965]

dave5599

Thanks for sharing extract from API 570.....that assist to calculate with the gievn reduction whether it is safe to operate or not.... however, in our case...i wish to know for the given application and piping specification...how can i know what is the allowable thickness to operate safely?

DSB123....i am cross cheking the service temp. with process and will let you know if any change is there and the pipe size as well.

 

[MJCronin]

ak1965...

dsb123 is correct.

At 800C (1472F) I believe that you are far beyond the acceptable range of the A335 P22 material that you are using.

The calculation of a minimum acceptable wall thickness involves reading an allowable stress from a table.

A table of allowable stresses exists in ASME B31.3 at that temperature (1500F) but it is for stainless and higher alloy materials.

-MJC

 

[ak1965]

DSB123


You are right...I got wrong process parameter. The serivce temerature of A335 P22 header pipe is 550deg.c .....!