If i want to carry out thickness measurement on piping system to ascertain the remaining wall thicknes, what code do i use and what is the minimum allowable dimmunition of thickness in percentage?.

I suggest to consult the Code of Construction that was used for the design of the piping.

When you know the nominal new thickness, establish the required thickness, and measure the actual thickness, you can determine the remaining lifetime-
Just calculate the corrosion rate (mm/yr) and determine the remaining life.
An inservice inspection after half of the remaining life is a good idea.

NBIC can help for inservice inspection questions.

DK

If i want to carry out thickness measurement on piping system to ascertain the remaining wall thicknes, what code do i use and what is the minimum allowable dimmunition of thickness in percentage?.

betrandma,

Use the material spec. For example SA106-B pipe then go to Section II Part A and the Code minimum allowed is 87%.

leem

Leem,

The material undertolerance has maybe not been considered in the design. Some piping Codes allow to calculate with the actual thickness, some even with the actual Yield strength. Therefore the 12.5% undertolerance is maybe not available.
Also we do not know if Betrandma knows the nominal thickness of the new pipe.

In some counties I have seen piping systems where nobody knew the material, schedule, design code or required thickness. The piping was just there, and the owner wanted to know how to repair it after an explosion.

For this reason, the question shall be more precisely.

DK

Let us assume it as a process piping,

To ascertain the remaining life --

check API 570(2006 edition), section 7.

Minimum allowable dimension of thickness in percentage --

The required thickness of the pipes shall be the greater of the pipe design thickness (or) the structural minimum thickness. For service with high risk, the piping engineer should consider in increasing the required thickness to provide for unanticipated (or) unknown loadings (or) undiscovered metal loss.

As per B31.3, Required thickness of straight pipe T = t + C
Where t is the pressure design thickness as determined by means of Internal (or) External pressure calculations & C is the corrosion allowance.(Refer 304,ASME 31.3,2004 edition)

Hope this will help you.