INSPECTION AND STANDARDS OF PIPES

                                             

INSPECTION AND STANDARDS OF PIPE

·         Inspection of pipe is carried on only two basic parameters that is its diameter and thickness.

·         In US based system pipe description is given as Nominal pipe size and schedule.

·         In British standards pipe description is given as nominal bore along with schedule.

·         As the schedule of pipes is increase then thickness of pipe wall is increase and vice versa.

·         Stainless steel pipes schedule are same as per Carbon steel pipe schedule but stainless steel pipes description contains suffix S to schedule size like Schedule 40S.

Schedule of pipe

·         After design calculation of system allowable working pressure through piping then the pipe schedule is selected as per given pressure rating.

 

Where,

·         P- Actual System working pressure

·         S- Material permissible stress (psi)

·         Let us take an example to understand better,

Example

·         For mild steel pipe having ultimate tensile stress of 65300 psi and permissible working pressure of the system as per design calculation is 2612 psi then calculate the schedule for 1 inch pipe.

·         S=65300, P= 2612 then

Pipe schedule number = (1000 X P) / S

                                       = 1000 X 2612 / 65300

                                       = 40

·         Hence we have to use 1 inch schedule 40 mild steel pipe for our system.

·         Inner diameter = outer diameter – 2 x thickness

Pipe dimensional standard

·         API 5L

·         ANSI/ASME B36.10

·         BS 1600 & BS 1387.

 

DIMENSIONAL TOLERANCE

·         ASTM A312 seamless and welded pipes

Pipe size up to 1.5 inch or 40 NB

·         Outside diameter: +0.40 mm, -0.79 mm

·         Allowable thickness: +12.5%, 6.4%

Pipe size of 1.5 inch/ 40NB to 4 inch/100 NB

·         Outside diameter: +0.79 mm, -0.79 mm

·         Allowable thickness: +12.5%, 6.4%

Pipe size of 4 inch/ 100NB to 8 inch/200 NB

·         Outside diameter: +1.59 mm, -1.59 mm

·         Allowable thickness: +12.5%, 6.4%

Note: All pipes should be hydrostatically tested.

 

PRESSURE RATING OF PIPES

·         It is permissible maximum working pressure of the pipe.

·         Schedule of pipes defines the pressure ratings.

·         Pressure rating is defines the ability of pipe to sustain the internal system pressure.

·         As the pressure rating increases wall thickness is also increases.

·         The given formula is stated that the minimum wall thickness of pipe.

Where,

·         Thickness t- required wall thickness of pipe in inches

·         Minimum thickness t_m – Minimum required thickness of pipe in inches

·         P- Design pressure in psi

·         D- Outside diameter of pipe in inches

·         C-Corrosion allowance in inches

·         S- Permissible stress in psi

·         E- Longitudinal joint quality factor of pipe

·         Y- Wall thickness correction factor

 

CODES AND STANDARDS

·         There are mainly four standards are used for pipes, they are as follows

·         ASTM- American society of testing of materials.

·         ANSI- American national standardization institute

·         ASME- American society of mechanical engineers

·         API- American petroleum institute

Following basic codes are used in various types of piping applications

·         ASME B 31.1: power piping

·         ASME B 31.2: Fuel gas piping

·         ASME B 31.3: Process piping

·         ASME B 31.4: Liquid piping

·         ASME B 31.5: Refrigeration piping

·         ASME B 31.8: Gas distribution and transportation

·         ASME B 31.9: Building service piping

·         ASME B 31.11: Slurry piping.