what is meant by "standard pipe".........?

Try Google or Wiki. It's a learning experience.

Will schedule 40 always refer to standard pipe............?

Good grief, get some tables from Google and check it out.

The answer is no.

Engr_mech, You wrote:
"What is meant by "standard pipe".........?"

It depends on the context and basis behind the question.

What might be the standard pipe used in one type of plant may not be the standard that is used in another type of plant.

Some processes require Glass Lined Pipe, that is the "Standard" for that plant. Another process may use all Aluminum Pipe so that is the "Standard" for that plant.

What type of plant and process are you involved in that causes you to ask this question?

Real context of my question was the extract from Wikipedia

http://en.wikipedia.org/wiki/Nominal_Pipe_Size, which states


"Some specifications use pipe schedules called standard wall (STD), extra strong (XS), and double extra strong (XXS), although these actually belong to an older system called iron pipe size (IPS). The IPS number is the same as the NPS number. STD is identical to SCH 40S, and 40S is identical to 40 for NPS 1/8 to NPS 10, inclusive. XS is identical to SCH 80S, and 80S is identical to 80 for NPS 1/8 to NPS 8, inclusive. Different definitions exist for XXS, but it is generally thicker than schedule 160."


here it refer "standard" to 40 schedule pipe(4th line).........??

Just think of standard wall or 'std' as any wall thickness in the same context as sch 10 or sch 20 or sch 30. The thickness or equivalence of 'std' varies with size.

For example 30" std wall is between sch10 and sch20, but 3" std wall is same as sch40 wall.

If you downloaded a file of pipe sizes you could easily have figured this for yourself.

Take a look on ASME B36.10M

Regards,