For piping falling under the scope of AS 4041 Pressure Piping, fittings can be ASME B16.9, ASTM A420 or MSS SP-97. Then there is a total 'get out' that allows the 'parties concerned' to use any suitable ISO, ASME or CEN standard if they so accept.
Now you are talking about thread types - you can obtain all of those - BSP is common for general usage and availability, but NPT is more common in oil and gas, and probably mining work.
I have noticed the standard design for most Australian pipe fittings is round. Usually, these pipe fittings are also hollow, complete with a hole in the middle. Many Australian, however, are installed upside down when viewed from the other side of the equator. This has caused problem when unscrewing threads backwards during disassembly to put them together improperly after repair and replacement. 8<)
/sarcasm
Seriously, when was what part of the plant built, and what rules did they use when it was FIRST designed and fabricated? Who designed and built the (new) replacement equipment - and what design standards did THEY use when it was rebuilt?
Standard (fractional or inches-based) piping were common in almost all of the British systems until metric fittings and designs became standardized. You easily could get dual metric and BS standards in the same company in different parts of the same facility. Not often in the same plant - but it has happened.
"have noticed the standard design for most Australian pipe fittings is round. Usually, these pipe fittings are also hollow, complete with a hole in the middle. Many Australian, however, are installed upside down when viewed from the other side of the equator. This has caused problem when unscrewing threads backwards during disassembly to put them together improperly after repair and replacement."
It's the water running up-hill that gives the greatest advantage.
Thanks everyone for all your help. We're doing a little redesign of a system on some mining equipment (low pressure stuff) that has both NPT and BSP fittings, and we figure we might as well make them all the same since we're replacing most of the parts anyway.
