1. **How to tell NPS vs NPT?**
**NPS (Nominal Pipe Size):** Refers to the *nominal diameter* of the pipe itself. It's a dimensionless number roughly representing the pipe's inside diameter (e.g., NPS 2, NPS 4). Actual dimensions are standardized by schedules (e.g., Schedule 40, 80).
**NPT (National Pipe Tapered):** Refers to a specific *thread standard* used for joining pipes and fittings. NPT threads are tapered (wider at the base, narrower at the end) to create a seal when tightened.
***Key Difference:*** **NPS** defines the pipe **size**, while **NPT** defines the **thread type** used to connect pipes/fittings.
2. **What is NP2 and NP3 pipe?**
**NP2 and NP3** were obsolete Japanese Industrial Standard (JIS G 3442) designations for **carbon steel pipes for ordinary piping**. They were replaced by the **STK** designation (e.g., STK 30, STK 41) around 1977/1978 and later by **STKR** (e.g., STKR 400).
* **NP2:** Generally corresponded to lower tensile strength pipe (similar to ASTM A53 Grade A or STK 30).
* **NP3:** Generally corresponded to higher tensile strength pipe (similar to ASTM A53 Grade B or STK 41/STKR 400).
3. **What is the meaning of NP 3?**
**NP3** was a specific grade designation under the old Japanese JIS G 3442 standard for **carbon steel pipes for ordinary piping**. It indicated a pipe with a *higher tensile strength* compared to NP2, roughly equivalent to ASTM A53 Grade B or modern STKR 400 pipe. It has been obsolete since the late 1970s.
4. **What does the NP stand for in NP3 pipe?**
In the context of the obsolete **JIS G 3442** standard, **"NP"** most likely stood for **"Normal Pressure"**, indicating pipes suitable for general, non-high-pressure piping systems. It differentiated these pipes from higher-pressure or specialized grades.
5. **What is the thickness of NP3 pipe?**
The **thickness (wall thickness)** of NP3 pipe was **not defined solely by the "NP3" grade**. Thickness was determined by the pipe's **Nominal Size (e.g., 15A, 20A, 25A)** and its **Schedule** or wall thickness designation under the old JIS standard (similar to SCH 40, SCH 80).
* **Example:** An old NP3 pipe with nominal size 20A (approx. NPS 3/4) and "Type 30" wall thickness would have had a thickness of **approximately 2.3 mm**.
* **Important:** NP3 is obsolete. Modern equivalent pipe (like STKR 400) follows current JIS or ASTM/ASME dimensions. The wall thickness for a specific size today depends on its schedule (e.g., SCH 40, SCH 80) per standards like ASME B36.10M. **You cannot state a single thickness for "NP3 pipe".**
