Stainless steel fittings connect pipes and tubing while controlling direction, flow, branching and system assembly. The right connection method depends on pressure, pipe size, maintenance requirements, installation method and whether the system needs to be dismantled.
BSP, buttweld and compression fittings solve different connection problems. Understanding the differences helps engineers and procurement teams specify fittings that match the piping system rather than selecting components by size alone.
Key Takeaways
- BSP fittings use threaded connections and suit systems where components need to be assembled or removed.
- buttweld fittings create permanent welded connections for many process piping applications.
- Compression fittings mechanically seal against tubing without welding or threading the tube.
- Pipe and fitting dimensions, materials and connection standards must be compatible.
- The operating pressure, temperature, fluid and maintenance requirements should guide selection.
Quick Decision Guide
| If you need… | Consider… |
| A threaded connection that can be dismantled | BSP fitting |
| A permanent process-piping connection | buttweld fitting |
| A connection to small-bore instrumentation tubing | Compression fitting |
| Reduced internal turbulence | buttweld fitting |
| Easy assembly without welding | BSP or compression fitting |
How Do BSP Fittings Work?
BSP fittings use standardised pipe threads to create a mechanical connection between compatible components.
BSP stands for British Standard Pipe. Steelmor stocks BSP stainless steel fittings in 316 stainless steel from 1/8 inch to 4 inches, including elbows, hose nipples, reducing bushes, barrel nipples, sockets, plugs, unions and ball valves.
BSP connections are useful where components may need to be removed for inspection, maintenance or replacement. The thread type must, however, be correctly matched to the mating component.
BSPP refers to parallel threads, while BSPT refers to tapered threads. ISO 228-1 covers parallel pipe threads used for mechanical assembly, while pressure-tight threaded joints are addressed by other standards.
When Should You Use Butt-Weld Fittings?
buttweld fittings are designed to be welded directly to pipe, creating a permanent connection.
This makes them suitable for process piping where leak control, flow characteristics and long-term joint integrity are important. Steelmor stocks buttweld fittings in 304/L, 316/L and 321/H stainless steel, with welded and seamless options in a range of schedules and sizes.
Common fitting shapes include elbows, tees, reducers and caps. The fitting is prepared for welding and becomes part of the pipe system once the joint has been completed.
ASME B16.9 specifies dimensions, tolerances, ratings, testing and marking for factory-made wrought buttwelding fittings.
How Do Compression Fittings Work?
Compression fittings create a mechanical seal between a fitting body and tubing using components such as ferrules and a nut.
They are commonly associated with small-bore instrumentation and fluid systems where welding may be impractical or where components need to be disconnected. Correct tubing selection and installation are essential because the fitting must grip and seal against the tube.
Steelmor’s instrumentation tubing range is designed for applications involving pressure switches, gauges, flow monitors and valves. Its existing guide to instrumentation tubing explains why tubing material, dimensions, operating pressure and fitting compatibility need to be considered together.
Swagelok’s technical guidance similarly recommends matching fitting and ferrule materials to the tubing material and following the manufacturer’s installation requirements.
Which Fitting Is Best for Pressure Piping?
The appropriate fitting depends on the complete system specification rather than pressure alone.
buttweld fittings are widely used in process piping and are covered by standards such as ASME B16.9. Threaded and socket-weld forged fittings are covered separately by ASME B16.11, showing why the connection method and fitting standard need to be specified together.
Compression fittings can also be used in pressure applications, particularly instrumentation and small-bore tubing systems, but their pressure rating depends on the fitting, tube dimensions, material and installation.
How Do You Choose Between BSP and Butt-Weld?
The key difference is permanence.
BSP fittings allow a threaded joint to be assembled and dismantled. buttweld fittings become part of the piping system after welding and generally provide a more compact connection with a smooth internal transition.
| Consideration | BSP | buttweld | Compression |
| Connection | Threaded | Welded | Mechanical |
| Dismantling | Relatively easy | Requires cutting | Relatively easy |
| Typical use | General piping | Process piping | Instrumentation tubing |
| Welding required | No | Yes | No |
| Best suited to | Serviceable systems | Permanent systems | Small-bore tubing |
What Should You Check Before Selecting a Fitting?
Start with the system rather than the fitting catalogue.
Check:
- Pipe or tube material
- Outside diameter and wall thickness
- Connection standard
- Operating pressure
- Operating temperature
- Fluid or gas being transported
- Corrosion exposure
- Installation environment
- Maintenance requirements
- Applicable engineering standards
Material compatibility also matters. Using stainless steel fittings with stainless steel tubing can help avoid problems associated with incompatible materials and differing mechanical properties.
Before You Specify a Stainless Steel Fitting
- Confirm the pipe or tubing material.
- Confirm the connection type.
- Check dimensions and wall thickness.
- Confirm pressure and temperature requirements.
- Check the applicable standard.
- Confirm the stainless steel grade.
- Consider whether the connection needs to be dismantled.
- Verify certification requirements.
Frequently Asked Questions
Are BSP and NPT fittings interchangeable?
No. BSP and NPT use different thread forms and should not be treated as interchangeable. The mating thread standard must be confirmed before ordering.
Are buttweld fittings better than threaded fittings?
Neither is universally better. buttweld fittings suit permanent process-piping connections, while threaded fittings can be useful where dismantling is required.
Where are compression fittings commonly used?
Compression fittings are widely used with small-bore tubing in instrumentation and fluid systems where a mechanical connection is preferred.
Can stainless steel compression fittings be used with stainless steel tubing?
Yes, provided the fitting and tubing are compatible and installed according to the fitting manufacturer’s requirements.
What stainless steel grades are available for buttweld fittings?
Steelmor stocks buttweld fittings in 304/L, 316/L and 321/H grades, with sizes ranging from 1/2 inch to 36 inches.
The connection, operating conditions, and maintenance requirements of the piping system determine the correct stainless steel fitting. BSP fittings provide threaded assembly, buttweld fittings create permanent welded connections, and compression fittings provide a mechanical connection commonly used with small-bore tubing.
The important step is to specify the fitting and the pipe or tubing as one connected system. Steelmor supplies stainless steel BSP and buttweld fittings alongside pipe, tubing, and instrumentation tubing. For project-specific requirements, contact Steelmor.