What are single-crimp and double-crimp connections in stainless steel water pipes? How do they differ?

In modern building water supply systems, stainless steel pipes are widely used due to their corrosion resistance, long service life, and hygienic safety. Among stainless steel pipe connection technologies, crimping has become the mainstream installation method. “Single-crimp” and “double-crimp” are the two most common types, and understanding their differences is crucial for engineering quality and cost control.
I. What is Compression Connection?
Compression connection is a mechanical fastening method. Using specialized tools, the connection points between fittings and pipes are compressed. This causes plastic deformation in the stainless steel pipe while simultaneously compressing the sealing ring inside the fitting, creating a dual sealing effect (radial contraction seal and end-face seal).

Single Compression Equal-Diameter Tee
II. Technical Analysis of Single vs. Double Compression
Core Definitions (per GB/T 19228.1 standard)
Single Compression (Type D): The socket end of the fitting has no extended straight section. Only one compression is applied to one side of the U-shaped groove, forming a single-sided bite and seal. After crimping, the joint typically appears hexagonal, secured by a single compression that compresses the sealing ring.
Double Compression (S-Type): The pipe fitting socket features an extended straight section. Two separate squeezes (or one dual-position squeeze) are applied to both sides of the U-shaped groove, creating a double-grip seal. The sealing ring is fully enclosed within the fitting, ensuring more uniform force distribution. The joint also typically forms a hexagonal shape.
Double Compression Equal-Size Tee
Single Compression vs. Double Compression Key Differences Comparison Table
III. Layman's Understanding and Selection Recommendations
Single Compression: Like pinching one side of a hose joint with your hand. Suitable for stable pressure and low-vibration scenarios. Cost-effective but carries slightly higher sealing risks under prolonged high pressure or significant temperature fluctuations.
Double Compression: Like gripping the joint firmly from both sides with both hands. Dual fixation + dual sealing. An upgraded version of single compression. Ideal for projects demanding high safety and durability. Offers greater long-term stability.
Selection Tips: Prioritize products compliant with GB/T 19228 standards. DN15–DN100 commonly use compression fittings. For high-rise buildings, hot water/drinking water systems, choose double compression fittings. Single compression fittings are cost-effective for standard multi-story cold water systems.