What ASTM A135 Covers
ASTM A135 is the standard specification for electric-resistance-welded (ERW) steel pipe for fire-protection use. It covers black and hot-dip zinc-coated pipe in nominal sizes, intended for water-based fire-suppression systems such as automatic sprinklers. The pipe is formed from hot-rolled or cold-rolled strip and welded by electric resistance welding, without filler metal, and the weld is heat-treated so that the seam properties match the base metal. A135 is one of the three pipe specifications commonly referenced by fire-protection codes, together with A53 and A795.
Grades and Properties
A135 defines two grades. Grade A has a minimum yield strength of 30,000 psi (205 MPa) and a minimum tensile strength of 48,000 psi (330 MPa). Grade B, the common choice, has a minimum yield strength of 35,000 psi (240 MPa) and a minimum tensile strength of 60,000 psi (415 MPa). The standard sets the chemical composition limits and the elongation requirements, and each pipe is hydrostatically tested. For fire-protection service the pipe must also satisfy the installation requirements of the governing code, such as NFPA 13.
Manufacturing and Testing
The pipe is made on an ERW mill: strip is cold-formed into a tube, the edges are fused by high-frequency resistance welding, and the seam is heat-treated and sized. Testing includes tensile testing, flattening and bend tests of the weld, and hydrostatic testing of every pipe. The weld seam is examined by non-destructive methods where required. The finished pipe is marked with the standard, grade, and the mill identification so that it can be traced through the fire-protection system.
A135 vs A53 vs A795
A53 is the general-purpose welded and seamless pipe standard for mechanical and pressure service. A795 is the standard written specifically for fire-protection use, with rigorous hydrostatic testing, joint restrictions for thin walls, and traceability marking. A135 is the ERW-only fire-protection standard: it covers the same fire-protection service as A795 but is limited to electric-resistance-welded production. All three can supply black or galvanized pipe of similar appearance, but the fire-protection codes specify which standard applies, and the certificate and markings must match the drawing.
Selecting Fire-Protection Pipe
The fire-protection pipe is selected by the system design: the hazard classification, the required pressure, the diameter, and the environment. Black A135 Grade B pipe is the common choice for standard sprinkler systems; galvanized pipe is used where the water or the atmosphere is corrosive, and where the code permits it. The wall thickness must be compatible with the joint method: threaded joints require a minimum wall, and thin-wall pipe is joined by welding or mechanical couplings. The applicable code, such as NFPA 13, should always be consulted, because it defines the acceptable pipe standards for each part of the system.
Frequently Asked Questions
Q: What is ASTM A135 pipe?
Electric-resistance-welded steel pipe for fire-protection service, supplied black or galvanized in Grades A and B.
Q: What is the difference between A135 and A53?
A53 is the general-purpose pipe standard covering several manufacturing routes; A135 is specifically for ERW pipe used in fire-protection systems, with the testing and marking tailored to that service.
Q: What is the difference between A135 and A795?
Both are fire-protection pipe standards. A795 covers welded and seamless pipe with specific fire-protection requirements; A135 is limited to electric-resistance-welded pipe.
Q: What is the yield strength of A135 Grade B?
The minimum yield strength is 35,000 psi (240 MPa) and the minimum tensile strength is 60,000 psi (415 MPa).
Q: Is A135 pipe galvanized?
It can be supplied black or hot-dip zinc-coated. Galvanized pipe is specified where the water or environment is corrosive.
Q: What code governs sprinkler pipe installation?
NFPA 13, the standard for the installation of sprinkler systems, governs the system design and references the acceptable pipe material standards.
