What are the selection requirements for oil and gas transportation?
Straight seam steel pipes must meet API 5L standards in oil and gas transportation, and LSAW or ERW high-frequency welded pipes are preferred. The wall thickness needs to be calculated according to the design pressure. High-pressure trunk lines require X60 and above steel grades, and must pass HIC (resistance to hydrogen-induced cracking) and SSC (sulfide stress corrosion) tests. Low-temperature environments (such as Arctic projects) require additional Charpy impact tests. 3PE coating or FBE lining is usually used for corrosion protection, and a mechanical protection layer needs to be added in mountainous areas.
How to choose straight seam steel pipes in building structures?
Straight seam steel pipes for building structures must comply with GB/T 3091 or ASTM A500 standards, and carbon steel Q235B is a common material. Square and rectangular pipes are preferred for large-span structures such as gymnasiums and high-rise buildings, and bending and compressive strengths need to be calculated. In seismic design, the steel yield ratio is required to be ≤0.8, and the sulfur and phosphorus content is controlled. For surface treatment, hot-dip galvanizing (weather resistance up to 30 years) or fire-retardant coating can be selected. During construction, attention should be paid to the mixed use of node welding and bolted connection.
What are the functions of straight seam steel pipes in water conservancy projects?
Mainly used for drainage pipes, culverts and pump station pressure pipes, the diameter is usually ≥DN800, and the material is Q355B or weathering steel. The wall thickness wear caused by sediment scouring needs to be considered, and concrete or polyethylene lining is required when necessary. Water conservancy projects require welds to pass 100% ultrasonic testing, and the water pressure test pressure is 1.5 times the working pressure. In saline-alkali areas, cathodic protection + epoxy coal tar coating double anti-corrosion is required.
What are the special requirements of the chemical industry for straight seam steel pipes?
Chemical pipelines need to be resistant to acid and alkali corrosion, and stainless steel (304/316L) or plastic-lined steel pipes are preferred. When transporting flammable media, 100% X-ray flaw detection of welds is required, and anti-static jumpers are required at flange connections. Thermal expansion compensation design needs to be considered for high-temperature pipelines (＞200℃). Special media such as liquid ammonia require seamless ERW steel pipes, and the chlor-alkali industry requires titanium composite pipes.
What are the standards for straight seam steel pipes for urban heating pipe networks?
Heating pipes generally use ERW steel pipes that meet the GB/T 3091 standard, and Q235B can be selected when the working temperature is ≤150℃. High-temperature hot water pipe networks (＞150℃) require Q345R pressure vessel steel. Prefabricated direct-buried insulated pipes must meet the CJ/T 114 standard, and the thickness of the polyurethane insulation layer must be ≥40mm. The compensator section requires L245N low-alloy steel pipes to resist fatigue. Thermal displacement stress needs to be monitored during installation.
