How high can plastic-coated steel pipes withstand

First, the temperature range of different coating materials for plastic-coated steel pipes
(1) Epoxy resin coating of plastic-coated steel pipes
Long-term operating temperature of plastic-coated steel pipes: -30℃~80℃, short-term (instantaneous) high temperature of 100℃~200℃. Epoxy resin steel pipes with special processes (such as high-temperature curing) can withstand temperatures above 200℃.
Application scenarios of plastic-coated steel pipes: Chemical industry, fire-fighting water supply, and other environments requiring resistance to chemical corrosion and high temperatures.
(2) Polyethylene coating of plastic-coated steel pipes
Ordinary polyethylene coating of plastic-coated steel pipes: Long-term temperature resistance -40℃~60℃, short-term temperature resistance 110℃.
Cross-linked polyethylene coating of plastic-coated steel pipes: Long-term temperature resistance increased to 90℃, instantaneous temperature resistance up to 150℃~200℃.
(3) Polypropylene coating of plastic-coated steel pipes: 
Temperature resistance above 120℃, suitable for high-temperature fluid transportation. Second, the highest temperature resistance of plastic-coated steel pipes under special processing: Instantaneous temperature resistance of plastic-coated steel pipes: The cross-linked polyethylene coating, under special processing, can withstand instantaneous high temperatures of 500℃, and some products are rated with a peak temperature resistance of 760℃ (such as seawater plastic-coated steel pipes).
Industrial applications of plastic-coated steel pipes: By adding high-temperature resistant fillers (such as carbon fiber and graphene), long-term temperature resistance can reach 200℃.

Third, application scenarios and temperature resistance requirements of plastic-coated steel pipes: 
For fire-fighting water supply, the recommended coating for plastic-coated steel pipes is epoxy resin, with a temperature resistance range of -30℃ to 120℃.
For chemical fluid transportation, the recommended coating for plastic-coated steel pipes is modified epoxy resin/polypropylene, with a temperature resistance range of -30℃ to 200℃. For outdoor overhead pipelines, the recommended coating is UV-resistant polyethylene, with a temperature resistance range of -40℃ to 90℃.

Fourth, National Standards and Acceptance Criteria for Plastic-Coated Steel Pipes
GB/T 23257-2017: Specifies the temperature resistance and coating thickness requirements for 3PE anti-corrosion steel pipes.
CJ/T 120-2016: Fire-fighting plastic-coated steel pipes must pass a 1.6MPa water pressure test and a salt spray test.
Acceptance Recommendations: Test coating thickness (inner wall ≥ 0.3mm) and adhesion (no peeling after cross-cut test).
Electrical spark test (no breakdown at 1500V).

Fifth, a guide to avoiding pitfalls when purchasing plastic-coated steel pipes:
Avoid the low-price trap: Plastic-coated steel pipes that are exceptionally cheap may have been made with substandard materials (such as insufficient coating thickness).
Prioritize reputable brands: Regular manufacturers typically support customization and product inspection.