3. Chemical Integrity: مكافئ الكربون والخدمة الحامضة

For subsea pipelines, weldability is paramount. To ensure the heat-affected zone (هاز) does not become brittle, ال مكافئ الكربون (EC) is strictly limited.

We typically use the IIW Formula:

For X65QO, $CE_{IIW}$ is usually kept below 0.39, ensuring that offshore welding can be performed with minimal preheating, speeding up the pipe-lay process.

بالإضافة إلى ذلك, because many offshore reservoirs contain $H_2S$, these pipes are often tested for HIC (Hydrogen Induced Cracking) و SSCC (Sulfide Stress Corrosion Cracking). This requires extremely low sulfur levels ($\leq 0.002\%$) and calcium treatment for inclusion shape control (converting elongated sulfides into spherical shapes).