1. Nature of Product
2. Design Life
3. Product Temperature
4. Thickness and Grade Selection
5. Handling and Transportation (diameter/wall thickness ratio to prevent buckling.
6. Type of line pipe
7. Installation Requirements
1. Material chemistry
2. Internal Coatings
3. Product Conditioning
4. Corrosion Inhibitors
5. Corrosion Allowance
1. The selection of the pipeline material type is a fundamental issue to be decided at the conceptual design stage of a pipeline project.
2. The most frequently used pipeline materials are metallic.
3. Non-metallic materials (e.g. GRP/GRE, flexible pipe) may be cost effective for specific applications, especially when the fluid is corrosive.
4. The occurrence and rate of internal corrosion is governed by a variety of process conditions which include:
1. Corrosivity of the fluid, in particular due to the presence of water combined with hydrogen sulphide (sour corrosion), carbon dioxide (sweet corrosion), or oxygen. Temperature and pressure can have a great impact on the corrosion rates.
2. Velocity of the fluid, which determines the flow regime in the pipeline. In pipelines transporting fluids containing water, too low velocities lead to settlement of water, which may lead to bottom of pipe internal corrosion; too high velocities can increase the overall corrosion rate and also destroy any protective scale or inhibitor films.
3. Deposition of solids, which may prevent adequate protection by inhibitors, and can create anaerobic conditions for the growth of sulphate reducing bacteria.
5. The potential long-term impact of corrosion shall be considered during design , and it shall be demonstrated that the pipeline can remain fit-for-purpose throughout its lifetime.
6. When sour service conditions are foreseen, as specified in NACE MR0175, the linepipe material and other materials shall be specified to resist sour service, regardless of whether or not the fluid is to be dehydrated.
7. Carbon steel linepipe material may be used in “light” sweet corrosive conditions (typically where corrosion rates would not exceed 0.5 mm/year without inhibition), with appropriate corrosion allowance and inhibitor injection, regular high resolution intelligent pig monitoring, and under strictly controlled operating conditions.
8. Corrosion allowances in excess of 3 mm shall not be considered without a detailed analysis by corrosion specialists.
9. Materials able to resist sweet corrosion include duplex stainless steels and carbon steels with internal austenitic cladding.
10. Internal coatings cannot be relied on for complete prevention of corrosion.
11. Internal lining (e.g. polyethylene) can be applied for internal corrosion protection.
12. Conditions which may cause pipewall erosion shall be avoided.
13. Various Materials Used Are :
1. Carbon Steel (CS)
2. NACE Carbon Steel
3. CRA Clad CS
4. CS with internal coatings
5. Non-metallic materials
Pipelines are commonly constructed with linepipe in steel grades X42 to X65 as defined in API Spec 5L. Lower grades such as Grade B and higher grades may be appropriate in some cases.
Appropriate derating factors, in accordance with Table 841.116A of ANSI/ASME B31.8, should be used for pipelines operating at high temperatures.
NOTE: Table 841.116A applies to carbon steel materials (derating required above 120 °C). For duplex stainless steel, derating is generally required at lower temperatures (approximately 50 °C).
For the sections of pipelines in locations where they may be exposed to pool or jet fires, reducing the strength properties of high yield material, the material grade should not exceed X52. If higher grades are used, X52 yield strength should be assumed, unless measures are taken to protect the pipe section against exposure to (pool/jet) fire.
Attention shall be given to the fracture toughness properties of pipe material for gas pipelines to prevent the possibility of long running fractures. This is particularly critical when low temperatures are possible, e.g. downstream of pressure reduction stations and at exposed above ground locations.
Carbon steel line pipe shall be in accordance with the following Shell specifications, which are supplementary to the API Spec 5L specification:
L-2-2/3 Carbon Steel Linepipe for Non-Sour Service
L-3-2/3 Carbon Steel Linepipe for Sour Service