10 Common Material Selection Mistakes

Material selection errors in piping systems cause corrosion failures, brittle fractures, and code violations that are expensive to fix after installation. These 10 mistakes cover the most frequent material-related errors in oil and gas piping.

Technical Mistakes

1. Using A106 Gr. B for Low-Temperature Service

Error: Specifying ASTM A106 Grade B pipe for design temperatures below -29°C (-20°F). Risk: A106 is not Charpy impact tested. Carbon steel becomes brittle at low temperatures, and the pipe can fracture under normal operating pressure. Fix: Use ASTM A333 Grade 6 (impact tested at -46°C) for low-temperature service. See pipe types and materials.

2. Confusing Duplex 2205 and Super Duplex 2507

Error: Specifying duplex 2205 (UNS S31803/S32205) where super duplex 2507 (UNS S32750) is required for highly corrosive chloride environments. Risk: Duplex 2205 has a PREN (Pitting Resistance Equivalent Number) of ~35. Super duplex 2507 has a PREN of ~43. In aggressive seawater or high-chloride service, 2205 will pit and fail where 2507 would survive. Fix: Base the selection on PREN requirements from the corrosion study. PREN >40 typically requires super duplex 2507.

3. Ignoring NACE MR0175 Hardness Limits

Error: Using standard carbon steel (A106 Gr. B, A105, A216 WCB) in sour service (wet H₂S) without hardness verification. Risk: Standard heat treatment can produce hardness above 22 HRC. Materials above this limit are susceptible to sulfide stress cracking (SSC), which causes sudden brittle fracture. Fix: Specify NACE MR0175/ISO 15156 compliance in the PO. Require hardness testing (≤22 HRC or 248 HV for carbon steel) and specific heat treatment.

4. Mixing A105 and A350 LF2 in the Same Low-Temperature System

Error: Using A105 flanges alongside A350 LF2 flanges in a piping system designed for low-temperature service. Risk: A105 is not impact tested. At low temperatures, the A105 flanges become the weak link; susceptible to brittle fracture while the A350 LF2 flanges perform correctly. Fix: Use A350 LF2 (or LF3 for temperatures below -46°C) for all flanges in low-temperature piping classes. See forged flange materials.

5. Exceeding Carbon Equivalent (CE) Limits

Error: Accepting materials with carbon equivalent above the project limit without weldability assessment. Risk: High CE (typically >0.43 per IIW formula) increases the risk of hydrogen-induced cracking in the heat-affected zone during welding. Field welds crack, requiring expensive repair. Fix: Specify CE limits in the material purchase specification. Require the mill to report CE on the MTC.

6. Wrong Stainless Steel Grade for the Corrosion Environment

Error: Using 304/304L stainless steel in chloride-containing environments where 316/316L is required. Risk: Type 304 lacks molybdenum and is highly susceptible to pitting corrosion and stress corrosion cracking (SCC) in chloride environments. Equipment fails within months. Fix: Use 316/316L (with 2-3% Mo) for chloride service. For higher chloride concentrations or temperatures, consider duplex stainless steels.

7. Not Specifying “L” Grade for Welded Stainless Steel

Error: Using 304 or 316 instead of 304L or 316L for welded fabrications. Risk: Standard grades (304, 316) have higher carbon content (≤0.08%) that causes sensitization during welding. Chromium carbides precipitate at grain boundaries, leading to intergranular corrosion in service. Fix: Specify L-grades (≤0.03% C) for all welded stainless steel components: A312 TP304L/TP316L for pipe, A403 WP304L/WP316L for fittings.

Commercial Mistakes

8. Accepting “Dual-Certified” Material Without Review

Error: Accepting material certified to both A106 Gr. B and A53 Gr. B (dual-stamped) without verifying it meets all requirements. Risk: Dual-certified material meets the lesser of the two specifications. A53 allows welded pipe (ERW), which may not be acceptable where A106 (seamless only) is specified. Fix: If the piping class requires seamless pipe, verify the manufacturing process on the MTC regardless of the ASTM stamp.

9. Not Verifying Material Origin for Restricted-Country Requirements

Error: Not checking the country of origin (melt and manufacture) when the project specification restricts certain source countries. Risk: Some projects and clients prohibit materials from specific countries due to quality concerns, sanctions compliance, or client specifications. Non-compliant material is rejected at site. Fix: Specify country-of-origin requirements in the PO and verify the mill source on the MTC.

10. Ordering Wrong Material for Cast Valve Bodies

Error: Specifying wrought material grades (A105, A182) for cast valve bodies, or cast grades (A216 WCB, A351 CF8M) for forged components. Risk: Wrought and cast grades have different chemical compositions, mechanical properties, and applicable standards. A216 WCB is the cast equivalent of A105 forging; they are not interchangeable specifications. Fix: Use cast material grades (A216, A351, A352) for cast bodies and wrought grades (A105, A182, A350) for forged components. See valve materials.

Frequently Asked Questions

Can I use A106 Grade B for low-temperature service?

No. ASTM A106 Grade B is not Charpy impact tested and should not be used below approximately -29°C (-20°F). For low-temperature service, specify ASTM A333 Grade 6, which is mandatory impact tested at -46°C (-50°F) per the standard.

What is the difference between duplex 2205 and super duplex 2507?

Duplex 2205 (UNS S31803/S32205) has a PREN of approximately 35 and is suitable for moderate chloride environments. Super duplex 2507 (UNS S32750) has a PREN of approximately 43 and is required for aggressive chloride, seawater, and high-temperature corrosive services where higher pitting resistance is needed.

What does NACE MR0175 require for materials?

NACE MR0175/ISO 15156 sets requirements for materials used in sour (H₂S-containing) environments: maximum hardness limits (≤22 HRC for carbon steel), specific heat treatment conditions, restricted alloy compositions, and in some cases, mandatory testing (HIC, SSC). Non-compliant materials risk sudden brittle failure.

Can I mix A105 and A350 LF2 flanges in the same piping system?

This is not recommended for low-temperature service. A105 flanges are not impact tested and become the brittle failure point in cold conditions. If the system sees temperatures below -29°C, all flanges should be A350 LF2 or LF3.

What is carbon equivalent and why does it matter?

Carbon equivalent (CE) is a formula that combines the effects of carbon and other alloying elements on weldability. Higher CE increases the risk of hydrogen-induced cracking in the weld heat-affected zone. Project specifications typically limit CE to ≤0.43 (IIW formula) or ≤0.25 (Pcm formula for low-carbon steels) to ensure safe field welding.