PIPING MATERIALS SELECTION CRITERIA
1. Basic Pipe Materials
(1) Basic pipe materials shall be selected from Table 1. When unlisted materials are used, they shall be verified as suitable for the service conditions and within the limitations of the applicable piping code.
Notes: (1) Unlisted materials are materials not listed in Appendix-A of ASME
B31.3.
(2) Only the following pipe may be used under Severe Cyclic Conditions (*1)
(Source: 305.2.3 of ASME B31.3):
(a) Carbon Steel Pipe
API 5L, Grade A or B, seamless
API 5L, Grade A or B, SAW, straight seam, Ej ≧ 0.95
API 5L, Grade X42, seamless
API 5L, Grade X46, seamless
API 5L, Grade X52, seamless
API 5L, Grade X56, seamless
API 5L, Grade X60, seamless
ASTM A53, seamless
ASTM A106
ASTM A333, seamless
ASTM A369
ASTM A381, Ej ≧ 0.90
ASTM A524
ASTM A671, Ej ≧ 0.90
ASTM A672, Ej ≧ 0.90
ASTM A691, Ej ≧ 0.90
(b) Low and Intermediate Alloy Steel Pipe
ASTM A333, seamless
ASTM A335
ASTM A369
ASTM A426, Ec ≧ 0.90
ASTM A671, Ej ≧ 0.90
ASTM A672, Ej ≧ 0.90
ASTM A691, Ej ≧ 0.90
(c) Stainless Steel Alloy Pipe
ASTM A268, seamless
ASTM A312, seamless
ASTM A358, Ej ≧ 0.90
ASTM A376
ASTM A451, Ec ≧ 0.90
(d) Copper and Copper Alloy Pipe
ASTM B42
ASTM B466
(e) Nickel and Nickel Alloy Pipe
ASTM B161
ASTM B165
ASTM B167
ASTM B407
(f) Aluminum Alloy Pipe
ASTM B210, Tempers O and H112
ASTM B241, Tempers O and H112
(*1) Severe Cyclic Conditions: conditions applying to specific piping components or joints in which SE computed in accordance with para.319.4.4 exceeds 0.8SA (as defined in para.302.3.5), and the equivalent number of cycles (N in para. 302.3.5) exceeds
7000; or other conditions that the designer determines will produce an equivalent effect.
(3) Carbon steel pipe used for hot potassium carbonate, amine solutions, caustic soda or similar services shall be seamless in principle. When welded pipe is permissible for large size piping the weld seam shall be stress relieved.
(4) When electric resistance welded (ERW) carbon steel pipe is used for water services such as industrial water, potable water, etc. there is a possibility of causing groove corrosion on a longitudinal weld seam, anti-grooving corrosion ERW pipe shall be used, or seamless pipe shall be used, or weld type other than ERW shall be selected.
(5) Use of aluminum and aluminum alloys shall be limited to low-temperature services only. When installed in hazardous areas, they shall be fire-proofed.
(6) Materials having a low melting point such as copper, bronze or copper alloys shall not be used in flammable or combustible services.
(7) Copper and copper alloys shall not be used in ammonia compounds. Copper alloys having a copper content greater than 50 % shall not be used in services where acetylene is present in a wet environment.
2. Materials for Hydrogen Services (*2)
(1) Materials to be used in hydrogen services shall be selected in accordance with the “Nelson Curve” in API 941.
(*2)
Definition
Hydrogen Services: service in which the process stream contains hydrogen at a partial pressure of 7 bar (abs) and higher. (DEP 31.38.01.12-Gen.)
Hydrogen Services: process stream containing relatively pure hydrogen and component streams containing hydrogen with a partial pressure of 350 Kpa (abs) and higher. (JERES-L-105)
(2) When the temperature and hydrogen partial pressure of fluid close to upper limit curve is not more than 28 ℃ (50 °Ｆ) and 344 kpaa (50 psia) as appropriate, the upper grade material shall be used.
(3) C-1/2Mo steel should not be used in hydrogen services. (due to the uncertainties regarding its performance after prolonged use.)
3. Materials for Wet H2S Service (Sour Service )
Materials used in Wet H2S environments shall be shall be considered resistant to sulfide stress corrosion cracking (SSCC) and hydrogen induced cracking (HIC).
Piping applied to NACE MR0175 /ISO 15156 or NACE MR0103 as applicable shall be made of suitable materials and fabricated according to its requirements.
3.1 Sulfide Stress Corrosion Cracking (SSCC)
The following (1),(2), and (3) requirements shall be applied to prevent the occurrence of SSCC, if:
(a) Process fluids contain water as a liquid,
(b) H2S partial pressure is greater than 0.34 kpaa (0.05psia) and the total pressure is greater than 450 kpaa (65 psia),
(1) Seamless Piping
PWHT is not required for thickness 20mm and below, provided that multi-pass welding is applied to circumferential, branch connection and socket welding and max. weld hardness is 22HRC (248Hv). For thickness over 20mm, PWHT is required.
(2) Welded Piping and Fittings (with longitudinal seam)
PWHT is required for longitudinal seam regardless of thickness.
PWHT is not required for circumferential weld of piping having thickness 20mm and below, provided that multi-pass welding is applied and max. weld hardness is 22HRC (248Hv).
(3) Hardness requirement
The hardness of all carbon steel welds shall not exceed 22HRC (248Hv).
(4) Bolting
Bolts for pressure containing parts shall conform to ASTM A193-B7M with nuts to ASTM A194-2HM.
3.2 Hydrogen Induced Cracking (HIC)
The following (1),(2) and (3) requirements shall be applied to prevent the occurrence of HIC, if:
(a) An operation temperature is between 0℃ and 100℃.
(b) H2S concentration exceeds 100ppm in the water phase.
(1) Seamless Piping
PWHT is not required for 20mm and below in thickness, provided that multi-pass welding is applied to circumferential, branch connection and socket welding and max. weld hardness is 235 BHN.
(2) Welded Piping and Fittings (with longitudinal seam)
Plate material shall have max. sulfur content of 0.003%.
PWHT is required for longitudinal seam regardless of thickness.
Max. weld hardness shall be 235 BHN.
(3) PWHT is not required for circumferential weld of piping having thickness 20mm and below, provided that multi-pass welding is applied and max. weld hardness is 235 BHN.
4. Materials for Sodium Hydroxide (Caustic Soda) Service
Materials used in sodium hydroxide service shall be selected in accordance with Appendix 1, depending on the combination of Naoh concentration and fluid temperature.
Area “A”
Carbon Steel: Welds, attachment welds and bends shall be post weld heat treated only for steam traced lines.
Area “B”
Carbon Steel: Welds, attachment welds and bends shall be post weld heat treated.
Area “C”
Nickel alloys to be considered in this area.
5. Materials for Amine Service
Amine is used for gas treatment in the following units:
- Mono-ethanolamine (MEA Unit)
- Di-isopropanolamine (DIPA Unit)
- Di-ethanolamine (DEA Unit)
- Methyl di-ethanolamine (MDEA Unit)
Generally, carbon steels are used for amine service, however amine stress corrosion cracking (ASCC) is concerned for carbon steels, and also carbon steel will exhibit excessive corrosion at high velocity (ave.2.4m/s) condition and/or in flash rich amine service. Type 304L stainless steel shall be applied to those conditions.
PWHT is an effective method for improving ASCC resistance, therefore the following shall be considered:
(1) MEA Unit and DIPA Unit
PWHT shall be applied to all carbon steels regardless of service temp.
(2) DEA Unit
PWHT shall be applied to all carbon steels exposed to amine at service temp. of 60℃ and higher.
(3) MDEA Unit
PWHT shall be applied to all carbon steels exposed to amine at service temp. of 82℃ and higher.
6. Materials for Hot H2S Service
When temperature exceeds 288℃(550°F) in hydrogen-hydrogen sulfide mixtures, severe corrosion occurs on carbon and low-alloy steels.
When high hydrogen sulfide concentration is present, then 18Cr-8Ni SS and 13Cr SS is usually selected; stabilized grades are commonly used to prevent attack by polythionic acid during downtime.
7. Naphthenic Acid Service
Naphthenic acid corrosion is an aggressive form of corrosion associated with crude oils. Naphthenic acids are generally considered corrosive to carbon steel only in the temperature range of 177 to 371℃ with corrosion peaking at around 277℃. Naphthenic acid corrosion encountered with crude oil and various side-cuts occurs with TAN (Total Acid Number) in the range of 0.5 to 6mg KOH/gm.
Type 316 and 317 molybdenum containing austenitic stainless steels have the highest resistance to naphthenic acids and provide adequate protection under most circumstances, and below is the recommended material selection against naphthenic acids:
Operating temperature 38 ～ 230℃ : Carbon Steel
Operating temperature 230 ～ 455℃ : Type 316L SS
8. Low Temperature Service
The Design Minimum Temperature (DMT), without impact testing for piping components, shall be as listed in ASME B31.3 Appendix A, except if modified by the requirements of Table 323.2.2. See paragraph 301.3.1 for definition of DMT.
The recommended material selection for low temperature service is shown below:
Note:
(1) Longitudinal weld metal and HAZ shall be impact tested.
(2) Longitudinal weld metal and HAZ shall be impact tested, and requirements of impact test on base metal depend on thickness, refer to Fig.323.2.2A.
(3) Requirements of impact test depend on thickness, refer to Fig.323.2.2A.
9. Seawater Service
Seawater is very corrosive fluid compared with freshwater.
Selection of materials shall be considered economical advantage and reliability, and the following metallic or nonmetallic materials which are high corrosion resistant are standard materials.
10. High Temperature Service
Carbon steels shall not be used for service above 427℃ (800°F) because conversion of carbides to graphite may occur after prolonged exposure to temperatures over 427℃ (800°F).
Austenitic stainless steels (18%Cr-8%Ni) are considered the susceptibility to intergranular corrosion of austenitic stainless steels sensitized by exposure to temperatures between 427℃ and 871℃ (800°F and 1600°F ). Therefore, stabilized (type 321SS, 347SS) or low carbon grades (304L SS, 316L SS) should be considered in case that austenitic stainless steels are used between 427℃ and 871℃ (800°F and 1600°F ).
Sensitization:
When austenitic stainless steels (18% Cr-8% Ni) are exposed to above 430℃, chromium and carbon unites and become chrom-carbides, which deposit along inter-granular of crystallization. Around grain boundary (inter-granular) of crystallization it is lack of chromium. Consequently the areas are apt to be corrosive.
11. Ammonia, Sulfur, Amine, or Caustic Services
Copper or copper alloys such as brass or bronze shall not be used in ammonia, sulfur, amine, or caustic services.