Section 10 — Material Requirements

Material Requirements for Aggressive

IPE Engineering Practice IPE-EP-10-2-1

Document number: IPE-EP-10-2-1 · Section: 10 — Material Requirements

SCOPE

• This Engineering Practice contains supplemental requirements for materials based on their use in certain aggressive environmental services. Requirements consist of items such as the need for PWHT and soda ash washing of stainless steels during downtimes. They apply to both new and existing equipment. Hardness requirements are provided in EP 10–2–3.
• Materials selection requirements for typical refinery units are provided in EP 10–1–1 to EP 10– 1–18.
• General supplemental materials, quality, fabrication, and testing requirements which are not related to aggressive environmental service are provided in EP 10–2–2.
• API 571 contains advisory information on metal loss mechanisms (both general and localized) due to aggressive environments, degradation due to cracking, such as stress corrosion cracking due to aggressive environmental services and metallurgical embrittlement, summaries of conditions leading to degradation, descriptions of the mechanism, NDE methods to detect/monitor damage, and recommended methods for control. Also included are corrosion design curves where appropriate.
• Any deviation from this Practice must be approved by the procedure described in EP 1–1–3.
• An asterisk (*) indicates that a decision or approval by the Owner or the Owner’s Engineer is required, or that additional information is furnished by the Purchaser.

2.0 REFERENCES

The latest edition of the following standards and publications are referred to herein.

STANDARDS AND PUBLICATIONS

STANDARDS AND PUBLICATIONS (CONT.)

DEFINITIONS

• AES - Aggressive Environmental Service. A service (stream composition/process condition) which can cause stress corrosion cracking or hydrogen attack. For those services listed in Table 1, AES specifically refers to the conditions listed in Table 1 that require PWHT for equipment.
• Amine - Organic compounds having amino functional groups which provide chemical reactivity. Amines are used to absorb hydrogen sulfide and carbon dioxide from various gases to meet a specification.
• Carbonate - A water containing phase that contains the CO3--ion.
• Caustic - NaOH or KOH.
• ES (Engineering Services) - ’s Refining Department Engineering Services Team.
• HF - Hydrofluoric Acid.
• Hydrogen Attack - The progressive degradation of carbon and alloy steels by decarburization and fissuring due to hydrogen at high temperature and pressures.
• Hydrogen Service - A service defined as a combination of hydrogen partial pressure and temperature above the curve for carbon steel per Figure 1 of API Publication 941, latest edition.
• Polythionic Acid - Acids formed by the reaction of oxygen and water with oxidizable sulfur compounds such as metal sulfides.
• PWHT - Post Weld Heat Treatment (often referred to as stress relief).

• Sensitization - A microstructural/chemistry condition that can occur in austenitic stainless steels such as Types 304, 316, and 321 SS. It is defined as the precipitation of chromium carbides at grain boundaries due to thermal treatment (welding, heat treatment, service). The carbide formation depletes the surrounding matrix of chromium and leaves this area vulnerable to localized corrosion/cracking.
• Wet H2S - A stream with H2S dissolved in a separate water/moisture phase.

REQUIREMENTS

• (*)Carbon steel and low alloy steel equipment and piping in AES service shall be PWHT’d per Table 1. These requirements are in addition to any requirements in ASME Code Section VIII - Division 1 or B31.3. The need to PWHT field erected atmospheric storage tanks shall be determined by the Owner’s Engineer.
• EP 5–5–2, EP 7–1–5 and EP 9–1–2 provide details of the required PWHT procedures and temperatures.
• Strongbacks are required for any leak repair clamps that are installed on piping which is subject to PWHT per Table 1 due to AES service.
• Materials selection for hydrogen service in terms of resistance to hydrogen attack shall be governed by API Publication 941.
• Requirements for existing C–1/2 Mo steel that is operating in hydrogen service above the API 941 “Nelson Curve” for CARBON STEEL are:
• Equipment and piping without an integral austenitic stainless steel cladding or weld overlay shall be replaced at the next turnaround or a fitness for service evaluation shall be conducted every turnaround or 5 years. Such an evaluation may include an estimate of the likelihood of attack and inspection by specialized ultrasonic techniques and replication for hydrogen attack. Weld overlaying the vessel may be a viable option to ensure long term fitness for service. The minimum required overlay thickness shall be determined by Engineering Services.
• Equipment and piping with an integral austenitic stainless steel cladding or weld overlay shall be evaluated at every major turnaround or 5 years. The stainless steel effectively lowers the partial pressure of hydrogen that the C–1/2 Mo base metal is exposed to. If the adjusted position falls below the carbon steel curve in API 941, then the only action required is to verify that the cladding is intact and not breached by cracking. If the adjusted position falls above the carbon steel curve or the cladding is breached, then Paragraph 4.5.1 applies. It is possible that some parts of a vessel will fall into one category and other parts fall into the other category, based on factors such as the base metal and cladding thicknesses.

• Requirements for protection of sensitized Stainless Steels.
• Regular and high carbon (non–L) grades of austenitic stainless steels, that are not stabilized with titanium or columbium, and are welded shall be considered sensitized.
• All grades of austenitic stainless steels, welded or not, that operate above 750°F shall be considered sensitized. The operating temperature is 850°F for Type 347 SS and for Type 321 SS which has received a stabilization heat treatment per EP 10–2–2.
• Sensitized stainless steels, other than weld overlays, that are in a service where sulfide corrosion products may be likely and which will be exposed to air, shall be protected at downtimes to minimize the probability of polythionic stress corrosion cracking. Protection can take the form of ensuring that the stainless steel is kept dry, for example by nitrogen purging or dehumidification, or by washing with an alkaline solution (soda ash) per NACE Recommended Practice 0170–85. The white film of soda ash shall be replenished if disturbed and all hydrotests/washes shall use the NACE solution.

5.0 TABLES

TABLE 1

REQUIREMENTS FOR CARBON AND LOW ALLOY

STEELS IN AGGRESSIVE SERVICES(1)

TABLE 1 REQUIREMENTS FOR CARBON AND

LOW ALLOY STEELS IN AGGRESSIVE SERVICES (1) (CONTINUED)

NOTES:

• For field weld repairs/modifications, requirements are subject to Owner’s Engineer approval.
• Equipment includes pressure vessels, heat exchangers, shop fabricated storage tanks, and the pressure boundary of machinery components.
• Piping includes pipe, valves, fittings, etc.
• Some services may contain both amine and wet H2S for example. The more stringent requirements apply in this case.
• CN- = Cyanide Ion DT = Design Temperature, SCE = Standard Calomel Electrode
• Extra Corrosion Allowance (ECA) is defined as follows: If an ECA is called for, the total Corrosion Allowance (CA) shall be a minimum of 0.250 in., even if the expected metal loss rates would normally result in a smaller allowance. The extra allowance is to facilitate potential crack grind–out repairs in the future.
• This applies for new construction if EP 10–2–2 and EP 10–2–3 are met in regards to carbon equivalent and hardness limits. For existing piping, PWHT is required if weld hardness exceeds EP 10–2–3 limits.

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