Managing Cold Temperature and Brittle Fracture Hazards in Ammonia-Related Industries

The intention of this article is to provide guidance so that costly and catastrophic brittle failures can be avoided. This paper identifies causes f or cold embrittlement hazards and brittle f racture for

ammonia plant equipment. Selected examples illustrate the main factors that contribute to brittle fracture, the importance of coordination of materials and potential operating condition inputs, and

the types o/safeguards and mitigation/elimination tools used to reduce risk and to assess brittle fracture concerns. This paper also discusses how to assess existing equipment pressure

vessels subjel..'! to cold conditions and brittle fracture concerns using API 579, Pari 3.

Daniel J. Benac, P.E., CFEJ Dorothy Shaffe r

David Wood, P.E.

Baker Engineering and Risk Consultants, Inc. (BakerRisk~ 3330 Oakwell Court, Suite 100

San Antonio, Texas 78218

Introduction

Brittle fracture occurrences in the ammonia industry are not common. However, sudden and unexpected catastrophic fa ilures have occurred in the

ammonia industry due to cold temperature brittle fractures. This paper reviews the sources for concern in the ammonia industry and provides infonnation on assessing the causes and potential hazards of brittle frachlre, includ ing methods to mitigate or reduce the risk of a catastrophic fa ilure due to cold temperature brittle fracture.

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Figure 1. Brittle fracture of a pressure vessel is sudden and catastrophic, resulting in loss of containment of product and energetiC fragmentation.

AMMONIA TECHNICAL MANUAL

Brittle Fr acture Defined

Brittle fracture occurs suddenly, without warning, and the failure IS typically catastrophic-equipment can spli t rapidly, or shatter into pieces that are thrown at high velocities. Figure I shows the brittle fracture of a vessel that was sudden and catastrophic, due to a small critical flaw at a repair weldment that had high material hardness and high residual welding stresses. The sudden release of pressure, parts, and contents is often hazardous to personnel and equipment. Brittle fracture can occur in the commonly used carbon and low-alloy steels that make up the piping, heat exchangers, towers, drums, and thick-plate constructions in process industries. Brittle fracture is defined as the sudden rapid fracture under stress where the material exhibits little or no evidence of ducti li ty [I]. Less energy is needed for a brittle fracture than a ductile fracture; hence, a brittle fai lure typically occurs through rapid crack propagation and minimal plastic deformation [2].

Key elements [3] that can cause a brittle fracture are:

• Low fracture toughness • High stress (residual or applied) • Presence of a crack-like flaw or defect

Low fracture toughness means that the material requires low energy to fai l, especially in the presence of a small flaw or material defect. Fracture toughness is a quantitative way of expressing a material 's resistance to brittle fracture when a crack or flaw is present. The conditions, mechanisms and/or degradations that can cause the loss of toughness need to be considered. Vessels and pipes with low toughness do not fail unless subjected to high enough stresses to cause fai lure. These stresses are often lower than the yield strength of the material. High residual stresses, as high as the yield stress, can be present due to welding and heat treatments. High applied stresses can occur due to internal pressures or stress concentrations that occur at comers or notches. A crack-like

AMMONIA TECHNICAL MANUAL 210

flaw or defect can fonn during the fabrication or be created by a service-induced operating condition. When all three of these conditions are present, the risk for failure is high. Therefore, it is essentia l to know whether these conditions are present, because these conditions can lead to a cold embrittlement condition.

Material Behavior

Carbon steel and alloy steel, unlike aluminum alloys and austeni tic stainless steels, can change ducti lity based upon exposure temperature and when subjected to high load or dynamic load conditions. Steels have a unique toughness at a given temperature. A typical impact energy curve or Charpy curve is shown in Figure 2. Curve A shows that as the temperature drops, so does the energy required to cause fracture. There is also a transition temperature from ductile-to-brittle fracture, often referred to as the ductile-bri ttle transition temperature (DBIT).

Temperature (OF)

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Figure 2. Charpy impact curves showing the transition from a ductile behavior to a more brilfle behavior as the temperature decreases.

Curve B shows a similar curve, but the curve is shifted to the right. This material has a higher OBIT and a lower toughness at a comparable temperature. Curve B could be representative of a

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vintage steel manufactured before treatments to improve brittle properties were implemented in the industry; other parameters discussed in this paper can reduce the toughness and thus shift the curve.

There are several material and fabrication factors that can affect steel behavior at low temperatures and which can be optimized to avoid brittle fracture. These factors include the following: • Steels with higher carbon weight percent can

have lower toughness. This can be the as­manufactured condition or due to carbon contamination from exposure to certain environments during use.

• Cleanliness of the steel affects the properties: for improved toughness, use steels with low weight percentages of sulfur and phosphorous. Older steel grades can have higher impurities and lower toughness.

• Non-stress relieved steels have lower toughness than those that are stress relieved.

• Welded materials with coarse grains can have lower toughness.

• Thicker steels such as those used for thick­walled pipe or vessels can have lower toughncss.

Brittle Fracture of Pressure Vessels

Brittle fractures in pressure vessels often are associated with the brittle behavior of carbon or low-alloy steels. Although more likely to occur at atmospheric or subfreezing temperatures, brittle fractures can occur at elevated temperatures if the metal has become embrittled by microstructural or metallurgical changes. In carbon and low-alloy steels, metallurgical characteristics imparted during manufacture or during usage may be important if they cause the ductile-to-brittle transition temperature to be near or above the ambient temperature experienced by the vessel during operations, and especially during hydrostatic testing. Poor quality steel or poor welding practices applied to pressure vessels can also cause brittle fracture. The presence of residual welding stresses and reduced toughness can increase the risk of brittle fracture.

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Pressure Vessel and Piping Codes

Pressure vessels are typically designed to meet certain code requirements. Construction codes, such as the ASME B31.3 for piping [4] and ASME Section VlII for vessels [5], provide extensive rules for carbon steel and alloy steel materials that are subject to low temperatures.

For new equipment, brittle fracture is best prevented by using the current ASME Boiler and Pressure Vessel Code to specify and incorporate materials designed specifically for low temperature conditions, which include upset and auto-refrigeration events.

For eXlstmg equipment, especially those manufactured prior to 1987, a brittle fracture assessment may need to be performed. Some of the earliest codes were deficient in heat treatment requirements or they may not have required stress relief at all. The design temperature of vessels prior to 1987 allowed tbe use of carbon steels and alloy steels to -29°C (-20°F) without the need of impact testing. If less than -29°C (-20°F), impact testing was required. However, after 1987, the pressure vessel code added rules including eliminating the impact testing exemption at -29°C (-20°F) and implemented a minimum design metal temperature (MDMT).

Because of the concern about brittle fracture in carbon steel and alloy steels even above -29°C (-20°F), modifications to the code would account for the lowest operating temperature, auto­refrigeration, and process upsets.

For example, for a 0.5" (13 mm) nominal thickness pipe or vessel made from an older grade carbon steel material, the vessel or pipe could be acceptable at -29°C (-20°F). However, as the material thickness of the pipe or vessel increases, the allowable temperature to avoid brittle fracture also must increase, as shown in Figure 3 [6]. If the operating temperatures are held below that minimum allowable temperature, then there is a risk of brittle fracture.

AMMONIA TECHNICAL MANUAL

To avoid ri sk of brittle fracture, either process controls have to be established to regulate the temperature or a material upgrade is necessary.

,. ASME UCS 66, ASME 31 .3, API 579

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Figure 3. Minimum allowable temperature (MAT) based on the material thickness and grade of material [4J.[5].

In 2007, a Jomt committee formed by ASME/API released the standard known as API 579-I /ASME FFS-I, covering Fitness-For­Service (FFS) assessments, to include Part 3 -Assessment of Existing Equipment for Brittle Fracture. The API methodology incorporated some of the design guidelines of ASME piping and pressure vessel codes and has also been widely used and accepted in the refining and oth­er petrochemical industries [6] .

Brittle Failures in the Ammonia Industry

In the ammonia industry, evaluation of low temperature brittle fracture appears deceptively straightforward. Although ammonia's boiling point of -34"C (-29"F) is slightly less than the common carbon steel minimum design metal temperature (MDMT) of -29"C (-20"F), only a limited portion of the ammonia process occurs at these temperatures in nonnal conditions. Refrigerated services typically require material specifications and/or Charpy impact testing to avoid introducing brittle fracture hazards in the plant.

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However, a number of instances and situations surface where brittle fracture failures are a concern in the ammonia industry. The use of carbon or low alloy steel, thick-walled loop equipment is likely to have increased MDMT. Auto-refrigeration can reduce the temperatures below the MDMT.

Process Safety Management practices, such as Process Hazard Analysis (PHA) and Safe Operating Limits or Integrity Operating Window Limits may reveal conditions where equipment is being operated below its MDMT, or identify situations in which the equipment MDMT is not clearly communicated to the operators. Repairs or improper welds can introduce stress points that lead to brittle failure or brittle material behavior if proper procedures are not followed. The ammonia industry also utilizes cryogenic temperatures in cold boxes, and in nitrogen service, that can introduce brittle failure hazards that may not be well understood.

For ammonia-related industries, these conditions are more often present in refrigeration, ammonia storage, and synthesis gas sections of the process. Brittle fracture can pose a catastrophic risk of a release of large quantities of ammonia or hydro­gen that may result in exposure of personnel to toxies, exposure of other equipment to cold con­ditions, exposure of equipment to major fire , andlor vapor cloud explosion hazards. Although the frequency/risk may be considered low, the consequence ranking is typically very high.

Revamps and equipment replacement provide opportunities to remove MDMT temperature concerns in conjunction with other projects. Hazard analyses perfonned during the changes can assist in verifying unusual conditions that may limit the MDMT and the proper specifications that would be needed. However, not all equipment needs to be replaced. Assessment techniques that can identify potential brittle failure concerns are avai lable. Often, the evaluation may allow mitigation or

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administrati ve control rather than equipment replacement.

Brittle Fracture Risk Factors

Evaluation of brittle fracture hazards may be difficult, yet they are necessary. Attempts to verify that the equipment is suitable for service can reveal a lack of proper materials or testing documentation when determining the material properties.

In general, potential ammonia industrial risks that may be prone to cold temperature embrittlement issues may include the following:

• Ammonia in refrigeration service • Cryogenic storage and cold box systems • Low temperature exposure • Liquefied-gases (including nitrogen) • Depressurization events • Inferior, vintage grade steels (before 1987) • Thick-walled pressure vessels • Hydrotesting with cold water

Some questions to consider when assessing the ri sk for brittle fracture are:

• Have the drawings and the materials of construction been verified?

• Was Charpy testing done during fabrication and at what temperature?

• Have modifications such as welding occurred after the vessel was installed that could drop the toughness of the material?

• Have the process conditions changed such that it would increase the possibility of low metal temperatures?

• Have the process conditions changed from what the vessels were originally designed for?

• Were the vessels built before 1987? • Has brittle fracture been considered in a PHA

rev iew if the temperature is lower than the original design or a depressurization event

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could occur, dropping the exposure temperature?

Examples of Potential Brittle Fracture A number of postulated scenarios and specific incidents illustrate brittle fracture hazards and how they may be mitigated.

Ammonia Tank Failure-South Africa. 1973 [7] A pressurized ammonia bullet-type tank operating near ambient conditions had weld repairs near a dished head seam. The tank had not been stress relieved at the time of manufacture, nor after the weld repairs. Later material testing also indicated poor toughness properties with the transition temperature above ambient conditions. An ammonia leak developed in the dished head, shown in Error! Reference source not found. , which would have chilled the area. A 4-foot portion of the dished head failed "in an explosive manner."

Risk Management: Evaluate the risk potential where existing equipment is made to standards that have been changed, such as lack of stress relief. and determine whether a brittle fracture assessment would be advised. Perform proper stress relief of weld repaired areas. A vessel can be removed from service and stress relieved even though it was made or welded in the past.

AMMONIA TECHNICAL MANUAL

Figure 4. Photo oJJoiled head [8].

e Fracture of an Ammonia Synthesis Heat Exchanger [9] : A synthesis gas compressor effluent cooler operating at 2-10' C (35-50' F) and 235 atm (24 MPa; 3450 psig) failed catastrophically, causing an explosion that heavily damaged equipment and the control building in the area. The 250 kg (550 Ibs) exchanger head was thrown the length of a football field, then "bounced" for another 100 meters (328 ft).

The failure reportedly initiated at a pre-existing crack and occurred in a brittle fashion. The exchanger wall was 85 mm, or over 3 inches thick. The transition temperature was specified at -60°C (-76°F), but the actual testing results at the time of manufacture indicated values of +30 to +60' C (86 to 140' F).

Risk Management: Evaluate materials and design of existing and proposed new equipment for their brittle fracture risk potential. Verify that heat treatments procedures and Charpy testing requirements are well designed for heavy wall vessels, and verify Charpy test values. The original investigation discovered that the standard heat treatment procedures and test sampling procedures were inappropriate for a heavy walled vessel , which likely contributed to the failure.

Ammonia Exchanger Hazard Mitigation: A syngas chiller used ammonia as a refrigerant. Although the MDMT was stated at -29' C (-20' F) for the tube side, operating data indicated that temperatures were typically below that level.

Risk Management: A bypass was installed that allowed wanner syngas to be diverted to the inlet of the exchanger in order to control the temperature above the fvIDMT, and temperature alanns were added. Operating procedures were modified to reduce the likelihood of sudden pressurization and depressurization that would exacerbate cold temperatures and stresses on the

AMMONIA TECHNICAL MANUAL 214

exchanger, avoiding high pressures at low temperatures. Hydrotest Failure: A heavy-walled loop separator typically operates at ambient conditions. During modifications to add a level nozzle, all necessary weld procedures including stress relief were perfonned properly. The vessel was prepared for hydrotest by filling with water, but the hydrotest was discontinued as night was falling. The next morning, the temperatures were cool. As the hydrotest pressure was increased, the vessel cracked as the metal temperature had fallen below the minimums for this heavy wall during the cool night.

Risk Management: The presence of flaws, high residual stresses, and a reduction in toughness can result in a brittle fracture during hydrotesting where pressures above the design are introduced. Use water temperatures above DBTI. The ASME Code [10] procedures include precautions to keep the vessel in the ductile range, including temperature of the vessel 30°F above the MDMT, and ensuring the vessel and the hydrotest fluid are at the same temperature. Other codes offer procedures that indicate using temperatures higher than 60°F [I I] or at least 30' F greater than the MAT. The appropriate codes should be reviewed for full details on safe and effective hydrotest procedures.

Cryogenics: At some sites, liquid nitrogen, oxygen, or carbon dioxide, and cold boxes introduce extreme low temperatures and process equipment must be designed and maintained appropriately. Because these operations are parts of the nonnal process, hazards are typically well understood and safety management practices should include brittle fracture considerations and other cryogenic hazards, For example, liquid nitrogen vaporizes at -195°C (-320°F) and has an expansion ratio of I to 700, so both the potential for brittle fracture and stresses due to high pressures are inherently present. Trapped cryogenic liquid that vaporizes can introduce high pressures with extreme low temperatures that could result in catastrophic failure. Liquid

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nitrogen used for purging is often a temporary operation that may be overlooked. Risk Management: A safety management review of pennanent and temporary installations on cryogenic systems is a good safety practice that would include safeguards such as robust relief controls, proper equipment and materials selection for the specified use, procedures and training. Nitrogen asphyxiation hazards should also be included in the program.

A Loop Heat Exchanger: A loop exchanger vessel is well within its design pressure and temperature during normal operations, but could chill below its MAT during some shutdowns because the pressure on the ammonia liquid is reduced.

Risk Management: Perfonn an engineering brittle evaluation using the stress ratio criteria to produce a curve for the maximum allowable temperature at a given pressure. Modi fy the plant startup procedures so that the pressure is raised as the temperature on the separator mcreases.

Risk Management Practice: Assessment of Brittle Fracture

For eXlsttng equipment, nonnal inspection practices cannot identifY the risk of equipment failure by brittle fracture [121. An engineering review is required. A cold temperature brittle fracture engineering assessment [13] as outlined in the API 579-11 ASME FFS- I Part 03 is considered "best engineering practice." A cold embrittlement review is a multi-disciplined review that assesses the materials used and the operating conditions in order to reduce the risk of a brittle fracture at facilities. Figure 5 shows a listing of parameters considered in such a review. This assessment also evaluates the safeguards in place to control required pressures and temperatures in order to avoid low temperature condilions and assess the malerial behavior oflhe equipment.

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Figure 6 shows a plot of the equipment minimum allowable temperature (MAT) as a function of pressure and stress. The assessment identifies potential scenarios for low temperature excurs ions and then reviews the process and equipment condition input from the plant to detennine the critical exposure temperature (CET). As a means to evaluate an auto­refrigeration phenomenon, the vapor curve of the process medium is also displayed. The CET is the lowest metal temperature that the material is exposed to in the coldest scenario. The CET is derived from either the operating or atmospheric conditions at maximum credible coincident combination of pressure and primary supplemental loads.

The CET is compared to the equipment MAT. This plot and the determination of the MAT has been readily generated using a proprietary BakerRisk® software tool for cold temperature embrittlement reviews based on criteria found in API 579 - Fitness for Service, Part 3.

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Figure 5. BakerRisf<® software input screen showing the parameters considered for brittle frac ture assessment

AMMONIA TECHNICAL MANUAL

Min Allowable Te mp (OF) vs. Operating Pressure ,. ,.

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Figure 6. Plot of the MAT curve as a function of decreasing pressure compared to the CET.

Once a decision is made to perfonn a brittle fracture engineering assessment, an evaluation may involve the fo llowing:

• Review selected low temperature scenarios that were identified from previous PHAs.

• Review the low temperature alann settings, interlocks, and overrides that were provided. All alarms less than a certain temperature can be considered for any cold embrittlement scenarios.

• Screen the process PFD's and P&IDs for potential cold embrittlement scenarios, focusing on material limits, process infonnation, instrumentation and controls, and potential risks. Start up, shutdown and nonnal operations can be considered in identitying potential low temperature scenarios. Review can consider material spec changes identified on the P&IDs. This is considered a screening Level I review.

AMMONIA TECHNICAL MANUAL 216

• Review the equipment drawings and U I s for design limits, thicknesses and materials of construction.

• Perfonn analysis of equipment to determine Minimum Allowable Temperature (MAT) curve based on information in equipment drawings and Uls. Figure 7(a) depicts how the MAT CUlVe can vary for equipment components based on respective material, thickness, etc. Note that only one of the three nozzles, Nozzle A, is represented. In this particular illustration, the shell, head, and nozzle are acceptable at the operating conditions.

• Assess the potential cold embrittlement concerns that are identified utilizing process modeling and equipment minimum allowable temperatures. Establish critical exposure temperatures based upon either known process conditions or with the plant's simulation models. Compare critical exposure temperatures to the minimum allowable temperatures. Figure 7(b) illustrates how given components (shell, head, nozzle, etc.) may not be acceptable at the CET. This particular illustration shows that the MAT curve for the shell and nozzle is above the CET [or borderline] and therefore may require additional review and/or process controls. This is considered a screening Level 2 review.

• Consider a Level 3 assessment be used when equipment is not within the acceptable criteria of the screening Level I and Level 2 reviews. A Level 3 detailed assessment involves a fracture mechanics methodology and approach.

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(a) Component MAT Curves

Min Allow4lble Temp (OF) VS. Oper.llting Pressure

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(b) Superimposed MAT Curves Figure 7. Brittle fracture review for a vessel assesses nozzles, shells and heads made of different materials and different thicknesses. 7(a) depicts MA T of equipment components in relation to operating conditions and 7(b) illustrates how risk for cold temperature embrittlement may develop if the temperature drops to the CET.

Safeguards against Brittle Fracture

While every faci lity may have a varying range of risk exposure based on certain generalized risk factors (Year of Fabrication, Material Type of

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Equipment, presence/absence of Post Weld Heat Treatment, presence/absence of Material Impact Testing, presence/absence of Hydro Testing), recommendations to reduce potential risk of cold temperature embrittlement fracture may include the following:

• • • • • • •

Add Process Safeguards Change or Upgrade the Material Modify Low Temperature Alarms Alter Process Critical Exposure Temperature Require Heat Treatment of Material Perform Impact Testing of Material

Conduct Hydrotesting of Vessel

Case Studies

For the following case studies, a pipeline and two pressure vessels at an ammonia-related production facility was taken into account.

Ammonia Pipeline: A facility located adjacent to a river transports ammonia via pipeline from barge shipments. A review indicated the ammonia barge transfer line was constructed in the late 2000s with over 11 58 meters (3800 linear feet) of 203 mm (8-inch) A333 Grade 6 pipe [Impact Tested; MAT -45'C (-SO' F)J . With design conditions of -33°C (-28°F) and MA WP of I.S MPa (220 psig), a MAT curve was developed (solid line in Figure 8) to confirm that there was no ri sk of cold temperature brittle failure at operating conditions [0.86 MPa ( 125 psig), -32' C (-25 ' F)J. Extensive dialogue on PHA scenarios reiterated that the -33°C (-28°F) was likely the coldest temperature the line would experience during a depressurization event. This infonnation verified that the line was suitable for service, a regulato!), requirement for this site. Additionally, the finding reinforced the need to require the same material specification if any future line segment was to be replaced. Figure 8 shows that the inadvertent replacement with a non-toughness tested material (dashed line in figure) would likely increase the risk for fai lure.

AMMONIA TECHNICAL MANUAL

Min Allowa ble Temp ' OF) \/5. Opera tl", Pressure

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Figure 8. Minimum allowable temperature vs. operating pressurefor Barge Transfer line.

High Pressure Purge Vessel: A high pressure purge gas separator was assessed for both operating and shutdown conditions. Constructed in the early I 960s, the vessel had 33 mm ( I V,-inch) thick shell and heads; A 106 and A234, respectively, and was stress relieved. With design conditions of -4"<: (25°f) and MA WP of 34 MPa (4950 psig), a MAT curve was d.eveloped which identified that there may be a nsk of cold temperature brittle failure at operating conditions [26 MPa (3900 psig), _4°C (25°F)], see solid line in Figure 9. Discussion identified that -33°C (-28°f) was likely the coldest temperature the vessel would experience during a depressurization event. A review of the avai lable documentation could not verify if Charpy impact testing was perfonned on the equipment. As the equipment is below the acceptable criteria of the screening Level 2 reviews, a Level 3 detailed fracture mechanics FEA assessment may be prudent (outside scope of this paper). Alternatively, process controls or low temperature alarms can be implemented to stay above the curve, or the decision can be made to replace this relatively small vessel with one that is known to have appropriate specifications and documentation (dashed line in figure).

AMMONIA TECHNICAL MANUAL 218

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Secondary Ammonia Separator Vessel: A high pressure ammonia separator was assessed for both operating and shutdown conditions. Constructed in the early I 960s, the vessel had 95 mm (3-3/4 inch) thick heads with A2 12 Or B (Fire Box Quality (fBQ)) per ASTM A300 which required a special treatment of a fine~ grained steel with -46°C (-50°F) guaranteed toughness properties; see solid line in Figure 10. Standard grade A2 12 without special heat treatment and low toughness properties is considered to be a vintage steel that historically has shown material properties susceptible to brittle failure at cold temperatures, see dashed line in figure. With design conditions of -33°C (-28°F) and MA WP of 35.6 MPa (5170 psig), a MAT curve was developed (solid line in figure), which detennined the vessel was acceptable at the operating condition and the depressurization event with the fine-grain material This infonnation was valuable to the facility as it gave them confidence in their vesse l knowing the possibility of the ri sk associated with the thick vintage steel. In this case, the fact that the material was impact tested provided the confidence that cold temperature brittle fracture was a low risk. Any subsequent repairs, however, could require re-evaluation.

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Min Allowable Temp I· F) vs. Operating Pressure

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Figure 10. Minimum allowable temperature vs. operating presslire for Ammonia Separator

Summary

Brittle failure is typically a high consequence hazard in an ammon ia facility. The factors that lead to brittle fracture risks should be understood so that possible hazards can be recognized in process hazard analyses, maintenance and mechanical integrity programs, engineering and management of change decisions, and in training.

Brittle fracture is a potential concern for vessels and piping, especially for older or thicker vessels that may not have adequate toughness for all operating conditions. Certain process upsets, shutdowns, and start-ups can sufficiently reduce the temperature such that the vessel or pipe is exposed to temperatures that may be low enough to reduce toughness and cause failure at the res idual and applied stress state. To understand and manage these risks, brittle fracture engineering assessments identify the potential hazards and poss ible safeguards for implementation that w ill mitigate or prevent brittle fracture. It is the goal of this paper to communicate that potential cold temperature embrittlement and brittle fracture risks can be identified and properly managed, to reduce the risk of failure.

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References

I.

2.

3.

4.

API 571, "Damage Mechanisms Affecting Fixed Equipment in the Refining Industry," Second Edition, Apri l 20 11. ASM Handbook Failure Analysis and Prevention, Volume J I. B. Macejka, " [s your plant vulnerable to a brittle fracture?" Hydrocarbon Processing, November, 2014 Volume 93, pp67-77. Fig. 323.2.2A Minimum Temperatures Without Impact Testing for Carbon Steel Materials, ASME B31.3-2004.

5. Fig. USC-66 Impact Test Exemption Curve, ASME Section vm Division 1_ 2007.

6. Auto-RefrigerationlBrittle Fracture Analysis of Existing Olefins- Translation of Lessons Learned to Other Processes by Ra lph King, Journal of Hazardou~ Materials, June 2006.

7. Anhydrous Ammonia Tank Catastrophic Failure, by Bryan Haywood, Safeteng.net

8. Ammonia Tank Failure- South Africa by H. Lonsdale, AIChE Ammonia ' Symposium Proceedings .

9. Brittle Fracture of an Ammonia Synthes is Heat Exchanger, by H.K. Karinen, AIChE Ammonia Symposium Proceedings.

10. ASME Section VIII Division 1-2007 Standard Hydrostatic Test, UG-99 (h). '

11. NB NBIC 3 (2007): National Board Inspection Code, Part 3, Section 4, Repairs and Alteration, 4.4.1 (a) (3).

12. ASME Boiler Pressure Vessel Code Section VI] I Division 1 Rules for Construction of Pressure Vessels, ASME 2013 .

13. API 579- I/ASME FFS·I, Fitness for Service Part 3 - Assessment of Existing Equipment for Brittle Fracture. June 5

y

2007.

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