Cathleen Shargay

Understanding the Multiple Purposes of Refractory Linings in Sulfur Recovery Units

Within Sulfur Recovery Units (SRU), many equipment and piping items are built with internal refractory linings, but between the various process areas, the refractory is being used for completely different functions. Understanding the “purpose” of the refractory is important for both the initial selection of the optimum type of refractory, and also for repair decisions whenever refractory damage is found during turnarounds. This paper will describe each area where refractory is used, the operating and turnaround conditions, and the four unique purposes of the refractory to provide a mechanistic understanding of the function of refractory. It will also discuss the relationship between the purpose and repair philosophies for use as a general guideline.Copyright

Comparison of ASME B31.12 Versus B31.3 for Hydrogen-Containing Piping in Refinery Services

For more than fifty years the oil refining industry has been using American Society of Mechanical Engineers (ASME) B31.3 “Process Piping” for the design of piping systems in hydrogen-containing services. In 2008, ASME B31.12 “Hydrogen Piping and Pipelines” was released, which caused uncertainty within the refining industry about which Code to apply in these services. The foreword of B31.12 states that it “applies to design, construction, operation, and maintenance requirements for piping, pipelines, and distribution systems in hydrogen service. Typical applications are power generation, process plants, refining , transportation, distribution, and automotive filling stations.” Typical refinery services containing hydrogen include a gamut of applications. Some operate at high pressures and/or temperatures; some also contain water, hydrogen sulfide (H2 S) and/or other corrosives and others are pure hydrogen at mild conditions. This paper describes the various services along with a summary of associated material degradation or cracking mechanisms and the measures used to prevent piping failures. This is followed by a discussion about whether the more rigorous requirements of B31.12 provide safeguards for these potential degradation mechanisms. A comparison of the two Codes in design, materials, fabrication and non-destructive examination (NDE) requirements is provided along with qualitative estimates of the cost differences. This comparison should help new design and construction projects choose which Code to apply. The paper also has suggestions for clarifying the scope of B31.12.© 2011 ASME

Considerations for Requiring Intermediate Stress Relief (ISR) for All Weld Types on 2 1/4 Cr-1 Mo-V Reactors

As an industry consensus, API 934-A is an excellent recommended practice on the materials and fabrication requirements for Cr-Mo reactors. However, it is cautious and somewhat vague on the topic of Intermediate Stress Relief (ISR) versus Dehydrogenation Heat Treatment (DHT) for the different types of welds — which reflects the industry’s varying practices. For the advanced steels, API 934-A states that DHT should only be used with Purchaser approval, and that it should not be used on restrained welds such as nozzle welds. As a result, it is common for a DHT to be permitted on longitudinal and circumferential seams to achieve the cost and schedule savings, and ISR is used for nozzle welds. There are risks to the fabricator however, as the welds remain extremely brittle after DHT (the toughness is restored after postweld heat treatment {PWHT}, and at intermediate levels after ISR), and welding defects that are acceptable per ASME Code criterias can lead to brittle fractures during subsequent fabrication steps. The costs of the repairs and delays can then be very high, especially if the cracking is not detected until after PWHT. This paper shows the risks of acceptable defects causing brittle fractures by fracture mechanics calculations, and presents some case histories of cracking. The relative costs of ISR versus DHT, versus repairs before and after PWHT are also reviewed.Copyright

Considerations of Stricter TOFD Acceptance Criteria for Severe Refinery Services

ASME Code Case 2235 and the new adoption of this Code Case into ASME Code Section VIII, Div. 2 has acceptance criteria which were based on predicted flaws and fracture mechanics modeled after the nuclear industry. These criteria were developed in response to a query about how to apply the acceptance criteria of ASME Article 4, Appendix 12 when using non-amplitude based ultrasonic methods such as phased array and time-of-flight diffraction. Since the traditional acceptance criteria were based on amplitude, they could not be applied for these alternative methods. The Code committees responded with a flaw size acceptance criteria based on the fracture mechanics properties of the materials and service conditions found in the nuclear industry. This was a major improvement and added a technical basis for the criteria lacking in past standards, however, there are no limitations or qualifications in CC 2235 on its applicability to other materials or service conditions. This is a concern for some oil refining and other plant services, especially those leading to embrittlement, various types of hydrogen-induced damage or high cycle fatigue cracking. The CC 2235 criteria were also not adequate for the recent major industry problem with reheat cracking in 2 1/4 Cr-1 Mo-V reactor fabrication. This paper summarizes the basis for CC 2235, describes the concerns with applying the acceptance criteria without consideration of material or service conditions, and suggests how to approach the issue from a better informed perspective and in some cases, establish stricter maximum flaw sizes.Copyright