Becht Engineering Blog

In this section of the site contributing authors submit interesting articles relating to the various services, industries and research & development efforts of Becht Engineering.
Becht Engineering staff are experts in piping, and include former chairman of various ASME piping committees, including ASME B31.3. Becht Engineering performs detailed design for complex piping systems including very high temperature and pressure systems such as piping for FCC flue gas expanders and high pressure LDPE systems, as well as design, a...nalysis, troubleshooting and fitness for service evaluation of piping. More

Why do Clamped Connections With Metallic Seals Sometimes Leak?

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Clamp connections with metallic seals can offer superior joint integrity over traditional flanged connections but caution must be exercised regarding the service conditions, especially when cyclic thermal loading is present. This blog post highlights aspects of a clamp connection analysis performed by Becht Engineering. The client had observed significant loss of bolt preload at several clamp connections installed in a refinery process unit where the fluid temperature regularly fluctuated by 700 o F. The client attempted to counteract the bolt preload loss by re-torqueing any bolts that showed a torque reduction from the initially applied torque only to find that, after a period during which thermal cycles occurred, the preload was again reduced. A typical clamp arrangement is seen in Figure 1 (with parts labeled). After reviewing the installation and service conditions, it was hypothesized that the cause of the bolt preload loss could be the differential thermal growth of the...
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Pipe Fabrication Dimensional Errors -- I Can't See You!!!

I_cant_see_you_Becht_dimensional_control Dimensional Errors? I Can't See You
Can a level, square and tape measure really measure up to today’s quality standards on complex spools? I was watching my baby girl cover her eyes as she had done something naughty. Doing this gave her the feeling that if she couldn’t see her mother or myself then she would not get into trouble. Despite her feeling of invisibility, she still ended up getting into trouble and having to apologize for what she had done. It’s funny as this is sometimes how the Chemical, Oil and Gas industry acts when it comes to assigning appropriate project dimensional quality control for pipe spools. Green field or brown field (based on a laser scan) projects are typically designed on a specialist CAD platform which enables the designer to design to levels where machine shops would be the only way to match the design model tolerances. This way of designing can provide huge levels...
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Grade 91 Steel - How Did We Get Here? Part 1

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This blog is the first part of a 3-blog series. To view the rest of the story click HERE for Part 2 and Here for Part 3 . Part 1: History Thirty years ago, Grade 91 (9Cr-1Mo-V) steel was hailed as the savior of the power generation industry [1]; now it’s behavior has been described as too variable to ensure safe operation [2].  What happened?  At the same time Grade 91 was being developed in the late 1970’s for high temperature nuclear reactor application [3], power plants that had been designed and operated as base-loaded were suddenly cycled on a regular basis.  The standard material for high temperature steam outlet headers was first 1¼Cr–½Mo (Grade 11) and later 2¼Cr–1Mo (Grade 22); in both cases headers rapidly began to experience severe cracking in and between header penetrations.  The cracking was termed “ligament cracking” [4] and by the mid-1980’s had become a complex...
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Grade 91 Steel - How Did We Get Here? Part 2

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Read Part 1 Part 2: Type IV Cracking and Inspectability The current concerns with Grade 91 are fundamentally and firmly rooted in inspectability of Type IV damage; while sensitivity of the material can be managed (see for example [1]), Type IV cracking is perhaps the Achilles heel of Grade 91.  At a high level, the thermal cycle(s) due to welding will create a thin band of material in the heat affected zone (HAZ) with properties much closer to Grade 9 than Grade 91.  While full re-normalization and tempering of the entire component after welding can greatly improve the situation, simple (subcritical) post-weld heat treatment (PWHT) does not.  Damage is overwhelmingly concentrated in this thin band of material during high temperature operation, such that when failure finally occurs, it has an almost brittle appearance since there has been little if any creep deformation or damage outside of the HAZ (see Figure 3...
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