Root Cause Analysis (RCA): 50% only heat transferring from Heat Exchanger threatens urea plant commissioning indefinite halt.
Note: This root cause analysis (RCA) is from real-time scenarios that happened in industries during the tenure of one or two decades ago. These articles will help you to improve your troubleshooting skills and knowledge.
A high-pressure U-tube heat exchanger (HE) exiting stream too high temperature halted a urea plant commissioning and baffled everyone.
Calculations showed the heat exchanger transfers nearly ½ the rated heat transfer only. Even a new exchanger receivable 9 months later only may not solve the problem, unless someone finds and removes the ½ heat transfer cause.
An immediate remedy was necessary to make the exchanger work to design soonest for commissioning completion and urea production start.
Several shell pullouts revealed no flaws baffled everyone. Each time the crew carefully supported the tube bundle by placing wooden sleepers at the baffle locations to avoid tube bundle sag and associated tube cracks.
The plant manager ordered to leave the heat exchanger dissembled hoping a solution for this Difficult to Diagnose, Unusual Despairing, Problem (DDUDP) – the plant name for such problems – may flash to someone.
An inspection engineer had a flash! He reviewed the heat exchanger drawing and root caused analyzed as below; Q-RCA queries and R – response:
Q: Why ½ heat transfer duty only?
R: Maybe water flows in ½ heat transfer area only
Q: Why so?
R: Several minutes thought and repeated drawing studies flashed response was: maybe the inlet water nozzle CL is not at the full baffle plate CL (above figure) – a fabrication mistake. In that case cooling water flows in ½ the exchanger and negligible in the other half; hence ½ heat transfer!
Q: How to verify?
R: Below are several minutes thought and few drawing studies suggested wayout:
The inspection engineer guided, a mill wright and welder team marked the nozzle new location (above figure), flame cut a 170 mm dia – 6” Nozzle OD – opening, saved the disc, flame cut the inlet water nozzle, welded it at the new opening and blinded the left out opening welding the saved disc. As the shell handles 3 bars CW only the welds are not that critical.
That team aided by a rigger cello taped a new gasket to the channel head gasket groove, pushed the shell in and bolted it to the channel head. In addition, they connected the inlet water pipe to the inlet nozzle – minor pipe line change job.
Operation crew put the exchanger in service and reported it performing better than design.
Author: S. Raghava Chari
Do you face any similar issues? Share with us through the below comments section.
If you liked this article, then please subscribe to our YouTube Channel for Instrumentation, Electrical, PLC, and SCADA video tutorials.
You can also follow us on Facebook and Twitter to receive daily updates.
Read Next:
Learn an example PLC program to control a pump based on level sensors using ladder…
In the PLC timer application for security camera recording, when motion is detected then camera…
In this example, we will learn batch mixing with PLC ladder logic program using timer…
This PLC example on manufacturing line assembly is an intermediate-level PLC program prepared for the…
In this article, you will learn the PLC programming example with pushbutton and motor control…
This article teaches how to convert Boolean logic to PLC programming ladder logic with the…
View Comments
Kindly share more information on Difficult to Diagnose, Unusual Despairing, Problem (DDUDP) methodology.
Regds
Avinash Shinde
Century enka Ltd.
Dear Avinash,
I thought the readers including you would have learnt the DDUDP solving methodology themselves from my description of how I solved so many of my DDUDPs: just follow the root cause analysis techniques: first get the subject in depth knowledge, e.g., in case of antifriction bearing problems, get in depth AFB knowledge from an AFB catalog study.
You will find, many of the AFB problems I solved remained unsolved for over 10 years, because knowhow lacking crews too tight fitted the AFBs, and their spurious AFBs mindset, prevented root cause analysis. Always, ensure the process operates at close to design conditions, e.g., see the case study of popping relief valve and rupturing rupture discs. In short, good job knowledge application, no mindset and RCA are essential for DDUDP solving.