Inspection of Heater Tubes

[irish]

At least I have not found any retiring hardness values imposed by any code for heater tubes.
P9 or P5 however must remain under 250 BHN in actual for safe operation. However, if other mechanical properties and metallurgical analyses are still OK with some increased hardness, operation may continue but the value 420 BHN is too high.
Replacement should be made asap.

[Farestt]

Hello Ashfaq,

Referring to your point # 4, we have experienced that high hardness is on the surface only because when the hardness reaches around 350 to 400 BHN, flakes/scale starts falling from external surface. When we take readings from new surface, it records around 200 BHN.

Pls. let me know regarding the mechanical tests required and also ways to reduce already increased hardness.

Thank you all for your valuable inputs.

[ashfaqanwer]

Please share the procedure how you take the hardness readings and the equipment you are using.
Also mention what are you firing the heater with.

The procedure is not as per any standard / code but may or may not bring some good results.
"Fire the heater if it isn't already in operation, get it up to nearly 600 ºC, maintain the temperature for half an hour and switch the burners down. Close all the points where air could squeeze in, including the burners. Fired heaters use to have a butterfly valve into the stack, so close that valve.
Let the heater cool down naturally, it'll take several hours to happen. When the temperature allows it, have someone get into the heater and take new hardness measurements.
I wouldn't be surprised if the BHN has lowered to acceptable levels."

For all types of applicable inspections required to be made on heater tubes, it is advisable that you must go through API 573 "Inspection of Fired Boilers Heaters". You may ask for any clarification, if required.

[Farestt]

We are using PROCEQ Equotip 2 hardness meter which measures the hardness by REBOUND method. Heater is being fired with 90% pure hydrogen gas.

[ashfaqanwer]

This instrument work ok in the hands of someone that has a good procedure, but there are so many variables that can cause the instrument to give you wrong information, such as material cleanliness, preparation, technique, calibration, and battery life. Those readings seem very high and because of the high readings there comes a question on the instrument and it is advisable to do some follow up / repetition of hardness readings with a mechanical tester.

[mechcolor]

It's a good idea to use Mechanical tester just to confirm the readings taken from Equotip. Difference sometimes can be as large as like 200 points.
Calibration checks must be done properly and the mode verification for material being tested shall also be made.
If the hardness readings get confirmed by mechanical tester and lie still in the range you mentioned, you must perform sample mechanical testing before going for continuous heater operation.