Number of thermocouples during PWHT according to ASME section I and B31.1 1

[JohnWE]

Hello engineers,
I am starting work on boiler pipelines according to ASME section I and B31.1. We will weld pipes with P no. 4, 5A and 15E with quite large diameters (up to 813 mm) and thicknesses (up to 57 mm). In his specification, the client specified the number of monitoring thermocouples (from 1 to 4 depending on the diameter), and there should be exactly as many control thermocouples as heating elements. Considering the large dimensions of the pipes, it results that up to 20 thermocouples should be used. We would have to use 2 annealing machines for 1 weld. Section I and B31.1 also require a large number of thermocouples. What do you think about this? From your experience, what is the approach to the number of thermocouples on projects according to ASME?

 

[hacksaw]

You'll have to explain what your customer means by "heating elements," and the purpose of the measurements.
You may need access to the piping layout drawings to sort out your question.

 

[r6155]

DO NOT DUPLICATE POST.

 

[JohnWE]

@hacksaw
By "heating element" they mean each heating mat. That is why performing PWHT with these guidelines in the case of large diameter pipes requires the use of a large number of mats.

@r6155
Sorry, I wasn't sure which section to ask this question in.

 

[goutam_freelance]

Refer B 31.1 Cl 132.7.
"Guidance for the placement of thermocouples on circumferential butt welds is provided in AWS D10.10, Sections 5, 6, and 8."

 

[JohnWE]

@goutam_freelance

Yes, I found these records in D10.10. They are practically the same as in the case of ASME section I. However, the customer specification imposes a completely different way of placing and number of thermocouples. Hence my question, are the guidelines from ASME (section I and D10.10) mandatory requirements or only recommendations? In section I it is written that these are "examples" of thermocouple locations and D10.10 has "recommended" in its name. I wanted to ask more experienced in ASME whether in practice such a large number of thermocouples are actually used as indicated in D10.10 and section I? Above DN 500 it is as many as 12 thermocouples.

 

[hacksaw]

You'll need to consider what your customer is trying to achieve.
Sounds like you are using heat mats to provide heat tracing of your piping or duct work.

At issue: thermowells are intrusive pipe fittings used to measure the process fluid temperature, whereas if you are trying to control the surface temperature of the piping, that's a different measurement.

Your statement "Above DN 500 it is as many as 12 thermocouples" needs a bit more detail.

Fluid,
Fluid phase, single or mult-phase
temperature,
fluid velocity,
degree of flow uniformity

How many sensors are you planning along the pipe run.

 

[JohnWE]

@hacksaw
The topic concerns thermocouples during heat treatment, not thermocouples used to measure the medium in the pipeline.

 

[weldstan]

They are not mandatory under B31.1 and Section I. They can become mandatory based on Customer specifications. During my last few years working after 2010 to 2016, D10.10 was becoming mandatory from a number of customers for local pwht of heavy wall P91 welds.