API 6A hardness issue

[metboss]

Dear Experts,

We placed an order for Wellhead equipment (Material AISI 75 KSI, Design pressure/Working Pressure: 7,000 psi; Test Pressure: 10,000 psi, API 6A standard). As per API 6A standard "minimum hardness" for 75 KSI material is 197 BHN. But, during the raw material testing, hardness is found to be 180 BHN. As per my interpretation of API 6A, this is not acceptable. However, our vendor now justifies that material with 180 BHN still can be acceptable from design point of view and also it can still withstand test pressure of 10,000 psi. Please advise if I can accept the material though with less hardness. If yes, can I ask for any additional docs (such as design calculation or any other analysis)?

 

[jmec87]

If this equipment has 7,000psi rated working pressure and 10,000psi test pressure, then it is not to API 6A per API 6A 21st Edition 4.3.1.1 (and is not API monogrammable). Therefore, the supplier can do whatever the customer and supplier agree on. You can ask for whatever you want; it is up to you and the supplier to negotiate what they will give you.

Note that per API 6A Table 7, 60K material is acceptable for 10,000psi rated bodies, bonnets, integral end connectors, and loose connectors. Per API 6A Table 20, 60K material only has 174 HBW minimum hardness. Therefore, API 6A allows lower hardness material for use in higher pressure applications than in your example.

If the supplier is responsible for the design (and is competent as a wellhead equipment designer), then they should be able to determine whether or not it is safe to use this material for this application. If you trusted them to do the initial design without reviewing their calculations, then you should be able to trust them to do this calculation without reviewing it.

If this is the customer's design, then the customer's engineer should review the situation to ensure it will be safe.

 

[metboss]

Thank you jmec87 for your advice.
The original rating is 5K; but, uprated to 7K (7000 psi). Based on the measured hardness, it is closer to 60K material. Can we accept 60K material for 7,000 psi working pressure and test pressure 1.5 x WP i.e. 10,500 psi for integral connection?

 

[jmec87]

Again, this is no longer a 6A product because of the 7,000 psi rating, so you can do whatever you and the supplier agree on. Based on the API 6A hardness requirements alone, I would not be concerned.

However, uprating from 5K to 7K pressure rating is weird (downrating from 10K to 7K would be more normal), and this raises significant concerns regardless of hardness. Are you using type 6B flanges on this design? How are you justifying the 7K pressure rating on a 5K-rated flange? If there is any relevant external authority (i.e. government regulator), how are you justifying this to them?

 

[jbeckhou]

What is the yield strength from the MTRs? What type of wellhead equipment?

Petrotrim Services, LLC

http://www.petrotrim.com

 

[metboss]

Original rating was 5K; but, as per OEM's design analysis, it is being uprated to 7K for intended service application.
In MTR, yield strength and tensile strength values are meeting 75K criteria. There is only issue with hardness value. Type of Wellhead equipment: Drilling adapter (as per API 6A) to connect two different sizes of Wellhead equipment.

 

[jbeckhou]

We have used 5k equipment for 7,500 psi rated equipment in the past. We hydro tested at 1.5 W.P. I would make sure the hardness test is being done correctly and the tools are calibrated.

Petrotrim Services, LLC

http://www.petrotrim.com