Testing Coatings for API 20E Fasteners

In recent months licensees of API 6A, 6D, 16A, 16C, 17D, 16F, have all adopted API 20E (Pressure Bolting for High Pressure and High Heat Applications). In doing so they have accepted the rulings in which were included in the standard. We have critical design and engineering that back up the material and formation of the bolt’s hardness and the mechanics it operates under. We have taken a back set when it comes to apply the last brush stroke to this master piece though and that is with the specifications related to the coatings that will be used.

We account for the dimensionsof a 60ºangle and give parameters for the coating thickness not to exceed 12.5µms (Multiple by 8 and divide by 25µms (=1 mil), which would give you 4 mils. clearance. This is the clearance given by ASME b1.1 on a 5/8” diameter between the internal and external threads, without oversizing.

We perform ASTM A194 “Proof load testing” on anything below 2.5” diameter.

Writing the Scope for Standardizing Bolt Coatings on API 20E material

1. ASTM B117- Testing with 7-9% Saline solution

• Subsea 120 HRS 
• Splash Zone 1200 HRS (*Standards state that bolting should not be utilized in a Splash Environment.)
• Topsides 240 HRS
• Surface 96 HRS

2. ASTM F1624 (RSL) Rising Step Loading test 35 HRC/ 42 HRC/ 52 HRC 

(This test would in replacement of ASTM F519.)

This is the Hydrogen embrittlement test portion that has been utilized in the Navy Fracture Toughness Testing and was developed by Dr. Louis Raymond decades ago and used in very high profile cases involving hydrogen embrittlement failures.

3. ASTM G3-14 (OCP) Open Circuit Potential measured using Ag- Ag Chloride reference in 3.5% saline solution.

• The coating should measure an OCP between -.900 to -.800mVsce when being applied to ASTM A320 L43 material. An L43 should have an      OCP= -.678mVsce. Which would not allow a coating to have an Ecorr difference of over 300mV. (Navy does not allow more than 300mVsce and NASA does not allow more than 150mV difference in metals or coating systems.)

4. Hydrogen Permeationis the uptick of hydrogen which passes through the substrate material. ASTM G148-18measures the permeability of substrates and substrates with coatings acting as an anode, or as a barrier. Coatings acting as a anode could potentially provide hydrogen directly to the substrate. This is a test that has been around since (1962) and is widely practiced in licensed labs.

5. Thickness of the coating has become a greater threat as coating thickness has outweighed thread dimension. API 20E had to actual state no over tapping of threads to allow clearances for coatings in the standard. Two ways in which coating thickness are measured are;

• ASTM E376 magnetic
• ASTM B567 (XRF) X-ray

6. ISO 16047 is a certification for a lab, to be able to read and give the (CoF) Co-efficiency of Friction. This entails the applicator what torque to utilize in order to apply the correct amount of force when installing the bolts. (ASME PCC-01-2013)

*7. ASTM A194- states the use of a proof load test under units of 2” diameter. When using bolting in thermal applications it is sometimes a good idea to subject the coating and bolt to thermal environments before running this test.

8. Most importantly you should coat/ plate or treat the fasteners prior to cutting samples from the substrate. Testing the material and the treatment together is the only way to collect the right test results. 

Last but not least, if you are a Lab that provides these services I have mentioned, please leave your information where others might be able to get a hold of you. These tests have been accepted around the world and are be utilized specifically in Subsea and Naval testing.  If you need help finding a lab in your area, I am more than likely able to find you the right lab, feel free to ask. I do not perform these test for the general public but only for my own research studies and as an active member of standard organizations.