MAOK’s coating solution for screw joints in pipes helps acquire gas tightness and aids expansion of casing strings with BUTTRESS thread
The MAOK-PLAUN® coating test was done on BUTTRESS screw joints of API Spec5CT standard casing pipes. The BUTTRESS joint with the coating of casing pipe with 146 in diametre of strength group N80 during tests for gas tightness withstood a pressure of 600kgs/sq cm for 65 hours. Consequently, the BUTTRESS screw joint of strength group H40 withstood the recommended testing pressure of 300kgs/sq cm, the company said.
The key feature of the coating, MAOK said, is it can be used for casing into the well-site instead of premium class thread, which also allows wells to be built with BUTTRESS casing pipes. For saving the screw joint of BUTTRESS casing strings from destruction due to high mechanical loads from the string dead weight, it is ideal to use pipes with a higher strength group in relation to pipes with premium thread. For instance, in construction of an Х-well a casing pipe with premium class thread and strength group H40 is provided. Here the BUTTRESS pipe with MAOK-PLAUN® coating and strength group N80 can replace the H40 pipe with premium thread, the company added.
Talking about cost-effectiveness, MAOK said that the difference in the increase in cost of BUTTRESS casing pipe with MAOK-PLAUN® coating in relation to a simple uncoated pipe is one per cent. Similarly the difference in the cost of a tonne of casing pipes with BUTTRESS thread and premium class thread is up to 300 per cent. Hence, the transfer to casing pipes with BUTTRESS thread instead of pipes with premium thread will allow the costs of construction of well sites, including offshore construction, to be greatly reduced, MAOK noted.
The coating is also hydrogen sulfide (H2S)-resistant, which means that the coating will work efficiently when constructing and operating wells with the high content of H2S. MAOK-PLAUN® protects not only the coupling body on which it is applied, but also nipple pipe thread ends connected with the coupling. This occurs because the coating has high plasticity, elongation being 13-18 per cent, and it tightly, without gaps or pores, encases the pipe nipple thread, making the joint tight in gas media. This is the case in both screw joints of casing pipes and screw joints of oil well tubing.
MAOK-GT® coating, meanwhile, has been designed to prevent screw joints from being affected by H2S and CO when combined with MAOK-PLAUN® coating. The standard casing pipes H40 could be used instead of highly alloyed steel pipes, which also leads to a reduction of costs of oil and gas companies. The increase in the cost of a tonne of the pipe with MAOK-GT® coating will only be 0.4 per cent of the cost of the uncoated pipe.
The MAOK-PLAUN® coating can also be used to protect threaded and sealing parts of couplings with premium class threads.
